: the force driving and sustaining mental activity <in psychoanalytic theory the source of psychic energy is the id>
: the capacity for doing work
Capacity for doing work. Energy exists in various formsincluding kinetic, potential, thermal, chemical, electrical (seeelectricity), and nuclearand 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 alsoactivation energy, binding energy, ionization energy, mechanical energy, solar energy, zero-point energy.