Gravitational potential energy  -  Is defined by the integral:

Where

is the force due to gravity and we define U(∞) = 0. Doing the integral gives:

which reduces to U = mgh near the earth.

Gravitational potential  -  Is defined as the gravitational potential energy that a 1 kilogram mass would have at some point in space. It is given by:

which reduces to Φ_g = gh near the earth.

Principle of Equivalence  -  Asserts that all types of matter fall at the same rate. That is, g for a brick is the same as g for water. This means that the inertial mass appearing in Newton's Second Law is equivalent to the gravitational mass appearing in the Universal Law of Gravitation.

Inertial mass  -  The mass m_i that appears in Newton's Second Law F = m_ia.

Gravitational mass  -  The mass that appears in the Universal Law of Gravitation.

Shell Theorem  -  States that any spherical mass can be treated as though all its mass were concentrated at its center for the purposes of calculating gravitational force. Also, that a spherical shell of matter exerts no gravitational force on a mass inside it.