Energy means work. It refers to the effort required to move a weight for some distance. The heavier the weight or the longer the distance, the more energy is required. Energy is measured in units called "joules," or sometimes as the heat equivalent to these joules, called "calories." In nutrition, both terms are used. A calorie is the amount of heat needed to warm one gram of water by one degree centigrade. A more convenient unit is the kilocalorie (kcal), which equals one thousand calories. In physical terms, energy has several forms, all of which can be converted into heat. These include potential energy, kinetic energy, chemical energy, and heat energy.
GEORGE A. BRAY