Gravitational Potential Energy
This type of potential energy represents the energy an object possesses by virtue of its location in a gravitational field.
PE = mgh
where h is the height above an arbitrary zero level that is convenient for the solution of the problem. For instance, the zero level might be assigned as the base of a cliff for a projectile being thrown from the top of the cliff or the zero level might be the floor for a marble rolling off a table onto the ground.
In this formula, m must be measured in kg, g equals 9.8 m/sec^{2}, and h is in meters. Note that this collection of units
kg (m/sec^{2})(m) = kg (m^{2}/sec^{2}) is also a joule (J).
The expression mg represents the objects weight or the force of gravitational attraction between the earth and the object. Forces are measured in newtons. Thus the expression
Nm also equals a joule (J).
