GP: the gravitational potential energy that a unit mass would have at a specific point, V.
V = - GM/r
V = GP in j kg^-1
G = G constant, Nm^2kg^-2
r = distance from centre of object
radial gravitational field
gravitational potential difference
GPD: the energy needed to move a unit mass between 2 points in a gravitational field.
/\W = m/\V
W = work done, J.
(/\)Ep = m(/\)V
Ep = gravitation potential energy, J.
Ep = m(-GM/r) = - GMm/r