# Energy

### mass body multiplied potential

**Energy**, in physics, the capacity to do work. There are various forms of energy. Kinetic energy is the energy of motion, and is equal to one-half the mass of the moving body multiplied by the square of its velocity (1/2mv^{3}). Potential energy is the energy a body possesses by virtue of its position. A body raised to a certain height, *h*, for example, has a potential energy equal to its mass multiplied by *h* multiplied by the force of gravity. If the body were dropped, it would fall, and its potential energy would become kinetic. Other forms of energy include heat energy (the vibration of the molecules or atoms that make up substance), electrical energy (the motion of electrons), chemical energy (released by chemical reactions). Nuclear energy is produced when the nuclei of atoms disintegrate or combine, producing both heat and atomic and subatomic particles. One of the consequences of Einstein's theory of relativity is that mass and energy are mutually convertible. The relation between the 2 is described by the formula *E=mc*^{2}, where *E* is energy, *m* is mass, and *c* is the velocity of light. Since *c*^{2} is a very large number, the transformation of even a small amount of matter (mass) into energy yields great quantities of energy. This is what happens in the explosion of a hydrogen bomb. Although matter can be transformed into energy and vice versa, and one form of energy can be transformed into another, neither mass nor energy can be created or destroyed. This is known as the law of conservation of mass-energy.

*See also:* Nuclear energy; Physics.

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