Potential energy is stored energy. A book on a shelf has it. So does water behind a dam, a stretched rubber band, and a charged battery. The energy is not doing anything yet, but it is ready to be released. The higher the book or the more water behind the dam, the more potential energy is stored.

Gravitational potential energy depends on mass, height, and the strength of gravity. The formula is mass times gravity times height. A 10-kilogram weight lifted 2 meters holds about 196 joules. Chemical potential energy lives in the bonds of molecules. A gallon of gasoline holds about 120 megajoules.

Potential energy converts to kinetic energy when released. A roller coaster car at the top of a hill has maximum potential energy. As it drops, that energy becomes kinetic. At the bottom, the kinetic energy peaks. The cycle repeats on the next hill, minus losses to friction and air resistance.

Common forms

• Gravitational
• Elastic
• Chemical
• Electrical
• Nuclear