Gravitational energy is energy contained in the gravitational field. The relationship governing gravitational energy can be simply derived by noting that gravity is a conservative force, and the work done by a body in a gravitational field is equal to the vector product of the force and the displacement. Newton's law of universal gravitation states that the gravitational force is proportional to the product of the masses of any two bodies, and inversely proportional to the square of their separation, F = G mm/ r2 , where m and m are the masses of the first and second bodies, respectively, and r is the magnitude of the vector displacement between the two bodies. It is straightforward to show, by integrating this force law against an infinitesimal outward radial vector displacement, and assuming that the total system energy is zero at infinite displacement, that the gravitational potential energy of...