energy /en″ərjē/ [Gk, energia] , the capacity to do work or to perform vigorous activity. Energy may occur in the form of heat, light, movement, sound, or radiation. Human energy is usually expressed as muscle contractions and heat production, made possible by the metabolism of food that originally acquired the energy from sunlight. Chemical energy is that released as a result of a chemical reaction, as in the metabolism of food. −energetic, adj.
