Newton and Gravity: Practice Problem Solutions

1. An object keeps moving in a straight line at a constant speed unless a force acts on it. So planets need no force to keep moving, only gravity to bend their path.

2. It falls to 1/4 of the force.

3. It drops to 1/9 (the force is divided by 3 squared).

4. Gravity pulls the Moon toward Earth all the time, and the Moon's sideways speed carries it past, so it keeps falling around Earth without hitting it.

5. About 7.8 km/s (about 28,000 km/h).

6. That the comet seen in 1682 would return in 1758.

7. Astronomers calculated from Newton's law where an unseen planet must be pulling on Uranus, then pointed a telescope there in 1846.