Original: An object at a certain height above the Moon 's surface has less gravitational potential energy than at the same height above the Earth 's surface because the Moon 's gravity is weaker . Note that '' height '' in the common sense of the term can not be used for gravitational potential energy calculations when gravity is not assumed to be a constant .
Simplified: The Gravitational Potential Energy formula used here is only used when the objects are very near the surface of the Earth , because the acceleration must be the same during the change in height .