1. Centripetal forces for planets and satellites
P3 Physics
Centripetal forces for planets and satellites

2. Lesson Objective
To be able to explain have a planet stays in orbit

3. Lesson Outcomes Key: to complete questions on orbiting
Stretch: to complete an exam question on this topic
Challenge: to carry out calculations for GFS for different planets

4. Starter
What are these and how do they stay there?

5. Isaac Newton Isaac Newton discovered Gravity.
He said that the force of gravity between two objects is:
Is an attractive force
Gets bigger with the mass of each object
Gets smaller with greater distance between the two objects

6. Gravitational Field Strength
Gravitational field strength on Earth is 10N/Kg, so the force of gravity on a person on the surface of the Earth is 500N is they are 50Kg.
The Moons is 1.6N/Kg so what is the force acting on the person on the moon?

7. Reason
The reason is because the Earths mass is much greater and therefore it exerts a greater force on the person, compared to the Moon.

8. Orbiting The Moon orbits us and we orbit the Sun.
Elliptical circle (slightly squashed)

9. Orbiting A planet will orbit an object that is far larger than itself
To stay in orbit the object must be travelling at a particular speed orbiting around the sun
What would happen if it is travelling to slow or too fast?

10. Satellites
Geostationary and Polar satellites (man made satellites)

11. Geostationary satellites
There are communication satellites which orbit the Earth at a particular height above the equator so that they have a period of 24 hours, and because they travel at the same speed as the Earth spins on its axis, the satellite remains above the same place of the Earth’s surface constantly.

12. Monitoring satellites
Monitoring satellites fitted with TV cameras pointing at the Earth. For these we have many uses, including weather forecasting, police and military surveillance and environmental observations. These are much lower orbits – purely so that we can see as much detail of the Earth as possible. One period of these satellites takes between two or three hours, and their orbits go past both the Poles, so they monitor the entire Earth all day long.

13. Plenary
Plenary Pyramid