Lift a book onto a shelf and you give it potential energy. The book is not moving, but it has energy stored in its position. Let it fall and that energy becomes kinetic energy. Potential energy is stored energy an object has due to its position or state. It comes in several forms. Gravitational potential energy depends on height and mass. Elastic potential energy is stored in a stretched or compressed spring. Chemical potential energy is stored in the bonds between atoms. Nuclear potential energy is stored in the nucleus of an atom.

Gravitational potential energy is calculated as PE = mgh, where m is mass, g is the acceleration due to gravity, and h is height. Double the height and you double the potential energy. Double the mass and you double it again. Elastic potential energy is calculated as PE = ½kx², where k is the spring constant and x is the displacement from equilibrium. Potential energy is always defined relative to a reference point. For gravitational potential energy, the reference is often the ground. For elastic potential energy, the reference is the unstretched position. Potential energy is not an absolute quantity. It is a relative one.

Potential energy facts

• Definition. Stored energy due to position or state.
• Gravitational. PE = mgh.
• Elastic. PE = ½kx².
• Chemical. Stored in bonds.
• Nuclear. Stored in atomic nuclei.

Potential energy is not the same as kinetic energy. Potential energy is stored. Kinetic energy is active.