EVERDAY PHYSICS 1

Everyday Physics for the Curious Scientist in You

Phys 181 Class of 2020

Edited by Zi Tong Wang and Michael Hilke

McGill University

EVERDAY PHYSICS 2

Abstract

The goal of this book is to explore the physics behind everyday phenomena. It is written such that every curious and interested mind can follow, regardless of the background. Ne need of a physics degree to understand the underlying mechanism of our daily universe. The book is written by the entire class of

2020 in for the “Everyday Physics” course given at McGill University.

Keywords: The Universe, Waves and Quantum, Physics of Life, Human made machines, Physics of food.

Table of Contents

Abstract ...... 2

Everyday Physics ...... 10

Chapter 1: The Universe ...... 10

Important Physical Concepts ...... 10

Facts – Theory - Model ...... 10

Interesting questions on the Universe ...... 13

1. Why does the sun shine? ...... 13

2. Why are the colors of the stars different? ...... 15

3. What would the Earth be like if the Moon didn't exist? ...... 17

4. How do we know that the Universe is expanding? ...... 19

5. What is at the very bottom of the ocean? ...... 21

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6. Where did earths water come from? ...... 23

7. Why do stars shine when we look at them at night? ...... 25

8. Can we realistically populate another planet? ...... 27

9. Where did water come from? ...... 29

10. What would happen to Earth if the Sun suddenly exploded? ...... 31

11. Is it possible for humans to survive on Mars? ...... 33

12. How do we know the Universe is expanding? ...... 35

13. Is there life in the Andromeda Galaxy? How can we know? ...... 37

14. Is it realistically possible for humans to populate to another planet? ...... 39

15. Why are the colors of stars different? ...... 41

16. Why are the colors of stars different? ...... 43

17. Why are the colors of stars different? ...... 45

18. Why does Earth rotate? ...... 47

19. What Is At The Very Bottom Of The Ocean? ...... 49

20. Why are there stars of different colors? ...... 53

21. What is gravity and where does it come from? ...... 55

22. How do we know the age of the Earth? ...... 57

23. How do we know the universe is expanding? ...... 59

24. Is the universe infinite? ...... 61

25. Is there gravity in space? ...... 63

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26. Why is the Earth round?...... 65

27. What is gravity and where does it come from? ...... 67

28. Why is the Earth round?...... 69

29. Where do black holes come from? ...... 71

30. Does the moon cause tides? ...... 73

31. What would the Earth be like if the Moon didn't exist? ...... 75

32. Can Humans survive on Mars? ...... 77

Chapter 2: Quantum and Waves ...... 80

Important Physical Concepts of Waves ...... 80

Interesting questions about waves ...... 81

33. How do wifi waves travel through walls when light can't? ...... 81

34. Why do objects look skewered or bent when it is under water and being viewed from the

surface? ...... 83

35. What is the physics behind clap-activated lights? ...... 85

36. How do humans perceive sounds as complex as music from the combination of simple

sound waves? ...... 87

37. How are we able to see images with our eyes? ...... 89

38. When we use the microwave oven to heat food, how is the energy transmitted? ...... 91

39. How do eyeglasses work? ...... 93

40. Qu’est-ce qu’un rayon X et comment cela fonctionne ?...... 95

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41. When we use a microwave oven to heat food, how is the energy being transmitted? .... 97

42. How do household microwaves use waves to heat up our food? ...... 99

43. Why do objects look skewered or bent went its underwater, being viewed from the

surface? ...... 101

44. How do Wi-Fi waves travel through walls when light can’t? ...... 103

45. Why is it said that light does not need a medium through which to travel? ...... 105

46. Why do objects look skewered or bent went its underwater, being viewed from the

surface? ...... 107

47. Why can the wifi waves penetrate the wall but the light wave cannot? ...... 109

48. How does a camera capture an image and turn it into picture? ...... 111

49. What is the difference between the way the brain sends signals and how an electronic

device sends signals? ...... 113

50. How do eyeglasses work? ...... 116

Important Physical Concepts of Quantum Physics ...... 118

Interesting questions about Quantum ...... 119

51. How is light both a particle and a wave? ...... 119

52. How does an MRI work? What are the physics behind it? ...... 121

53. What are X-rays? ...... 123

Chapter 3: The Physics of Life ...... 125

Important Physical Concepts of the Physics of Life and Biophysics...... 125

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Interesting questions about the physics of life ...... 127

54. How much force does it require to knock out an average human? ...... 127

55. What happens to the human body when it's exposed in outer space? How long can you

survive? ...... 129

56. How does the electrical conduction of the nerve system work? ...... 132

57. How does UV damage our DNA? ...... 134

58. Will we ever be able to cryogenically freeze our living bodies to be unfrozen in the

future? ...... 136

59. Will we ever be able to cryogenically freeze our living bodies to be unfrozen in the

future? ...... 138

60. What happens to the human body when it is exposed in outer space? How long can you

survive? ...... 140

61. What happens to the human body when it's exposed in outer space? How long can you

survive? ...... 142

62. What happens to the human body when it’s exposed in outer space? How long can you

survive? ...... 144

63. How does the electrical conduction work of the nerve system? ...... 146

64. What is the difference between the way the brain sends signals and how an electronic

device sends signals? ...... 148

Chapter 4: Human Made Machines ...... 151

Important Physical Concepts of Machines ...... 151

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Interesting questions about machines ...... 152

65. How do airplanes fly? ...... 152

66. How is electricity produced and transported to our homes? ...... 154

67. What is the physics behind clap-activated lights? ...... 156

68. How does an electric car work? ...... 158

69. How is electricity produced and transported to our homes? ...... 160

70. How does a touch screen work?...... 162

71. How do touchscreens work? ...... 164

72. What limits (physics, technology) are preventing humans from building spacecraft

capable of travelling close to the speed of light? ...... 166

73. How does a camera capture an image and turn it into picture? ...... 168

74. What is the physics behind clap-activated lights? ...... 170

75. How Does a Refrigerator Work to Freeze Food Inside? ...... 172

Chapter 5: Food and Physics ...... 175

Important Physical Concepts of Food ...... 175

Interesting questions about food ...... 175

76. Why is it that food loses nutrients after it is microwaved? ...... 176

77. How does Gazo (restaurant in Montreal) use nitrogen to make ice-cream? ...... 178

78. Some factories use radiations to kill the bacterias in the food. Do these radiations

influence the food safety? ...... 181

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79. Why does blowing on coffee cool it down ? ...... 183

80. Why is it difficult to cook at high altitudes? ...... 185

81. Why Does Popcorn Pop? ...... 187

82. Which way of cooking best preserve the nutrients in foods? ...... 189

83. Why is it that food loses nutrients after it is microwaved? ...... 191

84. Why does blowing on coffee cool it down? ...... 194

85. Why do bananas turn from yellow to brown/black? ...... 196

86. Why is it difficult to cook at high altitudes? ...... 198

87. Some factories use radiation to kill the bacteria in the food. Do these radiations

influence food safety? ...... 200

88. What is the physics behind popping corn? ...... 203

89. Why do bananas turn from yellow to brown/black? ...... 206

90. What is the physics behind popping popcorn? ...... 208

91. Why does cutting onions make you cry? ...... 210

92. Some Factories Use Radiations To Kill The Bacterias In The Food. Do These Radiations

Influence The Food Safety? ...... 212

93. What allows certain things to dissolve in water and others not? ...... 215

94. What are the different methods of heat transfer observed when preparing food? ...... 217

95. Some factories use radiations to kill the bacteria in the food. Do these radiations

influence the food safety? ...... 219

EVERDAY PHYSICS 9

96. Why is it difficult to cook at high altitudes? ...... 221

97. Why do bananas turn from yellow to brown? ...... 223

References ...... 225

EVERDAY PHYSICS 10

Everyday Physics

What do we mean with everyday physics? Is it possible to describe every phenomenon in a language everyone can understand?

There are a few books on everyday phenomena, e.g., (Griffith & Brosing, 2004) and (Bloomfield,

2015).

Chapter 1: The Universe

Important Physical Concepts

We start by looking at the differences between facts, theories and models in scientific context.

Facts – Theory - Model

Facts

What are facts? Shared observations can be defined as facts (e.g., the moon is circling the earth) as well as predictions that have a very high probability (tomorrow the rotation of the earth will take 24hrs).

These observations can be made repeatably by independent observers. This comes very close to 100% probability, even though there is an exceedingly small chance that the earth rotation might slow down. In reality, earth’s rotation is slowing down on average by 2 milliseconds per 100 years (Stephenson, 2003), due to the tides produced by the moon. Other cosmic events could conceivably reduce earth’s rotation speed even further. Yet, we keep defining 24hrs as the time it takes earth to do one rotation with respect to the sun. Hence truth be told, a fact is that a day is 24hrs long and corresponds to one rotation of the earth.

Some key facts about our Universe:

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• There are stars and galaxies. They can be observed with a multitude of telescopes and at

different wavelengths.

• There is a cosmic microwave background (CMB) radiation all around the universe with

small fluctuations in intensity.

• Our Universe is expanding.

Theory

What is a theory? Einstein’s theory of relativity is a theory because it made predictions that are verified experimentally. For instance, the clocks on satellites use Einstein’s theory of relativity in order to account for time dilation and contraction at high speeds and low gravitational fields. A related by-product of relativity are gravitational waves, which were a model of propagation of gravitation put forward by

Henri Poincaré (Poincaré, 1906), which became a theory once gravitational waves were observed experimentally (Abbott, et al., 2016). Even Einstein, who wrote one of the first papers on gravitational waves (Einstein, 1918), later claimed that they could not exist, before supporting their existence again.

This illustrates a common back and forth of models before they are eventually verified experimentally, at which point they become accepted theories. However, this doesn’t mean that these theories cannot be improved or modified. The classic example is the theory of gravitation by Newton, which was used to predict the motion of planets and stars, but which had to be corrected by Einstein’s theory of general relativity.

Some key theories about our Universe:

• Standard model of Cosmology (LamdaCDM). Big Bang, Dark Matter(25%) and Dark

Energy(70%), (only 5% is “normal” matter), age and accelerated expansion. They combine

predictions and observations.

Other important theories:

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• Theory of relativity and existence of black holes and gravitational waves

Important concepts:

• Total energy is conserved

• Total information is conserved

Model

What is a model? For example, string theory is a model. String theory assumes that elementary particles can be described by strings and vibrations of the strings (Rickles, 2016). It was introduced to unify Einstein’s theory of gravitation (general relativity) and quantum mechanics. However its predictions have yet to be tested and there is no consensus from the scientific community in terms relevance to the actual problem of quantum gravity (Castelvecchi, 2015).

Some key models about our Universe:

• String theory

• Black hole evaporation

• Warmholes

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Interesting questions on the Universe

1. Why does the sun shine?

This morning when I woke up, the sun was hiding behind the clouds and you felt something was missing. You start wondering what would happen if the sun would stop to shine? And first, why does it shine?

Fundamentally, the sun is like a ball of fire, but a very special one. While the heat of the fire creates light just like a fire does, it is also round. These are two competing mechanisms in the sun, the generation of the burning heat, which shines light while at the same time this fire is contained in a round ball because of gravity. Unlike a campfire, where the hot gas molecules are too few and dispersed, in the sun the gas molecules like hydrogen are so strongly compressed that the hydrogen in the sun is even denser than water. This illustrates the power of gravity that squeezes and holds the gas molecules together. However, the heat generated by the burning hydrogen exerts an outward pressure, which stops the sun of collapsing due to the gravity. We have to remember that the mass of the sun is 330,000 times the mass of earth.

Hydrogen will explode once ignited, as illustrated by disasters such as the Hindenburg Zeppelin, which was filled with hydrogen and exploded in New Jersey. However, in the sun, because of the high temperatures and pressure, the burning is mostly a fusion reaction. Fusion is the process of “fusing” the

Hydrogen atoms into Helium atoms. At these high

temperatures, where the electrons are ripped off the Hydrogen

atoms, the protons in the nucleus of the Hydrogen atom with

combine and form Helium atoms. This fusion reaction creates

a lot of energy, which is released in terms of heat and light,

EVERDAY PHYSICS 14 which keeps us warm. Once the sun runs out of Hydrogen it will stop burning through a big explosion and retract into a white draft that will not shine anymore. This process will take billions of years, since we still have more than 73% of Hydrogen left [1].

What is mind boggling, is that the sun has a light emission corresponding to 4 ∙ 1024 100W light bulbs, compared to 8 billion (8 ∙ 109) used on earth [2]. This also illustrates the potential for harvesting solar energy for our sustainable future. For the next 5 billion years the sun will keep on shining and provide us with loads of energy. On earth it is renewable energy and it makes a lot of sense to harvest it efficiently, but the sun itself will eventually burnout as it consumes itself even without an external interference.

Interesting experiment: It is possible to fill a small balloon with hydrogen and then light it up.

This will create a loud explosion with a big fireball. Care needs to be taken to not put more than

500ml of Hydrogen gas and to have it at least 1m away from anything, including your arm. So use a long stick as an extension on which you can tape a match and light the balloon form a safe distance. This needs to be done outside. This illustrates the power of Hydrogen even at human scale temperatures. Now imagine that the fusion reaction per Hydrogen atom is even more powerful (1000 times more), but fortunately much slower in the sun (because of the high heat).

[1] Asplund, Martin, et al. "The chemical composition of the Sun." Annual Review of Astronomy and

Astrophysics 47 (2009): 481-522.

[2] Davies, John A., and Donald C. McKay. "Estimating solar irradiance and components." Solar

Energy 29.1 (1982): 55-64.

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2. Why are the colors of the stars different?

I’ve always gazed up at stars in awe and wonder. One may believe, as I did, that most of the stars

appear white. Until about two hundred years ago, everyone that studied the stars thought that all stars were

white as well [1]. On the contrary, stars come in almost all the shades of the rainbow! Why is this so? Is

it possible to detect these different colors through the naked eye?

A star is an astronomical, luminous ball of gas, mostly hydrogen and helium, held together by its

own gravity. Much like planets and other stellar bodies in the universe, stars come in many sizes, shapes,

and even colors [2]. Over time, astronomers have come to detect several unique types of stars based on

these fundamental characteristics. Every star is born of a nebula made up of gas and dust, and each is

different. The total mass of the nebula, with the various elements that make it up, determine what kind of

star will result.

Different elements emit different wavelengths of

electromagnetic radiation when heated. In the case of stars, this

includes its main constituents but also the various trace elements

that make it up. The colour of the star is a combination of these

different wavelengths. How that light appears to the human eye can

be attributed to the fact that stars constantly emit light which is a Figure 1. Different colors of Stars (Source: planetsforkids.org) combination of several different wavelengths, and when the various

colors of the spectrum are combined, they appear white to the naked eye. Furthermore, the colour of a star

can change over time.

A star’s colour is also affected by its temperature. As it gets hotter, the overall radiated energy

increases, moving to shorter wavelengths. Simply put, the light it emits moves towards the blue end of the

spectrum. As stars grow colder, the situation is reversed [3].

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The third factor that affects the appearance of the light a star emits is the Doppler Effect.

Regarding waves, the frequency can vary based on the distance between the source and observer. In

astronomy, this effect causes a “redshift” and “blueshift”- the visible light coming from a distant star is

shifted towards the red end of the spectrum if it is moving away, and the blue end if it is moving closer

[3].

The hottest known stars in the Universe are the blue hypergiant stars. These are stars with more

than 100 times the mass of the Sun. One of the best known examples is Eta Carinae, ~180 times the radius

of the Sun, with a surface temperature of 36,000-40,000 K (72,000 F)[4]! The Star WR102, also has a

surface temperature of 2,10,000 K and is the hottest star ever recorded [4]. So next time we find ourselves

stargazing, remember they’re not simply white and twinkly!

Interesting experiment: It is possible to observe colors in a candle flame to explore links between matter, light, color, and temperature. These basic concepts can be put in an astronomical context to explain the various colors of stars. When heated to the right temperature, stars emit the same colors (or wavelengths) as visible light [6]. The candle’s flame could be blue, yellow, orange, and red – blue being the hottest part of the flame. Similarly, stars are different colors too. The color indicates the star’s temperature in its photosphere, the layer where the star emits most of its visible light [6].

For a fun demonstration on why stars are different colors, click here: https://www.youtube.com/watch?v=ELltX2xSddc

[1] “Why Are Stars Different Colors?” Planets for Kids, www.planetsforkids.org/why-are-stars- different-colors.html [2] OpenStax. “Colors of Stars.” Lumen, https://courses.lumenlearning.com/astronomy/chapter/colors-of-stars/ [3] Williams, Matt. “Why Are Stars Different Colors?” Universe Today, 25 Sept. 2016, www.universetoday.com/130870/stars-different-colors/ [4] Cain, Fraser. “What Is the Hottest Star?” Universe Today, 4 May 2017, www.universetoday.com/24596/what-is-the-hottest-star/ [5] Howell, Elizabeth. “Why Are There No Purple or Green Stars?” LiveScience, Purch, 29 Mar. 2013, www.livescience.com/34469-purple-stars-green-stars-star-colors.html [6] “Colour of Stars.” StarDate, https://stardate.org/teachers/plans/color-stars

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3. What would the Earth be like if the Moon didn't exist?

The Moon affects the Earth in many ways, and has had a vast impact on the way life is constituted on Earth and how humans have evolved. Through effects on the Earth’s tides, crust and rotation, as well as the oceans altitudes, it is safe to say the Earth would be nothing like it is today without the Moon.

The Moon is made up of material from Earth that flew off from a large object hitting Earth around

4.5 billion years ago1. This means that the Moon came into being just 60 million years after the Solar

System first existed2, and has been next to Earth for most of our planet's lifetime. The Moon’s gravitational force on Earth has changed everything.

The Moon affects our tides and the size of oceans to a vast degree. If there was no Moon affecting our tides, they would be only one third as big as they are now3. These tidal forces also affect our climate, as much of the heating and cooling of oceans are because of tides4. In addition, the Moon’s gravitational pull means that the areas closest to the

Moon, at the equator, have deeper oceans, whereas the poles of the ocean are more shallow. If there was no moon, this would not be the case, and the sizes of different areas of the ocean would shift. The tides, with the force of the Moon, are responsible for energy heating and dissipation of Figure 1: Motion of Tidal Bulges Created by energy on Earth. It has even been argued that the Moon is responsible Moon (Source: Aerospaceweb)

1 Yan, Isabelle. “10 Things: What We Learn About Earth by Studying the Moon – NASA Solar System Exploration.” NASA Science: Solar System Exploration. NASA, March 13, 2019. https://solarsystem.nasa.gov/news/812/10-things-what-we-learn- about-earth-by-studying-the-moon/. 2 Wall, Mike. “How Old Is the Moon? Scientists Say They Finally Know.” Space.com. Space, January 11, 2017. https://www.space.com/35291-moon-age-pinned-down.html. 3 Kershner, Kate. “What If We Had No Moon?” HowStuffWorks Science. HowStuffWorks, January 27, 2020. https://science.howstuffworks.com/no-moon.htm. 4 Foing, Bernard. “If We Had No Moon.” Astrobiology Magazine, October 29, 2007. https://www.astrobio.net/retrospections/if- we-had-no-moon/. Figure 1: Whitman, Justine. “Ask Us - Moon Motion & Tides.” Aerospaceweb, February 19, 2006. http://www.aerospaceweb.org/question/astronomy/q0262.shtml.

EVERDAY PHYSICS 18

for tectonic plates, through the heating of energy, because many planets without a moon do not have them5.

Moreover, the moon’s pull on the Earth’s mantle helps generate earth’s gravitational field through the

heating of this outer core6.

The Moon has a large impact on the Earth’s rotation, and slows down Earth’s spin by about 0.002

seconds each day this century7. Without the moon, our days would be between 6-12 hours, instead of 24.

This means that our years would have over 1,000 days in them8. If there were no Moon, our days’ length

Human Adaptation: The full would affect the amount of daylight we have. There would be increased moon was what hunters storms, wind would be much more intense, and our seasons would organized themselves around, change drastically9 . This could have a huge impact on the life and because of the light it gives off. species we have on our planet.

This has affected predator-prey Many planets, such as Mars, rotate with less consistency relationships, as well as the because they do not have a moon. Mars’ rotation, over a few million

years, changes by 60°. If the Earth, which is on a 23° angle, rotated less smoothly, there would be a larger

degree of climate change. This 23° angle ensures our planet is safe for habitation through its liveable

climate10. In addition, many animals have developed night vision due to the moon and many animals have

come have adapted to their tidal climates.

5 Foing, Bernard. “If We Had No Moon.” Astrobiology Magazine, October 29, 2007. https://www.astrobio.net/retrospections/if-we-had-no-moon/. 6 Yan, Isabelle. “10 Things: What We Learn About Earth by Studying the Moon – NASA Solar System Exploration.” NASA Science: Solar System Exploration. NASA, March 13, 2019. https://solarsystem.nasa.gov/news/812/10-things-what-we-learn-about-earth-by-studying-the-moon/. 7 Matthews, Robert. “What Would Happen If There Were No Moon?” BBC Science Focus Magazine. Accessed February 13, 2020. https://www.sciencefocus.com/space/what-would-happen-if-there-were-no-moon/. 8 Esiegel. “The Top 5 Things We'd Miss If We Didn't Have a Moon.” ScienceBlogs, August 8, 2013. https://scienceblogs.com/startswithabang/2013/08/08/the-top-5-things-wed-miss-if-we-didnt-have-a-moon. 9 “What Would Happen If There Was No Moon?: Summary, Facts & Impact.” The Nine Planets. Accessed February 13, 2020. https://nineplanets.org/questions/what-would-happen-if-there-was-no-moon/. 10 Foing, Bernard. “If We Had No Moon.” Astrobiology Magazine, October 29, 2007. https://www.astrobio.net/retrospections/if-we-had-no-moon/.

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Not only does the Moon have large geographical effects, but it also is the basis for many facts in scientific exploration. For one, from studying the moon, scientists have been able to discover what happened to earth four million years ago, because the moon preserves all craters and impact on its surface.

Because of the proximity of the moon to Earth, we are able to tell what happened to Earth during this period, and how long ago these craters would have affected Earth. Moreover, the Moon has had volcanic processes in the past, and the remnants of it could help scientists study how these processes happened on

Earth. Thus, without the Moon, not only would the Earth be affected, but humans would have less information about our surroundings.

4. How do we know that the Universe is expanding?

From all the things that our ancestors had in common, it is undeniable that their interest for the canopy of heaven was one of the most important ones, and until recently, we had but very little clue about the nature of what was above the sky. One of the remarkable progresses in our understanding of the

Universe is about its behavior: we today know that our Universe is expanding. This idea has completely transformed older models, which all predicted that we lived in a static Universe. This discovery preceded the birth of modern astronomy, which forged our modern understanding of the Universe. As it has been introduced, we have believed for a long time that we lived in a perfectly steady Universe. At first, people thought we were at the center of the Universe. The emergence of Renaissance and critical thinking has triggered scientific minds to reconsider this idea. Soon enough, it was established that the

Earth was in fact rotating around the sun. For hundreds of years, generations of physicists and astronomers continued to develop their model of the Universe. It was not until the early twentieth century that the idea of an expanding Universe was brought to the table by an avant-garde astronomer and Belgian priest named Georges Lemaître. Though, the idea was not taken seriously. The scientific

EVERDAY PHYSICS 20 community wasn’t enthusiastic about this hypothesis, that is until the observations of Edwin Hubble in

1929. The American astronomer, equipped with one of the finest telescopes on Earth at the time (that is, the Hooker telescope), had shown that massive gaseous structures, which we erroneously believed to be all inside our galaxy, the Milky Way, were in fact enormous star clusters located outside of our galaxy.

Not only Hubble had proven that our Galaxy was only one among others, but he also showed that these galaxies were all moving away from us! And the farther away they were, the faster they were moving away from us. How did he manage to make that conclusion? When observing these distant stars, one has to understand that photons are emitted by the stars and going towards our retina. If the observer and the star aren’t moving, the frequency of the photon emitted is the same as the one perceived. However, if either the observer or the emitter is moving away from the other one, The frequency perceived slightly shifts from the one emitted. This is known as the “Doppler Effect”, we experience it in another perspective in our daily life: when a police car passes in front of us, the pitch of the siren is high, and decreases when the car passes you. Think of the sound racing cars make. Even if it’s not the same, as one is about electromagnetic waves and the other about mechanical waves (through air), the understanding of the phenomenon goes the same way for galaxies. To go back to our friend Edwin, one of his major observations was that all his wavelength-measurements for these distant galaxies were off; all were shifted to the red part of the electromagnetic spectrum; i.e., the wavelength was increased and the frequency had decreased. It was then concluded, by the Doppler Effect, that these galaxies had to be all moving away from us.

This spectacular observation was a shock in the physics world; even Einstein strongly believed in a static universe! It makes you think about how strongly rooted ideas are sometimes simply incorrect, and how we need to accept this: we should always be open for progress, because this is the only way to advance science.

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"Cosmology / Elementary Tour Part 1: The Expanding Universe." Einstein-Online. Accessed February 12, 2020. https://www.einstein-online.info/en/expansion/.

Sutter, Paul. "The Cosmological Conundrum of the Expansion Rate of the Universe." Space.com. Last modified October 30, 2019. https://www.space.com/hubble-constant-universe- expansion-rate.html.

5. What is at the very bottom of the ocean?

Have you ever wondered what lurks below the surface of the water in an ocean? Have you ever

wondered what lurks 36,200 feet (11.03 km) below the surface? The deepest part of the ocean is known

as the Challenger Deep and is located at the southern end of the Mariana Trench that runs hundreds of

kilometres southwest of Guam. The average depth of the ocean is roughly 12,100 feet (3.69 km) (1) and

that is significantly deep water! Blue whales are able to hunt at depths of around 330 feet (100 m) in the

well-lit zone of the ocean. 831 feet (253 m) is the record for deepest free dive where the pressure is 26

times greater than at the surface of the ocean. The

maximum depth that whales can dive to is 1640 feet

(500 m). At 3,280 feet (1 km), sunlight cannot reach

anymore, and it is referred to as the midnight zone.

The Titanic is resting at 12,500 feet (3.81 km) below

the surface where the pressure is 378 times greater

than at the surface (2). Below 20,000 feet (6.1 km) to

the very bottom of the ocean is known as the hadal

zone, named after Hades, the god of the underworld. Jellyfish: 2016 Deepwater Exploration of the Marianas at depth of ~3.7 km. Retrieved from https://oceanexplorer.noaa.gov/okeanos/explorations/ex16 05/dailyupdates/media/video/0424-jelly/0424-jelly.html

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Its deep trenches have been formed by shifting tectonic plates (3).

In 2016, the National Oceanic and Atmospheric Administration (NOAA) sent down cameras to

explore the depths of the Mariana Trench. They have discovered jellyfish, fragile deep-sea corals,

crinoids, coral reefs, sharks, fish, amoebas, sea squirts, relicanthus anemone-like animals, acorn worms

and shrimp (4) which are able to thrive. It is also significant to mention that the hadal zone has been

pervious to the dumping of toxic waste. In the 1970s, tons of pharmaceutical wastes were dumped into

the Puerto Rico Trench and in a 1981 study, samples taken from the dump site demonstrated that the

ecosystems were seriously damaged by the pollution (4).

The study of such depths might also help our understanding with how life could possibly survive

in space. Creatures that thrive in these extreme depths and environments are called extremophiles. They

can survive with little to no oxygen, very low temperatures and high pressures (4). Pyrococcus CH1, is a

microorganism that lives in deep sea vents and could hint at life that could possibly exist on other

planets such as Europa, one of Jupiter’s moons (4). These animals may offer insight to scientists as to

how we might be able to survive in space where there is no oxygen, so more funding and exploration is

needed for deep sea missions.

Interesting fact: More people have been to the moon than have explored the hadal zone! Only three people in the world have ever made it to the bottom of the Mariana Trench. The film director,

James Cameron visited in 2012 and before that, in 1960, two scientists on the Trieste. At that depth, the water pressure is roughly eight tons per square inch or 100 elephants standing on your head (3).

References: 1. US Department of Commerce, & National Oceanic and Atmospheric Administration. (2013, June 1). How deep is the ocean? Retrieved February 12, 2020, from https://oceanservice.noaa.gov/facts/oceandepth.html 2. Insider, T. (2017, April 3). This Incredible Animation Shows How Deep The Ocean Really Is. Retrieved February 12, 2020, from https://www.youtube.com/watch?v=UwVNkfCov1k

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3. 8 Surprising Facts About the Deepest Part of the Ocean. (2017, January 16). Retrieved February 12, 2020, from https://www.mentalfloss.com/article/90796/8-surprising-facts-about-deepest-part- ocean 4. Gaines, J. (2019, June 1). A rover dived to the bottom of the ocean. 15 photos show what it found there. Retrieved February 12, 2020, from https://www.upworthy.com/a-rover-dived-to-the- bottom-of-the-ocean-15-photos-show-what-it-found-there

6. Where did earths water come from?

Water is a vital part of life and without it we would not be able to survive. Nearly 60% of the human body is composed of water [3] and about 71% of Earth’s surface is made up of large bodies of water [2]. Water undeniably plays a critical role in both human life and the overall function of the world, however, its origin remains unknown.

The origin of water has been long debated by scientists around the world, yet no theories have emerged from their research. A common methodology among all of these reports are that they examine the levels of deuterium to hydrogen levels in water around Earth’s surface and then use that finding to compare it to the water of where they believe it originated. One of the more popular theories, although yet to be verified, surrounds that of the asteroid Vesta. The study lead by Adam Sarafian was published in 2014[1]. They proposed that because Vesta is a carbonaceous chondrite, meaning a meteorite composed of mostly carbon, it was a likely candidate. Furthermore, it is known to have originated within the same region as Earth and has a very cratered surface which suggests a lot of collisions [1]. Although this theory presented itself as being quite likely, a new theory published in 2018 that was led by Peter

Buseck suggested otherwise [4]. The theory conducted by Buseck argues that although earlier theories give a good understanding, they fail to explain the higher ratio of deuterium-hydrogen which is present in water near the Earth’s Core. His theory suggests that as Earth was covered with magma during its early stages, the solar nebula, that was caused by the formation of the Sun, accounts for the higher deuterium-hydrogen levels near the core. It is believed that the result of the interaction between the

EVERDAY PHYSICS 24 magma and solar nebula this led to the creation of our first atmosphere. They observed that hydrogen present within asteroids was heavier and contained more deuterium than that from the solar nebula. This observation would lead to believe that the Hydrogen would be attracted to the Earth’s core, due to its attraction with Iron while its counterpart deuterium would stay and eventually form Earths mantel [4].

Although this theory correctly accounts for the differences in deuterium-hydrogen ratio around our

Earth, it has yet to be proven and the discussion is still up for debate.

Interesting Idea: As we have examined where water comes from and touched upon

how important it is for us, this leads to an obvious question of what would happen if we had

no water? It is usually suggested that the average adult can survive only 3 days without water.

This short time span is a result of the crucial part water plays within the body. Water is a vital

part of many operations that go on within our body throughout the day such as regulating

body temperature, delivering oxygen throughout the body and eliminating waste through

urine and breath [3]. As we can see, water is crucial for our everyday lives.

Although there is no definitive answer to the question, it provokes deeper thought to life outside of science. As researchers continue to search for an all-encompassing solution to the origin of water on

Earth, it reminds us of how ever vast the universe is. Further, it challenges our actual perception of human knowledge, although we as a species have learned a lot about our planet and our world, there is much more to be known and endless questions to ask.

[1] Fazekas, Andrew. “Mystery of Earth's Water Origin Solved.” National Geographic, 30 Oct. 2014, www.nationalgeographic.com/news/2014/10/141030-starstruck-earth-water-origin-vesta-science/. [2] Israel, Brett. “How Much Water Is on Earth?” LiveScience, Purch, 9 Sept. 2010, www.livescience.com/29673-how-much-water-on-earth.html. [3] Johnson, Jon. “How Long Can You Live without Water.” Medical News Today, 14 May 2019, www.medicalnewstoday.com/articles/325174.php#risks [4] Anderson, Paul Scott. “How Did Earth Get Its Water?” EarthSky, 12 Nov. 2018, earthsky.org/space/origin-earths-water-asu-solar-nebula.

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7. Why do stars shine when we look at them at night?

You probably love to admire a star-lit, summer night sky- but have you ever stopped to think

about why the stars are lit up? What causes these dreamy- romanticized objects to light up the sky?

Tonight, when you go outside and look up at the stars in admiration, you will finally understand the

physics of how it all works.

Before answering this question, we must understand what a star is made of and how stars are

formed. We must also find out how the stars temperature affects its physical workings? All of these are

likely contributing factors to why stars shine on a dark night. A star is composed of approximately 73%

hydrogen, 25% helium and the last 2% is many other elements. The entire universe was comparable to a

star, 13.7 billion years ago, after The Big Bang- it was a hot, dense sphere. During this brief period, the

universe underwent nuclear fusion reactions which converted hydrogen into helium which formed our

current day ratios of these elements (1). Nuclear fusion reactions are when the nucleus from two or more

different atoms combine to make one or more different atomic nuclei and

subatomic particles such as neutrons or protons (2). As the universe kept

expanding and cooling, the hydrogen and helium cooled down enough to start

combining with one another with their mutual (very strong) gravity. And just

(Source: Stanford University (2011) (3) like that, the first stars were born! Gravitational collapse happens because

of a stars very intense gravity, which causes it to contract, and draws matter inwards, towards the centre

of gravity, which causes the inside of the star to heat up (4). Did you know that the temperature inside of

a star can be 15 million Kelvin, which is 14999726.85 degrees Celsius? Thanks to this intense pressure

and temperature, nuclear fusions can occur which releases an enormous amount of energy in the form of

gamma rays. These gamma rays are in the core of the star and pushing against the gravitational

contraction of the star- this is the reason why stars don’t continue to grow forever! These gamma rays

EVERDAY PHYSICS 26 are fighting with the atoms of the star so that they can reach the surface of the star, but the atoms absorb them and then re-emit them- this is constantly happening and therefore it can take up to 100,000 years for the photon to reach the surface of the star from its core. Once the photons finally reach the surface, they are finally visible light photons and no longer the gamma rays that they started out as! These photons are finally able to travel through space on a straight path- until they bump into something (5)!

The Alpha Centauri star system is approximately 4.31 light years away from earth, this means that the photons which create the light that we see on earth is 4.3 years old (6)!

FUN FACT: Did you know that the sun is also a star? It is the closest star to earth which is why we see it seems a lot brighter than the other stars that we see at night (7)!

Although intuitively we would think that the sun is the brightest star, most of the stars you see in the sky at night are not only bigger, but also brighter than the sun! The Alpha Centauri is the dimmest star compared to the 50 most prominent stars seen from earth- and yet it is still 1.5 times brighter than the sun (8)! Next time you are outside with some friends, be sure to impress them with your knowledge about how and why stars are so bright!

(1) What are stars Made Of? Fraiser Cain. Universe Today. (February 6, 2009). https://www.universetoday.com/24796/what-are-stars-made-of/ (2) Nuclear Fusion. Wikipedia. https://en.wikipedia.org/wiki/Nuclear_fusion (3) Fusion Regulation in the Sun. Britton Olson. Stanford University. (March 7, 2011). http://large.stanford.edu/courses/2011/ph241/olson1/ (4) Gravitational Collapse. Wikipedia. https://en.wikipedia.org/wiki/Gravitational_collapse (5) Why Do Stars Shine? Fraiser Cain. Universe Today. (February 12, 2009). https://www.universetoday.com/25334/why-do-stars-shine/ (6) The Nearest Stars to Earth (Infographic). Karl Tate. Space. (December 19, 2012). https://www.space.com/18964-the-nearest-stars-to-earth-infographic.html (7) Why are some stars brighter than others? The children’s Museum of Indianapolis. (January, 31, 2017). https://www.childrensmuseum.org/blog/why-are-some-stars-brighter-others (8) 14 fun facts about stars to get your kids excited about astronomy, Camp Live Oak. https://www.campliveoakfl.com/14-fun-facts-stars-get-kids-excited-astronomy/

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8. Can we realistically populate another planet?

Although space exploration began in 1957 with the Soviet launch of Sputnik 1 into space, the first

artificial satellite, the intrinsic curiosity of wondering what is out there and if life exists elsewhere in the

universe has driven physics and astronomy forward since the early days. Furthermore, in a time in which

our planet is struggling to sustain the colossal resources demand of the ever-growing human population,

it is to be expected for our species to seek out any alternative homes that could provide us with the

necessities to survive. With overpopulation becoming a threat to our own species and to the Earth itself,

we can ask ourselves if it is possible to realistically populate another planet. To answer this, we must look

at if there are potential planets we could populate, and at the factors that limit our establishment elsewhere

in the Universe.

Interesting experiment/fact/idea/concept: NASA has 6 front-runners as Earth analogues; Kepler 452b, Kepler 22b, Kepler 69c, Kepler 62f and Kepler 186f [3] If we were to populate another planet, it would need to be an Earth analogue, a planet whose

environment and conditions are similar to those from Earth to allow human life to survive and prosper.

According to Dr. Caleb Scharf, astrobiologist at Columbia University, the exoplanet would need to have

the same dimensions and composition as Earth (small and rocky). It would also need similar atmospheric

composition, and temperatures within the freezing and

boiling points of water. Additionally, the analogue must

orbit in the habitable zone of its star so that the presence

of water in liquid form is possible [1]. In other words, the

planet must be far enough to not be fried by the star’s

radiation, but close enough not to become an ice ball. Of Figure 1: Habitable Zone needed for Earth analogues (Source: NASA, [3]) the 4116 exoplanets confirmed by NASA, about a dozen are already considered to be life-friendly [2]. Physicists

EVERDAY PHYSICS 28 also envision that with improved telescope technology, the number of potential candidates will inevitably rise. Therefore, the true question lies not on if there are alternatives, but rather on if we can reach them.

One of the exoplanets best associated to Earth, Kepler-62f, lies 1,200 light-years away from us in the constellation Lyra [2]. It best exemplifies perhaps the most obvious challenge facing exobiology; that we simply do not yet have the technology needed to travel such distances in a reasonable timeframe. Michel

Mayor, a Swiss astrophysicist and Nobel prize recipient for his work on exoplanet detection, states that

“things should be clear: we will not migrate [to another planet]. These planets are much, much too far away” [4]. There is, however, the idea of terraforming Mars, transforming it into a more habitable environment by reconstructing its atmosphere and changing its ground composition. Projects like these, nonetheless, represent immense costs that society would bear, funds that could go towards more pressing tangible needs.

Ultimately, the arrival of some advanced telescopes and technologies will allow astronomers to have a deeper look at each of these potential Earth substitutes. It must be reiterated however that the cost of such project, our limited travel speed, and the lack of proper technology, restrains this to the world of science-fiction. Instead, as other space experts themselves agree, the focus should be on taming the damage inflicted upon our current house and saving what we have, before moving on to a new environment to destroy.

1. Howell, Elizabeth, The 6 Most Earth-Like Alien Planet. Space, August 2015. https://www.space.com/30172-six- most-earth-like-alien-planets.html 2. Finding Habitable Planets, NASA. https://exoplanets.nasa.gov/what-is-an-exoplanet/how-do-we-find-habitable- planets/ 3. Brennan, Pat. Finding Another Earth, NASA, August 2015. https://www.jpl.nasa.gov/news/news.php?feature=4666 4. Green, Tristan. Why Migrating to Another Planet is a stupid and implausible idea, Insider, October 2019. https://thenextweb.com/insider/2019/10/11/why-migrating-to-another-planet-is-a-stupid-and-implausible-idea/

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9. Where did water come from?

Water is the most fundamental thing that sustains life on planet earth, including animals, agriculture, and humans among many others. This morning while I was taking a shower, I was staring at the running water completely spaced out and various things came to my mind like will water ever run out? Why is there salty and sweet water? and most importantly where did water come from? This led me to look deeper into the question of where water comes from.

Water is made out of three atoms: two hydrogen and one oxygen. About 70% of out planet’s surface is covered with water cycling from the oceans and rivers to the clouds and back again, which in turn sustains life, on land and in water. Water even makes up about 60% of our body. The truth is, we are extremely lucky, because our planet’s distance from the sun is what sustains life on earth. Had our planet been any further away from the sun and the water would completely freeze, and had our planet been any closer to the sun and the water would completely evaporate. Our perfect distance from the sun is called the “Goldilocks zone” [1].

Going back to my fundamental question, I realized that the answer would be way more complex than I expected. Before earth came into life, there was a large disc of gas and dust swirling around the sun. Water molecules were part of the dust swirl that coalesced into the sun and its planets, slowly building into crystals of ice. The water molecules then collided with earth, which was still a rock.

However, according to data, there were extreme temperatures at the earth’s location 4.5 billion years ago. Thus, if small amounts of water were present on earth when the rock formed, the high temperatures would cause it to evaporate back into space. Water would not be able to come back to earth until an atmosphere was formed through a process called “outgassing”. Outgassing is basically a process where volcanic gasses are released to the earth’s surface, creating a layer that can trap water, aka the atmosphere [2].

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Therefore, the theory that water formed along with earth was debunked pretty fast. So how did water get back to the planet? It must have been via extraterrestrial messengers [1]. According to scientists, water came to earth by ice bearing comets or asteroids that hit the earth billions of years ago.

In fact, models of the composition of asteroids and comets led to the conclusion that they have enough ice to deliver the amount of water our oceans have [4].

However, when meteorites were examined, research studies not only found that they contain water in their molecules, but their mineral chemical composition matches rocks on earth. This means that rocks on earth contained water inside of them and earth accumulated lots of water early on that was able to stay there, despite the temperatures and the lack of an atmosphere. Thus, water may have came from meteorites, was formed together with earth, or a combination of the two [3]. Scientists have not reached a robust conclusion to answer this question.

This question had me thinking: If water is only made by two atoms, is it possible to create water through machines and move to Mars? Would we be able to sustain ourselves there? What is interesting is that the water we drink, that is in the seas, lakes, etc. has many more particles than pure water. Does this mean that a pure water form cannot sustain life on earth? Interesting facts: Oxygen is one of the most abundant atoms in the universe & hydrogen

is the most abundant atom in the universe. 69% of fresh water on earth is trapped in glaciers. 70%

of the human brain is water.

[1]https://www.scientificamerican.com/article/how-did-water-get-on-earth/

[2]https://www.smithsonianmag.com/science-nature/how-did-water-come-to-earth-72037248/

[3]https://astronomy.com/magazine/2019/04/where-did-earths-water-come-from

[4]https://earthsky.org/space/origin-earths-water-asu-solar-nebula

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10. What would happen to Earth if the Sun suddenly exploded?

Often, we take the impact of the Sun on our lives for granted. The Sun is obviously vital to all life on Earth, but what would happen to Earth if the Sun were to disappear? All stars eventually die, and our Sun is no exception – so what will remain after its death?

Before we answer these questions, we should look at whether it is even possible for our

Sun to explode. The explosion of a star is called a supernova, and supernovae are the very bright and powerful explosions of stars in space. Fortunately for us, supernovae only occur to stars which are at least ten times the size of our Sun – so our Sun will never explode in a supernova; it will die out in a different way3. This is good news, because if the Sun were to explode in a supernova, our entire solar system would be destroyed3!

Just like any fire, the Sun requires fuel to continue to burn. The fuels that the Sun uses are hydrogen and helium gases. Once the Sun has burned through all its fuel (in about five billion years), the

Sun will expand and get colder, becoming what scientists call a “red giant” star3. The Sun will get so big

at this point, that it will consume Mercury,

Venus, and Earth3! The Sun will eventually

blow off its outer layers as a red giant, and

all that will remain is the core of the dead star – what scientists call a white dwarf3. Pictured above is a diagram showing the life cycle of the Sun2.

After our Sun is a white dwarf, Mercury, Venus, and Earth won’t be around because the

Sun consumed them during the red giant phase. But, the rest of the solar system will remain intact. The white dwarf Sun will be much smaller, darker, and colder than our current Sun, and life in the solar system will have a very hard time existing as a result3.

EVERDAY PHYSICS 32

While it is not actually possible for the Sun to explode in a supernova, we can still

explore the impact if it were to instant explode by some unnatural means. According to Newton’s law of

gravity, if the Sun were to explode suddenly, Earth’s orbit would be impacted instantly1. Unlike gravity,

it takes light about eight minutes to travel from the Sun to the Earth. So, if the Sun were to suddenly

explode, it would be about this long before we see the physical explosion from Earth. The destruction of

the Sun would be felt before the light reaches us, however, since the gravitational force that Earth feels

from the Sun would be gone as soon as the Sun is destroyed1. Without light from the Sun, Earth would

become too cold to sustain life, and so life on Earth would die, and Earth’ unfortunately.

While the death of our Sun and solar system is a scary topic, we have about 5 billion

years before this becomes an issue. Scientific advancements are occurring at an impressive rate, and

there is a great chance that scientists will have found some solution to the problems that the death of the

Sun present – whether that be colonization of other planets, or a way to prevent the Sun from burning

out.

Interesting idea: Even if the Sun were to collapse into a black hole, Earth would only feel [1] the effects of the lack of light from what once was the Sun. If there is some object that has the same mass as the Sun in the center of the solar system, all the objects far enough away from the object will continue to orbit in their usual ways.

Brown, Kevin. “If the Sun Were Suddenly to Explode.” If the Sun Were Suddenly to Explode, MathPages, www.mathpages.com/home/kmath585/kmath585.htm.

[2] Education, Siyavula. “Stellar Evolution.” Flickr, Yahoo!, 3 Apr. 2014, www.flickr.com/photos/121935927@N06/13598682634.

[3] Manser, Christopher. “Curious Kids: What Would Happen If the Sun Exploded?” The Conversation, 16 Oct. 2019, theconversation.com/curious-kids-what-would-happen-if-the-sun-exploded-115329.

EVERDAY PHYSICS 33

11. Is it possible for humans to survive on Mars?

Do you ever think about how one day, global warming might lead to the disappearance of planet

Earth, and even of humanity? Well, if yes then I might have good news for you. Even though the Earth may become uninhabitable one day, what if I told you that it was possible for humans to live on another planet, such as Mars? What conditions would we need to achieve such a goal?

To start off, life on Mars is not currently possible, however it might be soon (1). We know that the average temperature on Mars is -63°C, and that Mars’ atmosphere is mostly carbon dioxide (2). Moreover,

Mars is a barren land of dust and rocks, and most of the water on Mars is trapped in ice (3). At first sight, one may be skeptical about humans ever being able to live on Mars. However, with the pioneering work of many scientists, we may have a promising future. To live on Mars, we need to have breathable oxygen, we need to raise the temperature, and we need food, water, and shelter. To generate oxygen, Michael Hecht, a researcher at MIT, designed a machine called MOXIE, which produces oxygen from carbon-dioxide and would therefore allow humans to breathe on Mars (4). Then to heat up Mars, Elon Musk, the founder of

SpaceX, suggests that we could potentially use mirrors to converge solar radiation onto Mars to heat it up (5). Next, in order to obtain drinkable water, we can extract it from the soil on Mars, and to obtain food, we can produce them indoors using artificial lighting

(6). Lastly, in order to find shelter, humans could potentially send boring machines to Mars, in order to build underground systems to live in (7). Therefore, it is reasonable to believe that humans could Figure 1: Art showing a cross-section of a one day thrive on Mars. human base on Mars, where food production can take place (Source: NASA)

EVERDAY PHYSICS 34

Interesting idea: According to Elon Musk, the first human will land on Mars as soon as

2025! Ultimately, whether it is possible for humans to live on Mars is still a subject of debate.

Nevertheless, my take on it that it will be merely a matter of time before it happens because there are incredibly smart people working towards this goal. Even though Earth might disappear one day, we can nonetheless still be optimistic about humanity’s fate, since there is hope for us on Mars. If we focus on the sunny side of this story, perhaps we would wake up every day a little less sad when thinking about the future.

[1] NASA. “Overview: Mars The Red Planet”, Solar System Exploration (2020),

https://solarsystem.nasa.gov/planets/mars/overview/

[2] NASA. “10 Things: Planetary Atmospheres”, Solar System Exploration (2020),

https://solarsystem.nasa.gov/news/436/10-things-planetary-atmospheres/

[3] Space. “What is Mars Made Of?”, Science & Astronomy (2017), https://www.space.com/16895-what- is-mars-made-of.html

[4] NASA. “MOXIE”, Mars 2020 Mission (2020), https://mars.nasa.gov/mars2020/mission/instruments/moxie/

[5] Iflscience. “Now Musk Wants To Use Mirrors To Heat Up Mars (Or More Nukes)”, Iflscience (2019), https://www.iflscience.com/space/now-musk-wants-to-use-mirrors-to-heat-up-mars-or-more-nukes/

[6] Mars One. “Will the astronauts have enough water, food and oxygen?”, FAQ

(2020), https://www.mars-one.com/faq/health-and-ethics/will-the-astronauts-have-enough-water-food-and-oxygen

[7] Imagineering-eZine. “Making Shelters in which to Live”, Imagineering on Mars (2015), http://www.imagineeringezine.com/e-zine/mars-makeshelter.html

[8] NASA. “Future Exploration Artist Concepts”, Future Exploration (2005), https://www.nasa.gov/centers/ames/multimedia/images/2005/futureexploration.html

EVERDAY PHYSICS 35

12. How do we know the Universe is expanding?

If you were to look at the moon and put your finger up, you could cover it entirely. However, you

might fail to realize that you are also covering thousands of galaxies. The Universe is extremely huge,

and your finger is certainly not enough to cover even a tiny fraction of it. In fact, the Universe is

continually expanding. Even though we assume we know a lot about the Universe, you’d be surprised at

how unfamiliar we are with the place we live in. There are many mysteries that are yet to be solved, and

this causes us to ask certain questions, such as: will the expansion accelerate with time? Will there even

be an end to this or is the expansion infinite?

For all we know, the Universe is expanding according to

cosmic physics; therefore, it is important to question how they

concluded that the universe is expanding. In 1929, an astronomer

Figure 1: Red shift [2] named Edwin Hubble, discovered that the external galaxies are

moving away from the Earth. He then introduced “Hubble’s Law”, which explains that the speed at

which they travel is directly proportional to their distance from the Earth [1]. In other words, the more

distant galaxies are traveling at a faster rate than the ones nearby. Additionally, astronomers examined

the visible light emitted by galaxies. They observed an increase in the wavelength as the galaxies move

away us. In Figure 1, the wavelength moves towards the red end of the spectrum, and thus, is said to be

“red shifted” [2]. The degree of shift is used to determine the speed at which the galaxies are traveling

relative to Earth. Therefore, a large shift in wavelength (more redshifted) implies the galaxies are

moving at an accelerated rate. As a result, they provided evidence which supports the expansion of the

Universe.

Raisin bread analogy: A well-known analogy explaining this expansion is visualizing the universe as a loaf of raisin bread dough. The raisins are equally distributed across the dough, and once the dough rises and expands, the raisins move away from one another. What is particularly interesting is that the raisins at the edges move faster than the ones closer to the center. This relates to how the galaxies further away from the Earth travel at an accelerated rate compared to those that are closer to us [1].

EVERDAY PHYSICS 36

Nonetheless, is the rate of expansion really constant? According to current research, that does not

appear to be the case. In the late 1900s, physicists predicted that the forces of gravity would decrease the

rate of expansion with time. However, in 1998, when astronomers attempted to calculate the

deceleration rate, something unexpected was discovered. They found out

that the expansion was not slowing down, but rather accelerating as seen

by the red curve in figure 2 [3]. Currently, it is believed that the

acceleration is caused by a force called dark energy, which counteracts the

attractive gravitational pull of matter. It remains a mystery until today, but

Figure 2: Dark it is believed that this negative, repulsive force makes up 60-70% of the Energy [6] Universe [7].

We know how the Universe came about: The Big Bang theory which suggests that the universe

begun as an extremely tiny, primordial fireball that has been expanding for the past 13.8 billion years [4].

We also know about the present: observations of the movement of galaxies showing how the universe is

expanding at an accelerated rate. But what about the future? With our current technology, we cannot

determine what will happen many years from now; however, there are many theories that attempt to

explain the fate of our Universe. One theory is the “Big Rip”, which from its name suggests the

expansion rate will eventually tear the universe apart. Alternatively, the Big Crunch theory, which is

ultimately the reverse of the Big Bang, suggesting that the Universe will decay and shrink “in a crunch”

[5].

[1] www.loc.gov/everyday-mysteries/item/what-does-it-mean-when-they-say-the-universe-is-expanding/.

[2] www.science.org.au/curious/space-time/how-do-astronomers-know-universe-expanding.

[3] www.nationalgeographic.com/science/space/dark-matter/#close. Accessed 13 Feb. 2020.

[4] http://astronomy.swin.edu.au/cosmos/B/Big+Bang

[5] http://www.wired.co.uk/article/how-will-universe-end>.

[6] wmap.gsfc.nasa.gov/universe/uni_fate.html.

[7] https://www.scientificamerican.com/article/expanding-universe-slows-then-speeds/

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13. Is there life in the Andromeda Galaxy? How can we know?

Life on Earth has developed through complicated evolutionary processes. There has been an effort to look for planets similar to ours to find another home. But how far have scientists looked outside of our own Milky Way Galaxy? We could look at our nearest neighbouring galaxy being the Andromeda

Galaxy. Could there be life in the Andromeda Galaxy?

The first step to finding life in the Andromeda Galaxy is to properly detect the signs necessary for life. But what exactly are we looking for? We look for the molecule most necessary for life being liquid water. So how are we supposed to find molecules when the Andromeda Galaxy is so far away?

One method used by NASA is called spectroscopy. This method shines light onto a distant planet and what they see is bands of missing light (2). Why does it appear that some bands are missing? This is because some molecules can absorb certains regions of light within the spectrum shined onto the planet.

With this information, they can tell what molecules they can find on the planet analyzed. The difficult part is that many planets need to be in this “Goldilocks” region of a star in order to be able to have liquid water(3). But finding this has not been an easy task for scientists. Now the question is, has anyone ever looked in the Andromeda Galaxy for any signs of life? There has, and they are a group of scientists running a project called the Trillion Planet Survey (3).

This group of scientists have been working on finding life in many galaxies as well as the

Andromeda Galaxy. However, their work focuses more on utilizing various types of telescopes such as infra-red, optical, and radio. This is based on the assumption that they are surveying civilizations with

EVERDAY PHYSICS 38 technology similar to humans. Telescopes receive their respective signals, and amplify it by bouncing off the dish and amplifying it in the receiver (1).

With modern advanced photonics, light we produce today can extend to the entire universe, even the Andromeda Galaxy. Currently, the group is getting the process going, and acquiring images slowly via the optical telescopes, of which will all be woven into a final image. The images will be compared to pristine images to knock out interfering signals, and once it is all pieced together, will be compared to a

control image.(3) If the difference between them is zero, there is no

signal found, greater than one indicates a signal. Patience is required

as Andromeda is 2.5 million light years away and any signal that

occurred 2.5 million years ago could have died out. The processing

of data could take weeks, but the process could be repeated as many

times as required. We may not know the answer until several years to come.

With the answer so close but so far away, can we really know whether there is life in the

Andromeda Galaxy? With all this technology and telescopes, we have looked far and wide for any signs of life and to no avail. But what if aliens don’t want to be found? Perhaps they could be limiting their signals to not be detected. We may never know.

(1)https://public.nrao.edu/telescopes/radio-telescopes/ (Image from this source)

(2)Lovelock, James. “A Physical Basis For Life Detection Experiments.” Nature 207 No 4997 (1965) pp. 568-670

(3)University of California - Santa Barbara. "Where are they? Cosmologists search Andromeda for signs of alien life." ScienceDaily. ScienceDaily, 27 September 2018.

EVERDAY PHYSICS 39

14. Is it realistically possible for humans to populate to another planet?

When I watch the news these days, climate change and protecting Earth is always a hot topic.

People are spending so much money and effort in trying to preserve Earth while the population on Earth is continuously growing. So, I wondered if we could find another Earth and just move to another planet.

Would this thought be just chasing a rainbow, or can it actually happen?

As we all know, humans need the right temperature, water, atmosphere, energy and nutrients to maintain life. If the temperature is too high, we would literally be cooked alive and too low, we would be frozen. Water serves a crucial role of dissolving and transporting chemicals between cells. The atmosphere protects us from harmful cosmic rays. Energy and nutrients are used for organisms to run and maintain their life processes. [1] Like so, these various conditions must be met for a planet to be sustainable for life.

From what was observed by scientists, Mars is the nearest and most ‘Earth-like’ planet. The tilt of axis is 25 degrees, only 2 degrees different from Earth’s and the length of a day on Mars is roughly the same as Earth at 24 hours 37 minutes. This means that humans can adapt to the lifecycle on Mars

quickly. [2] However, a year on Mars is twice as long

than on Earth at 687 days and the surface of Mars is

fairly unforgiving because there is little oxygen

(0.13%) and the temperature is very low (-63 degrees

C) due to its atmosphere. [2] This means that humans

will need the help of spacesuits to stay outside on Figure 1: What life would look like on Mars (Source: Elon Musk’s Vision of Life on Mars)

EVERDAY PHYSICS 40

Mars. Although Mars’ gravity is only 40% of Earth’s gravity, scientists say that humans will have no

problem adapting.

Interesting fact: You may know Elon Musk, the CEO of Tesla, an electric car manufacturing company. But did you know that he also engages in businesses that are future and sustainability oriented? Space X is one of his companies that aims to have people living on Mars by 2024. Until now, Space X has been successful in inventing spacecrafts that could be reused, dramatically reducing space travel costs. By using these spacecrafts, Elon Musk aims to deliver cargo to build infrastructure on Mars by 2022 and have humans start establishing civilization by

2024. Realistically speaking, although humans could survive on Mars, it will be very difficult to

populate to Mars currently. First, since there is almost no oxygen in the atmosphere and little protection

from harmful rays, shelters have to be airtight, provided with oxygen and need protection from harmful

rays. This technology will be more costly than building homes on Earth. Second, as there is no surface

water on Mars, water would need to be extracted from the soil and various minerals extracted from

water as well. For food, there are some crops that can grow well on Mars’ soil such as potatoes, but in

order to grow the various types of food we eat on Earth, more research will need to be done. Lastly, in

order to facilitate these technologies to enable humans to live on Mars, electricity and energy is required

to run the facilities for extracting water, providing oxygen to shelters and monitoring crop growth. This

part is the trickiest because conventional power generation is very difficult on Mars.

Earth is oversaturated with human beings inhabiting the planet more than ever and emitting

pollutants. Natural resources on Earth is also running short. Although currently populating to another

planet is not viable, the human race is destined to seek another habitat and it won’t be long until we are

living on another planet.

EVERDAY PHYSICS 41

15. Why are the colors of stars different?

Humanity has always looked up to the stars, literally. When gazing upon the Sun, we see a yellow ball of light. But does that mean that all stars are yellow? Not quite. There are a variety of colors that stars can take on, from blue to red. So, the question that will be addressed is the question: Why are the colors of stars different?

To start off, the first definite answer to this question was discovered with the discovery of blackbody radiation in the 1800’s (1). According to Jasem Mutlaq from The AstroInfo Project, scientists noticed that the color of stars were like the radiation curves of temperatures. The hotter the temperature of a blackbody, the more light that is given out in the wavelengths (3). As a result, scientists were able to conclude that the color of stars were determined similarly to blackbodies, the color being represented by the surface temperature in Kelvin of the star.

The color of the star determines on the type of wavelengths being emitted by each star (2). For example, cooler stars, mostly emit energy from the infrared region of the spectrum, thus giving off a reddish color (as seen in the diagram). On the flipside, blue stars are blue due to the star emitting

ultraviolet light. The variety of color

in stars by coolest to hottest is Red

→Orange→ Yellow→ White→ Blue

(2). We notice that the closest star to

Earth is in the middle of the pack,

with the approximate surface

Figure 1: Colors of Stars temperature being in the range of (Source: The AstroInfo Project) 6000 Kelvins (2).

EVERDAY PHYSICS 42

Interesting Fact: No matter how far you are away from a star, the color of the star

will be constant (Whether looking from 1 KM or 2,000,000,000,000,000 KM away, our sun

will remainIn addition yellow) to being able to make general assumptions of the star’s surface temperature with the color, scientists have created an index to help

catalogue stars and find a more exact surface

temperature of the stars. This is done by utilizing the

B-V index which helps determine the surface

temperature to a more exact degree.

In conclusion, it is quite interesting to note the

differences between stars. Answering the question of

Figure 2: B-V Index why stars are different colors, we come to the (Source: The AstroInfo Project) conclusion that it is due to the differing surface temperatures As we continue to research the celestial bodies above and learn more about the great expanse, we will continue to learn more and develop more precise methods of explaining exactly why the colors of stars may be different.

Sources:

Mutlaq, Jasem. “Star Colors and Temperatures.” Star Colors and Temperatures, The Astroinfo Project, docs.kde.org/trunk5/en/extragear-edu/kstars/ai-colorandtemp.html.

“Colors of Stars.” Lumen Learning , Lumen, courses.lumenlearning.com/astronomy/chapter/colors-of- stars/.

Palma, Christopher. “Blackbody Radiation.” Blackbody Radiation | Astronomy 801: Planets, Stars, Galaxies, and the Universe, Penn State College of Earth and Mineral Sciences, www.e- education.psu.edu/astro801/content/l3_p5.html.

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16. Why are the colors of stars different?

On a cloudless night, we can often see countless shining stars. If you look at the stars through a telescope, you will see that they have different colors. Some stars are white, some are blue, and some are red. This is a very interesting phenomenon and you may wonder about the reason behind it.

Actually, except for a few planets, the majority of stars in the night sky is those that glow and give off the heat on their own, like the sun. As for planets, their colors are largely determined by the atmospheric and geomorphic properties of their surfaces. For example, the surface of Mars is reddish, so

it appears reddish. However, for stars, their colors are

entirely determined by the temperatures of their surfaces.

Normally, with a surface temperature around 25,000 °C, the

star looks blue. If the surface temperature is between 7,700

° c and 11,500 ° c the star appears white. When the surface

temperature is within the range of 5000℃ and 6000℃, the star looks yellow and the star is red if its temperature lies between 2600 ° c and 3600 ° c. As for the stars that we could observe, Rigel is blue, Sirius is white, and Antares is red.

The colors of the stars are not uniform. As stars age over time, their temperatures will change as well as their temperatures. Normally, young stars are bluish-white in color, and such stars are not uncommon in the universe. As the star gets older, its color will become darker and darker over time. A sudden decrease in the star’s surface temperature indicates that the life of the star is coming to an end. At this point, the aging star turns red. This is how many red giants evolved.

Additionally, another factor that could affect a star’s color is called Doppler effect. Each star has different frequency, and the frequency will increase or decrease based on the distance between the source and the observer. This effect will cause “redshift” and “blueshift”. In this case, “redshift” refers to

EVERDAY PHYSICS 44 the star moving away from us, “blueshift” means that the star is moving toward us. Thus, if the source is moving away (positive velocity), the observed frequency will be lower, and the observed wavelength will be greater (redshifted). Otherwise, if the source is moving towards us (negative velocity), the observed frequency will be higher, and the wavelength will be shorter (blueshifted).

Figure 1: The Image Figure 2: the image Figure 3: the image of

of Rigel of Wolf Antares

Source: Source: Source:

https://apod.nasa.gov/apod/Interesting fact: The sunhttps://apod.nasa.gov/apod/ is getting older and older as timehttps://apod.nasa.gov/apod/ap passing by and it will

ap180115.htmlbecome a red giant in the end. Butap000611.html don't worry, this is five billion120417.html years from now. Although the bright supergiant Rigel is blue now, it will also https://apod.nasa.go turn red in the future, just like anotherv/apod/ap000611.html star in the Milky Way, Rigel iv. Betelgeuse is also an old red giant star.https://apod.nasa.go Some scientists predict that it is highly possible for this starv/apod/ap000611.html to explode one day and if a nova explodes, it may become a black hole. Figure 4: The image of Betelgeuse

Source: https://apod.nasa.gov/apod/ap990605.html

Reference: “Why Are Stars Different Colors?” Planets for Kids, www.planetsforkids.org/why-are-stars- different-colors.html. Williams, Matt. “Why Are Stars Different Colors?” Universe Today, 25 Sept. 2016, www.universetoday.com/130870/stars-different-colors/. “Doppler Shift.” NASA, NASA, imagine.gsfc.nasa.gov/features/yba/M31_velocity/spectrum/doppler_more.html.

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17. Why are the colors of stars different?

Nowadays, there are more and more people interested in the universe. We search a lot of images from the website and are surprised by the beauty of the stars. But have you ever wondered will the colors of stars we see change someday? We should discuss why are the colors of stars different first.

Have you ever heard the magic photo mug? It is a kind of cup that can reveal your photo when pour the hot drinks. This is because the temperature increases and discolors the heat-sensitive material.

In fact, the color of the stars is also mainly

determined by their temperature. The

temperature determines wavelengths. Different

wavelengths correspond to different radiance

with kinds of colors. The higher temperature

they reach, their colors are cooler. Conversely,

if the temperature is low, they are more likely to

be red.

Figure 1: Ternary map

(Source: website)

But the problem is not so simple, there are more factors that affect the color of stars. Stars are made of hydrogen and helium, and also various trace elements, the colors are different. When the colors in the spectrum are mixed, the colors of the stars usually appear lighter. For example, the approximate temperature of sun is about 5778k [1]. Its corresponding color should be blue-green, but the color of the sun we see in our daily life is pale yellow. Finally, when there are other elements in the atmosphere, or light waves, sound waves, it may also affect the color of the stars we see, making them more colorful.

EVERDAY PHYSICS 46

This answers our related question. The colors of stars that we see will change, they may be bluer or redder.

In fact, in addition to making the night sky more beautiful, we should also get more inspiration. The color of the stars may also help us understand how long the stars exist in the universe.

Secondly, some special or abnormal color changes of the stars make us better understand the changes of the cosmic environment. To a certain extent, disasters may can be avoided. For example, an overheated star may explode and may affect the earth. If its color has changed before, we can do more preparation.

Although stars are part of the vast universe, they can also give us a better understanding of the universe.

[1] Williams, David “Sun Fact Sheet.” NASA, NASA, 23 Feb. 2018, Interesting fact: Why the sky is blue is actually related to the color of the stars. The blue sky we see is the effect of sunlight on the atmosphere. Sunlight is a mixture of multiple colors.

When passing through the atmosphere, several other colors are scattered by molecules, elements, and other factors. Finally, several colors are left, which are near the blue part of the spectrum. The color after mixing is the color of the sky we see

nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html.

EVERDAY PHYSICS 47

18. Why does Earth rotate?

Every day, around the world, the sun rises in the east and sets in the west. To us, that is reality, but it is not the sun that is setting and rising but us, on Earth, rotating as we orbit the sun. The rotation of Earth gives us our days, sustainable temperatures, and is a crucial part of our existence on this planet, but it begs the question: why does Earth rotate?

All planets in our Solar System rotate. Earth completes a rotation every 24 hours whereas it takes Mercury, the planet closest to our sun, 59 Earth days to complete one full rotation. This rate of rotation is somewhat arbitrary and is a direct result of the formation of our Solar System 4.6 billion years ago. In the beginning, there was just a vast cloud of dust and gas. As time passed, this vast cloud began to flatten and collapse causing its rotation to not only begin but accelerate. To visualize what occurred, imagine a figure skater or somebody sitting on a chair that can rotate freely. After the initial rotation begins, the closer the center of weight of the person spinning gets to the origin of rotation, the faster the figure skater or the person on the chair will rotate. This is as easy as bringing your arms to your chest if you’re spinning on the ice or in your office. This is what occurred nearly 5 billion years ago at the beginning of our solar system as this vast cloud of gas and dust began to collapse [1][2].

Within this massive swirling cloud there were smaller, more contained, swirls of gas and dust from which planets eventually formed. In the center of this flattening disk of gas and dust the sun

formed, and all of these relatively smaller planets formed

around it. Each planet, Earth included, formed as these

smaller swirls of gas and dust collapse further to create a

planet. With this further collapse, like pulling your arms

in while you spin, the rotation of these newly formed

EVERDAY PHYSICS 48 planets accelerated. With no atmosphere or external frictions to slow this rotation, the planets of our

Solar System have kept spinning to this day [1][2].

It is almost impossible to believe the chain of events that allowed for Earth to sustain human life. Our proximity to the sun and the speed of our rotation, which seemed to occur by the luck of the draw all those 5 billion years ago, play fundamental roles in the inhabitability of Earth. We have

Earth’s rotation to thank for our warm sunny days and cool dark nights and so much more.

Interesting Fact 1: The rotation of Earth is actually slowing down. According to NASA’s extremely accurate atomic clocks, in 100 years a day will be about 2 milliseconds longer. This is not noticeable but certainly interesting to think about [1].

Interesting Fact 2: Many scientists believe that a piece of debris the size of Mars could have collided with Earth in its infancy, actually accelerating Earth’s rotation, but sending debris into space that was once a part of Earth. One of these pieces of debris is thought to have become our moon. Over time, the moon has drifted farther from earth but has played a key role in the life cycle on Earth. The gravity from the moon determines the tides of Earth’s oceans. The friction between the tides and the rotation of Earth is thought to be the cause of the very gradual slowing of Earth’s rotation, as we saw in the first fact above [1].

[1] “Why is Earth rotating? Did it always have the same rotation period? Will it always have the same rotation period?” NASA. https://spaceplace.nasa.gov/review/dr-marc-earth/earth- rotation.html

[2] “Why does Earth spin?” CalTech. http://coolcosmos.ipac.caltech.edu/ask/59-Why- does-Earth-spin-

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19. What Is At The Very Bottom Of The Ocean?

To date, twelve people have reached the moon, but only three people have reached the bottom of the ocean floor. On first glance, this statement seems like it should be the other way around, considering the difficulty in reaching outer space compared to the ocean floor on Earth. However, there is still much that we do not know about our oceans.

To answer the primary question of “what is at the very bottom of the ocean”, we must also discuss the secondary question of why deep-sea exploration is so difficult. This will give the context behind why the primary question needs to be asked in the first place. First, we will look at the history behind deep-sea exploration and ongoing efforts at the present. Next, we will discuss the logistics involved in reaching the bottom of the ocean. Finally, we will discuss what we currently know exists at the bottom of the ocean.

The history of deep-sea exploration begins in 1521, when Ferdinand Magellan attempts to measure the depth of the Pacific Ocean (Helmenstine). This makes the field relatively recent in comparison to others. The deep sea is today considered to be parts of the ocean that are below 200m

(WWF), or where sunlight begins to become unable to penetrate down to the depths. The reason sunlight is unable to penetrate so deep is because most wavelengths of light are absorbed within the first 50m; blue light penetrates the farthest, down to the aforementioned depth of 200m (Graham). The deepest humans have reached is Challenger Deep at 10,929m, in 1960 by the submersible Triste (National

Geographic). But how do we know that this is the deepest part of the ocean? Well, while 95% of the ocean floor remains unexplored, humans have actually mapped the entire ocean floor; but only to a resolution of up to 5km (Kershner). Essentially, we can only see things that are more than 5km large.

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Knowing the history behind deep-sea exploration and its present status will now allow us to discuss why humans have not mapped more of the ocean; what are the logistics involved?

The logistics involved in deep-sea exploration is immense. Firstly, we should discuss manned exploration. Pressure is the biggest limiting factor to manned deep-sea exploration. This is because pressure increases when depth increases (NOS). This ocean pressure is called hydrostatic pressure, which exists due to the weight of the water. The further down you go, the greater the volume of water that is trying to squish you. This creates pressure that the human body cannot withstand. Thus, we must rely on submersibles that can withstand the immense pressure and protect us while we descend, in addition to the cold (due to sunlight fading beyond 200m).

Next, we should discuss unmanned exploration. This is primarily achieved through robots and sonar. Unmanned submersibles are advantageous in the sense that they do not have to bother with protecting humans from hydrostatic pressure. These are called autonomous underwater vehicles, or

AUVs. They do not need cables to operate, and are simply dropped overboard for exploration purposes.

One difficulty associated with AUVs are communicating with them at such deep depths; radio waves cannot penetrate that far down to communicate, rendering GPS useless. Increasing technological capabilities are resolving this problem, but even today AUVs have to use a system called “dead reckoning”, which identifies position based on where the submersible was dropped (M. T. Sabet).

Imagine being in a park at the dead of night. You cannot see where you are going, but you know that you started at the entrance of the park. Going from one point to another in a certain direction will allow you to track the distance between the two points based on the time it takes to get there. Going back and forth between enough points will give a rough picture of the terrain. Sonar is another method of deep-sea

EVERDAY PHYSICS 51 exploration. This is a method of using sound waves to rebound off a surface back to where it was first emitted. By analysing the data that is returned, one can “determine the range, bearing, and relative motion of the target” (Britannica). This allows people to map the ocean floor even from the surface.

We know that life exists even at the greatest depths of the ocean. Triste found evidence of life at the bottom of Challenger Deep. Thus, another question emerges; how can life survive in such inhospitable conditions? The primary reason for this is the incompressibility of water. This means that water cannot be squished to make room for anything such as air (USGS). Living things are largely composed of water, so living creatures at greater depths minimise the empty space in their bodies. Since these living creatures are largely composed of water, pressure does not affect them because they are largely incompressible (Lacey). In comparison, humans contain air cavities in many parts of our body, which makes it dangerous for us to go down too deep.

In conclusion, it is remarkable how little we know about the universe. We look towards the stars for knowledge beyond the stars, but we do not even know what lies on our own planet. It is our largest biosphere, filled with new possibilities that can provide answers to meaningful questions such as the emergence of life on Earth.

Works Cited Britannica. “Sonar”. Britannica. Web. https://www.britannica.com/technology/sonar Graham. “If You Are Trying To Find The Bottom Of The Sea The Water Is Black, Why Is That?”. University Of California Santa Barbara. May 2015. Web. http://scienceline.ucsb.edu/getkey.php?key=4903 Helmenstine, Marie Anne. “Deep Sea Exploration History and Technology”. Thoughtco. 25 June 2019. Web. https://www.thoughtco.com/deep-sea-exploration-4161315

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Kershner. “Do We Really Know More About Space Than The Deep Ocean?”. HowStuffWorks. Web. https://science.howstuffworks.com/environmental/earth/oceanography/deep-ocean- exploration.htm Lacey, Claire. “Curious Kids: How Do Creatures Living In The Deep Sea Stay Alive Given The Pressure?”. The Conversation. 1 March 2019. Web. https://theconversation.com/curious-kids- how-do-creatures-living-in-the-deep-sea-stay-alive-given-the-pressure-111940 M. T. Sabet, H. Mohammadi Daniali, A. Fathi and E. Alizadeh, "A Low-Cost Dead Reckoning Navigation System for an AUV Using a Robust AHRS: Design and Experimental Analysis," in IEEE Journal of Oceanic Engineering, vol. 43, no. 4, pp. 927-939, Oct. 2018. National Geographic. “The Marina Trench”. National Geographic. Web. http://www.deepseachallenge.com/the-expedition/mariana-trench/ NOS. “How Does Pressure Change With Ocean Depth?”. National Oceanic And Atmospheric Administration. Web. https://oceanservice.noaa.gov/facts/pressure.html USGS. “Water Compressibility”. United States Geological Survey. Web. https://www.usgs.gov/special- topic/water-science-school/science/water-compressibility?qt-science_center_objects=0#qt- science_center_objects WWF. “Deep Sea”. WWF. Web. https://wwf.panda.org/our_work/oceans/deep_sea/

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20. Why are there stars of different colors?

For centuries, people have looked up at the night sky in amazement of its twinkling stars that

seem to extend to infinity. To the naked eye, these stars appear as tiny specks of white light, however

stars are in fact much more complex entities that are not only massive

but also can shine in a multitude of colors. What makes these stars so

colorful?

The color of a star is not as trivial as it may seem; it reflects

important properties. These properties include the temperature, relative

velocity/distance and elemental composition of the star. The

relationship between color and elemental composition is central to Hertzsprung-Russell Diagram (source: google) understanding star color. A given star can vary in the elements that

compose it. For example, some stars may be hydrogen based while others can be helium based. When

different elements are heated, they emit different wavelengths at different colors and therefore, a star’s

emission spectrum (the collection of wavelengths it emits) will vary depending on its composition. The

color of a star will result of the combination of these emitted wavelengths. The temperature of the star

will also influence its color. The hotter a star, the radiated energy increases and the wavelengths of light

emitted shift towards shorter wavelengths, giving the star a bluer color. A less hot star will have

decreased energy of radiation of will have its emitted wavelengths shifted towards longer wavelengths,

giving the star a redder appearance. The relationship between temperature and color of a star is

summarized in the Hertzsprung-Russell diagram. Finally, the relative velocities of stars have an effect on

their color as well. Stars retreating away from Earth appear to us as redshifted meaning the light emitted

EVERDAY PHYSICS 54 from the star is shifted towards the longer wavelengths, making them appear to be more red. Stars moving towards Earth are blueshifted and therefore, appear to be bluer.

Interesting fact: Although the sun appears to be yellow/white to us, its peak emission

is actually in the range of green wavelengths! However, it is not only the peak wavelength

that determines the color of a star; as we now know, the other emissions mitigate the

perceived color of a star as well.

!

The colors of stars have larger implications than simply the beautification of satellite images in space. As we now know, the color of a star can tell us many things about the properties of said star, but it may also tell us about the planets that orbit that star. For example, by observing star color, we can infer the temperature of said star which could tell us about the habitability of the planets surrounding it in the search for inhabitable exoplanets. The information we can extract from this seemingly unimportant feature of stars reminds us that stars have more to offer us than their aesthetic, and this information allows us to learn about deep space that would otherwise be unreachable.

Works cited

“Why Are Stars Different Colors?” Planets for Kids, www.planetsforkids.org/why-are-stars- different-

colors.html.

“Hertzsprung-Russell Diagram: COSMOS.” Centre for Astrophysics and Supercomputing,

astronomy.swin.edu.au/cosmos/H/Hertzsprung-Russell Diagram.

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21. What is gravity and where does it come from?

It’s such an everyday phenomenon that we often take it for granted — so much, in fact, that we find it hilarious when astronauts retain habits from when they lived without it. Yes, gravity is something that we all interact with every day, but the reach of gravity goes far beyond what we experience here on Earth.

We will first examine how Sir Isaac Newton defined the law of universal gravitation. Then, we will look at several examples where gravity serves an important role in keeping our universe orderly and together. Finally, we will elaborate on how Einstein’s theory of general relatively has added to our definition of gravity and our understanding of how it works and where it comes from.

According to one classic tale, Sir Isaac Newton (1643-1727) suddenly realized the concept of gravity after observing an apple fall to the ground from a tree. Apple or no apple, Newton did eventually go on to find that gravity acts on all matter that has non-zero mass in a way that depends on both mass and distance [1]. He described it as a force that two objects with mass exert on each other. He

퐺∗푚 ∗푚 summarized it in the following equation: 퐹 = 1 2 [1]. This equation states that the force of gravity, 푔 푟2

Fg, is proportionate to the mass of the two objects, m1 and m2, and inversely proportion to the square of

Gravity in Space: Since astronauts in Space are much further from the Earth, they

experience much less gravitational force due to Earth’s mass. Consequently, everyday phenomena

that we observe here on Earth due to gravity aren’t necessarily experienced the same way up in

Space. In this video, astronaut Chris Hadfield demonstrates how something as simple as wringing

out a wet cloth appears differently in Space (there’s little gravity up there, but water still has surface

tension). Even something as simple as taking a poop needs careful engineering to design a suitable

toilet to match the gravitational environment up in Space. the distance, r, between them (G is a universal gravitational constant). What was amazing about

EVERDAY PHYSICS 56

Newton’s discovery is that it not only predicted the movement of apples falling from trees, it was also capable of predicting the revolution of the planets around the Sun (recall that the Sun has an enormous mass compared to the Earth) [1]. Indeed, without gravity we wouldn’t have tidal waves. Earth wouldn’t remain at the optimal distance from the Sun to sustain life [2].

Yet, there were some things about gravity that still escaped explanation, such as its mechanism and where it comes from. Enter Albert Einstein (1879-1955), who postulated that space and time were not separate entities, but rather they form a continuous fabric of spacetime [3]. Einstein reasoned that any object with mass would distort that spacetime fabric — objects with much greater masses would cause more distortion. Thus, gravity is a consequence of that distortion of spacetime, according to

Einstein’s theory of general relativity. His theory successfully predicted the bending of Mercury’s orbit around the Sun and the bending of starlight around the Sun during the 1919 solar eclipse (due to the interconnectedness of spacetime, the path of light around very massive objects would bend) [3].

Yes, gravity is such an everyday phenomenon that we barely think about it. Yet, as we spend more time thinking about gravity, we begin probe at even bigger questions about how our universe exists and came to be.

[1] Fuge, L. (2018). Explainer: What is gravity? Cosmos: The Science of Everything. Retrieved from https://cosmosmagazine.com/physics/explainer-what-is-gravity

[2] What Is Gravity? (2019). Retrieved from https://spaceplace.nasa.gov/what-is-gravity/en/

[3] Wood, C. (2019). What Is Gravity? Retrieved from https://www.space.com/classical- gravity.html

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22. How do we know the age of the Earth?

No matter where you grew up or how you were raised, one question that every human will

undoubtedly ask regards the age of our planet Earth. The answer is roughly 4.6 billion years old, and

when hearing such an astronomical number, a second question is posited; how could we possibly know

this if humans have only been around for a very small fraction of that time? The answer to the origin

story of Earth lies in the rocks, and more specifically in the radioactive isotopes found within these

rocks.

Those radioactive isotopes within the rocks can be measured using a process called radiometric

dating. The way radiometric dating works is by examining the rock to see what radioactive isotopes are

naturally present in it, with these radioactive isotopes being

known to decay into other elements. Radioactive elements decay

by giving off radiation and they do so because they have unstable

atomic nucleus that constantly try to shift to become more stable.

The way this is helpful in dating rocks is through the half-life of Figure 2: Acasta Gneiss; oldest rock found on Earth the radioactive isotope (which varies given the rock); that is the

amount of time it took for half of the starting radioactive isotope to decay. Different radioactive isotopes

will decay at different rates, and so accordingly there are several dating methods such as Uranium-Lead

dating, Rubidium-Strontium dating and many more.

To make this simpler, suppose you had a rock that had the mineral uranium present within it. We

know the decay rate of Uranium-238 and 235, meaning we know the length of time it took for those

original elements to decay to Lead-206 and 207 respectively. The half-life is how many years it took for

the initial isotope, in this case uranium, to decay into the daughter isotope, in this case lead. For

Uranium-Lead dating, this half-life is 4.5 billion years for uranium-238 to decay into lead-206, and 700

EVERDAY PHYSICS 58

million years for uranium-235 to lead-207. As such, you can apply this information to that rock to

compare the amount of uranium present relative to the amount of lead and use the half-life to help you

age the rock.

The oldest mineral found on Earth (their source rocks have yet to be found) is located in Interesting fact: The oldest rock found on Earth is called the Acasta Gneiss and is located in Northwestern Canada in the Great Slave Lakes. This rock is dated to be 4.03 billion years old and is believed to be a fragment of Earths continental crust.

Australia and is dated to be about 4.3 billion years old. Using this information, we know that Earth is at

LEAST 4.3 billion years old. How we determine the actual age of our planet is the most fascinating part

as we use information gathered from fragments of meteorites that

crashed into Earth, which allows us to know the age of our solar

system. Knowing this, the best estimate of Earths age comes not from

dating individual rocks but by considering the Earth and meteorites as

part of the same evolving system in which the isotopic composition of

lead, specifically the ratio of lead-207 to lead-206 changes over time

owing to the decay of radioactive uranium-235 and uranium-238, respectively [1]. Using this

information scientists can see the time it took for the oldest ores of lead found on Earth to change from

their primordial composition, which is measured from the meteorites, to their composition when they

separated from their mantle reservoirs on Earth. This time is estimated to be a mind-boggling 4.54

billion years.

[1] “AGE OF THE EARTH.” Geologic Time: Age of the Earth, Publications Services, 9 July 2007,

pubs.usgs.gov/gip/geotime/age.html.

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23. How do we know the universe is expanding?

When we look up at the night sky, we are treated to a wonderous view. Countless stars shine down on our world, enchanting and inspiring humans like us since the dawn of mankind. Yet, will our descendants one day look up to see darkness? That may be an implication of an expanding universe in which the distance between celestial bodies grows at an increasing rate. In this paper, we will explore how we know this to be true.

The Doppler effect describes how the frequency of a wave changes relative to an observer when the observer and the source of the wave are moving relative to one another. As the observer and the source of the wave grow further apart, the frequency of the wave decreases and vice versa (Figure 1). An everyday example of the Doppler effect is the increase and subsequent decrease in the pitch of an ambulance siren as an ambulance first approaches and then passes you. Just as this effect is observed in

soundwaves, it is also observed in waves in the

electromagnetic field. The totality of possible wavelengths

in the electromagnetic field form the electromagnetic

spectrum, of which visible light forms a subset. We see the

low frequency, longer wavelength end of the visible light Figure 1: The Doppler Effect (Source: Chris Crockett, spectrum as red. The opposite high frequency, shorter EarthSky) wavelength end of the spectrum is seen as violet. Just as

the soundwaves of the ambulance siren decrease in

frequency and drop in pitch as an ambulance moves away

Figure 2: Redshift of Distant Light (Source: Harold Stokes, BYU)

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from us, we would expect the light from a distant star to decrease in frequency and become redder as the

star moves further away. Measuring Redshift: When stars emit light, some of said light is absorbed by elements

within the star itself. This creates gaps in the spectrum of emitted light, called absorption lines,

which clearly indicate the presence of elements such as hydrogen and helium. When light is

redshifted, these lines move towards the red end of the visible light spectrum (Figure 2). By

observing the magnitude of this movement relative to lab controls, we can determine the magnitude The magnitude of this redshift reveals the speed at which said star is moving away from us. of redshift. When this data is compiled and aggregated, we find that distance between other galaxies and our galaxy

cluster is growing at an accelerating rate. Furthermore, this observation holds regardless of initial

reference point. This implies that other galaxies are not moving away from us. Rather, the cause of the

redshift is the expansion of space itself! In everyday terms, galaxy clusters are like points on the surface

of a balloon which is slowly being inflated. At each point on the balloon, it would seem as if you were

standing still while the other points were speeding away. So, what awaits our descendants? As space

expands, galaxies outside the Local Group will eventually become so distant that their light will never

reach the Earth. They will pass from the realm of what we could ever hope to see, with the night sky

becoming a relative sea of darkness.

Carnegie Institute for Science. Edwin Hubble discovers the Universe is expanding. Retrieved from

https://cosmology.carnegiescience.edu/timeline/1929

Crockett, C. (2012, June 4). What is a redshift? Retrieved from https://earthsky.org/astronomy-

essentials/what-is-a-redshift

Garner, R. (2019, April 24). Mystery of Universe's expansion rate widens with new Hubble data. Retrieved

from https://www.nasa.gov/feature/goddard/2019/mystery-of-the-universe-s-expansion-rate-widens-

with-new-hubble-data

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24. Is the universe infinite?

“To infinity and beyond!” that is the catchphrase of Toy Story’ astronaut Buzz Lightyear, but is our universe actually infinite? Can we even know its true size? that is what astronomist and physicist have been trying to solve for decades.

To answer this, we don’t really know, scientist and astronomists have been coming up with different models and theory that suggest that the Universe is either infinite or finite. To understand whether it is infinite or finite, we have to know the curvature of the universe or what is its shape.

Scientists with the help of the Wilkinson Microwave Anisotropy Probe have been able to determine the curvature of our universe to be flat with a 0.4% margin of error [2]. This has also been demonstrated by the more recent Planck satellite, they came up with this conclusion by studying the Cosmic Microwave

Background which is basically the theoretical leftover from the Big Bang, creating a snapshot of our

universe in one of its earliest moments [3].

People erroneously think that a flat universe that is

expanding is infinite, imagine an ant walking on a paper sheet

that is expanding at a higher rate than the pace of the ant, the Figure 1: A torus and a sphere (Source: Medium, The Poincare conjecture) ant will surely think that the sheet of paper will continue forever but that is not the case. The exact statement should be a flat universe that is simply connected implied an infinite universe. By simply connected it means that for example, for the sphere shown in the figure, if we were to create a loop like the blue line we would be able to contract it to a point but for a torus if we were to create a loop like the green line we would not be able to contract it to a point without leaving the surface. Therefore, if our universe is flat and spherical it will be simply connected thus infinite but if its flat and multiply connected like a torus it will be finite.

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We are also not sure on the exact size of the universe. To understand that we must distinguish between the observable universe and global universe. The observable universe refers to the spherical region of the universe that can be observed from Earth or its space-based telescope and probes at the present time, the global universe is made up of the observable universe plus what is beyond it. From the Planck satellite, we have been able to determine the edge of the observable universe to be 46.1 billion light years away from us, alternatively the observable universe have a diameter of 92.2 billion years with the Earth at its center [4]. Interesting experiment/fact/idea/concept: In theory to determine if the universe is spherical or flat, we could draw a gigantic triangle spreading across the universe. If the angles add up to 180ᵒ then we have no curvature and the universe is flat, if it adds up to more than 180ᵒ then there is a positive curvature and the universe is spherical. But in reality, it is much more complicated than that.

One thing we know for sure is that the universe is expanding, and we will technically never be able to reach its edge, if there is one. Indeed, the observable universe is 93 billion light-years across – that’s 28.500 megaparsecs, the expansion rate given by recent studies is 73/km/megaparsecs. This would mean that the points which are farthest away are moving away at a speed of light of about

2,000,000 km/s - higher than the speed of light [1]. Therefore, we will never be able to determine the exact size of the entire universe or if its finite or infinite with today’s technologies, it is a vast and mysterious place, equally marvelous and terrifying.

1. Andrei, M. 2019. Is the universe infinite? Retrieved from https://www.zmescience.com/other/feature-post/is-the-universe-infinite/ 2. Wollack, E. 2017. Wilkinson microwave anistrophy probe. Retrieved from https://map.gsfc.nasa.gov/ 3. Biron, L, 2015. Our flat universe. Retrieved from https://www.symmetrymagazine.org/article/april-2015/our-flat-universe?email_issue=725

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4. Siegel, E. 2018. How the Planck satellite forever changed our view of the universe. Retrieved from https://www.forbes.com/sites/startswithabang/2018/07/19/how-the-planck-satellite- changed-our-view-of-the-universe/#2f0bd3b37ad2

25. Is there gravity in space?

“That’s one small step for man, one giant leap for mankind.” Do you still remember seeing the

famous footage of the 1st human walking out of the spaceship and putting the flag on the moon? Do you

ever wonder why he is floating in the space and having a rope around his waist? Where does this feeling

of weightlessness come from? Now if you put a physics word into your question, it becomes, “Is there

gravity in space”?

Firstly, there is often some misunderstanding about the term “gravity” because of the story,

saying Newton was hit by the apple falling. We then thought gravity is a kind of one-side attraction

down going force that the earth acts on objects. If the objects are not on the earth, it would be “gravity-

free”. However, the gravitational force is a mutual interaction force that

pulls two objects with mass together. It is everywhere. While the earth

pulls on us, we also pull the earth. The pull force from us to the earth is

too small to move it, but we can fell weightiness because the earth

presses us against the floor / the ground. Back to the space scenario, as

the gravity rapidly decreases when distance increases; if you are far

away from the planet, you will receive less pull force from it. The

gravity becomes less significant to be felt. Plus, astronauts and their

spaceship in the orbit are falling toward the earth under the gravity at

the same speed, and there is no ground in the space to press Figure 1: Movie – “Gravity” (Source: https://addisstandard.com/wp- astronauts against, they feel weightless. content/uploads/2013/12/Movie- Review-p.-311.jpg)

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Gravity is also useful in scientific studies. It influences the paths taken by everything traveling

through space. It keeps planets in orbit. It makes it possible to use human-made satellites and to go to

and return from the Moon. It makes planets habitable by trapping gasses and liquids in an atmosphere. It

can also cause life-destroying asteroids to crash into planets [1].

Interesting experiment: You can experience the feeling of astronauts for a moment of weightlessness by taking a fast-moving elevator going down or a roller coaster going down a big hill.

I am one of the people that have believed zero-gravity in the space before working on this

question. This thought may be developed from astronauts’ interviews or sci-fi movies or my inanimation

of a magic universe. Overall, it is always beneficial to go search for scientific proofs or theories before

trusting yourself or others’ minds.

[1] Qualitative Reasoning Group, Northwestern University. "How does gravity work in space” Virtual Solar

system Project. http://www.qrg.northwestern.edu/projects/vss/docs/space-environment/zoom-grav.html Accessed

on Feb 12, 2020.

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26. Why is the Earth round?

Have you ever thought to yourself why the Earth is round and not some other shape, such as square, hexagonal or even flat? What makes the Earth and other planets round, and are they perfect spheres?

Long before Magellan first circumnavigated the globe, Greek Philosophers measured the circumference of the Earth using shadows and proved that the Earth was round [1]. From this point on, it has been largely accepted by all academics that the Earth is round. Thanks to scientific discoveries, we know that way in which the Earth and our solar systems form is due to gravity. Planets form from material

floating in space and as they start to clump together, their

gravitational pull increases with their mass and density.

Just like a bike wheel’s spokes, a planet’s gravity pulls

inwards equally in all directions, hence why they form as

three-dimensional spheres [2]. This means that planets

adopt sphere shapes rather than squares, triangles, or any

other obscure structures. But are they all perfect spheres?

Simply put, no. On the surface no planet is a Figure 1: Gravity pulling in towards the center of Earth. (Source: powerpoint) perfect sphere; for example, on Earth we have mountains, valleys and other protruding elements that stop it from being perfectly smooth. On the other hand, if we were to look at Earth from space, it would look like a round and smooth blue marble. However, it still would not be a perfect sphere, and here is why: the diameter, or distance between opposite ends of a circular object, is greater between two points on the equator than between the two poles. Just like when you are on a roundabout at a playground, you feel a centrifugal force pulling you outwards, and this same force occurs on the Earth’s surface. The centrifugal force pulling outwards is stronger at the equator versus

EVERDAY PHYSICS 66 at the poles, which makes the planet bulge along its equator [2]. Therefore, Earth and all other planets, are not examples of perfect spheres.

Interesting experiment: If you are ever near an ocean or harbour, you can prove that the

Earth is in fact round! Watch a ship as it sails out towards the horizon and you’ll notice that its mast and flags slowly start to disappear. Notice that they do not fade away but rather sink under the horizon. Don’t believe it or you think your eyesight is bad? Bring along a pair of binoculars to increase the distance that you can see [3].

While it’s interesting to learn why the Earth is round, it is also relevant to this day as a growing number of people believe that the Earth is flat. Just like our ancestors before us, it’s important to continually question the world around us and we should strive to seek the truth through scientific experimentation. That being said, it has never been easier to prove that the Earth is round, which can easily be done through simple experiments at home!

[1] Hogenboom, Melissa. “Earth - We Have Known That Earth Is Round for over 2,000 Years.” BBC, BBC, 26 Jan.

2016, www.bbc.com/earth/story/20160126-how-we-know-earth-is-round.

[2] Erickson, Kristen. “Why Are Planets Round?” NASA, NASA, 27 June 2019, spaceplace.nasa.gov/planets-round/en/.

[3] “7 Ways to Prove the Earth Is Round (Without Launching a Satellite).” LiveScience, Purch, www.livescience.com/60544-

ways-to-prove-earth-is-round.html.

EVERDAY PHYSICS 67

27. What is gravity and where does it come from?

Albert Einstein once said: “Gravitation is not responsible for people falling in love.” Although spoken in jest, gravity is indeed ubiquitous in our daily life. Why the mighty Niagara Falls flow down instead of rising into the air? What drags the thrown basketballs back to the ground? How can we stand, walk, and run in the streets instead of floating in the space? The answer to all of these normal but important questions is gravity.

So what is gravity and where does it come from? According to Isaac Newton, the great man inspired by the fall on the head of an apple, gravity is the force of attraction between any two objects.

His famous laws of gravitation claim that the gravitational force between a pair of objects is also defined by their mass and the distance between them. To be more specific, the greater the mass of the objects, and the shorter the distance will lead to a stronger gravitational pull. In his own words, “I deduced that the forces which keep the planets in their orbs must be reciprocal as the squares of their distances from the centers about which they revolve.” [1]

Einstein’s theory of relativity asserts that gravity

is more than a force, but a curvature in the space-

time continuum, and a consequence of the fact that

Figure 1: the curvature of matter warps space-time. In simple terms, the theory space describes how the mass of an object actively causes the space around it to curve and bend. While the human eye can’t see this curvature of space, it can be

EVERDAY PHYSICS 68

detected when observing the motions of objects. [2] For example, the celestial body’s gravity will

force objects moving toward it operating in a curved way.

Some scientists also come up with the idea of the graviton, which is the particle that causes

objects to be attracted to one another. However, gravitons have never been observed. Above all,

gravity is essential, for it keeps the world operate well, yet it is also challenging, for the unproven

Interesting fact: Isaac Newton was just 23 years old and back from university when he noticed an apple falling in his garden and began unraveling the mysteries of gravity. (It's probably a myth that the apple bonked him on the head though.) [3]

scientific secrets behind.

[1]Chandrasekhar, Subrahmanyan (2003). Newton's Principia for the common reader. Oxford:

Oxford University Press. (pp. 1–2).

[2]CABMATE (2016). https://www.labmate-online.com/news/news-and-views/5/breaking-

news/where-does-gravity-come-from/39071

[3]Ghose, Tia(2013). LICESCIENCE. https://www.livescience.com/37115-what-is-gravity.html

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28. Why is the Earth round?

Imagine you are in an airplane 35,000 feet above the ground and watching the sun beautifully set off the horizon, curving ever so slightly with the outline of the Earth. Then imagine a ship sailing into the distance, with what looks like the “end” of our planet first obscuring the front of the boat until the entire ship vanishes from your view. These two examples, though simple, clearly demonstrate a concept that is innate to most of us: that the Earth is round. But why is the Earth round? Why can’t we walk right off its edge into space?

The answer is gravity, which is “an invisible force that pulls objects toward each other” instead of pushing them apart [1]. An example of gravity’s force is that you do not float into space when you jump, but rather you are pulled back towards the ground! It also explains how planets were formed; gravity pulled together the countless pieces of dust and gas floating in our solar system until they had

enough mass to form the eight planets

and the Sun [2]. Its application to the

spherical nature of Earth is similar;

Earth’s gravity pulls equally in all directionsFigure with 1:a sphereEarth’s being Gravitational the natural Pulloutcome of this invisible pull [3]. Imagine that in Figure 1, which depicts a bicycle wheel and its spokes, gravity

pulls inward to the wheel’s core from every possible

possible direction. This is exactly what happens in space to

make Earth round!

Earth is not a perfect sphere, however. It rotates on

an axis in its orbit, just like the seven other planets in our

solar system. Because of this, its outer edges need to move Figure 2: Equatorial

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more quickly than the rest of it to keep up [4]. This results in an outward bulge at its equator, making

Earth spherical but not perfectly round. This can be seen in Figure 2. Its diameter measured across the

equatorial plane is 7,927 miles, while that measured between the poles is 7,900 miles, giving Earth an

equatorial bulge of around 27 miles [5]. Saturn has the largest equatorial bulge of all the planets in our

solar system, close to 7,000 miles [6].

Although we say Earth is round, much to the dismay of flat-earthers, what we actually

mean to say is that it is an ellipsoid. An ellipsoid is exactly what is depicted in Figure 2 on the right;

Who First Discovered the Earth Was Round? How Did He Do It?

Ancient Greek philosophers discussed the shape of Earth long before NASA could take pictures of it. Around 500 B.C., Pythagoras proposed that Earth was spherical because of the shape’s harmonious properties. From 384-322 B.C., Aristotle proposed arguments similar to my opening sentences to prove Earth’s roundness. In 240 B.C., however, a Greek librarian named

Eratosthenes calculated Earth’s circumference, proving that the planet was round. He used the

while the gravitational forces of the universe pull inward from every direction, the rotation of Earth

leads to its equatorial bulges on the sides. If the Earth were not shaped the way it is, it is possible that

our planet wouldn’t have gravity, that we could fall off it into nothingness, or that we would not receive

sunlight. Earth’s shape is integral to our existence and life as we know it!

[1] “What Is Gravity?” NASA, NASA, 14 Oct. 2019, http://spaceplace.nasa.gov/what-is-gravity/en/. [2] “Ask an Astronomer: Why Are All of the Planets Round?” Cool Cosmos, http://coolcosmos.ipac.caltech.edu/ask/194-Why-are-all-of-the-planets-round-. [3] “Why Are Planets Round?” NASA, NASA, 27 June 2019, http://spaceplace.nasa.gov/planets-round/en/. [4] Ibid. [5] Equatorial Bulge, http://cleonis.nl/physics/phys256/equatorial_bulge.php. [6] Choi, Charles Q. “Planet Saturn: Facts About Saturn's Rings, Moons & Size.” Space.com, Space, 13 May 2019, www.space.com/48-saturn-the-solar-systems-major-ring-bearer.html. [7] “Jupiter.” Astr 121, Winter '05, Chapter 11 Notes, http://pages.uoregon.edu/jimbrau/astr121- 2005/Notes/Chapter11.html. [8] “This Month in Physics History.” American Physical Society, www.aps.org/publications/apsnews/200606/history.cfm.

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29. Where do black holes come from?

Have you ever seen the movie Interstellar before? It’s a science fiction movie created by director

Christopher Nolan. In the movie, a fictional black hole called Gargantua is introduced to the audiences.

The whole movie reached the climax when McConaughey’s Character navigates ship into the black hole

and reaches a fifth dimension, where he communicates with his daughter across time and space

(Woodward, 2019). The black hole is so mysterious that it makes me wondering how do we know it

actually exists? Or first, where do black holes come from?

A black hole is an area or a region in space where the gravity is so strong that nothing can escape

from it. The origin of the name is because even light could be sucked in it (UNAWE, n.d). A black hole

forms when a massive star reaches the end of its life. The star is unable to support its heavy outer layers

of gas. The massive star’s gravitational force pulls on the gas and causes the star to become smaller until

its density reaches infinity at a single point, which is called “singularity”. The black hole can keep

growing by absorbing mass such as other stars from its surrounding, just like water going down a

plughole (UNAWE, n.d.). After a black hole absorbs enough material, it can become a so called

“supermassive black hole”. Such black holes are believed to exist in the centers of every galaxy,

including the Milky Way (Redd, 2019).

In fact, scientists can’t observe black holes in the usual way since it does not emit any light.

Instead, they observe it when the black hole interacts with other objects. As a matter is drawn toward the

black hole, it forms a disc around the black hole. As the disc spins

faster, it heats up causing enormous amounts of light and emit into

space as sparkling jets (UNAWE, n.d.). Those jets are extremely

bright and can be viewed from great distance by our telescopes on

Figure 1: First image of a black hole the Earth (Redd, 2019). (Source: EHT Collaboration)

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Interesting fact: There’s no direct image of black hole before. On April 10, 2019, the Event

Horizon Telescope team released the first image of a black hole. The image was constructed in two years after the images were taken. The reason behind is that the it is collected by all telescopes located worldwide and contains large amounts of data to transfer and reconstruct through computers (Redd, 2019). One thing that makes the movie “interstellar” so incredible is that it very closely predicted what the black hole might look like years ago before the first image of black hole was captured. The director hired the Nobel winner Kip Thorne as a consultant in order to make the movie close to the real science (Woodward, 2019).

Black holes are some of the unknown and fascinating objects in our universe. As the first image of the black hole is taken, it gives astronauts more insight about what a black hole looks like. After creating such a breakthrough, it certainly provides us more confidence and passion to explore the unknown of the black hole as well as the whole universe.

Redd, N.T. (2019, July 11). What are black holes? Retrieved from

https://www.space.com/15421-black-holes-facts-formation-discovery-sdcmp.html

UNAWE. (n.d.) Model of a Black Hole. Retrieved from

https://www.unawe.org/activity/eu-unawe1308/

Woodward, A. (2019, November 9). The movie ‘Interstellar’ came out exactly 5 years ago.

Since then, new discoveries have changed our understanding of black holes. Retrieved

from https://www.businessinsider.com/interstellar-anniversary-learned-about-black-holes-2019-

11

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30. Does the moon cause tides?

When you are relaxing at the beach, watching the sunset and stars coming out at night during the vacation, have you ever noticed that the sea level changes a lot? You start wondering what causes the sea level changes and how does it happen?

The periodic rise and fall of sea level at a particular place are called tides. When the sea level rises to its greatest height, it is known as a high tide. When it falls to its lowest point, we refer that as a low tide. Tides are primarily caused by the gravitational force of the moon. As the Earth rotates, the moon's gravity pulls on different parts of the Earth. Even though the moon only has about 1/100 the mass of the Earth, it still has enough gravity to move things around since it's so close to us (Hemer,

2019).

Part of the Earth facing the moon experiences a stronger gravitational pull towards the moon as compared to the Earth’s center. Hence, the part facing the moon is pulled away from the center of the

Earth, creating a bulge and thus increasing the sea level and causing a high tide. Another bulge occurs on

the opposite side since the center of the

Earth is also being pulled toward the moon

and thus away from the water on the far side.

In addition, the places in between the two

high tides, where the sea level drops, are

experiencing low tides (Hemer, 2019).

Figure 1: Tides and the Moon (Source: Hemer. M)

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Interesting fact: The World’s highest tides can be found in Canada at the Bay of Fundy

in the province of Nova Scotia. The bay separates New Brunswick from Nova Scotia and at some

times of the year the difference between high and low tide is 16.3 meters, taller than a three story

building. The tidal heights here have been measured for many decades and the highest one

recorded was in 1869 during a tropical cyclone, when a water level of 21.6 meters was measured

resulting from the combination of high winds, abnormally low atmospheric pressure and a spring

tide (White, 2016).

The tides can help humans in the modern society in a variety of ways. The most common way is

to transform tides in a form of energy called tidal energy, which is produced by

the surge of ocean waters during the rise and fall of tides. It is a renewable source of energy and is

considered as an ideal source of power (Rutledge, 2012). However, the amount of power produced so far

is relatively small. Engineers are now working to improve the technology of tidal energy generators to

increase the amount of energy they produce, which can reduce our dependence on fossil fuels such as

coal, oil and natural gas.

Hemer, M. (2019, October 24). How does the Moon, being so far away, affect the tides on Earth? Retrieved

from http://theconversation.com/curious-kids-how-does-the-moon-being-so-far-away-affect-the-tides-

on-Earth-105371

Rutledge, K. (2012, October 9). Tidal energy.

Retrieved from https://www.nationalgeographic.org/encyclopedia/tidal-energy/

White, D. (2016, November 28). The World's Most Interesting Tides. Retrieved from

https://www.theyachtmarket.com/articles/general/the_world’s_most_interesting_tides/

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31. What would the Earth be like if the Moon didn't exist?

The Moon affects the Earth in many ways, and has had a vast impact on the way life is constituted on Earth and how humans have evolved. Through effects on the Earth’s tides, crust and rotation, as well as the oceans altitudes, it is safe to say the Earth would be nothing like it is today without the Moon.

The Moon is made up of material from Earth that flew off from a large object hitting Earth around

4.5 billion years ago11. This means that the Moon came into being just 60 million years after the Solar

System first existed 12 , and has been next to Earth for most of our planet's lifetime. The Moon’s gravitational force on Earth has changed everything.

The Moon affects our tides and the size of oceans to a vast degree. If there was no Moon affecting our tides, they would be only one third as big as they are now13. These tidal forces also affect our climate, as much of the heating and cooling of oceans are because of tides14. In addition, the Moon’s gravitational pull means that the areas closest to the Moon, at the equator, have deeper oceans, whereas the poles of the ocean are more shallow. If there was no moon, this would not be the case, and the sizes of different areas of the ocean would shift. The tides, with the force of the Moon, are responsible for energy heating and Figure 1: Motion of Tidal Bulges Created by dissipation of energy on Earth. It has even been argued that the Moon Moon (Source: Aerospaceweb) is responsible for tectonic plates, through the heating of energy, because many planets without a moon do not have them15. Moreover, the moon’s pull on the Earth’s mantle helps generate earth’s gravitational field through the heating of this outer core16.

11 Yan, Isabelle. “10 Things: What We Learn About Earth by Studying the Moon – NASA Solar System Exploration.” NASA Science: Solar System Exploration. NASA, March 13, 2019. https://solarsystem.nasa.gov/news/812/10- things-what-we-learn-about-earth-by-studying-the-moon/. 12 Wall, Mike. “How Old Is the Moon? Scientists Say They Finally Know.” Space.com. Space, January 11, 2017. https://www.space.com/35291-moon-age-pinned-down.html. 13 Kershner, Kate. “What If We Had No Moon?” HowStuffWorks Science. HowStuffWorks, January 27, 2020. https://science.howstuffworks.com/no-moon.htm. 14 Foing, Bernard. “If We Had No Moon.” Astrobiology Magazine, October 29, 2007. https://www.astrobio.net/retrospections/if-we-had-no-moon/. Figure 1: Whitman, Justine. “Ask Us - Moon Motion & Tides.” Aerospaceweb, February 19, 2006. http://www.aerospaceweb.org/question/astronomy/q0262.shtml. 15 Foing, Bernard. “If We Had No Moon.” Astrobiology Magazine, October 29, 2007. https://www.astrobio.net/retrospections/if-we-had-no-moon/. 16 Yan, Isabelle. “10 Things: What We Learn About Earth by Studying the Moon – NASA Solar System Exploration.” NASA Science: Solar System Exploration. NASA, March 13, 2019. https://solarsystem.nasa.gov/news/812/10- things-what-we-learn-about-earth-by-studying-the-moon/.

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The Moon has a large impact on the Earth’s rotation, and slows down Earth’s spin by about 0.002

seconds each day this century17. Without the moon, our days would be between 6-12 hours, instead of 24.

This means that our years would have over 1,000 days in them18. If there were no Moon, our days’ length

Human Adaptation: The full would affect the amount of daylight we have. There would be increased moon was what hunters storms, wind would be much more intense, and our seasons would organized themselves around, change drastically19 . This could have a huge impact on the life and because of the light it gives off. species we have on our planet.

This has affected predator-prey Many planets, such as Mars, rotate with less consistency relationships, as well as the because they do not have a moon. Mars’ rotation, over a few million

years, changes by 60°. If the Earth, which is on a 23° angle, rotated less smoothly, there would be a larger

degree of climate change. This 23° angle ensures our planet is safe for habitation through its liveable

climate20. In addition, many animals have developed night vision due to the moon and many animals have

come have adapted to their tidal climates.

Not only does the Moon have large geographical effects, but it also is the basis for many facts in

scientific exploration. For one, from studying the moon, scientists have been able to discover what

happened to earth four million years ago, because the moon preserves all craters and impact on its

surface. Because of the proximity of the moon to Earth, we are able to tell what happened to Earth

during this period, and how long ago these craters would have affected Earth. Moreover, the Moon has

had volcanic processes in the past, and the remnants of it could help scientists study how these processes

happened on Earth. Thus, without the Moon, not only would the Earth be affected, but humans would

have less information about our surroundings.

17 Matthews, Robert. “What Would Happen If There Were No Moon?” BBC Science Focus Magazine. Accessed February 13, 2020. https://www.sciencefocus.com/space/what-would-happen-if-there-were-no-moon/. 18 Esiegel. “The Top 5 Things We'd Miss If We Didn't Have a Moon.” ScienceBlogs, August 8, 2013. https://scienceblogs.com/startswithabang/2013/08/08/the-top-5-things-wed-miss-if-we-didnt-have-a-moon. 19 “What Would Happen If There Was No Moon?: Summary, Facts & Impact.” The Nine Planets. Accessed February 13, 2020. https://nineplanets.org/questions/what-would-happen-if-there-was-no-moon/. 20 Foing, Bernard. “If We Had No Moon.” Astrobiology Magazine, October 29, 2007. https://www.astrobio.net/retrospections/if-we-had-no-moon/.

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32. Can Humans survive on Mars?

Mankind has yet to walk the surface of any planet other than our own and no human has ventured out of the Earth’s orbit since 1972. This begs the question, when will humans visit other planets? The most obvious choice for the first destination would be our closest planetary neighbour,

Mars. But what would this kind of mission look like? And could humans survive on Mars?

Interest in the concept of colonizing Mars has advanced immensely in the past decade, with big names such as NASA and SpaceX setting goals to put humans on the red planet well within our lifetimes. As far as getting there is concerned, the most efficient time to start the journey would be in

2033 as this is when Mars is closest to Earth in it’s 15 year orbit cycle. The round-trip length is estimated to take 400-500 days on the lower end, with other proposed missions spending an additional

500 days on Mars for fuel-saving purposes. The second challenge scientists face is getting astronauts to the planet’s surface. The landing capsule would need a heat shield to protect from the heat of entry into the atmosphere and a parachute to slow down the capsule to roughly 100mph. Following this, one option is to use a cushion of airbags accompanied with retro rockets which would allow the capsule to bounce to an eventual stop [1].

Once we have successfully planned out the mission to Mars the next step is being able to survive the journey. There are numerous physical challenges humans must endure when considering spending lengthy periods of time on Mars and in space. Some of these challenges include evaluating the health risks of long haul space travel and of exposure to forms of radiation such as cosmic radiation from stars and cosmic events. The average annual dose of cosmic radiation on Earth is around 1 millisievert (a unit of energy per kilogram of matter), whereas on Mars the dosage is upwards of 100 millisieverts [2]. This drastic increase in cosmic radiation has been estimated to raise a 40-year-old’s risk of dying from cancer

EVERDAY PHYSICS 78 to 5% [3]. Additionally, the astronauts will be weightless for prolonged periods of time which, based on studies done on astronauts aboard the International Space Station, may have negative effects on eyesight and blood circulation.

If humans successfully make it to Mars, the next step to consider is how to adopt a sustainable lifestyle. In order to achieve this, it is crucial that one builds a sustainable habitation. Such habitations are portrayed in the film The Martian, which presents an accurate image of the habitats NASA is considering. Since Mars is so far away, inhabitants could not rely on a steady stream of food supplies from Earth and would instead have to attempt to grow their own food. We are able to use red, blue, and green lights to grow vegetables (mainly lettuce) in small bags that contain fertilizer, providing a somewhat consistent food source. Considering there are no sources of water on Mars, it would be vital to create a form of technology for water recovery. A proposed solution to this is brine water which would theoretically recover every bit of water leftover from urine distillation. As far as shelter is concerned, NASA already has a proposed deep-space habitat named ‘HERA’ which would be two stories tall, complete with living quarters, workspaces, and bathroom facilities. Finally, a problem that has previously been solved but posed issues in the past is the lack of oxygen on Mars. It was solved through the Oxygen Generation System used on the International Space Station which “reprocesses the atmosphere of the spacecraft to continuously provide breathable air” [4].

Although the thought of humans living on an entirely different planet may seem outrageous, it is plausible to argue it could very well occur in our lifetime. Having humans live on Mars is more than just a standalone mission, it opens up the gateway for interplanetary travel and expanding the reach of mankind throughout space. Humanity was born on Earth and for the first time in history mankind could have a different planet to call home. Surviving on Mars is the frontier of human discovery and opens up endless possibilities.

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[1] Kim Orr, “Mars in a Minute: How Do You Land on Mars?” Video. (2015, July 1). Retrieved from https://www.jpl.nasa.gov/edu/learn/video/mars-in-a-minute-how-do-you-land-on-mars/

[2] Sue Lavoie, Photojournal: NASA's Image Access Home Page. (n.d.). Retrieved from https://photojournal.jpl.nasa.gov/

[3] The long road to Mars. (2018, June 27). Retrieved from https://physicsworld.com/a/the-long- road-to-mars/

[4] Fox, S. (2015, August 13). Nine Real NASA Technologies in 'The Martian'. Retrieved from https://www.nasa.gov/feature/nine-real-nasa-technologies-in-the-martian

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Chapter 2: Quantum and Waves

In this chapter we discuss some of the most fascinating implications of quantum physics and waves. Both share many common features we can see from the examples in this chapter. The most dramatic example is the particle-wave duality of quantum particles, such as light, which has properties of a particle that can hit you one by one, but also behave like a wave.

Important Physical Concepts of Waves

There are 4 different types of waves:

• Electromagnetic and light (oscillating electric and magnetic fields)

• Mechanical (vibration of atoms, molecules, solids, small magnets, charges,…)

• Quantum (any particle)

• Gravitational waves (f. ex., when two black holes rotate around each other)

An important characteristic of a wave is that the shape of the distortion, whether it is a material, such as water or an electromagnetic field will look the same at a later time at a different location. This shape propagates over time. A wave can propagate but it can also be a standing wave, like in a guitar string or in a microwave oven. In this case a material or field simply oscillates in time without propagating. This can also be described as two waves propagating in opposite directions so that the total wave looks like it is not propagating and just oscillates in time.

A generic proof of a wave is the interference it can cause. For example, when you shine a laser through two slits it will create an interference pattern and not simply two spots as shown here:

Source: hyperphysics.phy-astr.gsu.edu

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Interesting questions about waves

33. How do wifi waves travel through walls when light can't?

If you have ever watched Netflix from the comfort of your bed you have most likely been aided by the science behind wifi waves. Considering that it is 2020, your devices such as phones and laptops are not hard-wired to your modem, the device that transmits data between devices. Instead, the wifi waves travel through the walls. Although, this brings the question as to why wifi waves can travel through walls when light can’t? Why aren’t all waves created equally? Imagine the comfort of being indoors with a roof over your head and cool shade to go along with it all interrupted by sunlight! Lucky for us, we can examine this question with the assistance of everyday physics.

Light waves are comprised of a frequency and wavelength. These components determine two things: whether or not light is visible and what colour it is. When you, for example, shine the flashlight from your phone onto a solid object, there will be a shadow behind it which is effectively evidence that light is a wave. However, it depends on the composition of the wall you shine the light on. If made out of glass or of a paper thin thickness it could be possible for the light to pass through (light is not fully absorbed). It also depends on the intensity of light shone through. Although, for the purposes of this discussion we will consider a wall made out of lumber of average thickness such as that of your house.

In this case the wavelength is our main concern. Note, the visible light spectrum frequency range in the diagram. The wall basically acts as something of similar wavelength and frequency and as such absorbs

the light waves.

Whereas, wifi waves have a

wavelength in the range of radio and micro

waves. This has a few distinct features; a

long wavelength, low frequency, and low

EVERDAY PHYSICS 82 energy. To visualize this the approximate scale is between buildings and humans, rather large in comparison to that of visible light which would be equivalent to protozoans (1). Basically, because the wavelength, the difference between peaks separated by a trough in a wave, is very large the wall is too thin to obstruct it. In other words, the atoms in the wall are nowhere near the size of the wavelengths and as such are not able to block them. Therefore, the wifi wave is able to pass through.

I found an analogy that best describes this interaction. Suppose the wifi waves correspond to a person, light to an insect, and the wall as rain (3). A person can walk through the rain because they are much larger relative to the rain. However, the insect is of equal size to the raindrops and is immediately stopped. The same interaction occurs between wifi waves (person) to our walls (rain) and light (insect) blocked by the equal wall.

Wifi waves are increasingly becoming an ever more prevalent aspect of our lives. The science behind its ability to travel between walls enables a number of current and future applications through the internet of things (IoT) (2). Nowadays, this allows for the increasing interconnectedness between our everyday items, such as, thermostats to detect when you are coming home and adjust the temperature accordingly. Although this particular application is useful for households the IoT raises a number of privacy concerns moving forward. For example, if someone was able to access the data remotely it would become a threat to security with the knowledge of a home’s occupancy. As such, security measures in our devices will have to see continued improvement in order to evolve with the reach of networks through our everyday devices.

(1) “Cell Phones and Wifi Are Perfectly Safe.” Office for Science and Society, 1 May 2019, www.mcgill.ca/oss/article/general-science-health-and-nutrition-you-asked/cell-phones-and-wifi- are-perfectly-safe. (2) Burgess, Matt. “What Is the Internet of Things? WIRED Explains.” WIRED, WIRED UK, 16 Feb. 2018, www.wired.co.uk/article/internet-of-things-what-is-explained-iot. (3) “Inquiring Minds.” Fermilab | Science | Inquiring Minds | Questions About Physics, www.fnal.gov/pub/science/inquiring/questions/mikep.html.

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34. Why do objects look skewered or bent when it is under water and being viewed from the surface?

Have you ever immerged half of a spoon or a chopstick into the

water? If you did, you would find that the spoon looks like shown

in Figure 1. It gives people the impression that the spoon is broken

at the water surface. However, if we try to reach the part that we see

in the cup, we will touch nothing but water. In fact, this is an

identity of light that we see almost every day in our life --- the

refraction of light.

Figure 3 A spoon in a cup of water (Source: iStock)

Because of refraction, the spoon would look like skewered. When light is obliquely incident from one medium to another, the direction of the light changes, which causes the light to deflect at the interface of two different media. This phenomenon is called the refraction of light. Light enters water from the air. Since water is much denser than air, light would be refracted at the intersection of these two substances where light would no longer travel in the original direction. When we put the spoon in the water, what we see under the water surface is actually the light that has been refracted. In Figure 2, a demonstration of refraction is shown. The normal line is an imaginary line perpendicular to the surface.

And we can see from the figure that the angle of incidence is bigger than angle of refraction if substance

1 is less dense than substance 2.

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However, if the light is perpendicularly

incident to the boundary of two different

substances, the refracted light will also be

perpendicular to the surface. If we know the

indexes of refraction of substance 1 and 2 (n1

and n2) and angle of incidence (Assume to be

A), then we can calculate the angle of Figure 4 Demonstration of light refraction refraction B. The formula is: 푛1 sin(퐴) = (Source: University of Waikato) n2 sin (퐵).

Nowadays, refraction of light is applied in every aspect of our life. It is being used to invent convex or concave lenses, which are the most basic optical elements of magnifying glasses, telescope, microscope, etc. Physics is composed of little observations. And in many cases, these observations are the key to unlock numerous mysteries.

References:

⚫ Physics Tutorial: Refraction and the Ray Model of Light. (n.d.). Retrieved from https://www.physicsclassroom.com/class/refrn/Lesson-1/The-Cause-of-Refraction ⚫ Refraction of light. (n.d.). Retrieved from https://www.sciencelearn.org.nz/resources/49-refraction-of-light ⚫ Luba. (n.d.). spoon in a glass of water. Retrieved from https://www.istockphoto.com/ca/photo/spoon-in- glass-gm172155005-294753 ⚫ Question: How is electricity produced and transported to our homes?

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35. What is the physics behind clap-activated lights?

Messrs. Stevens and Reamer invented The Clapper, a device that was first sold in 1985 and received U.S. patent approval on Feb. 20th, 1996. The Clapper became a fad hit due to its novelty; consumers could turn on and off any standard household electrical appliance with a few claps. The

Clapper is sold by Joseph Enterprises Inc., also known for the popular Chia Pet product. Considering the patent application for The Clapper and secondary sources on the physics phenomena involved in the device’s operation will allow us to better understand clap-activated lights through a specific example [1].

At a high level, clap-activated lights require a device with a microphone to pick up the acoustic signal from clapping and feeding this signal to a switch, which turns the lights on and off. The device is plugged into a standard wall socket, and appliances such as lights are then plugged into it, shown below.

The main physics phenomenon at work in the device is the transformation of a mechanical sound wave into an electrical signal.

Starting with the first stage of this process, the microphone converts the audible acoustic signal of the clap to a non-audible electrical signal [2], and feeds this separately to an amplifier and a filter. The

amplifier and the filter correspond to the two modes of

operation for the device, which can be chosen between using

a remote control. The amplifier adds energy that is converted

from the wall socket to the signal from the microphone so

that the signal from a small noise is strong enough to operate

the device in its so called “away/intruder” mode. In this Figure 1: The Clapper (Source: Wikipedia) mode, a small noise such as someone entering a room will cause the lights to turn on for a set amount of time. The filter is used for operation of the device in the classic

“normal” mode, by removing any signal corresponding to sounds outside the frequency range of 2200 to

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2800 hertz, which is the “predominate frequency range of a typical hand clap” [1]. This filter aims to prevent the lights from turning on due to a non-clapping noise. The outputs of the filter and amplifier are sent to separate peak detectors which detect and holds the peak amplitudes of the signal. The analog output from the peak detector is fed to a microcontroller which converts this to a digital signal. This microcontroller can be thought of as a sort of processing station, in certain models the device allowing for two sets of lights to be activated by a different number of claps. This digital signal is fed to a power switch which enables the switch to operate the light that is plugged into the clap-activation device.

Interesting Fact: While the relatively simple design of clap-activation devices like The

Clapper allows them to be sold at a low cost, generally below $20 USD, this simplicity also leads

to some significant design flaws. One reporter chronicled his woes with the device, finding that it

frequently mistook common household sounds for clapping, turning appliances on and off. This

was because the sounds were within the same frequency band allowed by the filter in the device,

such as the reporter’s teenager running down the stairs with “house-shaking fury” [3].

[1] Stevens, C. R., Reamer, D.E. (1996). U.S. Patent No. 5,493,618. Washington, DC: U.S. Patent and

Trademark Office.

[2] Dirjish, M. (2012, October 3). What’s the difference between acoustical and electrical noise in components?. Electronic Design.

[3] Kauffman, M. (2005, February 6). Thumbs down for the clapper. The Hartford Courant.

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36. How do humans perceive sounds as complex as music from the combination of simple sound waves?

Imagine yourself in a coffee shop during its busiest hours or in a concert, listening to a great composition by Bach. In either scenario, your ears are being overrun with a variety of sounds, each drastically different from the other. You must wonder sometimes, how do our ears make sense of all this information all at once?

The process for separating different or competing sounds is found in the two step process called

Spectral Segregation. “In the first step, the components in the mixture associated with each individual sound source are isolated. In the second, the components belonging to each source are grouped” (1).

Sound segregation relies on the help of acoustic

cues, the majority of which is still unknown. One

of these cues is Harmonicity, which uses the fact

that tones have a certain base or fundamental

frequency. “Sounds that have different

fundamental frequencies differ in pitch and are

Figure 1: relatively easy to segregate” (1). As seen in Figure 1, two (Source: Acoustics.org)

You can take part in this small experiment yourself by listening to the sounds

generated by this link: https://acoustics.org/pressroom/httpdocs/147th/sinex_wave1.wav tones, when play ed at the same time, still resulted in hearing two different sounds due to how the components of each sound were isolated and then grouped back together. Part of how we separate different sound sources is through analyzing the properties of each individual wave.

Now that we know the process used to separate and distinguish between different sounds, we can better understand how we perceive complex sounds from music

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When listening to music, there many things influence how we perceive it. First, we could be watching a live performance or cooking dinner while listening to music through headphones. No matter the scenario, we always have our attention diverted to something else, affecting how we perceive each sound wave. In other words, it all depends on what we decide to focus on.

When composing music, composers often base the most or the entirety of the piece on one tone or melody to act as a central theme. The idea of tonality, or “the fact that within all the pitches that we decide we can play music with you often compose music such that it only takes a selection of these pitches” makes this process easier (2). Composers use this so that when a new movement with slight variations in the original melody is introduced, the audience can more easily identify the changes made, allowing us to focus on the new sounds introduced.

Another tool that is used to distinguish between instruments is attack time, or how quickly it takes for a sound to reach its full intensity. For instance, a piano has a very short attack time, but a clarinet takes longer to reach its full intensity. Based on this, we know if we are listening to a piano versus a clarinet. The “length of the attack time allows us to distinguish them” (2). Also, how much energy a sound wave has helps us perceive brighter or lower sounds.

Perceiving sound waves is both a scientific and subjective process. We can focus on just one sound wave, allowing us to perceive it better, also making it easier to separate between multiple waves.

Alternatively, in music we can focus less on the main melody, listening for new movements instead. The next time you are overcome with a multitude of sounds, think about the processes going on behind the scenes to see if it can help you notice something that you wouldn’t have noticed before.

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37. How are we able to see images with our eyes?

I was walking around McGill’s campus this past Friday, February 7th. A big snow storm was in the making and, just as I was passing the Y intersection, I thought to myself, “What a beautiful campus!”

Often times, we don’t realize how fortunate we really are when witnessing something beautiful. I am lucky enough to be able to see color, while others aren’t. This made me think what makes for someone to be color blind? But, most importantly, how do we see images with our eyes?

Our eyes are truly a thing of beauty! Not only are they, most commonly, the first thing someone looks at when you first meet them, but they are also one of the most complex systems in our body. We can almost think of our eyes as two camera lenses refocusing every time we blink. We can think of the iris as the shutter on our “Canon 700D”, letting in the perfect amount of light to create a perfect image.

That light is then turned into an image and sent through our nervous system so we can interpret it.

The process of receiving light into our eyes is actually quite simple. First, the light waves refract off an object. In my case, as previously mentioned, the light was refracting off the Arts Building and the snow on the ground. From there, the light waves “then pass through the lens, which changes shape so it can further bend the rays and focus them on the retina [1].” Only then is the light waves turned into distinct shapes [1].

Figure 1: Light waves entering the eye (Source: Kaiserscience)

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As far as color blindness goes, “this is done by the ability to detect differences in the wavelengths of light” [2]. This can actually be tested through the Ishihara chart. The chart will identify to what extent you are color blind.

I find it absolutely fascinating how something so small can be so complex and intricate. As I mentioned before, the sense of sight is extremely overlooked and taken for granted. So, maybe next time your walking around campus or in the presence of anything beautiful, just remember how fortunate you are.

Interesting fact: Glasses to help with color blindness are available on the market today.

They do have some flaws, but improvements are being made!

[1] How Your Eyes Work. (n.d.). Retrieved from https://www.aoa.org/patients-and- public/resources-for-teachers/how-your-eyes-work

[2] Visual Processing: Eye and Retina (Section 2, Chapter 14) Neuroscience Online: An

Electronic Textbook for the Neurosciences: Department of Neurobiology and Anatomy - The University of Texas Medical School at Houston. (n.d.). Retrieved from https://nba.uth.tmc.edu/neuroscience/m/s2/chapter14.html

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38. When we use the microwave oven to heat food, how is the energy transmitted?

It’s 3 am. You make your way to the kitchen to chef up a late-night snack. You pour yourself a plate of chips, top it with cheese, and pop it in the microwave. Within seconds you’re shoveling heaps of warm nachos into your mouth. As you fall asleep, your tummy filled, you begin to wonder: How do these magical boxes heat up my food?

To understand microwave ovens, we first must understand microwaves. Microwaves are the shortest waves of electromagnetic radiation which result from the collision of electric and magnetic fields traveling at 300,000 km per second [1] [2]. You cannot see these waves of energy because they are travelling at the speed of light. However, you come in contact with electromagnetic radiation all the time. Have you ever noticed how your skin feels warm when you are laying in the sun? The radiation that warms your skin from the sun is the same that warms the food you heat up in the microwave [2].

Unlike mechanical waves, like sound waves that must travel through water or air, these waves can travel through anything – even solids! When they pass through an object, they cause the molecules of the object to vibrate faster [3]. The vibration of molecules creates friction against one another and turns into heat energy. Try rubbing your hands together as fast as you can… notice how they are warmer now? Microwaves cause this transfer of heat energy simultaneously to all of the molecules in your food, allowing it to heat up quickly [3].

Now that we have a better understanding of electromagnetic radiation, let’s look at the inner

workings of the microwave oven. Inside there is a

generator, the magnetron, which converts electricity

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into microwave radiation [2]. These radiation waves are blasted into the food compartment via a wave guide and scattered by a fan. The waves bounce off the walls, penetrating the food, and vibrating the individual molecules. This transfer of energy from the microwaves to the molecules allows them to simultaneously heat up and warm your food.

What You Cook Matters! As we have just explored, microwaves can cook food very quickly via radiation waves. However, the consistency of your food can influence how it cooks.

For example, the liquid of food gets excited by the microwaves more strongly. The liquid portion of your food could be boiling while the rest is barely warm. The excitement of liquid particles can also result in drying out your food. Furthermore, these microwaves can only penetrate the food up to about 5 cm. Take a thick piece of steak for example. The outer layer will be penetrated and heated by the microwaves directly; the rest of the meat will cook from the outside in via conduction, like most conventional ovens cook. [2]

Some people may be concerned about the radiation waves microwaves use and their effect on the human body, but that is not something to be concerned about. The microwave itself is kept inside a sturdy black box that keeps the radio waves from escaping. Even if your microwave were to be so-called

“leaking” radio waves, it would need to be at a much higher power levels and for long periods of time for it to have any detrimental effects on the human body [2]. Nonetheless, your microwave is still very powerful; how do you think it melted those nachos for you!

[1] Phillips, Melba. “Electromagnetic Radiation.” Encyclopaedia Britannica. Encyclopaedia Britannica, Inc. October 18, 2027. https://www.britannica.com/science/electromagnetic-radiation. Date Accessed February 12, 2020. [2] Woodford, Chris. “Microwave Ovens.” Explain That Stuff. July 17, 2019. https://www.explainthatstuff.com/microwaveovens.html. Date Accessed February 12, 2020/ [3] Walch, Jerry. “Transfer of Energy in Electrical Appliances. “Home Guides \ SF Gate, http://homeguides.sfgate.com/transfer-energy-electrical-appliances-62247.html. Accessed 12 February 2020. Image: Image: http://thepantryreview.blogspot.com/2011/02/microwave-mushroom-and-camembert.html

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39. How do eyeglasses work?

Every day when I wake up in the morning, the very first thing I do before I get out of bed is reach for my real set of eyes; my glasses. Although every single part of our body is important, the entire world is blurry to me without a pair of glasses. It is more uncomfortable than you can ever imagine.

Statistically, over 4 billion out of 7.8 billion people in the world wear glasses. More than half of the entire population cannot clearly see things either too close or too far from them. Here is where the main problem arises. How many among the 4 billion who wear glasses do you think actually know how glasses work? Probably not even one percent. Let me introduce the logic and interesting facts about glasses for you so that you can be that top one percent.

First of all, let us talk about the history of glasses. The pioneer of the glasses and vision correction is an unknown Italian glassblower who lived in the middle of the 13th century. Back in the

13th century, obviously eyeglasses were very different from the average glasses we refer to today. They were just mediocre glass lenses intended for basic vision correction. The crucial breakthrough was in utilizing the difference in thickness of the two lenses for various corrections of vision, and these so- called “glasses” became the foundation of the modern eyeglasses and the two general types of lenses used today. Those two types are called the concave and convex lens.

Before we dive into how these two types of lenses work, let us take a step back and talk about how we see objects. Surprisingly, we do not see objects directly, meaning that the objects we see are actually merely reflections of the light bouncing off objects. That is why light must be present to reflect off an object in order for us to see it. The two main parts of the eye involved in vision are the cornea and retina. When light enters our eyes through a part called the cornea, it projects the corresponding image upside-down on the retina. Next, the image is sent to our brain, and finally, the brain turns the image right side up. Our vision becomes blurry when light is not focused onto the retina correctly. If the focal

EVERDAY PHYSICS 94 point of the light is in front of the retina (nearsightedness), it makes it difficult to see objects that are further away, and if the focal point is behind the retina (farsightedness) it becomes hard to see objects that are nearby.

Now to analyze the difference between the two lenses. As

show in the figure, a convex lens converges the light, while a concave

lens diverges the light. Let us think about our eyes. If we are

struggling with nearsightedness, we need to use a concave lens to

move the focal point further backward onto the retina. On the other

hand, in the case of farsightedness, the best way is to use a convex Figure 1: Type of lenses lens to move the focal point of light forward. These are the reasons why Source: [3] we wear eyeglasses to correct near/farsightedness.

Interesting experiment: Using a convex lens, it is possible to burn a paper with the focused light. Typically, a convex lens concentrates the light energy from sunlight onto one spot on the paper, and this makes the heat energy accumulate on that point to cause fire.

As technology advances, the forms of conventional “glasses” are changing. For example, these days a lot of people prefer contact lens rather than the eyeglasses I wear. I could say that contact lens work under the same scientific principles as the eyeglasses.

[1] “How many people in the world wear glasses?”

https://www.reference.com/world-view/many-people-world-wear-glasses-e1268cfa00bdbd41

[2] “How Eyeglasses Work and a History of Glasses."

https://www.allaboutvision.com/eyeglasses/how-glasses-work/

[3] “Convex Vs. Concave Lens: 10 Major Differences with Examples”

https://vivadifferences.com/convex-vs-concave-lens/

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40. Qu’est-ce qu’un rayon X et comment cela fonctionne ?

Avant 1895 quand on se cassait un os, on devait aller voir un médecin pour qu’il atteste la blessure et qu’il fasse un pronostic peu, voir pas concluant sur un membre mal en point. On mettait systémiquement les blessures dans un plâtres sans trop savoir comment les os allait reprendre ou si même les os étaient la source du problème. Cela, c’était avant l’invention de la machine à rayons X.

À la base, les rayons X sont des ondes électromagnétiques invisibles à l’œil nu émient par un système mit en place souvent par des spécialistes de la santé afin de voir la constitution osseuse et même parfois ligamentaire d’un membre. Le principe est relativement simple, les rayons créés synthétiquement pénètre facilement les matières moins denses, c’est-à-dire ceux principalement constituer d’éléments tels l’oxygène (comme l’eau) et absorber par les matières considérées plus dures comme les os, permettant de voir au travers des muscles, de la peau et des tissus mous, mais des bien voir les surfaces

solides, particulièrement les os. La découverte de ce phénomène est

attribuée au physicien allemand Wilhelm Röntgen en 1895 alors qu’il

nomme son invention par la variable inconnue en algèbre, soit X. Dans

un ordre d’idée un peu plus scientifique, il faut tout de même créer ces

fameux Rayon X, tâche ardue, mais étonnamment plus simple que

cela peu sembler. En effet, il y a deux principales façons de produire

ces rayonnements. La première est de faire fluctuer les couches

internes d’un noyau neutre, créant par le fait même une excitation

provoquée par le bombardement d’électrons à l’intérieur d’un tube à

rayons X. La deuxième, c’est par l’accélération des électrons dans Photographie de la main un tube à rayons X. Les électrons sont alors retirés du tube par un d'Anna Bertha Ludwig Röntgen prise fils métallique chauffé à haute température et envoyé dans un tube le 22 décembre 1895.

EVERDAY PHYSICS 96 sous vide créant un champ magnétique puissant. Ce champ magnétique est alors envoyé sur une pièce métallique en tungstène qui ralentit les électrons pour produire un faisceau continu.

La contribution du célèbre physiciste allemand va au-delà de son implantation de la machine à rayon X à des fins médicales. En effet, il est plus que probable que vous ayez passé par une machine à Fait intéressant, Röntgen a remporté le prix Nobel de physique en 1901 grâce rayons X à sa découverte qui lui aura permis d’être célèbre longtemps après sa mort en 1923. lors de votre dernier passage aux douanes alors qu’on projette ces rayons sur les gens dans une cabine afin de voir s’ils dissimulent quelque chose sous leurs vêtements. Cela semble anodins, mais c’est beaucoup plus simple que d’effectuer une fouille par palpation. On peut donc qualifier la découverte comme le pied dans la porte de l’imagerie de l’exosquelette et la possibilité de voir plus loin que ce qui est apparent à l’œil nu.

Références :

Rayon X. (2020, February 4). Retrieved February 12, 2020, from https://fr.wikipedia.org/wiki/Rayon_X#cite_note-19

Wilhelm Röntgen. (2020, February 6). Retrieved February 12, 2020, from https://fr.wikipedia.org/wiki/Wilhelm_Röntgen

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41. When we use a microwave oven to heat food, how is the energy being transmitted?

Microwave ovens are convenient, quick and efficient appliances that heat up our food at the press of a few buttons. Their ability to convert electricity into heat in order to safely cook our foods in just minutes has made them one of the most widely used kitchen appliances in the world. So how does a microwave oven heat up our food? We will delve deeper into how this revolutionary kitchen appliance works below but first a little background on the microwave oven.

The invention of the microwave oven resulted from the accidental discovery by Percy Spencer in the 1950’s. He was conducting experiments with magnetrons (which were mainly used for radar applications at the time) when he discovered that the chocolate bar he had in his pocket had melted due to the heat generated by the magnetron. This prompted Spencer to test his theory that a magnetron could be used to cook food and thus that gave rise to the birth of the microwave. Microwave ovens use a form of radiation called microwaves to heat food up. Interesting fact: The first microwave oven created was 750 lbs, 6 feet tall and costed $5000.

Microwaves are a type of electromagnetic radiation that fall between radio waves and infrared waves on the electromagnetic spectrum. The wavelengths of these electromagnetic waves range from one millimeter to one meter. Microwaves carry massive amounts of energy, travel at the speed of light and are invisible to the naked eye.

How do microwave ovens heat our food up? The magnetron inside a microwave oven will convert electricity from a power outlet into high energy microwaves when you start the cooking process (1). The magnetron will transmit these high energy microwaves into the cooking chamber through a waveguide (2). The food slowly spins around on a turntable during the process so that the microwaves penetrate into the food and heat it up evenly (3). As the microwaves penetrate into the food, this causes

EVERDAY PHYSICS 98 the particles inside to vibrate rapidly (4). The faster the particles vibrate, the more heat it will produce.

Therefore, microwaves transmit energy onto the particles, heating up the food in the process (5).

With conventional ovens, the food is cooked from the outside in by conduction. This explains why a pie can have burnt edges while the inner parts remain uncooked. With microwave ovens, many have claimed that it cooks food from the inside out. However, this statement isn’t exactly accurate. Since areas with higher water content absorb more microwaves, something that has higher water content in the middle will cook from the inside out. However, foods where the water content is dispersed evenly will cook from the outside in. Therefore, both methods apply when using microwaves depending on where the water content is concentrated.

Using microwaves can result in foods with boiling hot interiors and barely warm exteriors due to an uneven distribution of the water content in them. In addition, microwaves are only able to penetrate up to a few centimeters into the food, therefore for thicker and larger foods, the waves are only heating the outer layers while the inner layers are heated by conduction. Due to the different speeds and methods of heating, this will result in certain areas being hotter than others. Microwaves also tend to dry out foods as they heat up food by exciting water molecules.

Many people are concerned about being exposed to the radiation from microwaves while using the appliance. However, the waves from microwaves aren’t able to leak out as they are sealed in by metal containers. The metal grid in microwaves - which are big enough for light waves to pass through - are too small for microwaves to get through therefore they will remain trapped inside. Even if there is “leakage” somehow, the electromagnetic radiation you would be exposed to are less than those from cell phones, so there is no need to worry.

[1] https://www.explainthatstuff.com/microwaveovens.html/

[2] http://www.softschools.com/facts/science/microwaves_facts/2811/

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42. How do household microwaves use waves to heat up our food?

The microwave is undoubtedly one of humankind’s most revolutionary invention. Invented

accidentally by Percy Spencer in the 1940s, microwaves are now a common household commodity for

families all around the world. Microwaves are especially useful when people are too lazy to whip up

fancy meals and instead choose to fall back on convenient microwavable meals. However, have you ever

stopped to think about how your microwave works?

Figure 5: The Electromagnetic Spectrum (Source: National Aeronautics and Space Administration) Household microwaves are great tools used to cook food quickly and reheat refrigerated meals.

They work by channeling heat energy directly to water molecules inside the food. This heat energy is

transmitted in the form of microwaves, which is an electromagnetic wave having higher energy than

radio waves but lower energy than infrared radiation. In fact, microwaves used in ovens are typically

12cm from crest to crest and at this wavelength, microwaves are easily absorbed by water molecules in

Interesting idea: Hate getting soggy pizza crusts after the food [1]. Despite microwaves’ microwaving pizza? Here is a tip - place a glass of water in the small size, they carry considerable microwave together with the pizza. The glass of water acts as a sink that amounts of energy which causes food absorbs some of the microwaves. This moderates the heating process of to heat up efficiently. Next, we shall the pizza and the slower heating process ensures that the pizza crust delve into the interesting science remains dry and delicious, while simultaneously reheating the toppings behind microwaves.

[2].

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Firstly, a component in the microwave called magnetron generates microwaves by converting electricity from power outlets into microwaves. The waves are then transmitted into the cooking

compartment by an antenna. These

microwaves bounce around in the cooking

compartment due to the reflective metal

walls inside the microwave. This

phenomenon is similar to how visible light

bounces off a mirror. Next, microwaves are

absorbed by water molecules in the food and

this causes water molecules to twist back

Figure 2: How microwaves work and forth. This motion of twisting creates friction, effectively (Source: www.explainthatstuff.com) converting the energy absorbed into heat. Thus, foods higher in water content tend to be more effectively heated by microwaves. Microwaves cook food a lot quicker than traditional methods like frying pans as it heats both the inside and outside of food simultaneously. Microwaves concurrently excite water molecules right through the food, as compared to frying pans where only the portion of food in contact with the pan is heated up by conduction. Furthermore, microwaves have a glass turntable that rotates the food so that the food is heated up more evenly.

Now that you have unraveled the mystery behind microwaves, feel free to share this knowledge with everyone you know! Although microwaves constitute an integral part of our lives, you will be surprised as to how many people are not aware of the science behind them.

[1] - Spector, D. (2014, June 10). How Do Microwaves Cook Food? Retrieved from https://www.businessinsider.com/how-do-microwaves-work-2014-6

[2] - Helmenstine, A., & Helmenstine, A. (2018, May 26). Why You Should Microwave Pizza With a Glass of

Water. Retrieved from https://sciencenotes.org/why-microwave-pizza-with-a-glass-of-water/

EVERDAY PHYSICS 101

43. Why do objects look skewered or bent went its underwater, being viewed from the surface?

A spoon is made from hard materials that are quite difficult to break with our hands, and yet when you submerge the spoon in water. Suddenly, the spoon appears to be bent. However, when the spoon is lifted above the water, nothing has changed – the spoon retains its original form. Why does the spoon bend when it enters the water? Does the spoon always bend regardless of the liquid? Is this spoon- specific phenomenon, or do any objects work? All of these questions about the spoon bending event can be explained by none other than refraction. We may not know it, but refraction occurs everywhere around us at any time – your eyes, rainbow, camera lenses, and so forth. Refractions allow us to see correctly, enjoy the beautiful nature, and take pictures. It is a vital part of our lives.

Interesting fact: Light travels in a vacuum at 300,000 km per second! Light is a wave1! The speed at which light travels depends on its medium. The speed of light is determined to be the fastest when it is in a vacuum. If light travels through any other medium, it will slow down considerably. This is because light interacts with the molecules in the medium, and these molecules slow the light down. To determine how fast light passes through a medium can be determined by knowing the refraction index of the medium of question. The refraction index describes to us how fast light can travel through these media. The higher the refractive index, the slower the speed of light.

This is where the magic occurs. A change in speed is accompanied by a change in direction, resulting in

the light to bend2. For instance, in the image of the left, a pencil

is submerged in water. We see the imaginary pencil Y that is

created from pencil X being submerged in water. The light

coming from pencil X in the water hits the surface, and it is

EVERDAY PHYSICS 102 refracted due to a difference in the refractive index. Therefore, instead of seeing pencil X, we see the imaginary pencil Y. This is why the spoon bends when it is submerged. Most objects, in particular opaque objects, bend when submerged in water. It does not need to be water, particularly; however, light needs to travel through the medium to observe refraction.

We go through every day experiencing refraction, without knowing what it is, precisely.

Knowing more about refraction allows us to appreciate many stunning optical phenomena, such as mirages. Not only does it allow us to observe these beautiful daily phenomena, but the concept of refraction is also used in many powerful instruments, where the measurements obtained in these instruments are crucial in advancing science further and used to save human lives. Refraction is an important phenomenon that holds much importance and relevance in the present and the future to come.

References:

1. Jensen, R. E., The technology of the future is already here. Academe 1993, 79 (4), 8-13.

2. Khurana, A.; Khurana, A. K.; Khurana, B., Theory and practice of optics and refraction. Elsevier India: 2014.

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44. How do Wi-Fi waves travel through walls when light can’t?

The first thing I do, and I am sure most others do as well, in the morning, is check all the updates on social media through Wi-Fi, whose router is located far away in the living room. However, often times, I leave my lights on in the living room, but I am not able to realize that until I am there, so I wonder how Wi-Fi waves are able to travel through the walls but not light?

In order to understand why Wi-Fi waves and light waves travel so differently, we should be able to differentiate between them. The electromagnetic spectrum allows us to visualize the entire range of

wavelengths of energy that can

and can’t be seen by the human

eye. Electromagnetic radiation is

a form of energy that exists all

around us in different forms,

however not all of the energy is

detected by our eyes [1]. The Figure 1: Electromagnetic Spectrum (Source: Radio2Space) electromagnetic waves that the human eye can detect is visible light, which includes the light produced by the sun, lightbulbs, etc.

When using Wi-Fi, we don’t usually think about how it works and how we’re able to access it when we’re walls away from the router. Wi-Fi waves have a wavelength slightly shorter than radio waves and they have the unique ability to not be interfered by other signals when travelling through space. These data-encoded waves travel away from the router in a spherical or circular manner with the router being located in the center and they can extend to about 20-30 meters, without being interfered

[2]. The Wi-Fi router has the ability to simultaneously send data over many wavelengths which makes it able for us to accomplish many of our daily tasks.

EVERDAY PHYSICS 104

Light waves consist of very small waves that are not able to travel through walls because the size

of its wavelength is approximately the same as the atoms that made up the wall [3]. However, the size of

the wavelength of Wi-Fi is much larger than the atoms making up the wall which gives it the ability to

travel through walls undisturbed. Overall, since the Wi-Fi waves are much larger than light waves, they

are able to travel through walls unlike light waves.

Interesting fact: Wi-Fi is a non-ionizing form of radiation which can increases the possibility of tumor growth and cancer if exposed to or near the body for an excessive amount of time. An increase in the distance between you and the Wi-Fi router, will lower the strength of the radiation that your body will encounter which will help in preventing health issues related to radiation. For the future: Turn off the Wi-Fi router at night or any other time it is not needed.

This phenomenon demonstrates how technology has evolved so much that walls aren’t barriers

for communication anymore, as Wi-Fi has become an integral part of our daily routine and allows us to

access it from different corners.

[1] “Electromagnetic Spectrum - Introduction.” NASA. NASA, March 2013.

https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html.

[2] Neal, Meghan. “Here's What Wi-Fi Would Look Like If We Could See It.” Vice, July 22, 2013.

https://www.vice.com/en_us/article/9an9m7/heres-what-wi-fi-would-look-like-if-we-could-see-it.

[3] “Inquiring Minds.” Fermilab | Science | Inquiring Minds | Questions About Physics. Accessed February 13,

2020. https://www.fnal.gov/pub/science/inquiring/questions/mikep.html.

EVERDAY PHYSICS 105

45. Why is it said that light does not need a medium through which to travel?

Earlier, a friend had asked me “How does light from the Sun reach us when there is a vacuum right outside the Earth’s atmosphere?” The question kept lingering around in my head and I couldn’t wait till I got home to google the question. Of course, with that question arose follow-up questions such as: Is light matter? What is a medium? Prepare yourself for the journey I will accompany you to discover the ideas and facts of this intriguing and astonishing topic.

Light, which we see every day is in fact a wave in the electromagnetic spectrum. A medium is a substance through which matter propagates. It itself is comprised of matter. But what is the absence of matter? Vacuum. Yes, it is the same vacuum as in vacuum cleaners. Vacuum cleaners create a difference in pressure and cause the dust particles to get sucked in. However, the net pressure outside our atmosphere is pretty constant. Light travels as waves and therefore does not require a medium to transmit the energy. But then, you may be wondering that sound is a wave too. Does it require a medium to travel? If so, why?

Sound is a longitudinal wave and thus not an electromagnetic wave. For us to hear someone speak, sound needs to oscillate air particles to travel through the medium (air). However, that is not the case for light. Light, as stated earlier, is an electromagnetic wave and a transverse wave. A longitudinal wave has its oscillations parallel to the direction of propagation or motion. A transverse wave has its oscillations perpendicular to the direction of propagation. How does this affect whether the wave requires a medium to travel? Well, how sound waves work is that they compress and decompress particles through which they move. However, light propagates through the electric wave and the magnetic field. So, to answer whether light requires a medium depends on the definition of medium. If

EVERDAY PHYSICS 106

the electric and magnetic fields are not considered mediums, then no, light does not require a medium to

travel.

If light did require a medium to travel, we wouldn’t be able to observe beautiful phenomena

occurring in our universe beyond our universe in

space filled with vacuum, far across our

galaxies. The one in the picture is a planetary

nebula which is just an example of the many

possible occurrences we can only see because

light does not require a medium to travel.

So, we have answered the core question. A planetary nebula But we still haven’t answered one of the related http://annesastronomynews.com/photo- questions. Is light matter? The answer is two- gallery-ii/nebulae-clouds/ngc-5189-by-robert- fold. It is a particle and it is a wave. It exists as electromagnetic waves and photons (discrete packets of gendler/ energy) at the same time. Thus, they hold properties of both worlds – scientifically known as the “wave-

particle duality.”

I couldn’t wait to share these new findings with the friend who inserted the worm in my head by

asking that question. Now that we know light does not require a medium to travel, the next question is:

why does light slow down and thus refract in different media despite it not requiring a medium at all?

EVERDAY PHYSICS 107

46. Why do objects look skewered or bent went its underwater, being viewed from the

surface?

There’s a saying," seeing is believing ". However, when chopsticks are placed in a bowl filled

with water, chopsticks seem to bend upward. When we go into a river to play wanting to grab a tone that

we see at the bottom of the water. We can’t catch it in the place where our eyes see. Instead, if we reach

deeper we could touch the stone. Why is that happening? This is the amazing refraction of light and we

are going to explore the reasons for this phenomenon.

When light is slanted from one transparent medium to

another, the direction of propagation generally changes. This

phenomenon is called the refraction of light. As the light refraction

and reflection of light are at the junction of two kinds of medium,

only the reflected light to return to the original medium, while the

refracted light into another medium. The light propagation velocity in

Figure 1: two different materials is different. So that the direction of light refraction of light (Source: Google) propagation changes at the junction of two media. This is called the

refraction of light. As we explained above at the junction of two media, both refraction and reflection

occur. The speed of light of reflected light is the same as that of the incident light, but the speed of light

Interesting experiment/fact/idea/concept: When light is slanted from one transparent of medium to another, the direction of propagation generally changes.

refracted light is different from that of the incident light. For example, when a wooden stick is inserted

in water, the naked eye will think that the stick is folded when it enters the water. This is the refraction

of light that brings about this effect. There are many other examples in our daily life. For instance, fish

swim in the clear water and can be seen clearly. However, when you try to spear the fish in the direction

EVERDAY PHYSICS 108 you see it, but you can't. Experienced fishermen know that harpoons can only be reached by aiming below the fish. And when you put a piece of thick glass in front of the pen it looks like the penholder is misplaced. Such that it is very dangerous to think one river is very shallow when the bottom of the river seems close. However, the bottom of a river is deeper than it looks like based on the refraction of light.

People used the refraction principle to invent the lens including the convex lens and the concave lens. So that we don't have to worry about myopia and presbyopia. We can use glasses to help us see things clearly based on the principle of light refraction. People also invented other things like

Magnifying glass, telescope and microscope. Furthermore, the principle of total reflection of light was also applied to modern communication and optical fiber was invented.

References:

"Refraction". En.Wikipedia.Org, 2020, https://en.wikipedia.org/wiki/Refraction.

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47. Why can the wifi waves penetrate the wall but the light wave cannot?

Since 1971, the first UHF wireless packet network has been created in the Great Hawaii Island, and until 2020, we are starting to invent 5G network connection. Wi-fi has already been almost everywhere around us. One of the most interesting aspect for wi-fi is that it can transmit through the wall, but in the contrary, the light cannot penetrate the wall also as a kind wave. What is a wave? What is the difference between the wave particle of the light and the wave particle of the wi-fi? Is there any negative effect from the penetration of the wi-fi wave otherwise the benefits it brings us at the same time? In the further development of wireless network, these questions may help us further and more correctly develop our usage of waves.

For many people, although the wave from oceans and lakes are the most touchable waves, the wave related to our topic-Wi-fi in here is an invisibly stable equilibrium value repeated in one or more fields, in a medium, which is an electromagnetic wave instead of a mechanical wave. Firstly, the comparison Interesting experiment/fact/idea/concept: Beer-Lambert Law between the show the relationships between the material properties and the light frequency of attenuation during the traveling, usually being used for chemical analysis wi-fi wave and the measurements and the comprehension in physical optics, for photons, light wave can help us basicallyneurons comprehend or rarefied gases. the differences. In 2019, most of wi-fi wave frequency are 2.4 or

5 GHz and the light wave frequency is 430-750 THz, which seems like the frequencies decide whether the wave can penetrate the wall or other mediums. However, the nature of the material decides how far the electromagnetic waves can travel into. The penetration depth will basically become a function of wavelength. Due to the Beer -Lambert Law, the intensity of an electromagnetic wave inside a material

falls off exponentially from the surface as The deeper the

Figure 1: The change of penetration rate

Source:https://www.researchgate. net/figure/The-penetration-depth-of-an-

electromagnetic-wave-depending-on-the- relative-magnetic_fig3_312258996/

Figure 2: The speed of 5 G Source:https://www.google.com/search?q=speed+of+5+G&tbm EVERDAY PHYSICS =isch&ved=2ahUKEwizt5_hic3nAhUBNd8KHWjxBioQ2- 110 cCegQIABAA&oq=speed+of+5+G&gs_l=img.3...9842666.9846228..9 846598...0.0..0.79.754.12...... 0....1..gws-wiz- img...... 0j0i30j0i19j0i8i30i19j0i5i30i19j0i8i10i30i19j0i8i10i30.emBh 4Dm40c4&ei=CX5EXvOODIHq_Abo4pvQAg&bih=577&biw=1280# imgrc=evuo0RGDqOtqQM wave penetrate to the material, the lower the frequency and intensity the wave will be. In addition, the wavelength of visible light is about 5*10-7 m and the wavelength of wi-fi is 0.12 or 0.06m, which is much larger than the visible light’s. The intensity of light is largely depending on the wavelength.

Therefore, the main reason why the light wave cannot penetrate the wall is that the intensity of it is not strong enough to pass through the wall, but the wi-fi wave can.

Time flies, since the end of 2019, some places have already been popularize the fifth generation of wireless internet, which is approximately 5 times of 4G’s speed, and we don’t even need a router line at home, supporting more than 1 million clients in every square kilometers. Our sun is still shiny enough so that our Earth does not need to be wondering out of the solar system. However, plenty people might be concerned about the negative impact from the electromagnetic waves while we are enjoying the convenience from them, especially from the stronger radiation of the wave frequency.

Compared with the frequency, we are supposed to worried more about the power (rate of work) of the facilities. For example, if both of the microwave’s and the wi-fi’s frequencies are 2.4 GHz, the microwave is apparently more dangerous than the wi-fi, owing to its larger power (microwave: 1000w~; wi-fi router: 0.01w~). Staying alert and skeptical is a critical and beneficial thing for the development of human society in all the aspects, which also promotes us to correct and promote us to make more progresses in the wireless network technology.

Reference: French, A. P. Vibrations and Waves. Chapman and Hall/CRC, 2017. Skorucak,

Anton. If Gamma Rays Can Travel through Walls, and Radio Waves Can Travel through Walls, and They

Are on Opposite Ends of the Electromagnetic Spectrum, Then Why Can't Light Travel through Walls

Which Is Right in the Middle of the Spectrum?, www.physlink.com/Education/AskExperts/ae175.cfm.

EVERDAY PHYSICS 111

48. How does a camera capture an image and turn it into picture?

Do you like taking pictures of the beautiful scenery when you are travelling? Do you often take pictures of your friends? Do you like taking selfies after making up? Pictures and cameras are everywhere in our life and even some students choose this as a major for their university life. But how does camera work and what are the principles behind it? In this article, I intend to talk about cameras and pictures from the view of physics.

First thing we need to know is that how camera capture the image from objects. During this process, we need to understand how the images form in front of the camera. Usually how we can see objects are corresponded to lights emitted from them. Things that interact with particles of light are called photon.

The frequency of lights is related to the color of the objects. Different frequency of photons can reflect different color. When the photons pass through the opening of the camera, the image is formed just behind the opening. Second thing we need to talk about is the lens which are called aperture. It focuses the incoming photons to create a more clear image behind the aperture. By changing the location of the lens and different types of the lens, we can capture bigger or smaller area of the image. It are lens that allowed a camera to be compact. Thirdly, this part is what we use the camera to take a picture. As we all know, for most cameras, we press the button to take the photo. Button here is actually a key to control the shutter.

When we do not press it, shutter cuts down the way that the image

transfers to the sensor and it is only located just behind the

aperture. When we press, the shutter moved out of the way,

allowing the photons to contact with the sensor. There are many

factors to affect the speed of the photons and the size of the picture, like the size of the opening, the time that the shutter remains open, etc. Last but not least, it is how the image is recorded. In the old years, the technology was not quite developed so people invented the film

EVERDAY PHYSICS 112 cameras. When photons causes a reaction where they strike. Then the sensor transferred that reaction into brightness and make the final image. Later, to make the picture more beautiful, we want to make the picture more colorful. In order to do that, we add layers of the film to record the color of blue, green and red. A digital camera works similarly but more efficiently. Individual pixels, called photosites, build up an electrical charge based on the amount of charges. As the same principle, it breaks down into three colors and changes to the image that you see on the screen.

Now, I finish talking about the process of how camera works. We have a general idea how it works from the perspective of the physics. Personally, I like the camera and I would like to take pictures with my friends when we travel around the world. I hope in the future, the camera can be developed more

Interesting fact:

⚫ In Japan, phone camera shutter sounds cannot be muted. Filming and taking pictures up

the skirts of high school females has long been a hot topic in Japan. And also, the rate if

criminal about this is rising quickly. So the government of Japan makes the policy that

the smartphones are all designed to have this function to prevent the safety of the female.

⚫ Android was originally conceived as a camera operating system. As it develops more

and more useful, it expands its business to produce more technological products to make

our life easier. and more functionally.

[1] MCCLAIN, SHAWN. How Does a Camera Capture an Image? itstillworks.com/camera-capture- image-1129.html.

[2] Types of Lens. William Sawalich, 14 Aug. 2017, www.dpmag.com/how-to/tip-of-the-week/types-of- lenses/.

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49. What is the difference between the way the brain sends signals and how an electronic device sends signals?

Recently, I was watching George Lucas’s masterpiece Star Wars, and while watching intergalactic aliens fight one another, one thing caught my mind: the force. Jedi masters have the ability to move objects by the whim of their minds and that made me wonder, can I do that? Will it be possible to send brain waves to control everyday electronic devices? Why or why not? What is the difference between the way the brain and electronic devices send signals?

Fundamentally, the way that electronic devices send signals and the way our brain sends signals are the same. Elizabeth Dougherty, a professional science writer for MIT explains that they are both forms of electromagnetic radiation, which are waves of energy moving at the speed of light [2].

However, the difference lies in the frequency of

the wave. For example, let’s look at how

today’s hot new product: Airpods. These fancy

wireless, earphones work on Bluetooth.

Bluetooth works by transmitting low power

radio waves [3], that send signals for a device

Figure 1: Radio Frequency to interpret. Each device has an ‘address’, which allows Strengths Brain waves are on the far right communication between multiple products. Regulations (Source: NASA) limit the strength of these waves and that is why your Bluetooth earphones/speakers stop when you leave your phone in separate room far away.

Now that we have a better understanding of how radio waves work, the next step is to understand how brain waves work. Every time you make a movement, be it something as mundane as walking or reaching for the bag of chips, that is due to brain waves. Basically, inside our heads are billions of

EVERDAY PHYSICS 114

neurons which conduct electrical waves and send information throughout the body. There are five

different types of brain waves, depending on its frequency [1].

The main difference between the two types of waves is its respective frequencies. For electronic

devices to communicate, the waves must be stronger and more frequent than the very weak brain waves.

To illustrate, radio waves oscillate 50 million to one billion times per second, whereas the strongest

brain wave, which are gamma waves only 32 to 100 times per second. The stark difference is why our

brain waves do not interfere with radio waves to change the radio or change the activity of electronics

that surround us.

To summarize, brain waves are too weak at the moment to have force-like capabilities of a Jedi

Knight. However, plenty progress has been made in this regard. A recent study from the University of

California, San Diego found a new way to transmit data through magnetic signals through the human

body from wearable devices [5]. This provides users with a more secure, and an ultra-low power method

of communicating our bodies signals to wearable electronic devices. Thus, instead of dreaming to be the

next Jedi, perhaps becoming the next Iron Man is closer in our future?

Interesting fact: Contrary to popular belief, cell phone usage does not cause cancer. Radio waved emitted from cell phones may affect the metabolism of the brain, but there are no dangerous consequences [4].

d dangerous s

[1] A Deep Dive Into Brainwaves: Brainwave Frequencies Explained. (2019, April 1). Retrieved from

https://choosemuse.com/blog/a-deep-dive-into-brainwaves-brainwave-frequencies-explained-2/

[2] Dougherty, E. (n.d.). Home. Retrieved from https://engineering.mit.edu/engage/ask-an-engineer/can-

brain-waves-interfere-with-radio-waves/

[3] Franklin, C., & Pollette, C. (2019, November 11). How Bluetooth Works. Retrieved from

https://electronics.howstuffworks.com/bluetooth3.htm

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[4] Hamilton, J. (2011, February 22). Cell Phone Radio Waves Excite Brain Cells. Retrieved from

https://www.npr.org/2011/02/22/133968220/cell-phone-radio-waves-excite-brain-cells

[5] University of California - San Diego. (2015, September 1). Magnetic fields provide a new way to

communicate wirelessly: A new technique could pave the way for ultra low power and high-security

wireless communication systems. ScienceDaily. Retrieved February 12, 2020 from

www.sciencedaily.com/releases/2015/09/150901100323.htm

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50. How do eyeglasses work?

When I was a child, I was far-sighted. Because of that, I wore eyeglasses for more than ten years,

from 4 years old. Moreover, when I went to junior middle school, I found that almost every student in

my class wore eyeglasses. Then I wondered that how do glasses help us see?

Basically, the eyeglasses are composed of lenses and frames, used for vison correction such as

myopia, hyperopia, astigmatism, presbyopia or strabismus, amblyopia. Correspondingly, there are many

kinds of glasses including myopia glasses, farsightedness

glasses, presbyopia glasses and astigmatism glasses and

so on.

First of all, what is the principle of myopia

glasses? Myopia is mainly due to the deformation of the

lens, which causes the light to gather in front of the retina Figure 1: prematurely. For a convex lens made of the same material, The principle of treating hyperopia and myopia the greater the convexity, the greater the diopter, and vice (Source: https://faculty.washington.edu/chudler/sig versa. In other words, for the same eyeball, the higher the ht.html) degree of myopia is, the more prominent the eyeball is,

and the higher the degree of myopia is. The concave lens is used to correct myopia. Concave lens plays

the role of diverging light. The image of a concave lens is an upright virtual image smaller than an

object, which makes the image distance longer and just falls on the retina. Then the person who is

nearsighted can see much more clearly than before. Glasses degree is the diopter intensity of glasses is

generally expressed in degrees. A diopter is equal to D 1.00 in many countries, that is the 100 degree is

said by Chinese people or glasses shops.

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Similarly, hypermetropia refers to the abnormal refraction state in which parallel light passes through the refractive medium of the eye and focuses behind the retina. There are three reasons: 1.

Congenital shortness of eyeball. That is why I had it when I was a child.

2. Refractive media (such as aqueous humor and lens) lack of refractive power (low refractive index).

3. the cornea is flat, or the lens surface is flat.

The principle is similar to that of a myopic lens. Farsighted glasses are convex lenses. It is used to make the distant parallel light converge properly through a convex lens, and then refract through the eye to form a clear image on the retina

As I have mentioned before, there are so many students in China who are short-sighted. They need glasses to see things far away. The Chinese government is so worried about this that they are making sure all students spend some time outdoors instead of just being inside the classroom. Children are the future of the country, so it is urgent to protect children's eyes.

Interesting history: Scattered evidence exists for use of visual aid devices in Greek and

Roman times, most prominently the use of an emerald by emperor Nero as mentioned by Pliny

the Elder.[1]

Independently of the development of optical lenses, some cultures developed

"sunglasses" for eye protection, without any corrective properties.[2] Thus, flat panes of smoky

quartz, were used in 12th-century China.[3] Similarly, the Inuit have used snow goggles for eye

protection."

1. The Natural History, Book 37, Chpt.16. Pliny the Elder. John Bostock, M.D., F.R.S. H.T. Riley, Esq., B.A. London. Taylor and Francis, Red Lion Court, Fleet Street. 1855 2. A ment, Phil (4 December 2006). "Sunglasses History – The Invention of Sunglasses". The Great Idea Finder.

Vaunt Design Group. Archived from the original on 3 July 2007. Retrieved 28 June 2007. 3. Needham 1962, p. 121.

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Important Physical Concepts of Quantum Physics

The following concepts are the hallmarks of quantum physics:

• Particle-wave duality (wave is particle, particle is wave)

• Non-locality (1 particle can be in two places at the same time)

• Entanglement (spooky action at a distance)

• Statistics (spin)

• Fock space (almost infinite dimensions)

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Interesting questions about Quantum

51. How is light both a particle and a wave?

All of us encounter light on a daily basis, as it’s the reason we are able to see and interact with objects, but have you ever thought of what is light? What is it made of? Is it a particle? Is it a wave? To whet your appetite, it’s actually both! This characteristic is called the “wave-particle duality”. How amazing is it that a fundamental requirement of life can coexist as two things at the same time?! To get further into this topic, it’s necessary to introduce the physics behind waves and particles, and what astonishing observations were made to come up with this conclusion by physicists.

Before the 19th century, it was previously accepted that light is a wave whereby it propagates through space with a finite speed and varying frequencies/wavelengths (depending on the wave type on

the electromagnetic spectrum, i.e. different types of light). It can be

shown that light is a wave through an experiment called ‘double-slit

experiment’. In brief, since light interferes and diffracts, this

experiment demonstrates what occurs when light interferes after its

diffraction which shows the wave properties of light. This concept can Figure 1: Double-slit experiment be seen when using laser light (light of one wavelength, Source: https://medium.com/predict/the- ‘monochromatic’) whereby parts of light can be seen with maximum double-slit-experiment- demystified-disproving-the- intensity (antinode) and parts with zero intensity (node), as seen in quantum-consciousness- connection-ee8384a50e2f figure 1. Interesting concept: This wave property is such when two waves interact, their amplitudes

add up and result in new wavelengths of light. Since a wave has crests, troughs, and points of zero

amplitude, when two waves add up, the resulting wave is one with maximum amplitude ‘antinode’

by ‘constructive interference’ along with minimum amplitude ‘node’ by ‘destructive interference’.

This is

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The interesting concept explained above is shown in figure 2.

Now that we can accept the fact that light is a wave, how can it

be a particle as well, and can this be proved? Spoiler alert! It can! In

fact, Albert Einstein won the Nobel prize in 1921 for proving the Figure 2: Wave interference pattern. particle behavior of light. This was a big deal since this experiment Source: https://astro- chologist.com/synastry-and- changed the way we perceive light. To put it bluntly, he shined light of constructive-interference-big- announcement/ varying frequencies and intensities onto a metal surface then he detected the photoelectrons (particles emitted from a metal surface) emitted, and measured their frequencies and thereof calculated their energies. Based on the wave model of light, he predicted that increasing light intensity would increase the (kinetic) energy of emitted photoelectrons. However, it was observed that the energy of photoelectrons was only increased by the increase of frequency of the light shone, and this can only be explained by the particle-model of light (called ‘photons’). As a result, light can be both a particle and a wave.

To conclude, I personally think that this question has brought a huge amount of attention

Interesting fact: Albert Einstein did outstanding work in the world of physics, as you

probably know him when encountering the equation “E=mc2”, or when the word “relativity” is towardsmentioned, the world but he of only physics won and one resolved Nobel prize many for quandaries. that photoelectric These experi effectments discovery! were ground-breaking!

Not only has it changed the way we look at light, but also changed the way we perceive electrons since the same principle can be applied. From this concept, quantum mechanics came into place which is a whole another world! Who knows how far this can this lead to, this is what gives me hope for physics and new discoveries!

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52. How does an MRI work? What are the physics behind it?

Surely you know someone who has had a tumour, cancer, a heart problem or even a joint injury. If so, they probably had an MRI scan in order to diagnose it. The invention of the MRI is arguably one of the biggest leaps in modern medicine. It has saved lives and alleviated the suffering of many patients with serious illnesses, by allowing a non-invasive way to see inside someone’s body [1].

The advancement of this technology occurred in the 1970s, and Paul Lauterbur & Peter Mansfield were awarded the Nobel Prize in 2003 for its development [1]. Firstly, it is important to understand the function of an MRI. It stands for magnetic resonance imaging and is a method of obtaining clear images of the tissue inside the patient’s body. It differs from X-rays and CT scans since it does not use potentially harmful ionizing radiation [2]. Instead, it takes advantage of the body’s natural magnetic properties, using magnetic fields and radio waves to obtain a picture. There there are no known biological hazards associated with its use [3].

You may be wondering how a human can have magnetic properties? Our bodies are filled with protons, as they are found in abundance in water and fat. Protons “can be likened to the planet earth, spinning on its axis, with a north-south pole. In this respect it behaves like a small bar magnet” [3]. As

depicted in figure 1, naturally in one’s body, the protons

have a random axis of alignment. Then, when the patient is

placed in the MRI machine, the protons line up, similarly

shown in figure 1. An additional radio wave is introduced

into the picture. This causes the magnetic vector to be

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deflected and causes the protons to resonate [3]. Then, the radiofrequency is turned off, causing the protons

to return back to the state they were in when only the magnetic field was present, and this in turn releases

a radio signal [3].

This signal is what is used to recover the MR images.

The signals are received by the receiver, which are then

plotted on a grey scale. This process is repeated many times,

using different frequencies of radio waves, because different

frequencies target different “slices” of the body. They are

plotted together, creating a high-resolution image of the tissue in question [3].

The future of the MRI is bright, as investments are being made in combining MRI machines

with other diagnostic tools, such as PET machines This will allow doctors to diagnose patients with cancer

more efficiently, as well as diagnose brain injuries in a much shorter timeframe after they occur [1].

References:

Interesting fact: The MRI machine uses superconducting magnets, which are made of many coils of wire. These create a magnetic field of 0.5-2.0 tesla, which is equivalent to 5,000-20,000 gauss. This is huge when you compare it to the Earth’s magnetic field of only 0.5 gauss [4]. These magnets are incredibly powerful! In order to have this strong of a field, the resistance of the wires must be greatly reduced to almost zero, which is done by keeping them extremely cold. They are constantly bathing in liquid helium at -269.1 degrees Celsius [4]. This is 23 times colder than the average winter day in Montreal!

[1] American Institute of Medical Sciences & Education. “The Evolution of MRI Imaging Equipment.” AIMS Education. (2013) [2] Marcin, J. “What to know about MRI scans.” Medical News Today. (2018) [3] Berger, A. “Magnetic Resonance Imaging.” BMJ. (2002): 35 [4] Gould, T. A. Edmonds, M. “How MRI Works.” How Stuff Works. (2010)

EVERDAY PHYSICS 123

53. What are X-rays?

X-rays which is a kind of wave have a wavelength ranging from 0.03 to 3 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3x1016 Hz to 3x1019) and energies in the range 100eV to 200keV. [1] X-rays can generate ionizing radiation, which is harmful to our bodies. X-rays with strong energy will cause radiation sickness, and the X-rays with lower energy will increase the risk of radiation-induced cancers.

There are two types of waves: The X-rays with lower energy are called soft X-rays; the X-rays with higher energy are called hard X-rays. We always use hard X-rays in our daily life because hard X- rays can traverse relatively thick objects without being much absorbed or scattered. [2] They can give us images of a lot of things that we cannot see by our eyes, such as our organisms.

X-ray machines

X-ray machines are a machine that

involves and generates X-rays. To generate

the X-rays, we need a machine with a

vacuum tube which contains a cathode and an

anode. A cathode is to direct a stream of

Figure 1: An X-ray generator electrons into a vacuum, and an anode (Source: will collect the electrons and is made of https://www.youtube.com/watch?v=LtX3rYJASik tungsten to evacuate the heat generated by the collision. [3] Electrons, which are directed and attracted https://www.youtube.com/watch?v=LtX3rYJASik) by the cathode and the anode, will create a great amount of energy. 1% of the energy is x-radiation and the rest (99%) is heat. The x-radiation is used to produce the image and the heat will be removed by the cooling system. Most X-ray generators use the water or oil to cool down.

Applications of X-ray machines

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X-ray machines can use in a large number of fields, for example, medicine, security, operation.

In the medical area, we can use X-ray machines to create images of our body; in security areas, we can use X-ray machines in airports or railway stations to find out the dangerous things.

Reference

Interesting application in medicine field: Now we all know X-rays can transverse through thick objects, but how the images of X-rays can reflect our body and how doctors use the

X-ray machines. X-ray images are the shades of grey. If X-rays are passing through the dense parts, like bones, it will come up white; if the parts are less dense, like the heart, it will come up as a shade of grey. To present different parts of our body, the doctors who control the machine can change the amount and strength of x-rays. [4]

[1] Website: https://en.wikipedia.org/wiki/X-ray

[2] Attwood, David (1999). Soft X-rays and extreme ultraviolet radiation. Cambridge University. p. 2. ISBN 978-

0-521-65214-8. Archived from the original on 2012-11-11. Retrieved 2012-11-04.

[3] Website: https://www.ucd.ie/vetanat/radiology2001/the_x-ray_tube.html

[4] Website: http://theconversation.com/curious-kids-how-do-x-rays-see-inside-you-85895

EVERDAY PHYSICS 125

Chapter 3: The Physics of Life

In this chapter we discuss some of the physics of life and biophysics. This not only covers the physical properties of living materials such as DNA or neurons, but also some physical tools and their physical principles to study humans or biological entities. Common tools are X rays and MRIs used in diagnostics. Many of these tools or properties have similar underlying physical principles, which are listed here:

Important Physical Concepts of the Physics of Life and Biophysics

• What is life and the physical constraints of life. Many elements such as water and oxygen

play a dominant role.

• Water and its properties (surface tension, strong dipole moment, high heat capacity and

latent heat of evaporation).

• Temperature, temperature regulation and thermodynamics play important roles in

biological systems.

• Scaling laws, which describe how physical properties such as strength depend on the size

or how evaporation and cooling scales with surface rather than volume. This is also

related to various pattern formations, such as the wing structure in fruit flies and more

generally to different levels of complexities.

• Human and biological systems have various sensing and emission schemes, such as touch

(mechanics), sound, light, temperature, particles (smell).

• Energy and in particular energy conservation play an important role in all biological

systems. The work produced by muscles needs energy. Cells and animals will transform

chemical energy (food) into physical energy. Reproduction, is also limited by energy

EVERDAY PHYSICS 126

conservation rules. Cell division or offspring requires energy in the form of calories or

food.

• Brownian motion is the random motion of particles in a liquid. This is relevant, for

instance, in the motion of red blood cells or the diffusion of medication in the blood

stream.

• Breathing and its related gas flow, or propulsion and flying are other highly relevant

functions that involve physical properties, such as flow, pressure, and volume

relationships.

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Interesting questions about the physics of life

54. How much force does it require to knock out an average human?

We have all been there - you are watching TV and your favorite character gets into a physical altercation. One swift punch later and the bad guy is knocked out cold and justice is served. Yet, you have probably wondered if knocking someone out is as easy as it looks, and whether you could impress the girl of your dreams with one punch to a bad guy.

Think of your brain as firm jello, which is surrounded by a thin protective layer of fluid that stops it from moving around in your skull. However, the impact from a well-placed punch can overcome this protective layer and lead the brain to violently slam into the inside of your skull, as shown in figure

1. This is Similar to what you experience when you slam the brakes in your car and your whole-body uncontrollably lunges forward as your car slows down. This whipping motion and the impact itself will

place significant stress on your brain and your brain stem,

which connects it to the rest of your body. As a result, parts

of the brain will shut down as a protective response and this

is what causes that instant knockout21.

Figure 1: An octagon star (Source: powerpoint)

Figure 6: Impact of the brain with the inside of the skull

Fun fact: The Average heavy weight boxer can transfer between 1200 and 1700

pounds of force per square inch they impact. Similar to the biting force of a Grizzly bear!

21 https://www.zmescience.com/medicine/mind-and-brain/why-we-get-knocked-out/

EVERDAY PHYSICS 128

Now you are probably thinking that you need years of training to execute this flawless maneuver, right? Well you would be correct since the knockout blow is less about direct punching force and more about punching technique. The protective fluid around the brain is more capable of protecting against direct impacts than it is at impacts that cause rotation of the neck and brain. As a result, accurate punches to the jaw or temple are more likely to cause a knockout, but what Hollywood does not tell you is that a knockout comes with serious medical repercussions. You would potentially leave this bad guy with memory loss, brain swelling, and dangerous brain bleeds 22.

That said, researchers have yet to pin down a set number at which your punching force will knock someone out since this is dependent on many factors. An unexpected blow is way more dangerous since your body can’t stiffen your neck muscles to absorb some of the impact forces. Also, genetic factors like neck thickness and your susceptibility to brain injury will impact your ability to withstand a punch23.

As cool as it looks in the movies, don’t go around stirring trouble with your fists since you are bound to seriously hurt someone. Athletes that undergo repetitive strikes to their head develop severe brain trauma and end up living with a long list of complications. Instead, you can impress the girl of your dreams with your newly acquired facts about the brain and Hollywood magic!

Fact source24 Image source25

22 https://www.livescience.com/6040-brute-force-humans-punch.html 23 https://www.livescience.com/6040-brute-force-humans-punch.html 24 https://shortboxing.com/average-boxers-punch-in-psi/ https://www.sciencefocus.com/nature/top-10-which-animals-have-the-strongest-bite/

25 https://www.scienceabc.com/sports/people-get-knocked.html

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55. What happens to the human body when it's exposed in outer space? How long can you survive?

So you’re trapped in a suit in the middle of space. There is absolutely nothing you can do. Do you take the slow way to death and stay trapped in your suit? Or do you take the quick more gruesome way out and leave your suit to just dangle in the middle of nowhere in the middle of nothing? Well, let’s find out what happens if you take the quick way.

From the perspective of one being on Earth, space is a zone that occurs for about 100 kilometres above the planet. A zone where there is no oxygen or even any air to breathe in or scatter light. So what is space? So most of the outer space, which is almost 75% of it is basically dark energy, a cosmic field that penetrates everything. 20% of space is dark matter, which is still claimed as a mysterious subject which interacts with our universe only through gravitational pull. And only about 5% of outer space consists of baryons, the particles which make up what atom which in turn make up the molecules leading to everything we touch smell and taste. Baryons and dark matter are often found to clump

together due to their gravitational pull, while dark energy

pushes everything apart causing the universe to not only just

expand, but to accelerate in that expansion.

So, back to the question, what exactly happens to the

human body when it is exposed to in space? Well for starters,

no one has actually been subjected to this phenomenon in outer

space but

numerous

experiments

have been

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conducted in vacuum chambers to see what the results would be. To start with, one would not freeze or

explode in space. Thermal radiation (the heat you feel from the stove while at a distance from it, sun’s

rays) becomes the only source of heat transfer in space and hence if one was exposed to the sun’s rays,

they would naturally feel warm however if one was shaded from the sun’s rays, their body would start to

radiate out their own body heat and hence they would feel cool. Even if one was dropped off in deep

space where the temperature might be (-)565°F, one would not instantly freeze as heat transfer occurs

fairly slowly via radiation alone. However, what is worse than the temperature is the absence of normal

atmospheric pressure. The sudden decompression in vacuum would cause expansion of air in a person’s

lungs is likely to cause the lung to expand and rupture unless that air is immediately exhaled and

released from the body, which is why holding your breath in outer space is the worst one can do.

Decompression however can lead to a case embolism where reduced pressure of the environment causes

the boiling temperature of the body fluids to lower initiating transition of liquid water in the

bloodstreams and the soft tissues into water vapour.

One of the hardest aspects scientists are not being able to overcome is to sustain humans in space

for long periods of time. There are numerous physiological limitations to humans travelling in space for

a very long time, but one thing is for certain. If exposed to outer space absence of air, do not hold your

breath in. Breathing in outer space with no air surrounding you is the way to survive the longest. Science

Interesting fact: During the long time period astronauts spend on the International Space Station, they tend to grow up to 3 percent of their original height.

Without the presence of gravity, the spine has no inhibition and is free to expand.

However, once they return to earth, after a few months, the astronauts return to their pre-flight height due to the presence of gravity.

EVERDAY PHYSICS 131 fiction movies often depict outer space as an entity which is not entirely true, but it is often believed that the way science will go forth and answer this question is through science fiction.

Bibliography

BostonHeadInjury, Charter, J., & Traynor, P. (2013, August 12). The human body in space: Distinguishing fact from fiction. Retrieved from http://sitn.hms.harvard.edu/flash/2013/space-human- body/

Hurley-Walker, N. (2018, August 11). What is space made of? It's complicated ... Retrieved from https://www.abc.net.au/news/science/2018-08-12/what-is-space-made-of-its-complicated/10078824

Kramer, M. (2013, April 18). The Human Body in Space: 6 Weird Facts. Retrieved from https://www.space.com/20730-human-body-spaceflight-weird-facts.html

Starr, M. (2014, July 28). What happens to the unprotected human body in space? Retrieved from https://www.cnet.com/news/what-happens-to-the-unprotected-human-body-in-space/

Why is space black? (2002, December). Retrieved from https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question52.html

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56. How does the electrical conduction of the nerve system work?

Throughout a day, there are millions of processes going on in your body that allow you to

engage in your daily activities. All important in their own way, electrical conduction in the nerve system

is no exception. It’s important to answer several questions to dissect this phenomenon. First, what is

the nervous system? Second, what is a nerve? Third, how do nerves transmit signal to each other? In

order to illustrate this, we’ll compare each question to a part of a relay race in track and field.

First, let’s look at the nervous system. The nervous system is a “complex collection of nerves and

specialized cells known as neurons that transmit signals between different parts of the body”

(Zimmermann). So, as a whole “the nervous system’s activity controls the ability to move, breathe, see,

think, and more” (What Are the Parts of the Nervous System). In addition, the nervous system is broken

up into two distinct parts. The central nervous system and the peripheral nervous system. The central

nervous system can be thought of as the one directing and planning actions. The peripheral nervous

system can be thought of as revolving around the senses. For our relay race analogy, the nervous

system would essentially be the entire relay team with each of its participants, and the baton that they

pass to each other. The two divisions of the nervous system can therefore be thought of as different

teams running on the same track, the track of our body.

If the nervous system is the entire track team and the baton they are passing, nerves are the

individual runners on the team. A nerve is a bundle of something we call neurons. A neuron has three

important parts: the dendrite, the axon, and the axon terminal. The

dendrites receive information in the form of an electrical impulse

and pass it through the axon all the way to the axon terminal. The

Figure 7 (simple.wikepedia.org)

EVERDAY PHYSICS 133 electrical signal can be thought of as the baton that each runner is passing to the next, and the axon is the distance that is ran by each runner.

Finally, it’s time to look at how the electrical conduction works. To illustrate this, we’ll use the example of taking a step. In order to take a step, somehow your muscles need to get the information from your brain that you wish to put one foot forward. For this to happen, your brain sends an electrical signal through a first neuron. From the dendrite, this signal goes all the way to the axon terminal where it is transformed into a chemical signal instead. This is so that it can send this to the next neuron where the process is repeated until it reaches its destination. An interesting note is that some neurons transmit signals faster than others thanks to myelin! Myelin can cover an axon in order to insulate it, just like an insulated electrical wire. To return to our relay race analogy, the fast axons can be thought of as sprinters whereas the slow ones could be thought of as marathon runners. The signal will get there either way, but the speed may differ.

So, the next time you’re walking around or playing a sport, think about the amazing circuitry that is running throughout your body to make it possible. Also, keep in mind that damaging this circuitry could have disastrous effects, so take care of it at all costs!

“Neural Communication.” THE BRAIN FROM TOP TO BOTTOM, thebrain.mcgill.ca/flash/d/d_01/d_01_cl/d_01_cl_fon/d_01_cl_fon.html.

“What Are the Parts of the Nervous System?” Eunice Kennedy Shriver National Institute of Child Health and Human Development, U.S. Department of Health and Human Services, www.nichd.nih.gov/health/topics/neuro/conditioninfo/parts.

Zimmermann, Kim. “Nervous System: Facts, Function & Diseases.” LiveScience, Purch, 14 Feb. 2018, www.livescience.com/22665-nervous-system.html.

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57. How does UV damage our DNA?

Though may these depressingly cold, windy, and snowy days keep us inside the dreadful buildings, it cannot make us stop from planning for the summer that will for sure arrive soon enough.

With the mark of the end of the final exams, I will be so ready to go out, enjoy the beach under the glaring sun, with my swimsuits, sandals, sunglasses, and…did I forget anything? Yes, the sunscreen! Not only you are going to get sunburn, but might even get “skin cancer” if you are not careful with the exposure to the sun. But, have you ever wondered how so?

Our sun is emitting its light in broad spectrum. We can classify the lights (a.k.a radiation) depending on their associated energy: infrared, visible and ultraviolet (UV) lights, respectively in the order of going from low to higher energy. Because of the high energy, it is the UV rays (wavelength of

10 to 400 nm) that can be harmful to us; it causes damage on our DNA [1].

Before we begin addressing how the UV rays damage the DNA, let me briefly recap what DNA is. DNA is a library of genetic instructions that your cell ever needs. It is essentially a long double- stranded sequences, composed of four nucleotides (Adenine, Guanine, Cytosine, and Thymine). The specific order/sequence of the nucleotides spells out what kind of proteins should be made in order for the cell to proliferate and/or to replicate. You can think of it as a recipe book. A wrong step in the recipe can make a food go horribly wrong, and so is our DNA.

One strand of the DNA double-helix is complementary to the other strand. The nitrogenous bases of the nucleotides are paired by hydrogen bonds, such that adenine is paired with thymine on its complementary strand, and so is cytosine with guanine. However, when the photon of high-energy UV rays hits the DNA, this rule of base pairing can get overwritten. The DNA absorbs the energy from the photon, and becomes reactive and in high energy state for a short time before it finally dissipates the

EVERDAY PHYSICS 135

energy as heat [2]. And when the high-energy state is

prolonged, the excited DNA can undergo a reaction where two

thymines placed next to each other on the same strand are now

favoured to create a four-carbon ring between them, instead of

its rightful pairing with adenines on the complementary strand

[2]. This makes errors for the DNA reading/ replicating enzymes that can ultimately result in abnormal or inactive proteins; in extreme cases, leading to cancer or cell death.

So, it is an undeniable fact that UV rays damage the DNA when we are exposed to it. But then, we do not see everyone suffering from the consequences all the times. How is that so? Life has evolved around the sun ever on this planet. And we have evolved to cope with this mechanism that our cells are equipped with very elaborate enzymes that can recognize the UV-damaged DNAs (i.e. fused thymines)

Interesting Concept: We learned that UV can be harmful by damaging DNA. But can we exploit this idea and use it to our merit? UV rays do not discriminate over species. As long as an organism has a genetic makeup made of DNA or RNA, it is equally damaged via same mechanism. Then, we apply this idea to sterilization. We can effectively kill or inactivate microorganisms by disrupting their DNA by beaming UV lights, leaving them unable to perform vital cellular functions [3].

and successfully repair them.

[1] “UV Light.” Stanford Solar Center, solar-center.stanford.edu/about/uvlight.html.

[2] Nature News, Nature Publishing Group, www.nature.com/scitable/blog/scibytes/how_ultraviolet_light_reacts_in/.

[3]“Ultraviolet Germicidal Irradiation.” Wikipedia, Wikimedia Foundation, 4 Feb. 2020, en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiation.

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58. Will we ever be able to cryogenically freeze our living bodies to be unfrozen in the future?

We live in a time of technological wonders. Every aspect of our lives is constantly changing

with every new technological advance, making one wonder how technology will shape the future.

Imagine that one day, someone told you that is was possible to travel to the future. Will it ever be

possible to cryogenically freeze our living bodies to be unfrozen in the future?

Cryogenic refers to the “production and application of low-temperature phenomena” [1]. It

ranges from -150 degrees Celsius all the way to absolute zero, being -273 degrees Celsius. At such low

temperatures, gases act differently than in higher temperatures. For example, nitrogen is able to absorb

the heat of products it touches, completely slowing down the aging process of the product it touches [1].

Another way to look at it, it is to imagine nitrogen as the start of winter, where animals start hibernating

because of the cold, and it makes one wonder, could it be used to force humans to “hibernate” into the

future?

Humans have tried to experiment with low

temperatures on humans since the 60s. It is only

legal to experiment with cryonics on dead people, so

it is difficult to test the idea of preserving people’s

live. However, even when considered legally dead,

some parts of the human body are still alive, and

some even came back to life [2].

With the experiments done, there is no way

Figure 1: Concept of cryogenically frozen to predict whether it is possible or not to humans. Source : https://wonderfulengineering.com/cryogenics/ cryogenically freeze a living body to be

EVERDAY PHYSICS 137 unfrozen in the future. Although, no paper was ever published that denies its feasibility and there more reasons to believe that one day, humans can be revived after being cryogenically frozen. There have been whole insects, vinegar eels and some types of human tissue that have been unfrozen and revived.

Add this with the fact that healing technologies have greatly increased, especially in stem cells, all of which could potentially help to revive humans after cryogenically freezing them. It just needs to find the right technology to do so.

Imagine being revived in a completely new time, where humans look different, where there are flying cars, where teleportation exist and where there are stuff we have never thought about before.

Interesting fact: Many firms can fulfill your dream of being cryogenically frozen once you are

dead. For example, Cryonics Institute demands a one-time payment of $28,000 at the time of death, which

can be paid in entirety by your life insurance. If you want to contribute to science and have a chance to be

revived, it is best to be cryogenically frozen then to die forever buried underground.

Cryogenically freezing humans could also help to preserve history by “sending” a human to the future to transfer knowledge from the past. Do consider volunteering your body to being frozen, since there is a high possibility that you are the first human to be revived from being frozen and to be known in history for it.

[1] The Editors of Encyclopaedia Britannica. “Cryogenics.” Britannica Retrieved from: https://www.britannica.com/science/cryogenics

[2] Cryonics Institute. “Frequently Asked Questions.” Cryonics Institute Retrieved from: https://www.cryonics.org/about-us/faqs/

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59. Will we ever be able to cryogenically freeze our living bodies to be unfrozen in the future?

What will be the world be like in the year 2120? Will there be flying cars or will the world be ruled by robots? The only way for us to know is to be alive until then. Humans have been seeking to live longer life. Eating a lot of vegetables and fruits and exercising are not enough to fulfill humans’ greed for longevity. So Robert Ettinger, in the 1960s, posed a question: what if we temporarily die then resurrect?

Cryonics is the effect of storing the human body after freezing it. Robert Ettinger published a book in 1962 called “The

Prospect of Immortality”. Ettinger suggested cryonics as the Figure 1: Cryonics Tank (Source: The Cryonics Institute) solution to immortality. People who are ‘clinically’ dead can be cryogenically frozen. How can they be dead first then potentially come to life again? Being “clinically” dead means that the blood circulation and breathing of the human body have ceased[1]. The cryopreservation process follows immediately after death. Respiration and blood circulation are artificially continued and the organ preservation solution and the cryoprotectant solution replace the blood and water in the body to protect the cells as water will freeze under the temperature the bodies are put in. After this process, the body is cooled down to -130°C then transferred to be stored in a huge container, as shown in figure 1, filled with liquid nitrogen at -196°C[2]. We use liquid nitrogen in freezing food as well since nitrogen has a very low boiling point of -196°C, the liquid nitrogen vaporizes and extracts heat from the food. Similarly, the liquid nitrogen in the tank allows the body to be sustained at a constant temperature.

Whether the process of cryonics actually works is another question. Advocates believe advanced nanotechnology will cure the damage done to the body by the cryonic process like tissue engineering.

They believe small, nano-sized repair devices will be injected into our bodies and restore our body

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system when technology is advanced enough. However, there has not been a single success in reviving a

frozen person. The brain and other organs in the body are too complex to simply just stop and resume

working when thawed; and, there is also no scientific evidence that the solutions added to the body can

effectively protect the cells from being ruptured.

Though it sounds plausible, and in fact about 350 people are currently in the cryonics tank and

about 2000 who are listed to be cryogenically frozen once they are dead, this idea of immortality is

nowhere near being accomplished.[3] The basic life principle is that if you are born then it is natural to

die. Even if cryonics actually worked, I doubt one would be happy living in a new environment without

anyone, anything familiar.

Interesting fact: The idea of cryonics came from some animals that are able to freeze themselves for months for hibernation. One example is wood frogs: during winter, the water in the frog’s body freezes. The frog mixes its urine and glucose from the liver in the blood to prevent cells from losing too much water. It can survive until 60% of water in the body turns into ice.

[1] “Clinical Death." TheFreeDictionary.com. Accessed February 12, 2020. https://medical-

dictionary.thefreedictionary.com/Clinical+death.

[2] Mishra, Samiran. "What is Cryogenics and How Does It Work?" Blasting News. Last modified November 18,

2016. https://uk.blastingnews.com/world/2016/11/what-is-cryogenics-and-how-does-it-work-001267799.html.

[3] Pettit, Harry. “Human Corpses Frozen by Cryogenics Could Be Brought Back 'in 10 Years’.” Mail Online. Last

modified January 15, 2018. https://www.dailymail.co.uk/sciencetech/article-5270257/Cryogenics-corpses-brought-10-

years.html.

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60. What happens to the human body when it is exposed in outer space? How long can you survive?

I believe that a majority of people ask themselves questions when they are still kids looking into the beautiful sky at night:“What will happen if we go out of the earth? What will happen to our body when it is exposed in outer space? How long can we survive?” This is an exciting topic to talk about because most things in outer space are unknown to us. In order to discover the mysterious relationship between space and life, astronauts from different countries made great efforts for decades to test people’s reactions in the laboratory imitating the outer space situations. They also launched several rockets into space and onto the moon for research.

In the early 1960, scientists used animals as experimental materials to simulate the outer space in the laboratory and started an experiment on the impact of the space environment. According to a real case

scenario, an astronaut named Jim LeBlanc was exposed to a near-

vacuum environment due to a leak in his spacesuit. Jim remained

conscious for about fourteen seconds. From Jim’s memories,

exposing the outer space caused his tongue to start boiling, and

he could feel tongue bubbling before he passed out. The other

people who were involved in this experiment were found out about the same accident. After Jim was exposed to the vacuum for fifteen seconds, and then the air was injected into the air tank in time. That was how Jim was rescued. Through the experiment, the scientist has come up with two basic outcomings. Firstly, people’s bodies will not burst into outer space since the air pressure difference between outside and inside of our bodies. Secondly, for human beings, we need oxygen to survive, but there is no oxygen in outer space at all. If our body goes straight to space without any oxygen supply, then the oxygen in our blood could sustain our lives up to only around two minutes. Scientists

EVERDAY PHYSICS 141 discovered that there is a possibility that people can survive at the very beginning, but what happens in the next 90 seconds could cause fatal damages. People will not pass away immediately, but we are going to die slowly. For example, the body systems will stop working, getting blind, and even suffer nerve problems.

Therefore, when a human's body suddenly exposures to a vacuum environment, we only have 5 to 10 seconds to survive. Once the heart stops beating, we cannot avoid death.

All in all, we have no chance to survive once our bodies are exposed to outer space recently because outer space cannot meet our essential living conditions such as water, oxygen and sunshine. People need to take food and drink water, stay in the suitable temperature and air pressure range, breathe in oxygen for blood circulating. Without the basic requirements of lives, we couldn't survive. Human beings are so vulnerable in outer space. We are so lucky and grateful to have the earth, the only planet we could rely on in the endless space. We only have one earth. One sentence touched me: “The last drop of water on the earth will be people’s tears.” We have a great mission to love our earth, cherish resources on earth, take care of the environment and live harmoniously with animals if we want to survive in space.

References:

1. Anderson, David, and Rob Ludacer. “Here's How Long Humans Could Survive in Space without a

Spacesuit.” Businees Insider, www.businessinsider.com/how-long-human-survive-outer-space-without-

spacesuit-2017-5.

2. Gosline, Anna. “Survival in Space Unprotected Is Possible--Briefly.” Scientific American, Scientific American,

14 Feb. 2008, www.scientificamerican.com/article/survival-in-space-unprotected-possible/.

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61. What happens to the human body when it's exposed in outer space? How long can you survive?

The 1981 movie “Outland” shows a scene where a worker in space gets a hole in his suit [1]. As his body is suddenly exposed to outer space, the character swells up and explodes. This is a recurring theme in today’s Hollywood science-fiction films, which feature intense sequences of astronauts getting tossed into outer space without their spacesuit. As humans get closer to an era where many explorers will be living and working in space, a lot of questions arise about what it will really be like “out there”.

Some may wonder: what happens to an unprotected human body in outer space, and how long can you survive?

Contrary to popular belief, your body will not explode, and your blood will not boil [2]. Your skin does a good job at keeping your insides inside, and it also keeps your blood pressure high enough to prevent your blood from boiling [2]. However, you will begin to inflate and swell [1]. Due to the absence of atmospheric pressure in outer space, the nitrogen that is dissolved in your bloodstream near the surface of your skin will begin to collect itself into bubbles [1]. These bubbles will then expand and puff you out to almost twice your size [2]. If left unchecked, the inflated nitrogen bubbles can cause serious tissue damage [1].

You will also immediately notice the lack of air in outer space. There is no air in space, which means that there is no oxygen either [1]. Your circulatory system will continue to function, but only unoxygenated blood will cycle past your lungs and reach your brain [1]. Starved of oxygen, your brain will shut down in order to conserve energy [1]. This means that after approximately 15 seconds, you will lose consciousness [2].

Additionally, being left unprotected in outer space exposes your body to a tremendous amount of unfiltered cosmic radiation and charged particles emitted from the sun [2]. Physically, you will

EVERDAY PHYSICS 143 experience severe skin injury through sunburns, but space radiation can also cause other health problems such as central nervous system damage and changes in motor function [1]. Moreover, the vacuum of space is extremely cold [1]. You will not freeze immediately as heat does not transfer away from the human body very quickly, but unprotected exposure to outer space will eventually cause you to freeze to death [1].

But how long would you be able to survive in outer space? After 2 minutes, all your organs will shut down due to the lack of oxygen [2]. At this point, you would be medically considered as being dead. However, if you hold your breath, the absence of pressure in space will cause the gas inside your lungs to expand and you will suffer from ruptured lungs [1]. As a result, your estimated survival time will be reduced to 90 seconds [1].

Interesting fact: Due to the lack of oxygen, a dead human body will not decompose in

outer space [1]. The body would mummify if it was near a source of heat, and it would freeze

otherwise [1]. Whichever the case, the body would last for a very long time and could drift in

space for millions of years [1].

The resiliency of the human body is truly fascinating. There have been past cases where parts of astronauts’ bodies were exposed to outer space when their suits were damaged [2]. They were able to survive due to quick actions as well as the physical and psychological training that they had previously undergone [2]. If returned to a normal atmosphere quickly, a person would survive with few, if any, irreversible injuries [2].

[1] Greene, N. (2019, October 6). An Astronaut is Stuck in Space Without a Spacesuit: What Happens? Retrieved

February 12, 2020, from https://www.thoughtco.com/human-body-in-a-space-vacuum-3071106

[2] Sutter, P. (2015, July 28). Lost in Space Without a Spacesuit? Here's What Would Happen (Podcast). Retrieved

February 12, 2020, from https://www.space.com/30066-what-happens-to-unprotected-body-in-outer-space.html

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62. What happens to the human body when it’s exposed in outer space? How long can you

survive?

Space looks like an incredibly peaceful place: complete silence, not many people around to

disturb you, and a beautiful view! However, it is extremely dangerous for humans to be exposed in

space. Why is this? What processes would go on in our body if this were to occur?

On Earth, a protective envelope saves us from the dangers of our universe. We wouldn’t last a

minute in space without any protection! As opposed to common thought, you would not immediately

freeze if unprotected in space. Eventually you probably would, but you would be long gone by then!

First, your blood, saliva, tears and all fluids in your body would bubble up like your favorite soft drink

within 10 seconds. This is due to a process called ebullism [3]. Because space is a vacuum – meaning

there is no air – there is no pressure like there is on Earth, and this causes a lowering of the boiling

temperature of liquids (just like how water boils at a lower temperature at the top of Mount Everest) [1].

Your liquids will turn into gas, causing your body to swell up, though your skin will not burst since it is

so stretchy [2]! This will not be the death of you though…[3] In a vacuum like space, there is no air,

therefore no oxygen. In these conditions, the oxygen in your bloodstream will actually diffuse out,

actively leaving your system within 15 seconds, as if the

oxygen is being sucked out of you [1]. This is not like holding

your breath, where oxygen remains in your bloodstream, but

Figure 1: This image would look eventually runs out since you are not inhaling more. The lack very different without a spacesuit! (Source: http://www.humansinspace. of oxygen in your blood causes hypoxia (oxygen deprivation). org/tag/featured/page/37/)

Interesting fact: In regions that are not exposed to sunlight in space, the “shade”, temperatures can be as low as -250°C. But, where the sunlight (or light from any star if you are close enough) can reach you, the temperature can surpass +250°C [4]! You would either freeze or burn!

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For your body to function, oxygenated blood needs to be delivered to your organs, but this is rendered impossible. Once the deoxygenated blood reaches your command central, the brain, your organs fail and you lose consciousness, but still stay alive for about a minute [1]. Furthermore, the lack of atmospheric pressure will make the air in your lungs expand, most likely rupturing your lungs [2]. It would be better to exhale all your breath to avoid this predicament! Also, remember your mother telling you to put sunscreen on before going outside? This would be virtually useless in space… The strong ultraviolet

(UV) radiation emitted by the sun would immediately sunburn you regardless, as there is no atmosphere to partly absorb the UV rays like there is on Earth [1].

We romanticize the notion of space, without realizing the dangers of our universe. Without the protection of a spacesuit, you would certainly have the most beautiful backdrop for your death, but would you really be able to enjoy your last 15 seconds while painfully being boiled up and losing all capacities?

[1] Springel, M. (July 30th, 2013). The Human Body in Space: Distinguishing Fact from Fiction. Retrieved from http://sitn.hms.harvard.edu/flash/2013/space-human-body/.

[2] Starr, M. (July 27th, 2014). What happens to the unprotected human body in space? Retrieved from: https://www.cnet.com/news/what-happens-to-the-unprotected-human-body-in-space/.

[3] Edwards, A. (September 11th, 2016). SiOWfa16: Science in Our World: Certainty and Controversy.

Retrieved from https://sites.psu.edu/siowfa16/2016/09/11/can-humans-survive-in-space-without-a-spacesuit/.

[4] Monzon, I. (August 10th, 2019). NASA Astronaut Reveals What Happens Without Spacesuit in Space:

“Your Blood Will Boil”. Retrieved from https://www.ibtimes.com/nasa-astronaut-reveals-what-happens-without- spacesuit-space-your-blood-will-boil-2842089.

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63. How does the electrical conduction work of the nerve system?

Every day, we encounter different stimuli and respond differently based on those stimuli.

However, how come we recognize and perceive these stimuli differently? For example, if you touch a

hot plate, you will feel the texture of the plate and retract your arm instantly, but the pain only comes in

later.

Fundamentally, we perceive different signal inputs differently is because of the differences in the

connectivity of nervous system and structures of different neurons.

The structural differences will lead to different conduction speeds.

To understand how electrical conduction works in our nervous

system, we can imagine an underwater pipeline with a sensor on Figure 1: Action Potential Transduction the surface. Normally, the cells in nervous systems (neurons) have lower electrical (Source :(3)) potential than the outside environment due to the presence of more negatively

charged molecules inside. We can think of it as water pressure underwater is higher than the water

pressure inside the pipe. When we touch the hotplate, it activates the sensory receptor on the skin (think

of it as the surface sensor) and it changes the composition inside the neuron. The receiver portion of the

neuron will have a more positive charge than the outside due to surface channels opening up to let in

positively charged ions from the outside. It’s as if we let some water from outside into the pipe, and the

pressure difference will push the water inside the pipe forward. Similarly, when a patch of the neuron

becomes more positive on the inside, this positivity will be propagated (transmitted) to the nearby patch

and eventually to the end of the neuron. This positive signal is called an Action Potential (shown in

Figure 1). The action potential is sensed and propagated by nearby channels which will open if the

inside becomes more positive. (1) It is as if along the pipe there are holes that are coupled with sensors

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and will open to let in more water if a wave of water comes close. The action potential is then passed

onto the subsequent connecting neurons. This is how electrical conduction works in nervous system.

But why are conduction speeds different for pain and touch? This is because the pain-sensing

neurons are less insulated, which lead to a slower conduction speed. (4) Think of it as the pipe has many

leaks, so the water pressure inside is not well-preserved.

Interesting experiment/fact/idea/concept: A lot of animals have giant neurons for faster conduction speed, such as crayfish. Crayfish has a tail flip response as a built-in reflex to escape predators. If you touch the crayfish tail, it will quickly whip its tail and escape backwards. It has sensory receptors in its tail to collect information. Once its tail has been touched, it will send a signal to a giant neuron called Lateral Giant. The thick Lateral Giant neuron provides a fast input to Fast Flexor Motor Neurons, which innervates the muscles in the crayfish tail and lead to the contraction of those flexor muscles and elicit the tail flip response. (2)

What’s interesting is that our nervous system is very similar to other animals, even squids!

However, lots of animals have thicker neurons for a quicker conduction to better escape from predation.

The complete mechanisms on many fronts are still not yet fully understood. So, many more researches

are being conducted on animals such as squids to better understand it.

1. Y. Grossman, I. Parnas, M.E. Spira; Mechanisms involved in differential conduction of potentials

at high frequency in a branching axon; J Physiol, 295 (1979), pp. 307-322

2. Simmons, P. J., & Young, D. (2012). Nerve cells and animal behaviour. Cambridge: Cambridge

University Press.

3. https://www.sciencedirect.com/topics/neuroscience/cell-signaling

4. https://www-ncbi-nlm-nih-gov.proxy3.library.mcgill.ca/pubmed/32040075

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64. What is the difference between the way the brain sends signals and how an electronic device sends signals?

Recently, I was watching George Lucas’s masterpiece Star Wars, and while watching intergalactic aliens fight one another, one thing caught my mind: the force. Jedi masters have the ability to move objects by the whim of their minds and that made me wonder, can I do that? Will it be possible to send brain waves to control everyday electronic devices? Why or why not? What is the difference between the way the brain and electronic devices send signals?

Fundamentally, the way that electronic devices send signals and the way our brain sends signals are the same. Elizabeth Dougherty, a professional science writer for MIT explains that they are both forms of electromagnetic radiation, which are waves of energy moving at the speed of light [2].

However, the difference lies in the frequency of

the wave. For example, let’s look at how

today’s hot new product: Airpods. These fancy

wireless, earphones work on Bluetooth.

Bluetooth works by transmitting low power

radio waves [3], that send signals for a device

Figure 1: Radio Frequency to interpret. Each device has an ‘address’, which allows Strengths Brain waves are on the far right communication between multiple products. Regulations (Source: NASA) limit the strength of these waves and that is why your Bluetooth earphones/speakers stop when you leave your phone in separate room far away.

Now that we have a better understanding of how radio waves work, the next step is to understand how brain waves work. Every time you make a movement, be it something as mundane as walking or reaching for the bag of chips, that is due to brain waves. Basically, inside our heads are billions of

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neurons which conduct electrical waves and send information throughout the body. There are five

different types of brain waves, depending on its frequency [1].

The main difference between the two types of waves is its respective frequencies. For electronic

devices to communicate, the waves must be stronger and more frequent than the very weak brain waves.

To illustrate, radio waves oscillate 50 million to one billion times per second, whereas the strongest

brain wave, which are gamma waves only 32 to 100 times per second. The stark difference is why our

brain waves do not interfere with radio waves to change the radio or change the activity of electronics

that surround us.

To summarize, brain waves are too weak at the moment to have force-like capabilities of a Jedi

Knight. However, plenty progress has been made in this regard. A recent study from the University of

California, San Diego found a new way to transmit data through magnetic signals through the human

body from wearable devices [5]. This provides users with a more secure, and an ultra-low power method

of communicating our bodies signals to wearable electronic devices. Thus, instead of dreaming to be the

next Jedi, perhaps becoming the next Iron Man is closer in our future?

Interesting fact: Contrary to popular belief, cell phone usage does not cause cancer. Radio waved emitted from cell phones may affect the metabolism of the brain, but there are no dangerous consequences [4].

[1] A Deep Dive Into Brainwaves: Brainwave Frequencies Explained. (2019, April 1). Retrieved from

https://choosemuse.com/blog/a-deep-dive-into-brainwaves-brainwave-frequencies-explained-2/

[2] Dougherty, E. (n.d.). Home. Retrieved from https://engineering.mit.edu/engage/ask-an-engineer/can-

brain-waves-interfere-with-radio-waves/

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[3] Franklin, C., & Pollette, C. (2019, November 11). How Bluetooth Works. Retrieved from

https://electronics.howstuffworks.com/bluetooth3.htm

[4] Hamilton, J. (2011, February 22). Cell Phone Radio Waves Excite Brain Cells. Retrieved from

https://www.npr.org/2011/02/22/133968220/cell-phone-radio-waves-excite-brain-cells

[5] University of California - San Diego. (2015, September 1). Magnetic fields provide a new way to

communicate wirelessly: A new technique could pave the way for ultra low power and high-security

wireless communication systems. ScienceDaily. Retrieved February 12, 2020 from

www.sciencedaily.com/releases/2015/09/150901100323.htm

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Chapter 4: Human Made Machines

In this chapter we discuss interesting examples of human made machines in contrast to biological functions discussed in the previous chapter.

Important Physical Concepts of Machines

There is a lot of physics involved in most machines. For instance, forces, mechanics, acceleration, friction are omnipresent. Other phenomena such as light, electromagnetism, properties of materials also play important roles.

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Interesting questions about machines

65. How do airplanes fly?

You and your friends are about to fly to Cancún for the spring break to escape the horrible winter. While your pilot is waiting for their turn to take off, you stare at the window and see other airplanes taking off one at a time. You begin to wonder, how do airplanes fly? And what keeps them flying?

Fundamentally, flight relies on four principles of aerodynamics, or the study of how air moves around objects. These principles are thrust, lift, drag, and gravity [1].

Thrust is when an object is pushed forward with a force. Airplanes use their jet engines to suck in

air, compress it, mix it with gas, and ignite the mixture

in a burst of energy that shoots out the back of the

engine, which pushes the plane forward. Thus, creating

thrust. Jet engines produce a lot of thrust that airplanes

can fly at extremely high speed of up to 965 kilometers

per hour [3]. Figure 1: Four forces helping airplanes fly. Lift is the force that pushes the airplane upwards (Source: sciencelearn [2] ) and keeps it in the air. Airplanes depend on their wings to produce lift. The wings have a special shape called an airfoil. The top of the wing bulges out, creating a smooth bump. When the wing moves through air, incoming air particles either go above or below it. The air on top of the wing moves faster than the air on the bottom of the wing due to the bump. These particle speeds create lower air pressure above the wing and higher air pressure underneath it. This concept is called Bernoulli’s Principle. The high air pressure pushes the wing up, creating lift [3].

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Drag is when a moving object blocks the flow of air, which causes the object to slow down. You can feel drag if you put your hand out the window of a moving car. Your arm gets pushed backwards as the air rushes by. Thrust is always fighting drag so airplanes need to have enough thrust to overcome the amount of drag it produces. Thus, airplanes are designed to have air flow as smoothly as possible around the body [3].

Gravity is the force that pulls all objects down toward the earth. Lift can overcome gravity if it is strong enough as it always fight gravity. Based on the weight of the plane, people who design airplanes do a series of equations to find the right wing size as well as flying speed to create the right amount of lift [3].

While all these forces help airplanes fly, a pilot is still needed to fly them [1]. Most pilots turn the autopilot system on so they can focus on other operations. However, autopilots do not replace human operators, instead they assist them in controlling the airplane [4]. Nevertheless, I believe that autopilots will completely replace pilots as technology advances. Interesting fact: The first airplane was invented and flown by The Wright brothers

in 1903. It was considered the world’s first “sustained and controlled heavier-than-air

powered flight.” Their aircraft, the Wright Flyer, flew about 120 feet. Today, the newest

Boeing 787 can fly 10,000 miles on a single tank of gas [5]. [1] https://www.nasa.gov/audience/forstudents/k-4/stories/ames-how-do-planes-fly-text.html

[2] https://static.sciencelearn.org.nz/images/images/000/000/286/full/Forces-affecting- flight20151001-11211-n1h4n3.jpg?1522293568

[3] https://www.popsci.com/how-do-planes-fly/

[4] https://en.wikipedia.org/wiki/Autopilot

[5] https://www.factretriever.com/airplane-facts

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66. How is electricity produced and transported to our homes?

In a flick of a switch, that’s how easy we got electricity. Electricity has been part of our life almost 24/7, it is used to keep us warm or cool, allow us to see clearly during the night time, keep the LRT working, etc.. However, have you ever wonder how is electricity produced? Where is it produced and how does it transport to our homes?

Electricity exist in nature as lightning in thunderstorm, electric fish, etc.. Electricity can be generated as well to power our electronic gadgets, LRT, and many more. First of all, what is electricity? According to Natural Resources Canada (2019), electricity is the flow of electrons from a negatively charged body to a positively charged body. Electricity used by our everyday life are generated in the power station by electromechanical generator where it converts mechanical energy into electrical energy. The electromechanical generator uses either or both renewable and non-renewable energy as the energy source. Fossil fuel is commonly use as energy source whereas due to the geography of Canada, moving water is use as the energy source where it generate almost 60% of the energy supply (Natural

Resources Canada, 2019). The burning of fossil fuel and the movement of water turns the blade of the turbines where the turbine will then turn the generator and creates electricity.

So, now we know how electricity is

produced, but how is the electricity produced

transported to our homes? The electricity produced

by the power plant is transported by the national

power grid. The national power grid is a system of

cables and transformers linking the power station to

consumers (Canadian Electricity Association, n.d.).

Once the electricity is generated, the electrical current is sent to a step-up transformer, which will

EVERDAY PHYSICS 155 increase the voltage and reduce the current. This allows the transfer of electricity more efficiently where lesser energy is loss during transmission in the form of heat. When the electrical current has reaches a substation, the voltage is lowered and can transmit on a smaller power line. The electrical voltage is the lowered again by a step-down transformer so that the power is safe to use in our homes (Solar School, n.d.).

In short, electricity is produced in the power station. Before electricity is safe to use in our homes, the electrical voltage is increased by a step-up transformer and is carried by the transmission lines across the country. The electrical current is decreased by a step-down transformer when arrive in smaller power line and is decreased again before it reaches our home. Electricity has become an essential utility in our everyday life for keeping us warm, cooking, entertainment, transportation and many more.

References

Alliant Energy Kid. (n.d.). How electricity is made and delivered to your home. Retrieved from

https://www.alliantenergykids.com/AllAboutEnergy/HowElectricityIsMade

Canadian Electricity Association. (n.d.) North american power grid. Retrieved from

https://electricity.ca/learn/electricity-today/north-american-power-grid/

Natural Resources Canada. (2019). About electricity. Retrieved from

https://www.nrcan.gc.ca/energy/electricity-infrastructure/about-electricity/7359

Solar School. (n.d.). How electricity flow. Retrieved from

https://www.solarschools.net/knowledge-bank/energy/electricity/flow\

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67. What is the physics behind clap-activated lights?

Messrs. Stevens and Reamer invented The Clapper, a device that was first sold in 1985 and received U.S. patent approval on Feb. 20th, 1996. The Clapper became a fad hit due to its novelty; consumers could turn on and off any standard household electrical appliance with a few claps. The

Clapper is sold by Joseph Enterprises Inc., also known for the popular Chia Pet product. Considering the patent application for The Clapper and secondary sources on the physics phenomena involved in the device’s operation will allow us to better understand clap-activated lights through a specific example [1].

At a high level, clap-activated lights require a device with a microphone to pick up the acoustic signal from clapping and feeding this signal to a switch, which turns the lights on and off. The device is plugged into a standard wall socket, and appliances such as lights are then plugged into it, shown below.

The main physics phenomenon at work in the device is the transformation of a mechanical sound wave into an electrical signal.

Starting with the first stage of this process, the microphone converts the audible acoustic signal of the clap to a non-audible electrical signal [2], and feeds this separately to an amplifier and a filter. The

amplifier and the filter correspond to the two modes of

operation for the device, which can be chosen between using

a remote control. The amplifier adds energy that is converted

from the wall socket to the signal from the microphone so

that the signal from a small noise is strong enough to operate

the device in its so called “away/intruder” mode. In this Figure 1: The Clapper (Source: Wikipedia) mode, a small noise such as someone entering a room will cause

EVERDAY PHYSICS 157 the lights to turn on for a set amount of time. The filter is used for operation of the device in the classic

“normal” mode, by removing any signal corresponding to sounds outside the frequency range of 2200 to

2800 hertz, which is the “predominate frequency range of a typical hand clap” [1]. This filter aims to prevent the lights from turning on due to a non-clapping noise. The outputs of the filter and amplifier are sent to separate peak detectors which detect and holds the peak amplitudes of the signal. The analog output from the peak detector is fed to a microcontroller which converts this to a digital signal. This microcontroller can be thought of as a sort of processing station, in certain models the device allowing for two sets of lights to be activated by a different number of claps. This digital signal is fed to a power switch which enables the switch to operate the light that is plugged into the clap-activation device.

Interesting Fact: While the relatively simple design of clap-activation devices like The

Clapper allows them to be sold at a low cost, generally below $20 USD, this simplicity also leads

to some significant design flaws. One reporter chronicled his woes with the device, finding that it

frequently mistook common household sounds for clapping, turning appliances on and off. This

was because the sounds were within the same frequency band allowed by the filter in the device,

such as the reporter’s teenager running down the stairs with “house-shaking fury” [3].

[1] Stevens, C. R., Reamer, D.E. (1996). U.S. Patent No. 5,493,618. Washington, DC: U.S. Patent and

Trademark Office.

[2] Dirjish, M. (2012, October 3). What’s the difference between acoustical and electrical noise in components?. Electronic Design.

[3] Kauffman, M. (2005, February 6). Thumbs down for the clapper. The Hartford Courant.

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68. How does an electric car work?

As technology improves electric cars are becoming more common. Many view this technology

as a key tool in the fight against global warming, but how does it really work and are electric cars the

messiah they appear to be?

The answer to this question will focus solely on fully electric vehicles, not hybrids. If you have

ever ridden in an electric car one of the first things you notice is that its nearly silent. Electric cars first

appeared at the end of the 19th century but only recently became viable for most consumers. They have 3

main parts. First is the electric motor, which replaces the gas

engine, then the controller and the batteries. The first step in

driving an electric car is to charge the battery. This powers

everything it does. Just like a tank of gas, the battery is

limited in how much energy it holds. Instead of gallons of

gas, the energy is measured in kilowatt hours Figure 1: A Tesla Model 3, the most popular electric car outsold every other electric car by at least 750% Source: Business Insider (kWH). Different electric cars will go further

Did you know?: In 1912, a gasoline powered car cost only $650 compared to $1,750 for an

electric car. Today the cost gap is much smaller thanks to decreases in the price of lithium-ion batteries.

per kWH than others. Once you start the car the controller then sends power to the motor. The controller

takes inputs from your gas pedal and then determines how fast it needs to ‘flicker on and off’ or ‘pulse’

to deliver the appropriate amount of power. A controller will use variable resistors called potentiometers

to tell how much power to send based on the position of the gas pedal. Think of a simple ‘on-off’ light

switch. The only options are on or off. On a light with a dimmer you can control the amount of light you

want. This is basically what a controller does using pulses. The potentiometers tell the controller for

what percent of pulses it should be switched to ‘on’. If you want full power, then it would be 100% of

EVERDAY PHYSICS 159 pulses, half power would be 50% and so on. This process can cause vibrations in the motor housing creating noise. To fix this most controllers will pulse more than 15,000 times per second and at this range humans cannot hear the vibrations. The motor then turns the current into mechanical energy. This is done using magnetic fields. The current supplied to the battery creates a rotating magnetic field which then cause a rotor to spin. This spinning rotor is then used to turn the gears and thus the tires. In electric cars, the motors contain an alternator, a device that allows them to recharge when your foot is off the gas pedal.

Electric cars have been hailed as the future, but the technology has much room to improve.

Currently the batteries are expensive, bulky and have limited capacity. There are more efficient batteries, but right now they are too costly. There are also concerns that electric cars just shift emissions generation to the source of the electricity or power plants. Some also worry that the lithium used to create batteries is too limited in supply and that we are just replacing our dependence on one non- renewable resource with another. In any case, most people agree that electrical vehicles are an environmental improvement over gasoline powered ones. With the technology still in its infancy, there is room for hope that the electric vehicles of the future will be even more clean and powerful than they are today.

Sources:

1. Brain, M. (2002, March 27). How Electric Cars Work. Retrieved from https://auto.howstuffworks.com/electric-

car4.htm

2. How Electric Vehicles Work. (n.d.). Retrieved from https://www.myev.com/research/ev-101/how-electric-cars-work

3. Matousek, M. (2019, July 14). The 10 best-selling electric vehicles in the US this year so far. Retrieved from

https://www.businessinsider.com/best-selling-electric-vehicles-united-states-so-far-2019-2019-7

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69. How is electricity produced and transported to our homes?

Every night, people charge their electronic devices before going to their beds so that they can use them tomorrow. The power source for them is electricity, which is fundamental nowadays. What if we lose electricity in our houses suddenly? People might be terrified because their devices will not be charged, and they cannot find a way in the darkness. Through this assumption, people might wonder how people make electricity and send them to our neighbors?

In general, most electricity is generated in the power plants which use various kinds of resources like gas, wind, water, solar and fossil fuels. Famously, burning from fossil fuels produces electricity, and this method dominates the production of electricity. In specific, combustion oil and coal break down the carbon bonds, and it emits energy in the form of steam. It generates machines which are named,

“turbines,” and it produces electricity with a spinning magnet with high energy. [1]

Interesting fact and idea: Coal-burning power plants are recognized as the worst industrial polluter because they emit a large volume of carbon which threatens our health and environments. Therefore, for exercise, we should think about renewal energy that will reduce the pollution towards our lives

From these kinds of power plants, they send the transformed energy(electricity) to the high- voltage transmission lines, because the strong electricity sends itself quickly for a long distance. Then, it is transmitted to local electric distribution lines. We can easily observe those kinds of pillars in our daily lives. When it gets close to our neighbor, the electricity’s voltage is lowered into 110V or 220V, so we can use them in our houses. [2]

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Figure 1: The path of electricity to our lives (Source: English-online.at/science/electricity/electricity.htm)

Through this research, we can observe that the dominated power planet harms our environments and our health. In my thought, I would recommend running the power plants with solar panels rather than combustion of fossil fuels. Sunlight is always close to our lives. It gives natural energy without any harms towards human beings and environments, so we have to efficiently use the free energy as a gift.

The installation of sun panels will cost a big amount of money in short term. However, as we need electricity every day, it will save our money for long-term, and it will lead a lot of positive effects to our environments which must be kept for our next generation. Thus, we should replace the material of power plants to solar panels with these advantages.

Work Citation

[1] “HOW DOES ELECTRICITY GET TO MY HOME?” Renaissance Power & Gas, 1 Oct. 2019, www.renaissancepowerandgas.com/how-does-electricity-get-to-my-home/.

[2] “How Electricity Is Made and Delivered to Your Home.” Alliant Kids, www.alliantenergykids.com/AllAboutEnergy/HowElectricityIsMade.

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70. How does a touch screen work?

Smartphones have become commonplace in everyday life – I don’t know how I could live without mine! At its core, what makes the smartphone so useful is the plethora of apps that are easy to use thanks to the invention of the touch screen! But how exactly do touch screens work? It makes you wonder: What are the different kinds of touchscreens and how do we use them?

Figure A: Resistive Screens; (Source: Chassis Plans [4]) In other words, what are the inner workings of a

touch screen? When I touch the screen, why does the

interface respond? To understand this, it is important to

recognize that there are two main types of touch

screens: resistive (see Figure A) and capacitive (see

Figure B).

Resistive touch screens are most often seen at ATMs and grocery store check-outs. A specialized grey pen is utilized to create a signature on the screen. If you press hard enough while writing your signature, you can feel the screen bend slightly. It is as though the screens are “resisting” the force of the pen. Tiny dots are used to separate two inner screens, that are capable of transmitting electrical currents.

When the screen is pressed upon and the two inner screens make contact, the flow of electricity changes at that particular spot. The software sees this change and does the designated job it is at that spot, for instance, showing the imprints of your signature. The down side of resistive touch screens is that they are difficult to read because the many sandwiched layers reflect more ambient light.

This is where capacitive touch screens, found in your everyday smart phone, come in. Rather than using the pressure of your finger, these screens are similar to a grid of electrical charges that utilize the physical contact of the screen with another electrically charged substance, such as human skin. This is the reason you cannot use your smart phone while wearing gloves. Unless created with special

EVERDAY PHYSICS 163 electrical transmittable material, clothing has no electrical charge. A very tiny electrical charge is transferred to the finger causing a disruption in the circuit at that location. Similar to the resistive screen, the software sees this disruption and executes the job specified at the disruption location, for instance opening an app.

Figure B: Capacitive Screens; (Source: Electrotest [5]) Fun Fact: Carnegie Mellon University researchers are

working on products that can turn anything (think: walls, bikes, even

cheesecake!) into touch sensitive surfaces by combining electrodes,

materials that allow electricity to enter or exit, to conductive

materials.[1]

In this modern day and age, although almost everyone uses a smart phone with a touch screen, many are unable to use them due to biological reasons or simply because the touchscreen is faulty or damaged. Scientists are constantly researching and coming up with new inventions to ensure better access to technology for everyone. Luckily, touch screens are easily fixed by experienced technicians (or it can be done at home with the right instructions and equipment!)

Sources [1] http://www.figlab.com/ [2] https://scienceline.org/2012/01/okay-but-how-do-touch-screens-actually-work/ [3] https://electronics.howstuffworks.com/iphone1.htm [4] https://cp-techusa.com/whitepapers/touch-screens-in-industrial-computer-systems/ [5]http://www.electrotest.com.sg/cap_touch.htm [6] https://interestingengineering.com/ever-wondered-how-your-touchscreen-works

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71. How do touchscreens work?

From the moment you wake up in the morning, you use your smart phone. From turning off your morning alarm, texting your friends, to calling your parents, your smartphone is utilized in everyday life.

Most smartphones are touch screen, meaning that your finger is used as a cursor to control movements on your phone. Additionally, other smart devices such as music players, e-book devices, and even some laptops have added touch screens to their devices. But how do touch screens work? Do they differ in how they work?

To understand how touch screens work, we have to look at the inner workings of your phone.

But not all phones utilize touch screen technology the same. There is more than one way to sense touch, this article will go over the two most common types, resistive and capacitive touch screens.

Resistive touchscreens:

Resistive touchscreens work in a similar manner to the way your laptop keyboards work [1]. There are two layers – the first layer is thinner, typically made of polyester plastic that is laid upon a thicker layer of glass, both made of material that is conducting; the only thing separating them is an insulating membrane [1] When your finger touches the screen, the polyester plastic is forced to Figure 1: Resistive touch screen mechanism touch the glass and a circuit is completed, then a chip inside the (Source: explainthatstuff.com) screen figures out exactly what you pressed and your smart device reacts accordingly [1] What is great about resistive touchscreens is that they will register input from different types of touch, meaning that whether you have gloves on or not, your touchscreen will work. The downside is that they do not always register multi-touches [3].

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Capacitive touchscreen:

Capacitive touchscreens work differently than resistive

touchscreens. In the image below, the green and blue bar both conduct

electricity, and the gray space between them is an insulator. In essence, the

touchscreen acts as a capacitor, which is an insulator sandwiched between

two conductors that stores electrical energy [2]. When your finger is

pressed upon the screen, the electrical field is affected, and the location of Figure 2: Capacitive touch screen mechanism (Source: explainthatstuff.com) your finger is sent for processing [1]. Multi-touch is apparent in

capacitive touchscreens. The Capacitive touchscreen is more durable than the resistive touchscreen, as it

is less receptive to damage in the touch screen but as such, is more expensive to manufacture [3].

Touchscreens have changed the way we use our devices. By understanding this technology, we

Interested in what kind of touch screen your device uses?

Resistive touchscreens: Nintendo 3DS, WiiU [4], GPS systems, ATMS,e tc. [5]

Capacitive touchscreens: iPhones, Samsung’s, etc. [5]

Have you noticed a difference between the two groups when using their touchscreens?

can make more informed purchases and understand how our everyday devices work!

[1] Woodford, C. (2019, December 6). How do touchscreens work? Types of touchscreens compared. Retrieved from https://www.explainthatstuff.com/touchscreens.html [2] Woodford, C. (2019, May 3). How do capacitors work? Retrieved from https://www.explainthatstuff.com/capacitors.html [3] Understanding Your Options: Capacitive vs. Resistive Touchscreens. (2016, November 18). Retrieved from https://www.touchdynamic.com/understanding-your-options-capacitive-vs-resistive- touchscreens/ [4] Savov, V. "Nintendo 3DS has resistive touchscreen for backwards compatibility, what's the Wii U's excuse?". Engadget. AOL. Archived from the original on 12 November 2015 [5] Glatter, M. (2019, December 12). How do Phone Screens Work? Retrieved from https://ww w.ubreakifix.com/blog/how-a-smartphone-touch-screen-works

Ni

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72. What limits (physics, technology) are preventing humans from building spacecraft

capable of travelling close to the speed of light?

Have you ever wondered how far away is the nearest inhabitable zone? Let me tell you, it’s called

Proxima Centauri and it’s about 4.24 light-years away from us, converting to kilometers it’s about 40

trillion kilometers, which translates to 6 300 years of traveling using current technology [1]. It implies if

we can travel at the speed of light, we will make it there with only 4 years, which is much shorter than 6

300 years, so what’s preventing us from traveling at the speed of light?

The fundamental reason is that light is massless, and our spacecraft is not. Since spacecraft are not

massless, it requires energy to accelerate. To better understand it, we have to understand Einstein’s theory

of Special Relativity. Briefly, energy must be expended to make an object accelerate. The amount of energy

required is different when the object (i.e. a spacecraft) is at rest versus when it’s already moving at a

certain speed. According to the Special Relativity theory, when the object is traveling at large speed, it

will need increasingly larger amounts of fuel. Eventually, even tiny incremental gains in acceleration

require huge amounts of energy. For example, if a spacecraft is traveling at 90% speed of light, an

enormous amount of energy will be necessary to accelerate it to 91% speed of light. In other words, it

would require an infinite amount of energy [1]. So fundamentally, it’s impossible to travel at the speed of

Interesting experiment/fact/idea/concept: On Jan. 29, 2020, NASA’s Parker Solar probe becomes the fastest-ever human-made object at roughly 393 044 km/h, but that’s achieved with the help of Jupiter’s gravity. Even then, that’s merely a microscopic 0.04% of the speed of light.

Another interesting fact, light can go around the Earth more than 7 times in only one second [2].

light, at least not under current technology. However, there’s a project initiated in 2016 called

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Breakthrough Starshot that’s partially funded by Stephen Hawking, and it aims to send nanocraft to Alpha

Centauri, the star system in which Proxima Centauri is located, at roughly 15% to 20% speed of light. If achievable, they could reach Proxima Centauri in as little as 20 years, which is also one giant step closer in reaching the speed of light [3].

What’s even more fascinating is to ponder on what lies beyond the observable universe. Despite the astonishing speed of light, there’s still light that has not reached us yet from the incredibly distant places that lie outside our observable universe, and chances are they will never reach us because some parts of the space are expanding faster than the speed of light [4]. It means even if humanity is eternal there will still be an unknown number of places in the universe that we will never know about or never see, let that sink in.

[1] Singal, Tanmay & Singal, Ashok. “Is interstellar travel to an exoplanet possible?” Physics Education (2019): 2-18. [2] Brown, Geoff. “Parker Solar Probe Reportd Successful Record-Setting Fourth Close Encounter of the Sun” NASA (2020) [3] Daukantas, Patricia. “Breakthrough Starshot” Optics&Photonics News (2017) [4] Guth, Aan H., “Eternal Inflation.” Annals of the New York Academy of Sciences 950.1 (2001): 66–82.

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73. How does a camera capture an image and turn it into picture?

Do you like taking pictures of the beautiful scenery when you are travelling? Do you often take pictures of your friends? Do you like taking selfies after making up? Pictures and cameras are everywhere in our life and even some students choose this as a major for their university life. But how does camera work and what are the principles behind it? In this article, I intend to talk about cameras and pictures from the view of physics.

First thing we need to know is that how camera capture the image from objects. During this process, we need to understand how the images form in front of the camera. Usually how we can see objects are corresponded to lights emitted from them. Things that interact with particles of light are called photon.

The frequency of lights is related to the color of the objects. Different frequency of photons can reflect different color. When the photons pass through the opening of the camera, the image is formed just behind the opening. Second thing we need to talk about is the lens which are called aperture. It focuses the incoming photons to create a more clear image behind the aperture. By changing the location of the lens and different types of the lens, we can capture bigger or smaller area of the image. It are lens that allowed a camera to be compact. Thirdly, this part is what we use the camera to take a picture. As we all know, for most cameras, we press the button to take the photo. Button here is actually a key to control the shutter.

When we do not press it, shutter cuts down the way that the image

transfers to the sensor and it is only located just behind the

aperture. When we press, the shutter moved out of the way,

allowing the photons to contact with the sensor. There are many

factors to affect the speed of the photons and the size of the picture,

EVERDAY PHYSICS 169 like the size of the opening, the time that the shutter remains open, etc. Last but not least, it is how the image is recorded. In the old years, the technology was not quite developed so people invented the film cameras. When photons causes a reaction where they strike. Then the sensor transferred that reaction into brightness and make the final image. Later, to make the picture more beautiful, we want to make the picture more colorful. In order to do that, we add layers of the film to record the color of blue, green and red. A digital camera works similarly but more efficiently. Individual pixels, called photosites, build up an electrical charge based on the amount of charges. As the same principle, it breaks down into three colors and changes to the image that you see on the screen.

Now, I finish talking about the process of how camera works. We have a general idea how

Interesting fact:

⚫ In Japan, phone camera shutter sounds cannot be muted. Filming and taking pictures up

the skirts of high school females has long been a hot topic in Japan. And also, the rate if

criminal about this is rising quickly. So the government of Japan makes the policy that

the smartphones are all designed to have this function to prevent the safety of the female.

⚫ Android was originally conceived as a camera operating system. As it develops more

and more useful, it expands its business to produce more technological products to make

our life easier. it works from the perspective of the physics. Personally, I like the camera and I would like to take pictures with my friends when we travel around the world. I hope in the future, the camera can be developed more and more functionally.

[1] MCCLAIN, SHAWN. How Does a Camera Capture an Image? itstillworks.com/camera-capture- image-1129.html.

[2] Types of Lens. William Sawalich, 14 Aug. 2017, www.dpmag.com/how-to/tip-of-the-week/types-of- lenses/.

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74. What is the physics behind clap-activated lights?

Sometimes you wish that you did not have to get up from your comfy bed to turn off the bedroom light. Fortunately, this wish can now be realized by an invention called the Clapper [1]. You wonder what is the physics behind this magical technology? How does sound control the appliances from a distance? More importantly, what impact does it have on our daily lives?

A clap-activated light is designed based on a circuit system that can turn itself on or off by detecting the clapping of hands. Imagine this as an assembly line. Every sound that hits the clap- activated light is "heard" by the microphone. It will be turned into an electrical signal and then sent to the electronic sound filter. The filter’s job is to determine which sounds are from claps by recognizing sounds that fall within a certain frequency range [2]. For example, the frequency range of normal human

claps is usually between 2200 to 2800 hertz, if a sound

with this frequency is being detected by the filter, it

will classify the sound as a clap. Each time the filter

receives a clap sound, it delivers a signal to an

Figure 1: Clap Switch Block electrical switch. This generated signal is then Diagram (Source: amplified by the succeeding transistor stage (a www.ijser.org/researchpaper/Clap- transistorSwitching.pdf is a semiconduct) or device used to amplify or switch electronic signals and electrical power). It will then be delivered to a bistable flip flop circuit - a circuit that can be flipped from one state to the other by an external trigger pulse [3]. When the state of the transistor has been switched, it further generates a signal to the circuit amplifier, which eventually switches on/off the appliances.

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The clap-activated light has a huge impact on people’s day-to-day lives. Recalling a daily situation when we woke up in the middle of the night needing to use the bathroom downstairs. It was pitch-black and the light was on the other side of the hallway. We could not see the staircase. At this moment, a few clap-activated lights would be extremely helpful in terms of convenience and safety. In addition to that, clap-activated lights also help people with physical disabilities by allowing them to turn on or off appliances that are difficult for them to reach. There are still so many ways out there for the clap-activated light to improve people’s lives and make society a better place, which we believe is the ultimate goal for all inventions.

Interesting concept: Nowadays technologies such as Amazon Alexa and Google voice assistant

employ Automatic Speech Recognition (ARS) to help people complete simple daily tasks using

their voice. The difference between ARS and the clap-activation technology is that instead of

only detecting the clapping sound, ARS detects the patterns in audio waveforms, matches them

with the sounds in a language, and identifies which words people spoke. [4].

[1] Hopper, Tristin. “How the Clapper Works.” HowStuffWorks, HowStuffWorks, 22 Feb. 2010, home.howstuffworks.com/clapper.htm.

[2] Bagchi, Somangshu, et al. “Clap Switching.” International Journal of Scientific &

Engineering Research, Volume 4, Issue 11, November-2013, pp. 1361.

[3] Iwa, Tom A.C. “Design and Construction of Clap Activated Switch.” International Journal of

Engineering Trends and Technology, vol. 60, no. 1, 2018, pp. 33–40. doi:10.14445/22315381/ijett- v60p204.

[4] Cleirac, Estienne. “Les Us, Et Coutumes De La Mer, Divisees En Trois Parties, Etc.”

Amazon, Rouen, 1671, developer.amazon.com/en-US/alexa/alexa-skills-kit/asr.

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75. How Does a Refrigerator Work to Freeze Food Inside?

Nowadays, refrigerator is an important and essential household appliance in everyone’s kitchen.

This significant invention first came out as a small refrigerating machine by Scottish professor William

Cullen in 1755. Through centuries of development, refrigerator has undergone several periods from commercial use to domestic use with various styles. A question we tend to ask as children but gradually ignore as we grow up is that how does refrigerator work to freeze food inside? How does this machine keep temperature within a desired range 24/7? What are the mechanism and physical logic behind this commonly used house appliance? This book will lead readers to the answers of these questions and give more insights into how refrigerator significantly helps us live a comfortable life.

First and foremost, a concept called refrigeration cycle needs to be introduced. In the refrigeration cycle, there are five basic components: compressor, condenser coils, ventilation fins,

expansion device and evaporator coils.

More specifically, refrigerators use the principles of

pressure, condensing and evaporation of a fluid in a closed circuit

to absorb heat and decrease temperature inside the refrigerator.

First, the compressor at the bottom of refrigerator needs to

constrict the refrigerant vapor, raising pressure inside of the

compressor and pushes it into the coils attached to the outside of

the machine shown in the graph above. To complete this process, gas at low pressure and low temperature enters the compressor and then the gas will be compressed to a higher pressure along with the rising temperature. The logic behind this is similar to a bicycle pump that gets warmer when pumping up a tire with frictions. This process also consumes majority of electricity needed for a refrigerator. Then, the hot gas goes into the condenser coils and meets the cooler air which

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turns into a liquid at this point. The heat is released through cooling ventilation fins on the back of the

fridge. Next, the liquid will go through the expansion device where the pressure abruptly decreases so

that some liquid will quickly turn into vapor. This change of the state will absorb heat inside the

refrigerator and therefore has a cooling effect. Lastly, the previous liquid has completed its task by

absorbing warmth and it will turn back into a low temperature gas at low pressure in evaporator and be

sent to compressor for recycling. Until here, a complete refrigeration cycle completes, and the repetition

of this process keeps the temperature stable. With the rising awareness of environmental protection,

most residential refrigerators are designed to run 23 hours a day when the compressor should be cycling

off periodically. If the machine is on all the time, the cause could be leaky gasket on condenser coils or

fading compressor.

In the future, the refrigerator will join internet of things network and be connected to other

devices like Amazon’s Alexa or Siri on your phone. Some engineers are also dedicated to inventing

zero-energy bio refrigerator with cleaner energy. A Russian designer Yuriy Dmitriev released a gel-fill

The Fact We Need to Know: according to World Bank, in 2010, the average US citizen consumed about 13,395 kWh per year, in which their refrigerator drew roughly 500 kWh. The consumption of electricity from US refrigerators was more than that of an average person in

Nigeria (135 kWh), Ghana (299 kWh), or Bangladesh (274 kWh).

refrigerator in 2015, which utilizes gel-like substance to freeze food. I believe, the energy consumption

issue and deteriorating climate change will draw more attention in the future and energy-saving

appliances will become new member of more households.

References

How Does a Fridge Work? (n.d.). Retrieved from

https://www.fantasticfridges.com/YoungLearners/HowdoesaFridgeWork

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Lynch, T. W. (2013, September 24). Your Fridge Uses More Electricity than the Average Tanzanian.

Retrieved from https://www.reviewed.com/refrigerators/features/your-fridge-uses-more-electricity-

than-the-average-tanzanian

Parrish. (2018, April 25). Why Does My Refrigerator Run All the Time? Retrieved from

https://www.hunker.com/13409907/why-does-my-refrigerator-run-all-the-time

Refrigerator. (2020, February 12). Retrieved from https://en.wikipedia.org/wiki/Refrigerator#History

Sforza, N., & Sforza, N. (2017, September 22). How Does a Refrigerator Work? Retrieved from

https://www.realsimple.com/food-recipes/tools-products/appliances/how-does-refrigerator-work

Zero-energy Bio Refrigerator cools your food with future gel. (n.d.). Retrieved from

https://inhabitat.com/zero-energy-bio-refrigerator-cools-your-food-with-future-gel/

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Chapter 5: Food and Physics

In this chapter we discuss the physics involved in food, such as the mechanism of hardening when you boil and egg, for example. This can seem counterintuitive, since usually one thinks of solids melting, when it is heated, like ice or even metals, but in eggs the polymer chains composed of amino acids change properties when heated, which instead leads to solidification. We now turn to the important concepts.

Important Physical Concepts of Food

Important concepts include the definition of Calories, which constitutes the basis for providing energy to living organisms. While a calorie is defined as the amount of energy required to heat 1g of water by 1 degree it is also a measure of energy in foods, be it proteins, fats or sugars. Other important concepts are related to phase transitions and thermodynamics, such as ice to water transitions or vice versa, crystallization, or also the properties of gels in gelatin. Pressure, heat, and cold play important roles in food, so do material properties, such as density in suspensions and foams.

Interesting questions about food

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76. Why is it that food loses nutrients after it is microwaved?

How many times has your mom told you that microwaving your food is bad? That you should heat up your food on a pan or in the oven? How many times have you reluctantly agreed with her, while thinking “this is useless… I am wasting my time and am going to have to do more dishes.” Well today is the day this ends as I will explain, once and for all, how microwaves actually work, how food can lose nutrients, and how the two are linked.

Let’s start off by understanding how a microwave works. A microwave (the appliance) will use microwaves (a type of electromagnetic wave) to heat up your food. Microwaves are light waves whose wavelength is about 12 cm, that is a wavelength shorter than radio waves but longer than infrared waves26.

The microwaves heat up food by interacting with the water molecules inside. During this interaction, the waves make the molecules vibrate, and the faster they vibrate, the hotter the food gets1.

When food is cooked, no matter if it is in a microwave or a pan, nutrient content changes. Proteins, for example, need to be cooked for our body to be able to get the most of them. Fruits and vegetables are a different story. They contain water soluble vitamins (like C and B), fat soluble vitamins like (A, D, E,

K) and some minerals like potassium, magnesium, sodium and calcium27. These nutrients can be lost in the cooking process because they dissolve in the water (or another medium) and thus leave the vegetable or fruit. This is why boiling vegetables is the worst way of cooking in terms of nutrients. Steaming is much better since there is less contact with water and you do not have to drain before eating.

Interesting facts:

26 Spector, Dina. “How Do Microwaves Cook Food?” Business Insider, Business Insider, 10 June 2014, www.businessinsider.com/how-do-microwaves-work-2014-6. 27 Spritzler, Franziska. How Cooking Affects the Nutrient Content of Foods. Healthline, 7 Nov. 2019.

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Most Essential Vitamins and Minerals our Body needs: 28 - Vitamin A: healthy eyes and growth, Source: carrots - B Vitamins: Energy production, immune function, Source: potatoes, bananas, lentils - Vitamin C: Strengthening blood vessels and giving skin its elasticity, Source: Citrus - Folic Acid: Cell renewal and preventing birth defects, Source: Asparagus, Broccoli - Iron: Build muscle and health blood, Source: lentils, spinach These top 5 nutrients can all be obtained from vegetables. Here is what happens to their nutrients when you cook them29: - Vitamin A: 35% loss after cook and drain, 10% after reheating - B Vitamins: 50-65% loss after cook and drain, 45% after reheating - Vitamin C: 50% loss after cook and drain, 10% after reheating - Folic Acid: 75% loss after cook and drain, 30% after reheating - Iron: 40% loss after cook and drain, 0% after reheating When microwaving food, another phenomenon occurs. Not only is there nutrient loss due to dissolution in water, but the waves also break down a certain percentage of the nutrients. Vitamin C for example is very easy to break down with heat. However, since microwaving is the cooking method where food is in contact with heat for the least amount of time, it is actually the cooking method that preserves the most nutrients overall. 30

Therefore, next time your mom tells you to avoid using the microwave because it is bad for you, let her know that it is actually the best way to preserve nutrients. You should however be careful with the materials you put in a microwave. Some materials, specially some plastics are not meant to go in a microwave. Parts of it could dissolve in your food and while you may have more nutrients, I guarantee it will be bad for you.

28 “11 Essential Vitamins and Minerals Your Body Needs.” Goodnet, 3 Nov. 2019, www.goodnet.org/articles/11-essential-vitamins- minerals-your-body-needs. 29 “Nutritional Effects of Food Processing.” Nutrition Data Know What You Eat., nutritiondata.self.com/topics/processing. 30 Harvard Health Publishing. “Microwave Cooking and Nutrition.” Harvard Health, www.health.harvard.edu/staying- healthy/microwave-cooking-and-nutrition.

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77. How does Gazo (restaurant in Montreal) use nitrogen to make ice-cream?

Ice cream is, without a doubt, the one dessert considered as the best remedy against sadness and stress caused by our lives. Luckily for us, there are many ways do make this succulent dessert, ranging from mixing ingredients in a plastic bag or even using a Kitchen Aid before placing it in a freezer.31

However, is it possible to make ice cream without a freezer? Gazo, an ice cream shop in Montreal, uses liquid nitrogen to provide a different approach in making ice cream. Therefore, my goal is to clearly explain what liquid nitrogen is, determine the steps that Gazo takes to make their ice cream, and analyze the various effects and risks associated to this new culinary discovery.

To begin, nitrogen is a colorless, odorless, and tasteless element that can be found anywhere on

Earth as it constitutes of about 78% of our atmosphere.32 An important characteristic of this element is

that it goes from a gas to liquid substance once reached -

195.8°C, which means that its liquid form is a very cold

substance.33 To make this clearer take water as an example, it

can evaporates once it reaches 100°C (turns liquid into gas) and

freezes once it reaches 0°C (turns liquid to solid), and vice

versa. 34 Nitrogen, just like water, has the same property of

changing from one substance to another (from gas to liquid),

Figure 1: Nitrogen and water boiling point but only once it reaches -195.8°C as it then becomes “Liquid

comparison

31 Crazy, Blessed Beyond. “4 Different Ways to Make Homemade Ice Cream.” Header Image, 2 Aug. 2017. 32 Brownlee, Allie. “What Is Liquid Nitrogen?”.2018 33 “Liquid Nitrogen.” Air Products and Chemicals. 2019 34 Helmenstine, Anne Marie. “At What Temperature Does Water Boil?” ThoughtCo, 6 Oct. 2019

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Nitrogen”. Due to its extreme cold temperature, Liquid Nitrogen is often used as an element to instantly freeze things, especially in the culinary field.

Interestingly, Gazo uses this substance to instantly freeze all the ingredients that are used to make ice cream, such as cream, milk, sugar, and other additives.35 For a closer perspective, the following standardized steps will show how Gazo makes their ice cream:36

Source: https://www.youtube.com/watch?v=2jUFdH7gvfY Most people would ask themselves if this ice cream would taste the same or better than the traditional way of making ice cream. Or even, if there are risks associated to ingesting liquid nitrogen. At first, since nitrogen is tasteless, there is no taste transmitted to the ice cream when mixing it. However, when shops use liquid nitrogen to freeze the ingredients, it permits them to instantly make the ice cream

35 “Liquid Nitrogen Ice Cream Recipe.” 101 Cookbooks, 7 Mar. 2006 36 Khatz, David. ACS Office of Highschool chemistry. “Liquid Nnitrogen Ice Cream Recipe”, 2003

EVERDAY PHYSICS 180 fresh rather than letting the ingredients rest in the fridge for long periods of time.37 On the other hand, it bares certain risks. The FDA does not recommend eating any food mixed with liquid nitrogen due to few cases of skin and internal organ damage after its abuse.38 To conclude, it is amazing that Gazo uses liquid nitrogen to provide a tastier option for ice cream. However, be careful to not get addicted!

37 “Cooking with Gas: Nitrogen, Food and You.” Gas Detectors and Sensors - The Analox Blog, 6 Sept. 2019. 38 Shoot, Brittany. “Why the FDA Just Issued a Life-Threatening Warning About Ice Cream, Cereal and Cocktails.” Fortune, Fortune, 4 Sept. 2018

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78. Some factories use radiations to kill the bacterias in the food. Do these radiations influence the food safety?

When looking into your refrigerator, are you considering the potential bacterias on the products you have bought at the store? Many of the foods one purchases can be a host for various bacterias, insects, molds or even food borne illnesses like salmonella or E. coli. However, with the development of food irradiation, many of these concerns regarding bacterias in food have been able to make many foods safer for consumption.

Food Irradiation is a process that improves food safety by reducing or eliminating bacteria, microorganisms and insects39 through radiation technology. Food irradiation has been proven to produce many positive benefits including; the prevention of foodborne illness (like salmonella or E.coli), the extension of the shelf life of some foods, the control of insects on produce, the delaying of sprouting/ripening of produce and sterilization of foods to increase their storage life40. For example, irradiation can be used to prevent sprouting or germination in potatoes and onions41. The foods that are irradiated (based on approval by Health Canada) in Canada as of 2019 include; potatoes, onions, wheat, flour, whole wheat flour, whole and ground spices, and dehydrated seasoning preparations42. In Canada,

you can tell if a food has been through the irradiation process if it has the

government mandated “IRRADIATED/IRRADIÉ” sticker (see left). Despite

speculation, research and testing have widely recognized that “irradiation is a

safe and effective method of reducing harmful bacteria in food products, and

39 “What You Need to Know: Food Irradiation”, U.S. FDA Center for Food Safety and Applied Nutrition 40 “Food Irradiation” Government of Canada, Canadian Food Inspection Agency, (2016). 41 Schwarcz, Joe. “Is Food Irradiation Dangerous?” McGill Office for Science and Society, May 29, 2018. 42 “Food Irradiation” Government of Canada, Canadian Food Inspection Agency, (2016).

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safe to eat while retaining their nutritional value, taste, texture and appearance”43.

Generally, irradiation is the process of employing radiation energy to a material. Radiation

energy refers to the processes of emission and propagation of energy, either through the wave

phenomena or by the kinetic energy from the particles44. In food irradiation specifically, ionizing

radiation is used at very specific levels that sends enough energy into the bacterial or mold cells to break

down chemical bonds, which damages the pathogens enough for them to die or not be able to multiply

further, reducing illness or spoilage. Food can be irradiated through three different methods; gamma rays

(emitted from radioactive forms of the elements cobalt or the element cesium), x-rays (produced by

reflecting a high-energy stream of electrons off a target substance and electron beams (a stream of high-

energy electrons propelled from an electron accelerator into food)45. However, all three of these methods

work the same way; the packaged food passes through a radiation chamber on a conveyer belt, passing

through a radiation beam, like a large flashlight or spotlight on the food as it passes by on the conveyer

belt.

The irradiation of food stems from a long tradition of food preservation that was first developed

in ancient times. Since the early days of humanity, people have been using radiation on meats, fish, and

produce from solar energy. Next time you are in the grocery store, make sure you are looking out for

irradiated foods, and perhaps try them out! Interesting Experiment: Go to your local grocery store and pick up two of the same products (for example, onion) but make sure only one of them has been through the process of food irradiation by checking for the irradiated sticker. For the next two weeks track how fast the onions spoil in comparison to one another. I bet you the irradiated onion will expire slower than the non-irradiated onion!

43 “Food Irradiation.” Food Irradiation. Environmental Protection Agency, March 6, 2019. 44 Lima, Fabiana, Kássia Vieira, Miriam Santos, Poliana Mendes, and Souza. “Effects of Radiation Technologies on Food Nutritional Quality.” IntechOpen. IntechOpen, November 5, 2018. 45 “What You Need to Know: Food Irradiation”, U.S. FDA Center for Food Safety and Applied Nutrition

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79. Why does blowing on coffee cool it down ?

During the winter months, consuming hot beverages becomes second nature to many. Whether it

be hot chocolate, tea, or coffee, we oftentimes resort to these beverages as a complimentary method to

keep ourselves warm and protected from the frigid temperatures of winter in Montreal. As much as we

like the smell of that freshly brewed Tim Hortons coffee though, most of the time, it is too warm to drink

right away. And so, we blow on the coffee. But why exactly does blowing on coffee cool it down?

Ultimately, when we blow on coffee, we are disrupting the conditions in both the coffee and the

air directly above it, which actually causes the coffee to cool down fast. But before we dive into why, we

must understand what thermal energy is, as it is the basis of why

liquids cool and heat. Essentially, as the temperature of a liquid

increases, the individual molecules inside move around and

Figure 1: Molecules in a bounce off each other more rapidly [1]. See Figure 1. The energy high temperature liquid vs low temperature produced here is known as thermal energy, and the important Source:https://cpanhd.siteh concept to understand is that the energy created can then be transferred to other molecules in nearby ost.iu.edu/C101webnotes/matter- regions, until they all have similar energy levels. In simple terms, as energy is transferred between two and-energy/specificheat.html molecules, one molecule slows down in movement (it cools), meanwhile the other speeds up (it warms).

This process continues to occur until both molecules have the same amount of energy (temperature).

This is an important concept to keep in mind because this energy transfer cycle is what causes liquids to

warm and cool. Now that we’ve understood what thermal energy is, we will apply its concepts to the

cooling of coffee. If we just left the coffee without blowing on it, some of the energy from the molecules

in the coffee would be transferred to the molecules in the air directly above it to even out the energy

levels. Now, the coffee would become a little cooler since the molecules in the coffee would have less

energy after the transfer, and the air would be a little warmer. After some time, the molecules in the air

EVERDAY PHYSICS 184 and coffee would reach equilibrium and then there would be very little to no heat transfer anymore, because the molecules now have relatively the same amount of energy and therefore temperature.

Overall, the coffee would cool much slower because both environments (the air above the cup and the coffee) would be similar. What happens when we blow on our coffee, is that we disrupt that equilibrium by replacing the now warm air above the coffee with our cooler breath! Now, we have changed one of the environments; the air, and it is now cooler than the coffee. And thus, the processes described above cycle again! Energy transfer begins to occur at a much faster rate between the warm coffee and the cool air, which causes the coffee to cool even more, until the air and coffee’s environments reach equilibrium again. Another factor that contributes to the faster cooling is evaporative cooling. Essentially, as a liquid gets warmer it has more energy, as described above, and the higher amounts of energy result in the possibility of the water molecules being able to change from liquid to gaseous state! The change in phases here absorbs a lot of energy so when it occurs it substantially reduces the energy of the remaining coffee and thus cools it even more [2].

In conclusion, both the transfer of heat and evaporation are increased when blowing on coffee, which in return cools it. In fact, the processes described above not only occur in liquids, but also in foods/solids too. So next time your beverage or food is scorching hot, and you blow on it to cool it down, you now know exactly what is happening! ☺

Interesting experiment: Although the transfer of energy cannot be seen in coffee and the air, if you drop food colouring into two jugs of water; one hot, and one cold, you can clearly see the difference in how fast the food colouring disperses! Source: https://www.forbes.com/sites/startswithabang/2016/02/02/why-does-blowing-on-your-hot-drink- cool-it-down-the-surprising-scientific-answer/#5ec1719d130b

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80. Why is it difficult to cook at high altitudes?

Have you ever thought why high altitude would make your cooking process more difficult and time consuming? It would be difficult to notice the difference in our daily lives, because the real difference happens when we are on a real high altitude, on which most of us have never tried cooking. Let us talk about some of the effects high altitude has on cooking, the reasons behind it and the ways through which we can make the process more efficient.

First of all, what most cookbooks consider high altitude is 3000 feet above sea level

(FSIS). In those altitudes, cooking requires some considerations and extra equipment, because on that level, the air is thin and as a result, there is less oxygen and less atmospheric pressure(FSIS). This lengthens the cooking time and alters temperature of the foods, making moisture quickly evaporate from everything. Due to the thin air, water and all kinds of liquids evaporate faster and boil at lower temperatures. At sea level, water boils at 212 F and with each 500 feet increase, the boiling point of water decreases by 1 F. As a result, foods that are cooked by boiling or simmering take longer, but cook at a lower temperature. The process is respectively as follows: As altitude increases, the atmospheric pressure decreases and the boiling point of water lowers as well and to compensate the lower boiling point, the cooking time has to be increased.

Interesting Fact: A lot of people, who live in high altitude cities do not know the fact that their cakes, cookies and all kinds of cooking improve a lot just by making some adjustments to the recipe they are using. They attribute the low-quality results to their own poor culinary skills, but sometimes in those cities, it is all about a fact about chemistry and physics. So, a person living in a high-altitude city might use the exact same recipe as a person living in low altitude, and the results can be pretty shockingly different and disappointing for one.

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There are some techniques that can make your cooking process on high altitudes more efficient.

First of all, because the moisture in foods evaporate quickly, covering foods during cooking will help to keep the moisture in. Turning the heat up is not the answer, because water will just boil quicker and the food will dry, and it will be undercooked. One of the most common techniques used in high altitudes is utilizing a pressure cooker, which compensates for the low atmospheric pressure. Pressure cooking replaces the moisture, leaving the food much juicier and succulent in a much faster and safer way

(Corrie, 2018). So, next time you try to cook on high altitudes, keep these information in mind and use a pressure cooker!

Sources:

“FSIS.” High Altitude Cooking and Food Safety, www.fsis.usda.gov/wps/portal/fsis/topics/food- safety-education/get-answers/food-safety-fact-sheets/safe-food-handling/high-altitude-cooking-and- food-safety/ct_index.

Corrie Cooks. “Why Are Pressure Cookers Recommended for High Altitude Cooking.” Corrie Cooks, 2 Dec. 2018, www.corriecooks.com/pressure-cookers-recommended-high-altitude-cooking/.

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81. Why Does Popcorn Pop?

Perhaps one of the world’s oldest snacks, popcorn has been around for thousands of years and it is believed that the first wild and cultivated corn was for popping. It is so old in fact, that archaeologists have found popcorn ears that date back to about 4000 years old [1]. To make the tasty treat, individual kernels of popcorn are heated until they explode in an exciting display. If you have made this snack before you have surely wondered, why does popcorn pop?

Other than popcorn, there are three basic types of corn. Dent corn is grown primarily to feed livestock, flint corn comes in a wide range of colours and is used mainly for decoration and sweet

corn or “corn on the cob” is what you might eat for dinner

[2]. Popcorn differentiates itself from these other types as

its kernels have a hard exterior and a soft starchy centre.

The structure of a popcorn kernel is the main reason it

“pops”. A kernel is made up of three main components: the

endosperm, germ and the pericarp. The germ is the living Figure 1: Cross section of a popcorn kernel (Source: CBSC). part of the kernel located in the centre. The endosperm consists of soft and hard starch as well as a bit of water and is a carbohydrate used to provide the germ with food, allowing the kernel to grow. The outer hull of the kernel is called the pericarp, which is a hard shell made of cellulose and is key to the process of popcorn popping [3].

When a popcorn kernel is heated, the trapped water in the endosperm begins to evaporate into steam. The steam has nowhere to go as the pericarp holds it inside the kernel; this causes air pressure to build up inside. The inside of the kernel becomes very hot and holds a lot of pressure, turning what was soft starch in the endosperm into a gelatinous substance. Once the inside of the kernel exceeds

EVERDAY PHYSICS 188 a certain amount of pressure the pericarp bursts causing the gelatinous starch to explode out. The starch solidifies instantly when exposed to the cooler air outside the kernel, giving popcorn its unique shape and texture. The popping noise you might hear when making your popcorn comes from the pressurized air rupturing the hard pericarp and escaping the kernel.

Popcorn is one of the most popular snacks worldwide and its theatrics and the science behind Interesting experiment: The science behind why popcorn pops can be put to the test in

your own home. For example, try poking a hole in the pericarp allowing air to escape. How does

this change the popping process? Perhaps try leaving popcorn kernels outside on a hot, sunny day,

reducing the water content inside and then try popping them. There will be no pressure buildup

inside the kernel, therefore the pericarp will not rupture, and the popcorn will not pop! them make it one of the most interesting. However, it is much more than just an exciting snack as it is low in calories, a whole grain, a good source of fibre and low in fat [4]. Arguably the perfect snack, popcorn has been around for thousands of years and it is almost certain it will continue to stand the test of time.

[1] Popcorn.org (N.D.). Early Popcorn History. Retrieved from

https://www.popcorn.org/Facts-Fun/History-of-Popcorn/Early-History-of-Popcorn

[2] Popcorn.org (N.D.). From Seed to Snack. Retrieved from

https://www.popcorn.org/Facts-Fun/From-Seed-to-Snack

[3] Isley, M. (N.D.). The Science of Popcorn. Retrieved from

https://www.carolina.com/teacher-resources/Interactive/the-science-of-popcorn/tr23952.tr

[4] United States Department of Agriculture (2019). FoodData Central: Popcorn, Popped in Oil,

Unbuttered. Retrieved from

https://fdc.nal.usda.gov/fdc-app.html#/food-details/340253/nutrients

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82. Which way of cooking best preserve the nutrients in foods?

When I was young, one of the food I ate the most was the steamed egg which my grandmother would prepare for me every morning. Although I really loved the steamed egg she made, I have always wondered why she never made omelet or boiled eggs instead. Interestingly, my grandmother told me that steaming the eggs would best preserve the nutrition in the eggs, that is why she preferred making steamed egg instead of others. In the following, I would state a couple of reasons

to describe why steaming is the best way of cooking.

First, steam cooking is a simple way of cooking, all we need is to boil the water and put the food in and let it steam; most importantly it does not require constant attention. The thermal energy from water vapor transfers to the food during the steaming process, and cooks the food by heating. In comparison with pan-fry, steaming provides temperature distribution, which prevents the food from

being uncooked on one side and burnt on another side. Second,

steaming also moisturizes the food on top of heating. Of course

the extend of hydration depends on the hydrophobicity of the

surface chemical, but steaming helps to preserve the “juice” in

food. The water comes into contact with the food in a gassy

form, without immersing it in liquid. The water does not

become “dirty” so there is no “boiling-point elevation” and

EVERDAY PHYSICS 190 the temperature remains practically constant (Fine Dining Lovers, 1970). Third, vitamins and other nutrition could not survive at high temperature, steaming, which could maintain temperature at lower than 100℃, would not break too much nutrition. At the same time, food are placed on water, so all trace elements are retained and the original taste of food can be reflected. On top of all the advantages mentioned above about steaming, oil-free cooking is the most important factor that one should consider if one wants to have a healthy and nutritious diet. Furthermore, steaming keeps one’s kitchen clean and tidy, which could save a lot of time on cleaning after standing for a couple of hours to prepare a delicious meal.

In conclusion, steaming not only could preserve all the nutrition but also keeps the food away from contamination. Furthermore, steaming creates no oil and smoke in the kitchen, which could help keep the kitchen tidy and neat. Steaming is definitely the best way of cooking.

Interesting fact/idea/concept: Rice cooker is the best healthy cooking utensils for steam cooking.

(constant temperature control, keep pesticide residues from sticking to the food)

References:

「1」Fine Dining Lovers. (1970, June 20). The Science of Steam Cooking. Retrieved from https://www.finedininglovers.com/article/science-steam-cooking

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83. Why is it that food loses nutrients after it is microwaved?

The majority of McGill students including myself do not have enough time nor a necessary tool to cook a full meal, so we tend to resort to microwaves and frozen foods. However, as convenient as it is, I think that we should be aware of the pitfalls that could render a loss in nutrients of the food we consume. Given that most students, including myself, do not have the most well-balanced diet due to the inconvenience of cooking, it is crucial retaining the nutrients of the food as it can possibly be. According to the concern, how can we reserve the nutrients and the vitamins of the food at the highest level?

There are three main factors affecting nutrient losses when utilizing a microwave to heat up any type of frozen food, vegetables, and etc. Temperature, time, and moist level are considered to be the biggest factors that are resulting in the destruction of the nutrients. First, we should know how the microwave is processed in order to heat up the food. The fundamentals are that it utilizes thermal energy,

in which is caused by the molecules to vibrate,

which simply is put as the heat energy. The

waves of the energy are similar to the radio

wave, but it is shorter, which is called

magnetron. As the heat resonates by using

magnetron with the wavelengths of the food,

we can conveniently and quickly have a

delicious hot meal by using the microwave.

The loss in nutrients are usually caused in heat sensitive minerals, such as, vitamin b and c, which are water soluble. This can be connected to the concept of the higher the liquidity, the more loss of the nutrients derived. For instance, in 2003, there was an interesting experiment conducted by the board of

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science of food and agriculture, where they discovered that when heating up a broccoli in a microwave,

it resulted in the loss of 74%~97% of antioxidant particles [2]. This clearly shows heating up a food in a

microwave depletes the nutrients of the foods’ vital nutrients, which is extremely unfortunate to us, the

poor and broke university students.

Interestingly, a number of researches has shown that every cooking method can destroy

vitamin d and other nutrients of the food. Therefore, which method is ideal to heat and cook up the food?

It is still miserable, but since the longer the food cooks, the more nutrients tend to break down, so I am

assuming that we should stick to our best friend microwave.

Interesting fact: In 1947, the microwave was first used in a vending machine called

“Speedy Wendy,” in which were to be located in a Grand Central Terminal to serve a “sizzling delicious” fresh hot dogs. (Us, the University students’ all-time favourite) The first microwave that was introduced “Radarange” was an immense invention weighing 750 pounds with five feet tall costing $5000 dollars. However, as the time emerged, the researchers became concerned about the negative health effects that the microwaves has caused to the public [5].

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[1]Garden, H., HowStuffWorks, Lifestyle, Food, & Living. (2015). Do microwaves kill nutrients in food?. HowStuffWorks. Retrieved 13 February 2020, from https://recipes.howstuffworks.com/do- microwaves-kill-nutrients-in-food.htm [2]Publishing, H. (2020). Ask the doctor: Microwave's impact on food - Harvard Health. Harvard Health. Retrieved 13 February 2020, from https://www.health.harvard.edu/staying- healthy/ask-the-doctor-microwaves-impact-on-food [3] Publishing, H. (2020). Microwave cooking and nutrition - Harvard Health. Harvard Health. Retrieved 13 February 2020, from https://www.health.harvard.edu/staying-healthy/microwave-cooking- and-nutrition [4] Lisa Drayer, C. (2020). Does microwaving food cause nutrient loss?. CNN. Retrieved 13 February 2020, from https://www.cnn.com/2018/09/26/health/microwave-nutrient-food- drayer/index.html [5]Facts about Microwave Ovens - Interesting Facts and Myths . (2020). Historyofmicrowave.com. Retrieved 13 February 2020, from http://www.historyofmicrowave.com/microwave-facts/interesting-facts-about-microwave-ovens/

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84. Why does blowing on coffee cool it down?

I remember that today's morning I was rushing into Starbucks and got myself a cup of hot

caramel macchiato. When I drank the first bite, I find it was too hot to drink, subconsciously I tried to

cool it down by blowing it with my mouth. When I arrived in the class, I was thinking why blowing on

coffee could cool it down? What's the physical principle it applies?

First of all, I could feel the coffee was hot because the temperature is high. More theoretically

speaking, the moving speed of individual molecules determines the temperature. As the thermal energy

is measured by the kinetic energy of the molecules. If you

focus on individual molecule, there is a subtle change of their

speeds then their energies. You could notice that after an

amount of time, they will move at the same average speed so

their average energy will be identical as well. The process of

thermalization is introduced, once molecules collide with each

other, their inner energy will be exchanged. The speed of most

Figure 1: moving molecules molecules is determined by the average temperature. However, (Source: Wikimedia Commons user A.Greg, under c.c.a.-s.a.-3.0.) some will be hotter and some will be colder. By observing the

steam from the hot coffee, the steam is raised from the most energetic molecules so they have sufficient

energy to become a gas state, soon it will become to droplet as the cool air involved.

Back to the question, when blowing on the coffee by mouth, there will be air generated by mouth

to interact with the coffee, since the air generated by a person is cooler than the coffee, the energy will

be exchanged and the molecule speed will approach an average speed, then the coffee could be cooler

faster. Besides, when blowing on the coffee, the number of molecules increases, the rate of evaporation

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of the hottest molecules increases, since the hottest molecules escapes from the coffee, the thermal

energy decreases, the coffee will become cooler.

Interesting experiment: As discussed above, the temperature of the coffee is determined by the moving speed of molecules. In order to more distinctly and straightly observe the moving speed of molecules, we could substitute the coffee with regular water, as the regular water is transparent, one cup of hot water and one cup of cold water are needed, putting the same amount of blue ink into both cups, it is easily to find that ink in the hot water disperse way faster than the one in the cold water. Therefore it infers that the molecules in a higher temperature environment moving faster than they are in a lower temperature environment. Hence we can conclude that hot water has higher thermal energy than the colder water.

As we discussed above, the cooler coffee is derived from the exchange of the energy, so we can

easily find other ways to cool down our coffee or even cool down other stuff. For example, from my

personal experience, I prefer to put some ice into the coffee, so that the energy inside the ice will

exchange with the energy inside the coffee, as the molecule speed gap between these two are bigger,

they are tend to become an average speed faster, then my coffee could be cooler faster. Or if I'm not in a

rush, I could simple leave the coffee for a long while, since the cold air in Montreal could also help the

coffee become cooler.

Reference: Why Does Blowing On Your Hot Drink Cool It Down? The Surprising Scientific

Answer https://www.forbes.com/sites/startswithabang/2016/02/02/why-does-blowing-on-your-hot-

drink-cool-it-down-the-surprising-scientific-answer/#757387fb130b

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85. Why do bananas turn from yellow to brown/black?

Bananas are notorious for their changes in colour during the various stages of the ripening process. One day the fruit is green, the next it is yellow and before you know it, it becomes brown and mushy. This makes purchasing bananas quite tricky! Have you ever wondered what is occurring chemically when bananas turn brown and start to rot? In order to address this question, it is important to look at what causes the various stages of the ripening process, what molecules are responsible for the changes in appearance and taste, and what effect oxygen has on the ripening process.

The unripened banana is saturated with chlorophyll, a molecule found in plants that is essential for photosynthesis, the process used by plants to generate sugar and oxygen. In addition to the green colour, chlorophyll causes the fruit to be hard as well to be more acidic than sweet. This is why it is often unappealing to eat green bananas.

There exists a naturally occurring ripening hormone called ethylene gas, which is found not only in bananas, but also in other fruits such as apples, peaches, tomatoes, etc. As time goes on, as the banana produces more of this gas, it triggers the breakdown of acids, the softening of the fruit and the chlorophyll pigments to be broken up. At this stage, the banana has a yellowish hue and is sweeter, making it more appetizing.

However, as time goes on, these yellow fruits begin to turn brown. Have you ever wondered what makes bananas more susceptible to this process than other fruits?

Bananas produce very large amounts of ethylene gas compared to other foods that produce this chemical. These very high amounts of hormone cause the yellow pigments to decay, leading to brown

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spots on the fruit. This is similar to what happens when the banana is bruised or damaged. You might

therefore imagine that it would be useful to place bananas in a paper bag in order to get them to ripen

faster because of the ethylene trapped inside. This is true as long as it is not placed in there too long

since the excess exposure to the gas will cause the fruit to spoil.

Like people, bananas need to breathe, taking in oxygen and releasing carbon dioxide. The more

oxygen it is exposed to and the more it respires, the quicker it ripens. Unlike other fruits, however, the

respiration rates in bananas speed up and they become unpleasantly soft as time goes on. Bacteria then

begin to grow on the peel and cause the fruit to rot.

Interesting concept: It is interesting to imagine what would occur if you put a high ethylene-producing fruit like bananas in the same vicinity as other fruits. Due to the high amounts of ethylene produced, bananas may accelerate the ripening of other fruits and may eventually cause them to spoil.

It is amazing to think about all the complex chemical reactions that give rise to the everyday

phenomena we witness throughout our lives. It is astonishing to imagine that certain chemicals, which

are made up of tiny particles invisible to the naked eye, have the ability to affect the quality of the food

we eat. As scientists, we should constantly remind ourselves of how little we actually know and in doing

so, we can put ourselves on a path for discoveries that can revolutionize the quality of our resources and

lives.

• ACS Chemistry for Life. “Good news for banana lovers: Help may be on the way to slow that rapid over-ripening”. Retrieved from https://www.acs.org/content/acs/en/pressroom/newsreleases/2012/august/good-news-for-banana- lovers-help-may-be-on-the-way-to-slow-that-rapid-over-ripening.html • Bry-Air. “Control of Ethylene in Fruits and Vegetables Warehouses and Cold Stores”. Retrieved from https://www.bryair.com/technical-articles/control-of-ethylene-in-fruits-vegetables- warehouses-and-cold-stores/ • Encyclopedia Britannica. “Why Do Bananas Turn Brown?” Retrieved from https://www.britannica.com/story/why-do-bananas-turn-brown

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86. Why is it difficult to cook at high altitudes?

Picture this, you’re camping with your friends in the mountains. You brought pasta supplies with

you and try to boil the pasta, but it never cooks. You and your friends are shocked, why is the water

boiling and not cooking the pasta? And why is it difficult to cook at high altitudes?

We all know that water boils at 212 F, but suppose you live in Denver (5,000 feet altitude) where

the water boils at 202 F. A lower boiling temperature means that the cooking process becomes harder

and longer. Pasta would take 7 minutes to cook at sea level but could take 15 minutes to cook in Denver.

This is due to the difference in atmospheric pressure

depending on the elevation. Atmospheric pressure is the

force exerted on us by the air above being pushed down

by gravity. Atmospheric pressure lowers the boiling

point of water by 1 F for each 500 feet of increased

Figure 8: Approximate boiling point of water, by elevation. elevation. But why?

(Source: Pew Research Centre [3]) Atmospheric pressure decreases with

altitude because as we go higher in the atmosphere, there are fewer air molecules above us pushing

down and creating mass. You may be wondering why more pressure leads to a lower boiling

temperature. To boil water, you need energy from heat to break down the water molecules and turn them

into vapor, this creates bubbles in the water and the water starts to boil. In high altitudes, it takes less

energy to break up the water molecules, therefore less heat. The higher up we go, the lower the boiling

temperature!

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Myth: You may think that a lower boiling temperature means faster cooking, but

that is false! Cooking takes longer at a high altitude because the temperature of the water

cannot get hotter than the boiling temperature. So, you can’t get water hotter than 193 F at

an altitude of 10,000 feet

Interesting fact: At 10,000 feet you can boil eggs for a month at a boiling point

of water and never cook the eggs.

This can be a real problem to people who live at a high altitude. Do they never boil eggs, for example? Luckily, the answer is no: we have found solutions to this problem, like using a pressure cooker to compensate for the low atmospheric pressure. So next time you’re planning on making pasta in the mountains, bring a pressure cooker with you!

[1] https://www.thespruceeats.com/cooking-at-high-altitude-995438

[2] https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact- sheets/safe-food-handling/high-altitude-cooking-and-food-safety/ct_index

[3] https://www.pewresearch.org/fact-tank/2015/09/14/does-waters-boiling-point-change-with-altitude- americans-arent-sure/

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87. Some factories use radiation to kill the bacteria in the food. Do these radiations influence food safety?

What if I asked you to choose between eating food contaminated with Vibrio or Salmonella and eating food exposed to nuclear radiation? What would you be more scared of? Most people would likely take their chances with food poisoning rather than with irradiation food because of the public fears that give this irrational misconception. However, it’s a pity since this processing technology of food present many benefits that outnumber any risks people think it may have. So, how does it work? What are its benefits? Is it safe?

Factories use food irradiation as a processing technology for controlling spoilage and removing foodborne pathogens by using energy from ionization radiation including, gamma rays, x-rays, and electron beams. Gamma rays are released from elements such as Cobalt 60 or Cesium 137 radioactive forms. These radiations are also used regularly for the sterilization of medical, dental, and home products. Whereas, X-rays are created by reflecting from a target material (typically one of the heavy metals) a high-energy stream of electrons into food. Similar to X-rays, an electron beam is created by an electron accelerator that propels a stream of high-energy electrons into the food (1).

Food irradiation is analogous to airport X-raying luggage. The food is transferred to thick-walled chamber which contains a source of ionizing radiation. Once the food is irradiated, the radioactive source itself never touches it, it kills bacteria by exposing them to highly reactive, free radicals, coming from the radiations mentioned beforehand, which can disrupt cell division. Food is exposed momentarily to the radiations at controlled strengths (wavelengths) and thus, do not cause the food itself to become radioactive or dangerous in any way (2). When people undergo chest X-rays, they do not become radioactive when the performance is done. So, why would food be?

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This process is used to successfully remove pathogens that cause foodborne illness, such as E. coli or Salmonella. In addition, it is used for the preservation and increase of food shelf life by destroying or inactivating species that trigger decomposition and rot (3). Also, it helps in the control of insects, without the use of chemical insecticides. Furthermore, irradiation can sterilize foods which are, in hospitals, useful for patients with severe illness like AIDS or cancer. Fun fact: NASA astronauts consume meat exposed and sterilized by irradiation to prevent

foodborne illnesses from arising when they are in outer space.

Concerning the safety of this technique, public health authorities such as FDA and WHO

have approved and classified all food irradiated as safe, after 30 years of

researches. There is almost no difference in the nutritional value of irradiated

and non-irradiated foods, but irradiation may cause similar chemical changes to Fig.1: Radura Symbol those caused by cooking the food. Items such as beef, poultry and, fruit, like (3) spinach and mangoes, and even spices are among the many food items presently undergoing food irradiation. Today, a Radura symbol is required for any food product irradiated and sold in supermarkets

(2).

To sum up, no one was ever killed by exposure to gamma rays from a source of cobalt-

60 used in food irradiation. Yet, people are continuously dying because of food poisoning that this technology could prevent. In other words, be informed not influenced, as the future of irradiating food, which is the possible combinations of irradiation procedures with other preservation methods, depends on an informed and aware public.

References

1) Center for Food Safety and Applied Nutrition. Food Irradiation: What You Need to Know [Internet]. U.S.

Food and Drug Administration.

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2) Department of Health & Human Services. Food irradiation [Internet]. Better Health Channel.

Department of Health & Human Services; 2012

3) Realizing the Benefits of Food Irradiation [Internet]. IFT.org. [cited 2020Feb13

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88. What is the physics behind popping corn?

Have you ever taken out a bag of popcorn out of the microwave only to be disappointed by the amount you actually get? “How can I get all the kernels to pop?” you stop to wonder. “And what makes corn pop, anyway?”

Popcorn is the only common corn species that is able to transform into the beloved snack we have today. But why is that? It has to do with the shape and properties of the kernel. To understand this,

we must first know what the kernel is composed of. A

popcorn kernel is composed of 3 parts: the pericarp,

germ, and endosperm (Isley, 2020). The germ is found

deep within the kernel, below the endosperm containing

the starch. The pericarp is the outer layer that holds the

germ and the endosperm and gives the kernel its shape

(Figure 1). Popcorn kernels are more spherical than other Figure 1: The composition of a popcorn kernel [Credit: Cereal Process Technologies, corn kernels (Netburn, 2015), and its pericarp is four 2016] times stronger than that of regular corn which allows for higher pressures within the kernel (Foer, 2005).

When the kernels are heated, the corn shell acts as a pressure cooker that locks moisture inside the kernel (Quin et al., 2005). As this pressure builds up, the trapped water in the endosperm evaporates and the moisture under pressure transforms the starch into gelatinized starch (Isley, 2020). However, the strong pericarp is only able to stay put for so long. After 9.2 atm, the outer layer breaks. Once the shell falls out, the gelatinized starch is revealed to cool and solidify as a fluffy, foamy structure. The now inverted kernel has become eight times less dense and twice as large as it was before (Netburn, 2015).

But why don’t some kernels pop? If a popcorn kernel is heated too slowly then the steam leaks out of the tip of the kernel instead of the pericarp and doesn’t create the environment needed to explode

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(Helmenstine, 2019). The process of creating a “pop” rests upon basic physics concepts: the changing of water from a liquid to a gas is called the kinetic molecular theory, the direct relation between temperature and pressure is stated as the the law of pressure, and the ideal gas law shows us that which is an equation that calculates the ideal gas (lsley, 2020).

Interesting fact: The microwave was developed during the Second World War, when the

British Army was looking to make a high frequency radar for the war effort. In 1946, while testing

this new technology, Percy Spencer, a self-taught engineer, accidentally discovered that the

machine melted his chocolate bar. He recreated this with popcorn, eggs, and a variety of foods,

and soon after, he and his team found themselves refining and improving this technology. Years

later, Spencer and his team turned this sophisticated technology into a post-war appliance (Puiu,

2018). Popcorn was a key aspect to many of Spencer’s experiments, as he saw it as a primary

product for his modern microwave. So next time you look at a microwave, know that the “popcorn”

button has a deep history, and it would not be around had it not been for the war and an engineer’s

accidental discovery.

The physics behind popcorn proves to us all that we can see fundamental concepts behind our world in even the most mundane and elementary of things. Everything around us falls under laws that create the building blocks for life: from the far scope of the Universe, all the way to our kitchen. So next time you have a moment while your popcorn is getting ready, marvel at the complexity and physics of the world around us, rather than being disappointed at the few non-popped kernels at the bottom of your bag.

Arkhipov, Aleksandr et al. "POPPING UNDER PRESSURE: THE PHYSICS OF POPCORN". Pdfs.Semanticscholar.Org, 2005, https://pdfs.semanticscholar.org/693b/b80895c7327949ac9ced8fba98f5f3ec2b1b.pdf. Accessed 12 Feb 2020. Foer, Joshua. "The Physics Of . . . Popcorn". Discover Magazine, 2005, https://www.discovermagazine.com/the- sciences/the-physics-of-popcorn. Accessed 12 Feb 2020.

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Isley, Mike. "The Science Of Popcorn". Carolina, 2020, https://www.carolina.com/teacher- resources/Interactive/the-science-of-popcorn/tr23952.tr. Accessed 12 Feb 2020. Netburn, Deborah. "The Physics Of Popcorn: Watch The Explosion In Slow Motion". Los Angeles Times, 2015, https://www.latimes.com/science/sciencenow/la-sci-sn-popcorn-science-20150210-story.html. Accessed 12 Feb 2020. Puiu, Tibi. "How The Microwave Was Made: Its History And How It Works". ZME Science, 2018, https://www.zmescience.com/science/physics/microwave-oven-from-ww2/. Accessed 12 Feb 2020.

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89. Why do bananas turn from yellow to brown/black?

This morning, I was very excited to eat the bananas I had gotten from the groceries a week ago.

They were not quite ripe when I bought them, so I let them sit to ripen. To my disarray, when I woke up

this morning, the bananas had already turned brown. This got me wondering, what is the reason that

bananas turn brown/black?

Bananas can turn brown or black through 2 different ways. In the example given earlier, if a

banana is left sitting for too long, it can become overripe and turn brown. Otherwise, not unlike bruising

on a person, a banana can become brown at certain locations through a process called enzymatic

browning (1).

Every fruit in the world contains a molecule called ethylene. Ethylene is a

molecule that helps the fruit ripen. In bananas, ethylene also causes browning

when bananas are kept for too long. At first, ethylene allows the banana to ripen

from a green, hard banana to the delicious soft golden fruit we are used to. It

allows for the breakdown of large sugars into smaller ones and for the breakdown

of pectin (a protein that keeps the banana firm) (3). When this happens, the green

pigments of the banana are also broken down and replaced by yellow pigments.

However, bananas produce high amounts of ethylene. The banana continues

ripening very quickly even when ripe and yellow. At that point, the yellow Figure 1: Ethylene pigments get broken down and they are not replaced. This leaves the banana to be causes browning in leaves brown in color (3). and bananas (Source: Utah

State University and

Encyclopaedia Britannica).

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An interesting experiment that could be done is to see if storing the banana in a fridge has any effect on how fast the banana browns. As it turns out, it is not the case. Ethylene is a gas. If you keep the banana in the fridge, that gas will be trapped and will have a stronger impact on the banana. Also, the cold will lower the effectiveness of enzymes working to keep the banana from browning. Thus, the banana would brown even faster

(4). Just like humans, bananas can also bruise. The molecular process by which this happens is

evidently different, but the idea is the same. Whenever you cut, peel or bruise a banana, there is a

specific enzyme that is released which causes the breakdown of molecules in the banana, resulting in the

brown color. This enzyme is called polyphenol oxidase. It breaks down the dopamine molecules found

in the banana, and this pathway ultimately leads to the formation of brown pigments, one of which is

melanin (the brown pigment also found in our skin) (2).

The browning of bananas, and fruits in general is a process that is heavily studied. Indeed, people

are tirelessly working in trying to find ways to delay or prevent the browning altogether. When products

brown, they are no longer seen as desirable in grocery stores. They thus have a limited shelf life.

Finding a method to delay this process could lead to less food waste, a big issue in society currently.

[1] University of California, Santa Barbara. "What causes banana peels to turn brown?", UCSB Science

line, https://scienceline.ucsb.edu/getkey.php?key=1213, visited February 12th 2020.

[2] Palmer JK. Banana Polyphenoloxidase. Preparation and Properties. Plant Physiol. 1963;38(5):508–

513. doi:10.1104/pp.38.5.508

[3] Hogenback, Jonathan. “Why Do Bananas Turn Brown?”, Encyclopaedia Britannica,

https://www.britannica.com/story/why-do-bananas-turn-brown, visited February 12th 2020.

[4] Saraswat, G.G. “Why does banana skin turn black even if kept in refrigerator?”, The Times of India,

https://timesofindia.indiatimes.com/Why-does-banana-skin-turn-black-even-if-kept-in-

refrigerator/articleshow/344002.cms, visited February 12th 2020.

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90. What is the physics behind popping popcorn?

You’re about to sit down and watch a movie, but the experience is not complete without that legendary snack. We are all familiar with the characteristic “pop” noises closely associated with the movie snack that even has a spot in the snack’s name: popcorn. But what process taking place within the popcorn kernel is actually responsible for the “popping” process, as well as the noise it produces?

Even the biggest fans of popcorn likely take for granted that a simple popcorn kernel can transform into a fluffy treat with the push of a microwave button. But where some just see a fun movie snack, others see a physics phenomenon waiting to be explained. Before it is popped, a popcorn kernel is comprised of mostly starch and water [4]. In 2015, French engineers Emmanuel Virot and Alexandre

Ponomarenko used a high-speed camera to examine a popping kernel at 2,900 pictures per second and understand the forces that make kernels “pop” and produce the iconic sound [1].

Virot and Ponomarenko discovered that when the temperature reached 100°C, the moisture inside the kernel began to turn to steam. As the temperature continued to rise to 180°C, pressure inside of the kernel climbed to levels that the outer shell could no longer withstand [4]. The outer shell burst open, causing a quick release of pressure which forced the kernel’s starchy interior to expand and solidify into the familiar fluffy white solid that we eat [2].

Fun Fact: The “pop” noise is not caused by the breaking of the outer shell, but by the release of the built-up water vapor [4].

The scientists concluded that 180°C creates the critical pressure level for this process to take place, regardless of the size or shape of the kernel [3]. During the expansion of the kernel into the fluffy, starchy exterior, a “leg” puffs out which launches the kernel into the air. The angle at which the leg forms causes the popcorn to fly throughout the air, rotating in a somersault-like motion [4].

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Figure 1: Diagram of kernel popping process

Source: foodxddict.wordpress.com

Did you ever think that one of the most dramatic transformations in physics could happen in your microwave, and taste so delicious? The case of popping popcorn is a powerful example of how the laws of physics apply to everything, even the food we snack on. The next time you heat up a bag of popcorn for a movie night, think about the amazing thermodynamic processes taking place right in your microwave. You just might gain an extra appreciation for the fun, noisy snack!

Sources:

[1] https://www.latimes.com/science/sciencenow/la-sci-sn-popcorn-science-20150210-

story.html

[2] https://phys.org/news/2015-02-physics-food-secrets-popcorn.html

[3] https://royalsocietypublishing.org/doi/full/10.1098/rsif.2014.1247

[4] http://colgatephys111.blogspot.com/2015/10/the-physics-of-popcorn.html

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91. Why does cutting onions make you cry?

With 9.2 million acres of onions harvested annually around the world, it makes sense that they are one of the most common vegetables when cooking, such as in salads and omelets (1). However, working with onions are not always as pleasant as eating them. You may have realized that when cutting onions, your eyes tear up and soon begin to cry. But why? Why do onions have the ability to hurt us and is this mechanism of any use?

Onions are a type of root vegetable that grow beneath the surface. As they thrive in the soil, these plants are often surrounded by many insects and animals who will try to eat and damage the plant. Think of it like this, if us humans were being hunted by a large predator, wouldn’t we want to have a way to fight for our lives? For instance, we can kick, scream and run away. Now think of onions as humans, having a mind of their own and wanting to survive and reproduce, except their defense mechanism against bugs and animals is to generate a chemical to turn them away. As a result, onions have developed a fascinating evolutionary way to protect themselves. The soil contains many minerals, biological materials and elements necessary for adequate plant growth, and sulfur is of particular importance.

Sulfur that is found in the dirt mixes itself during Syn- propanethial-S the growth stages of the onion and is used to oxide (LF) produce amino acid sulfoxides, which are lachrymator y-factor synthase compounds that can readily turn into a gas (1). enzyme Sulf When you cut into an onion, these sulfoxides and

oxides an enzyme called lachrymatory-factor synthase is Figure 1: Chemical reaction for the production of the lachrymatory factory released to create sulfenic acid and then syn-propanethial-S-oxide (Source: Science daily) (simply known as the lachrymatory factor)(1). The lachrymatory factor (LF), is a technical term for a

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chemical that stimulates the lacrimal tear glands, where tears are

produced (1). This gas floats up from the chopped onion and repels

pests and causes humans to cry. Since our eyes are quite sensitive,

react to the gases and contain nerves that detect potentially harmful Figure 2: Location of tear glands substances, our body protects the eyes by producing tears to flush (Source: Medical News) away the gas (2). Gases that are produce from chopping onions are not harmful and rather safe. It is only a temporary sensation with no long-term effects (2). Some ways to avoid crying when cutting onions are to wear goggles, cut onions in a bowl of water, or use eyedrops to lubricate the eyes before cutting.

In conclusion, one of the reasons onions have survived hundreds of years is due to their unique

Interesting fact: Similarly to how hot peppers have varying degrees of spiciness, onions

vary how much they can irritate our eyes. White, red and yellow onions all have higher

concentration of the enzyme necessary to produce syn-propanethial-S-oxide (LF) while green

onions, sweet onions and scallions have less of them. If you are highly sensitive to the gases

from preparing onions, its best to cook with the latter 3 types mentioned above. ability to defend themselves against predators. Chemical protection is just one way of doing so and there definitely may be other defense mechanisms that exist in the plant or animal kingdom that we have yet to discover. Perhaps this area of study could be of important use to uncover various functions and mechanisms. Everything in life must adapt to their ever-changing environment and it seems that vegetables are smarter than we think!

1. Texas A&M University. "Why do onions make you cry?." ScienceDaily. ScienceDaily, 20 June

2017. www.sciencedaily.com/releases/2017/06/170620122950.htm

2. https://www.medicalnewstoday.com/articles/318811.php#2

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92. Some Factories Use Radiations To Kill The Bacterias In The Food. Do These Radiations

Influence The Food Safety?

GMOs, trans fat, pesticides, but what about radiation? Not the first thing you may think about

when you consider food safety. So why do some factories use radiation to kill the bacteria’s in food?

How does it work? Do these radiations influence the safety of the food? And most importantly, how does

it affect you?

Radiation can be a scary word, but it doesn’t have to be. Food irradiation, according to the

government of Canada, is the “treatment of food with a type of radiation energy known as ionizing

radiation”46, this can include gamma rays, X-rays, and electron beam radiation. The waves pass through

the food in a similar manner to the way microwaves pass through foods

when you use a microwave oven, the difference is the waves used for

food irradiation do not cause the food to heat up but still kill any

organism that could cause food to spoil.47 These interesting waves work

in higher doses to kill insects, molds, bacteria and other Figure 1: A Farmers Market (Source: microorganisms that could be harmful. At lower doses they extend the https://bramptonist.com/top-10-farmers- markets-in-and-around-brampton/) shelf-life of food products48 by delaying ripening, improving

rehydration, increasing juice yield, and inhibiting sprouting.49 Who doesn’t like a juicier orange, right?

Now, the word radiation always leads to the question of “oh my God, is it radioactive?!”, to which the

answer is no, your food is not radioactive, the amount of radiation used is too minimal to create

46 https://www.inspection.gc.ca/food-safety-for-industry/information-for-consumers/fact-sheets-and- infographics/irradiation/eng/1332358607968/1332358680017 47 https://www.betterhealth.vic.gov.au/health/HealthyLiving/food-irradiation 48 Ibid. 49 https://www.sciencedirect.com/topics/medicine-and-dentistry/food-irradiation

EVERDAY PHYSICS 213 radioactive material.50 In fact, the World Health Organization and the Government of Canada both support food irradiation. It is used as an alternative to canning or pasteurization and is actually safer than either of those processes. Food irradiation has had extensive nutritional assessments, toxicity studies, and feeding trials that have demonstrated that there is no risk to humans Did You Know?! The use of Food and the Center for Disease Control and Prevention approves of its Irradiation leads to less usage of pesticides, usage.51 The FDA also approves food irradiation as being safe and preservatives, and lowers your chances of developing food-borne diseases! indicates that it does not compromise nutritional quality, and does not noticeably change the taste, texture, or appearance of food.52 To answer the most important question though, food irradiation affects you only in a positive way. It effectively eradicates organisms that cause foodborne illnesses such as E.coli, meaning less recalls on romaine lettuce (here comes caesar salad!) and less food poisoning, it allows your food to last longer (eating raspberries over the course of 7 days instead of 3 days?! Revolutionary!), and is especially helpful for individuals that may have compromised immune systems from illness or chemotherapy and need sterilization as food irradiation does this too.53 Now, it is understandable that not everyone would be completely okay with radiated food and because of this food that has been irradiated is always labelled, nothing is hidden or a secret.54

Overall, food irradiation is an innovative technique that helps reduce the use of other potentially harmful substances and can improve the quality of life for those already ill. It is approved in over 50 countries and in my opinion a ground-breaking process of futuristic technology. I don’t know about you,

50 https://www.betterhealth.vic.gov.au/health/HealthyLiving/food-irradiation 51 https://wwwnc.cdc.gov/eid/article/7/7/01-7706_article 52 https://www.fda.gov/food/buy-store-serve-safe-food/food-irradiation-what-you-need-know 53 Ibid. 54 https://www.inspection.gc.ca/food-safety-for-industry/information-for-consumers/fact-sheets-and- infographics/irradiation/eng/1332358607968/1332358680017

EVERDAY PHYSICS 214 but I would love my fruit to last longer, be juicer, and have less risk of infecting me. Say goodbye to pesticides and salmonella and hello to food irradiation.

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93. What allows certain things to dissolve in water and others not?

I was just laying by the beach drinking lemonade and started thinking why is it that the sugar in my lemonade has perfectly dissolved in my water but the sand from the beach hasn’t dissolved in the ocean. I started wondering what makes water so special? And what allows certain things to dissolve in water and others not?

Water is a liquid with solvent properties that can dissolve various molecules and compounds

referred to as solutes. A solution in which the water is the solvent

is called an aqueous solution. It is then important to ask: what is

it about water that makes it an excellent solvent? That is because

of water’s polarity and ability to form hydrogen bonds with

other compounds. Water is polar a molecule because it is made

of 2 Hydrogen atoms and one Oxygen atom. Hydrogen atoms

consist of a partial positive charge, whereas oxygen atoms carry

a partial negative charge. The polar property of the water

Figure 1: Hydrogen molecules allows for covalent bonding with other molecules. Bonding (Source: University of Water interacting with a polar molecule leads to the dissociation Arizona)[1] of the solute into positively and negatively charged ions. The positively charged ion of the solute is attracted to oxygen atom while the negatively charged ion is attracted to the hydrogen atom. Therefore, in order for solute to dissolve in water, ionic compounds should be formed in order for covalent interactions to occur, which is only possible with polar molecules. [1]

On another hand, non-polar molecules cannot be dissolved with water. Non-polar molecules cannot separate into charged ions. Therefore, formation of a covalent bond is not possible. To better understand this, let’s look at examples. Salt is a dissolvable substance in water. That is because salt is polar

EVERDAY PHYSICS 216 molecule with weak ionic bonds. Sodium and chloride ions separate once placed in water and form covalent interactions due to water molecules being able to break the ionic bond between sodium and chloride atoms. However, oils, fats, sand, etc. do not dissolve in water because they are non-polar substances and their bonds cannot be separated by the charges on the water molecule. [2]

Another question that might come to mind is that how come at some point water stops dissolving the solute? That is because of a concept called saturation. Saturation occurs when the amount of solute in the solvent is in excess thus all the water molecules are occupied and can no longer make covalent bonds with other molecules. Therefore, the excess solute cannot be dissolved in the solvent any further until more water is added and more water molecules become available for covalent bonding with the solute. [1]

Interesting concept: if oil doesn’t mix with water, then how can soap and water clean oil?

The reason why soap can clean oil and grease is because one end of soap molecule is polar, thus soluble in water. But the other end of the soap molecule is not polar, thus resembles oil and grease. Soap molecules surround the grease, leaving the soap’s water-soluble parts on the outside so that the water can wash the grease away. Therefore, soap molecule provides a link between 2 substances [1]“Chemistry that otherwi Tutorial:se would The Chemistry not mix. of [3] Water.” biology.arizona.edu, January 28, 2003. http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/page3.html.

[2]“Water Molecules and Their Interaction with Salt Molecules.” Us Department of the Interior. Accessed February

12, 2020. https://www.usgs.gov/media/images/water-molecules-and-their-interaction-salt-molecules.

[3]“Why Oil and Water Do Not Mix.” Florida State College. Accessed February 12, 2020. http://web.fscj.edu/Milczanowski/psc/lect/Ch10/slide10.htm.

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94. What are the different methods of heat transfer observed when preparing food?

How are meats, eggs, and rice edible? What allows us to unlock the gourmet taste of dishes that raw fruits and vegetables lack? What do you think of doing when your tea is at room temperature?

There are many cooking methods, but they all rely on one of the three types of heat transfer:

Convection, Conduction, Radiation.

Imagine placing your hand on a bedsheet, then on a metal desk. Clearly, the metal desk feels colder to the touch. Different materials conduct heat with varying degrees of effectiveness, so the bedsheet initially feels warmer than the desk; the metal quickly carries heat away from your hand and distributes it throughout the desk, whereas the bedsheet is much slower at doing so. This type of heat transfer is conduction, which happens exclusively via direct physical contact [1].

Now imagine going outside on a windy day.

The weather forecast states that it’s 25 degrees, but the

air feels much colder than your room. The air is

carrying heat away from you via convection, where

molecules in a liquid or gas rise and fall due to

temperature differences [2]. Warm molecules are less

dense than cold molecules and rise, and cold molecules fall. As the air molecules gain heat from nearby objects, they slowly begin to rise and gather more heat from people like you. Later, they distribute the heat across the atmosphere.

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Radiation refers to waves, especially electromagnetic waves that are very energy-dense. As they propagate through the air and hit an object, both the air’s molecules and the object’s molecules begin to vibrate due to the transfer of energy [1]. If you have ever felt sweaty while sitting under sunlight at home, you have experienced this type of heat transfer.

When baking, a combination of convection and conduction is used; the air inside the oven is very hot, and the oven racks are metal in order to transfer heat as much heat as possible to the food via direct contact. When boiling liquid on a stove, you are relying on conduction to transfer heat from the stove

top the pot, then convection to transfer heat from the water to

the food. When microwaving, radiation in the form of

microwaves is used to stimulate the food molecules and

induce heat.

It is remarkable that humans have been using

conduction and convection to heat our foods since the dawn

of humanity, but have only recently managed to use radiation via microwave ovens. Perhaps in the future we will have a means of cooking food by simply firing a heat gun at it. No more stoves, no more ovens, just a pocket-sized device.

Interesting experiment: Place your hand on a metal desk for 10 seconds and pull it back.

Place your hand back on the desk. Why does the desk now feel warm?

[1] Oldenburg, W. B. (n.d.). Conduction, Convection and Radiation. Retrieved February 12, 2020, from https://www.greenteg.com/heat-flux-sensor/about-heat-flux/3-types-of-heat-transfer/

[2] Convection. (n.d.). Retrieved February 12, 2020, from https://www.sciencedirect.com/topics/materials- science/convection

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95. Some factories use radiations to kill the bacteria in the food. Do these radiations influence

the food safety?

One of my favorite foods is mango. Not mangoes you can buy in Montreal, but much sweeter

and juicier mangoes grown in India and Pakistan. I always wondered how mangoes were able to come

from thousands of miles away without insects and without ripening. Food preservation techniques are

often scrutinized, and the use of radiation to kill bacteria in foods, called irradiation, is one of the most

controversial. However, food preservation enables us to safely import and remove bacteria from food

and improve shelf-life.

Without preservation methods, the risk of disease from bacteria or spoiled food is immense.

Some traditional food preservation techniques that you may be familiar with include freezing,

fermentation, chemical treatment, heating, and drying [1]. However, sometimes bacteria can exist in

crevices we cannot see. This is why we need modern techniques. Food irradiation is a preservation

technique which involves exposing foods to ionizing radiation. Some

examples of ionizing radiation are X-rays, alpha, beta, and gamma rays. These

rays provide electromagnetic energy which releases electrons from their

atomic bonds [1]. Essentially, ionizing radiation uses energy to kill bacteria in

food without even touching it! The process entails exposing foods to a Figure 1: The international food irradiation symbol specific dose of ionizing radiation. How much is this dose? Well, it (Source: World Health Organization) depends on the food you are preserving and the goal of preservation [1]. For example, preventing fruits Interesting fact: In 2006, an E. coli outbreak occurred in the United States. Following from this the FDA (Food and Drug Administration) legalized the use of irradiation in spinach and ripening iceberg lettuce. However, due to misconceptions about ionizing radiation, as of 2009 the takes a industry had yet to use irradiation on these products, and only uses them on imported spices lower and fruits [3]. Would you eat spinach labeled with the irradiation symbol? (Figure 1)

EVERDAY PHYSICS 220 dose of ionizing radiation compared to sterilizing spices [2]. This is because sterilization requires more energy than preservation, and additionally spices can withstand higher amounts of radiation. Irradiation is different from other methods because it does not change the temperature, so it can be used on frozen foods. Also, since it does not directly touch the food, it can be used through packaging, which prevents further contamination [1].

The transfer of energy rips electrons from their bonds which kills bacteria. This changes the chemistry of the food which some people believe is harmful. One misconception about this is that irradiation can cause radioactivity in foods. The levels of radiation needed to cause this are not used in food irradiation, so this is not a valid concern [1]. The most cited reason against irradiation is that it changes the nutrition and flavor of food. While this is true, other preservation methods alter these attributes much more. For example, at home I roast broccoli in my oven until it becomes crispy. This process obviously alters the taste and texture of the food, but it also decreases the nutritional value.

Irradiation does this to a far lesser extent, and lawmakers prevent the use of irradiation when the process alters these factors to an unsafe degree [1].

With the recent spread of the coronavirus, food safety is a serious and relevant topic. The potential for irradiation to solve food crises in tropical environments, where diseases spread easier, or developing countries is great. Right now, only a few domestic foods are preserved using irradiation, but maybe in the future this method will become more widely accepted.

[1] World Health Organization. (1988). Food irradiation: a technique for preserving and improving the safety of

food. World Health Organization.

[2] Loaharanu, Paisan (1990). "Food irradiation: Facts or fiction?" IAEA Bulletin. 32 (2): 44–48.

Retrieved March 3,2014.

[3] Martin, Andrew. Spinach and Peanuts, With a Dash of Radiation. The New York Times. February 1, 2009.

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96. Why is it difficult to cook at high altitudes?

It has been a long-running joke that university students don’t know how to cook, and that we subside on a bleak fare of grilled cheese sandwiches, instant noodles, and KD mac and cheese.

Fortunately, around fourth year, students finally start to smarten up and get comfortable in the kitchen.

Unfortunately, this newfound confidence is shattered as soon the budding chef attempts the same recipes in a high-altitude location, such as Boulder, Colorado or Machu Picchu, Peru. But why is it so difficult to cook at high altitudes?

The answer has to do with pressure. At sea level, air

presses down at 14.7 pound per square inch. However, at

higher elevations, there are fewer air molecules above a

given surface, resulting in less pressure. This decrease in

pressure produces a small but noticeable change in the

boiling temperature of water, a key element in many

recipes. Because there is less pressure, water is able to

escape its liquid form and enter its gaseous form more

Figure 1: With each 500-foot easily; there is now a lower boiling point temperature increase in elevation, the boiling point of water is lowered by about 1 °F. necessary for this transformation. With each 500-foot

(Source:_https://cdn.britannica.c om/42/110442-004-59FAAB73.gif) increase in elevation, the boiling point of water is lowered by about 1 °F.

Let’s say we were cooking in Boulder, Colorado at approximately 6,000 ft above sea level. This would result in a new lower boiling point temperature of 200° F. Perhaps in Montréal it took us approximately ten minutes in boiling water to get a perfect al dente farfalle pasta serving. However, in

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Boulder, the water is still boiling, but now at a lower temperature. Consequently, we need to approximate an extra three to four minutes to get the same pasta result.

Recipe Changes to Make at High Altitudes:

Boiling Time Increase boiling time Boiling point temperature is lower, therefore food must cook longer. Oven Temperature Increase baking Baking temperature is temperature increased because products such as cake expand more quickly at higher altitudes with less pressure. Baking Time Decrease baking time Higher temperature = food done faster

Even the most seasoned chefs can get a little bamboozled by tricky changes in atmospheric pressure. However, now that we know that decreased atmospheric pressure is the cause, it’s easy to find simple solutions to adjust recipes. The best solution is, of course, a pressure cooker; then you don’t have to worry about the pressure!

[1] https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food- safety-fact-sheets/safe-food-handling/high-altitude-cooking-and-food-safety/ct_index

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97. Why do bananas turn from yellow to brown?

Banana contains a sort of nutrition that we need, like sodium, and it also very delicious. However, bananas always turn from yellow to brown. What is the reason?

Actually, fruits change their color in their life cycle. That is because they produce an element called ethylene. ‘However, unlike most fruits, which generate only a tiny amount of ethylene as they ripen, bananas produce a large amount. While a banana in the beginning of the ripening process might become sweeter and turn yellow, it will eventually over ripen by producing too much of its own ethylene. High amounts of ethylene cause the yellow pigments in bananas to decay into those characteristic brown spots in a process called enzymatic browning.’1

(source: www.britannica.com)

‘Brown bananas have a higher level of antioxidants than yellow or green, unripe bananas.

They're also easier to digest for people with digestive ailments, including irritable bowel syndrome and

Interesting question: can we eat brown bananas? functional abdominal bloating.’2 That is to say, brown bananas also can be eaten. In my opinion, if you think that is ugly and you don’t want to eat it, you can choose to make banana juice.

Reference

1. https://www.britannica.com/story/why-do-bananas-turn-brown 2. https://www.livestrong.com/article/528371-brown-banana-facts/

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Observation of gravitational waves from a binary black hole merger. Physical review letters, 116,

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Bloomfield, L. A. (2015). How things work: the physics of everyday life. John Wiley & Sons.

Castelvecchi, D. (2015). Feuding physicists turn to philosophy: string theory is at the heart of a debate

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Einstein, A. (1918). Über gravitationswellen. Sitzungsber. Preuss. Akad. Wiss. Berlin (Math. Phys.),

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Griffith, W. T., & Brosing, J. W. (2004). The physics of everyday phenomena: A conceptual introduction

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Rickles, D. (2016). BRIEF HISTORY OF STRING THEORY. Springer.

Stephenson, F. R. (2003). Historical eclipses and Earth's rotation. Astronomy & Geophysics, 44, 2-22.

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