KS3 Space Lesson 5: Orbits Learning Objective To explain how objects travel in an orbit.

Success Criteria

• To define what an orbit is.

• To describe the difference between a natural satellite and a humanly- constructed satellite.

• To investigate the relationship between time period and radius of an orbit. Target: 10 Points

1 Point 2 Points2 Points 3 Points 3 Points SunWhat is at the centre of ourMercury, List Venus, the planets Earth, in orderOur planet Explainhas an atmospherewhy there is whichlife on Solar System? Mars, startingJupiter, Saturn,from the centrecontains of the theEarth correct but mixturenot on other of gases to UranusSolar and System Neptune. and travellingsustain life.planets This is duein our to Solar System. outwards. photosynthesis and the production of oxygen. Earth is at just the right distance from the Sun which allows water to exist as a liquid on its surface. Which is the largest planet? Explain why Pluto is no longer Explain why no other Jupiter Pluto isdescribed now known as a as planet. a Other planetsplanets are too or galaxiesfar away have from dwarf planet. It is much Earth for mannedbeen explored spacecraft by humans.to get to. smaller than the other Other galaxies are much too far away. planets in our solar system and has an orbit on a different plain. Which planet is closest to What is a light year? Describe, in one paragraph, theMercury Sun? The distance light travels A day (24 hours)the difference is the time between taken for in a year. In a year, light the Earth todays, spin months once on and its axis. years. A can travel around 10 year (365 days) is the time taken for the trillion km. Earth to orbit the Sun. A month (approximately 28 days) is the time it takes for the moon to orbit the Earth. Orbits

An orbit is a curved path that an object takes around another object. An object that orbits another object is called a satellite. A satellite orbits an object when its speed is balanced by the object’s gravitational force.

There are natural satellites, for There are humanly-constructed example: satellites, for example:

• The Earth’s moon. • communication satellites • The planets orbiting the Sun. • navigation satellites • GPS satellites • polar satellites Orbits

This image is computer generated by NASA. It shows all of the objects in Earth’s orbit that were being tracked in 2005.

Only around 5% of these dots are functional satellites and the rest are debris. Image by [Wikimedia.org] is licensed under CC BY 2.0 There is a ring of objects around 35,786km above the Earth’s equator. They are in geostationary orbit. These satellites travel in the same direction and at the same rate as Earth is spinning. From Earth, these satellites look like they are standing still because they are always above the same place on Earth.

The animation shows a satellite in geostationary orbit. Orbits

The other common type of orbit is made by a polar satellite.

Polar-orbiting satellites travel north to south, crossing over both poles. Their orbit is fixed in space so as they travel, the Earth rotates inside their orbit.

This means these satellites are able to scan the entire surface of the Earth in a day.

Polar satellites: useful if you want to scan the entire Earth.

Geostationary satellites: useful if you want to bounce signals to and from them because you will always know where they are. Types of Satellites

Put the different satellites into the correct columns in the table.

Natural Satellites Humanly-Constructed Satellites Geostationary Polar Mars communications weather forecasting Earth’s moon GPS military observations Halley’s comet TV

Earth’s moon Halley’s comet Mars military observation satellites communications satellites navigation (GPS) satellite weather forecasting satellites TV satellites Keywords

Write definitions for these keywords.

An orbit: a curved path that an object takes around another object.

A satellite: an object that orbits around another object.

Sketch a quick diagram of a satellite in orbit around Earth. Can you name the type of orbit you have drawn?

geostationary orbit polar orbit Investigating Orbits

Method

1. Find a clear space in the room, away from other people and any obstacles. 2. Measure the length of string attached to your bung and check it is 100cm long. 3. Time how long it takes to swing the bung around your head once and record the result. 4. Repeat for 80cm, 60cm, 40cm and 20cm lengths of string.

How could we improve this investigation? Investigating Orbits

Method

1. Find a clear space in the room, away from other people and any obstacles. 2. Measure the length of string attached to your bung and check it is 100cm long. 3. Time how long it takes to swing the bung around10 times your around head your once head.and record Divide the the result.measurement by 10 and record the result. 4. Repeat forthree 80cm, times 60cm, and 40cm calculate and 20cm an average. lengths of string. 5. Repeat for 80cm, 60cm, 40cm and 20cm lengths of string. Keywords AHow result do iswe accuraterepeatable calculateif the itif is theaverage? close original to the experimenter true value. repeats the investigation using the Addsame up method the three and measurementsequipment and gets and the divide same the results. total by three. How could we improve the accuracy of this investigation? How will we know if our results are repeatable? Time how long it takes to swing the bung 10 times around your head. Divide the measurementRepeat three times by 10 and and calculate record the an result. average. Investigating Orbits

Length of Time for 10 Orbits (s) Average Time Average Time for String for 10 Orbits (s) One Orbit (s) (cm) Repeat 1 Repeat 2 Repeat 3 100 7.00 6.70 6.78 6.83 0.68 80 6.13 6.08 6.03 6.08 0.61 60 5.21 5.38 5.66 5.42 0.54 40 3.71 4.11 3.72 3.85 0.39 20 2.14 2.40 2.29 2.28 0.23

What is the relationship between the length of the string and the time taken to orbit? As the length of the string decreases, the time taken for the object to orbit decreases. Planet Orbits

Planet Orbit Time (days) Velocity (m/s) Mercury 88 47.4 Venus 225 35.0 Earth 365 29.8 Mars 687 24.1 Jupiter 4331 13.1 Saturn 10 747 9.7 Uranus 30 589 6.8 Neptune 59 800 5.4

UseThink the back results to your from investigation. your investigation At which to predictlength did what the will bung happen spin theto the fastest? orbit time of the planets as they get further from the Sun. Predict what will happen to the velocity of the orbits as the planets get further from theAs the Sun. planets get further from the Sun, the time taken to orbit increases. As the planets get further from the Sun, the velocity decreases. Extension

There is a ring of objects around 35,786km above the Earth’s equator. They are in geostationary orbit. These satellites travel in the same direction and at the same rate as the Earth is spinning. From Earth, these satellites look like they are standing still because they are always above the same place on Earth.

Why do all geostationary satellites need to be at the same height above Earth? The distance above the Earth affects the time an orbit takes. To orbit the Earth in the time it takes for the Earth to rotate once, this distance needs to be 35,786km. Image by [Wikimedia.org] is licensed under CC BY 2.0 Escape the Room!

Answer the following questions to gain the code, allowing you to leave the classroom.

1. Neptune is the 8 th planet from the Sun. 2. There are 4 letters in the name of the Earth’s natural satellite. (moon) 3. The time it takes for the Earth to orbit the Sun is 365 days.

Leaving Code: 8 , 4 , 3 , 6 , 5 ,