PHY205H1F Summer Atoms Physics of Everyday Life • Atoms are the building blocks of all matter Class 4: Liquids & Gases • They are too small to be seen with visible light • One gram of water has a volume of 1 cm3 and • Pressure • The Atmosphere contains more than 1023 atoms! • Buoyancy in a Liquid • Atmospheric • 1023 = • Archimedes’ Principle Pressure • This is a scanning tunneling • The Barometer • What Makes an Object microscope image of graphite Sink or Float • Boyle’s Law taken by Igor Fridman, a • Pascal’s Principle • Buoyancy of Air graduate student in U of T • Surface Tension • Bernoulli’s Principle Physics • Capillarity • Plasma • The dots are individual carbon [image from http://www.physics.utoronto.ca/~ifridman/ ]

Atoms • Atomic structure is composed of: Check your neighbour • An atomic nucleus, which contains The nucleus of an electrically neutral iron atom contains 26 protons. How many electrons • Orbiting are in this iron atom? • The nucleus is composed of and , which are in turn made of smaller A. 52 quarks B. 26 • Protons have electric charge: C. 24 • Electrons have electric D. 28 charge: E. zero • All atoms have the same number of protons as electrons

[Image retrieved Jan.10, 2013 from http://www.safetyoffice.uwaterloo.ca/hse/radiation/rad_sealed/matter/atom_structure.htm ]

1 Atoms The Elements Challenge Question: Do you know it?

Atoms The atomic number of an element matches the • Refer to particles that make up a substance number of

Elemental substance A. protons in the nucleus of an atom. • Composed of only B. electrons in a neutral atom. – Lightest and most abundant is hydrogen. C. Both of the above. • To date, about 115 elements are known. D. None of the above. – 90 occur in nature. – Others produced in laboratory are unstable. Words and can be used interchangeably.

[Image retrieved Feb.4 2013 from http://parisbreakfasts.blogspot.ca/2011/09/financiers.html ]

Periodic Table of the Elements Discussion question: What do you think?

What is the approximate density of water?

−5 3 A. 10 kg/m B. 0.01 kg/m3 C. 0.1 kg/m3 D. 1 kg/m3

3 E. 1000 kg/m

© 2010 Pearson Education, Inc.

2 Atoms Density Check your neighbour • Amount of mass per unit volume of a If the volume of an object were to double, with no material. change in mass, what would happen to its density?

mass Density = A. It would remain unchanged. volume B. It would double.

C. It would decrease by a factor of two. 3 3 • Unit of density is kg/m or g/cm . D. None of these. • Example: Density of water is kg/m3, or g/cm3.

[Image retrieved Jan. 11, 2013 from http://www.amazon.com/Evian-Water-Liter-Pack/dp/B0041HVMU0 ]

Pressure Pressure CHECK YOUR NEIGHBOR • Pressure is the per unit that one object When you stand on one foot instead of two, the force you exert on the floor is exerts on another A. less. • In equation form: B. the same. Pressure = force area C. more.

• Depends on area over which force is distributed • Units: N/m2, or ( )

3 Pressure CHECK YOUR NEIGHBOR Pressure in a Liquid • Force per unit area that a liquid exerts on an When you stand on one foot instead of two, the object pressure you exert on the floor is • dependent and not dependent

A. less. Example: Swim twice as deep, then twice as much B. the same. weight of water above you produces twice as much C. more. pressure on you.

Buoyancy in a Liquid Pressure in a Liquid Buoyancy Effects of water pressure • Apparent loss of weight of a submerged object • Acts to surfaces • Amount equals the weight of of a container

• Liquid spurts at right angles from a hole in the surface. – The greater the , the greater the exiting speed.

4 • Displacement rule: http://www.dairygoodness.ca/butter/butter-tips-tricks/how-to-measure-butter A completely submerged object always displaces a volume of liquid equal to .

Example: Place a stone in a container that is brimful of water, and the amount of water overflow equals the .

• When butter is in hard, irregular shaped pieces, fill a 2-cup liquid measuring cup with water to the 1 cup mark. • Add enough butter pieces until the level reaches 1-1/4 cups. • Drain off the water and you’re left with of butter!

Archimedes’ Demonstration Prediction • A steel mass of 0.75 kg hangs from a spring Principle scale. • When it is not accelerating, the spring scale • Discovered by Greek reads 7.5 N. scientist Archimedes in 250 • If Harlow dips the mass into an open container BC. of water, then stops the motion and lets the • Relates buoyancy to scale settle, what will be the reading on the displaced liquid. scale? • States that an immersed body (completely or A. Less than 7.5 N, but not zero partially) is buoyed up by a equal to the B. More than 7.5 N weight of the fluid it displaces. C. About 7.5 N • Applies to gases and liquids. D. zero [ image retrieved Jan.17 2013 from http://personal.maths.surrey.ac.uk/st/H.Bruin/MMath/archimedes.html ]

5 Flotation Ch.13 Problem 8 • Principle of flotation: • Your friend of mass 100 kg can just barely float in fresh- – A floating object displaces a weight of fluid equal to its water. Calculate her approximate volume. own weight. Example: A solid iron 1-ton block may displace 1/8 ton of water and sink. The same 1 ton of iron in a bowl shape displaces a greater volume of water—the greater buoyant force allows it to .

Flotation CHECK YOUR NEIGHBOR You place an object in a container that is full to the brim with water on a scale. The object floats, but some water spills out. How does the weight of the object compare with the weight of the water displaced?

A. Weight of object is greater than weight of water displaced. B. Weight of object is less than weight of water displaced. C. Weight of object is equal to weight of water displaced. The Falkirk Wheel’s two caisson are brimful of water and D. There is not enough information to decide. the , regardless of whether there are boats in them. This makes rotation and lifting almost effortless.

[image from http://en.wikipedia.org/wiki/File:FalkirkWheelSide_2004_SeanMcClean.jpg ]

6 Archimedes’ Principle What Makes an Object Float or Sink? Denser fluids will exert a greater buoyant force on a body than less dense fluids of the same volume. Whether an object floats or sinks depends upon the Example: Objects will float in saltwater 3 (density = 1.03 g/cm ) than in freshwater • Weight of the . 3 (density = 1.00 g/cm ). • Weight of the .

The weight of the fluid displaced depends on . So what really counts is the weight of the object per . This is related to the average of the object.

[ image retrieved Jan.17, 2013 from http://famoustourisms.com/2011/05/dead-sea-enjoy-the-charm-and-sensation-swim-here/ ] [ image retrieved Jan.17 2013 from http://en.wikipedia.org/wiki/File:Kylpyankka.jpg ]

What Makes an Object Float or Sink? What sinks? What floats? CHECK YOUR NEIGHBOR 1. An object more dense Two solid blocks of identical size are submerged in than the fluid in which it is water. One block is lead and the other is aluminum. Upon which is the buoyant force greater? immersed will . [ from http://www.flickriver.com/photos/rhosoi/popular-interesting/ ] 2. An object less dense A. On the lead block than the fluid in which it is B. On the aluminum block immersed will . C. Same on both blocks D. There is not enough information to decide. 3. An object having a [ from http://weeboopiper.wordpress.com/tag/pier-7/ ] density equal to the density of the fluid in which it is immersed will . [ from http://www.123rf.com/photo_10758041_bluefin-tuna-thunnus-thynnus-saltwater-fish-underwater-blue-sea.html ]

7 Pascal’s principle: Pascal’s Principle • Discovered by Blaise Pascal, a scientist and • Application in hydraulic press theologian in the 17th century Example: • States that a change in pressure at any point in an enclosed fluid at rest is – applied to the left piston is transmitted transmitted to to the right piston. all points in the fluid – A load on small piston (left) lifts a load of on large piston (right). • Applies to all —gases and liquids

]

/ tension

Surface Tension - Surface Tension

surface

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The tendency of the surface of a liquid to - 42 - • Surface tension is caused by molecular and thus to behave like a stretched elastic . membrane. • Beneath the surface, each molecule is attracted in every direction by neighboring Examples: molecules. • Insects can stand on the

http://austincoppock.com/2012/04/astrology • A molecule on the surface of a liquid is surface of water, even if they pulled only by neighbors on each side and are more dense than water. from image downward from below; there is no pull • In a small droplet of water, the [insect . surface will contract until it • These molecular attractions tend to pull the forms the shape with the molecule from the surface the liquid, smallest surface area for its causing surface tension. volume: a sphere

[image from http://www.dailymail.co.uk/news/article-1371416/Photographer-Adam-Gormley-captures-ant-trapped-raindrop.html#axzz2K9hLsZGF ]

8 Tips for the 2 hour Test Test on Wednesday during class time • No phones / ipods etc allowed. You • Location: EX310 (last name A-M), EX320 (last name N-Z) will need a regular calculator, and a • Test will begin promptly at 10 minutes after the hour and watch could be handy as well! will be 1 hour and 50 minutes long. • Time Management: • Please bring a calculator, and, if you wish, a 8.5x11” aid – Skim over the entire test from front sheet upon which you may write anything you wish on to back before you begin. Look for both sides problems that you have confidence • Test will cover Hewitt chapters 2-5, 7, 8, 13 and 14, and to solve first. will include: – If you start a problem but can’t • 6 short-answer problems for which you must show your finish it, leave it, make a mark on reasoning the edge of the paper beside it, and come back to it after you have • 16 multiple choice questions – you fill in a bubble sheet solved all the easy problems. • Questions will be similar in style and level to the Exercises • Bring your T-card or other photo ID, and Problems at the end of the chapters in Hewitt as we will be collecting signatures

PHY205 Atmospheric Pressure Physics of Everyday Life Chapter 14: Gases

• The Atmosphere • Atmospheric Pressure • The Barometer • Boyle’s Law • Buoyancy of Air • Bernoulli’s Principle The global average sea-level pressure is • Plasma Pa, or 1 atm.

© 2010 Pearson Education, Inc. [image from http://blog.testfreaks.com/information/thq-and-disney-pixars-up-the-videogame-preview/ ]

9 Atmospheric Pressure in this room What is the force of air pressure on the top of your Discussion Question outstretched hand? • A suction cup sticks to a wall. It is A. pulled to the wall by the vacuum.

Atmospheric Pressure: B. pushed to the wall by the atmosphere. 2  N  m   pounds C. both of these 100,000 2     = p.s.i.  m  inch   N  D. neither of these 20 square inches = pounds! Why don’t you feel that force pushing your hand down? What if all the air below your hand was removed (a vacuum)? [image from http://www.flippersandfins.net/bettabreedingarticle.htm ]

Atmospheric Pressure Pressure and “Suction” CHECK YOUR NEIGHBOR A fluid can only walls or objects; a fluid cannot pull on a wall. In drinking soda or water through a straw, we What we call “suction” is when the fluid on make use of one side has a higher pressure than the fluid on the other side. A. capillary action. It is the pressure which creates a pushing B. surface tension. force into the lower pressure area (into the vacuum). C. atmospheric pressure. This is how we breath: D. Bernoulli's principle. 1. We expand our lung cavity, lowering the E. none of these inside. 2. The higher air pressure outside air into our lungs.

10 Atmospheric Pressure The Barometer • Pressure at the of a column of air reaching to the • The barometer is a device to top of the atmosphere is the same as the pressure at the measure . of a column of water m high. • Consequence: The highest the atmosphere can push water • It consists of a tube up into a pump is 10.3 m. upside down in a dish filled with mercury. • The height of the mercury column tells us the atmospheric pressure.

• Atmospheric pressure decreases with increasing

altitude, so it also measures • Mechanical pumps that don’t depend on atmospheric —an altimeter. pressure don’t have the 10.3-m limit.

Barometer CHECK YOUR NEIGHBOR Boyle’s Law

Why don’t barometers use water instead of • The product of pressure and volume of a given mercury? mass of gas will always remain the same.

A. Water cannot be used because it does not exert = pressure. B. Water cannot be used because it sticks to the

glass. LARGE Small Small LARGE C. Water can be used but the barometer will be too Pressure Volume Pressure Volume tall. D. None of the above.

11 Discussion Question Buoyancy in Air • When a party balloon is compressed to Archimedes’ principle applies to as well one-third its volume with no change in as liquids. temperature, what happens to the gas • An object surrounded by is buoyed up by a pressure in the balloon? force equal to the weight of the displaced A. It drops by a factor of 3 B. It drops by a factor of 2 C. It remains the same D. It doubles E. It triples

[image downloaded Jan.24 2013 from http://saigon-hobby.com/products/2739-air-swimmer-nemo.aspx ]

In-class Discussion Question Buoyancy Example: If you wish to support a mass of 80 kg (one person) with a helium-filled balloon, how big should the • You put your thumb over the end balloon be? of the a hose, thereby reducing the area through which water can exit the hose. • What must change about the water so that the amount coming in the hose equals the amount leaving the hose? A. The velocity must increase. B. The velocity must decrease. C. The pressure must increase. D. The pressure must decrease.

12 In-class Discussion Question Bernoulli’s Law • We study the steady flow of water from a • Consider an ideal fluid, flowing through a tube water tap, e.g., in your kitchen sink. The which narrows. jet of water A. broadens as it falls.

B. narrows as it falls.

C. does not change its • It increases its . This means the kinetic cross-sectional shape. energy per volume of the fluid will . D. slows before hitting the • How can this be? There must be a which does work on the fluid to speed it up. bottom of the sink. • The force must come from a difference. • Pressure must be in the region of increased fluid velocity.

Bernoulli’s Principle Bernoulli’s Principle Streamlines • Thin lines representing fluid motion • Closer together, flow speed is and pressure within the fluid is • Discovered by Daniel Bernoulli, a 15th century Swiss scientist • Wider, flow speed is and pressure within the fluid is • States that where the speed of a fluid increases, internal pressure in the fluid (and

vice versa)

• Applies to a smooth, steady flow

13 Bernoulli’s demo, lift. Applications of Bernoulli’s principle • Blow on the top surface of a paper and the paper • If the air were flowing equally rises. above and below the beach-ball, there would be no force on the ball Reason: Pressure of the moving air is than the due to the Bernoulli effect. atmospheric pressure beneath it. • The ball would then fall due to its • Wind blowing across a peaked roof can lift the roof own weight until the point where off the house. most of the flow is over the top of Reason: Pressure is the ball, reducing the pressure as wind gains there. speed as it flows over • The ball sits at a point of stable the roof. The greater equilibrium, where these forces pressure inside the balance. house lifts the roof up.

In-class Discussion Question Plasma • When wind speeds up as it blows over the • Plasma is the top of a hill, what happens to the state of matter atmospheric pressure over the hill? (after solids, liquids A. It decreases and gases). B. It increases C. It stays the same • A plasma is an . The atoms that make it up are ionized, stripped of one or more electrons, with a corresponding number of free electrons.

14 In-class Discussion Question Before Class 5 next Monday • Which of the following is in a plasma • Please read Chapters 15 and 16, or at least watch state? the 20-minute pre-class video for class 5 • Pre-class reading quiz on chapters 15 and 16 is due A. Dry ice Monday June 3 by 10:00am B. A torch flame • NOTE C. Molten lava • Midterm Test: Wednesday 1-3 in TBA • Test will begin promptly at 1:10 and will be 1 hour and 50 D. Liquid hydrogen minutes long. E. Helium gas • Please bring a calculator, and, if you wish, a 3x5 notecard upon which you may write anything you wish on both sides • Test will cover Hewitt chapters 2-5, 7, 8, 13 and 14, and will include some multiple choice and some short-answer

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