Quiz

1. What keeps a planet rotating and orbiting the Sun?
2. Where do objects get their energy?
3. What determines the strength of gravity?
4. How does Newton's law of gravity extend Kepler's laws? 
5. How do gravity and energy allow us to understand orbits?
6. How does gravity cause tides?
7. Write down Newton's formula for the force of gravity.
8. What is Earth's escape velocity?
9. What is Sun's escape velocity?
10. What is Jupiter's escape velocity?

You can use Wikipedia.