Energy See Also: Energy, Sources Of In physics, the ability or capacity to do Work. Forms of energy include Heat, chemical energy, and, according to the theory of Relativity, Mass (see Nuclear Energy); other forms of energy are associated with the transmission of Light, Sound, and Electricity. Energy and work are measured in the same units: Joules, ergs, electron-Volt, calories, foot-pounds, or some other, depending on the system of measurement being used. When a force acts on a body, the work performed (and the energy expended) is the product of the force and the distance over which it is exerted. Potential energy is the capacity for doing work that a body possesses because of its position or condition. For example, a Weight lifted to a certain height has potential energy because of its position in earth's gravitational Field (see Gravitation). Kinetic Energy is the energy a body possesses because it is in Motion. The average kinetic energy of the atoms or Molecules of a body is measured by the Temperature of the body. Energy (or its equivalent in mass) can be neither created nor destroyed (see Conservation Laws), but it can be changed from one form into another.