n.
Capacity for doing work .
Energy exists in various forms
including kinetic , potential , thermal , chemical , electrical (see electricity ), and nuclear
and can be converted from one form to another. For example, fuel-burning heat engines convert chemical energy to thermal energy; batteries convert chemical energy to electrical energy. Though energy may be converted from one form to another, it may not be created or destroyed; that is, total energy in a closed system remains constant. All forms of energy are associated with motion . A rolling ball has kinetic energy, for instance, whereas a ball lifted above the ground has potential energy, as it has the potential to move if released. Heat and work involve the transfer of energy; heat transferred may become thermal energy. See also activation energy , binding energy , ionization energy , mechanical energy , solar energy , zero-point energy .