Physics help from experts.
Gravitational Potential Energy may be absolute or relative.
Absolute gravitational potential energy is the work done on an object moving it from infinity to a location in a gravitational field. This value can not be greater than zero.
Relative gravitational potential energy is the energy stored by an object because of its height in a gravitational field. Since height is chosen with respect to some other position, height and relative gravitational potential energy may be positive, zero, or negative.