1. P5 – Space for reflection Lesson 1 – circular motion

2. Starter Word search - Find the planets (P5a1 – old course) Solar system game

3. Learning objectives Describe gravity as a universal force of attraction between masses. Explain that the orbital period of a planet depends upon its distance from the Sun. Describe the variation of gravitational force with distance Explain the variation in speed of a periodic comet during its orbit around the Sun

4. Success criteria Be able to describe why planets orbit the sun. (Grade C) Explain the variation of gravitational force with distance (Grade C) Explain why orbit time of a planet depends on its distance from the Sun. (Grade A)

5. To do – Questions 1.What is gravity? 2.In which direction does gravity act to cause the Earth to circle the Sun (draw a sketch) 3.What is the equation for calculating speed? Harder question 4. a) Use the data on the planets (P5a1 - old course) to find the rotational speed of Mercury and Earth (assume that they travel in a circle) b) Do you think that Saturn will have a greater or smaller speed than Earth? Explain your answer?

6. Answers 1.Gravity is a force which acts between masses 2.Gravity acts towards the centre of the Sun (gravity brainpop)gravity brainpop 3. Speed = distance/time 4. a) speed of mercury = distance / time = 2πr / T = 3.6 x 10 11 / 0.24 x 60 x 60 x24 x 365 = 48149.3 m/s speed of Earth = 29885.8 m/s b) Saturn will have a smaller speed because it is further from the sun and therefore has a smaller force of gravity acting on it.

7. http://www.bbc.co.uk/science/space/universe /questions_and_ideas/gravity#p009gynr http://www.bbc.co.uk/science/space/universe /questions_and_ideas/gravity#p009gynr

8. Gravity Every object in the Universe attracts every other object. There is a force of attraction between all objects. The planets stay in orbit around the Sun due to the gravitational attraction between them. Any object moving in a circle has a force acting towards the centre of the circle to maintain its path. This is called a centripetal force.

9. Geostationary Satellites Geostationary satellites are placed in orbit above the equator. They take 24 hours to orbit the Earth (same speed as the Earth’s rotation), which means they stay above the same spot. The time for an orbit is known as the orbital period. It increases with height above the Earth.

10. Gravitational force There is a gravitational force between masses. One of the simplest equations for the force of gravity, relates the mass of an object to the gravitational field strength: F = mg

11. To do: Use the information given to draw a graph of F against d. Explain in as much detail as you can what the graph is showing you. F (N)9.82.50.60.150.038 d (mm)6.412.825.651.2102.4

12. The Answer The further away a mass the smaller the gravitational force. When a mass is twice as far away, F quarters. This is an inverse square law: F is proportional to 1/d 2

13. Learning objectives Describe gravity as a universal force of attraction between masses. Explain that the orbital period of a planet depends upon its distance from the Sun. Describe the variation of gravitational force with distance Explain the variation in speed of a periodic comet during its orbit around the Sun

14. Success criteria Be able to describe why planets orbit the sun. (Grade C) Explain the variation of gravitational force with distance (Grade C) Explain why orbit time of a planet depends on its distance from the Sun. (Grade A)

15. Comets From what you know about how gravitational force varies with distance, explain how the comet’s speed will change throughout its orbit. Plenary