law of conservation of energy

Main Entry: conservation of energy
Function: noun
: a principle in physics: the total energy of an isolated system remains constant irrespective of whatever internalchanges may take place with energy disappearing in one form reappearing in another called also first law of thermodynamics, law of conservation of energy

conservation of energy   A principle stating that the total energy of a closed system remains constant over time, regardless of other possible changes within the system. It is related to the symmetry of time invariance. See also invariance, thermodynamics.