13.3.3 Newton’s Theory of Gravity

Newton’s theory of gravity is more than just Equation 13.2. The theory of gravity consists of:

1. A specific force law for gravity, given by Equation 13.2, and

2. The principle of equivalence, and

3. An assertion that Newton’s three laws of motion are universally applicable. These laws are as valid for heavenly bodies, the planets and stars, as for earthly objects.

Consequently, everything we have learned about forces, motion, and energy is relevant to the dynamics of satellites, planets, and galaxies.