This is the universal-law-of-gravitation expression for
gravitational potential energy. The gravitational potential *energy
U* (written *U*_{G} if it needs to be
distinguished from other kinds of potential energy) for a pair of
objects is the negative of the universal
gravitational constant *G* times the product of the
masses of the objects, all divided by the separation *r*
of the centers of masses of the objects.

Note: The expression is exact for point particles and for cases in which the objects do not overlap and both of the objects are spherically symmetric. For other cases, it is a good approximation as long as the length of the longer object is small compared to the separation of the centers of mass.

**Pitfall Avoidance Notes:** The *r* in the denominator is not squared.
Also, the *r* is the center-to-center distance, not the
surface-to-surface distance.