Joule

Joule, pronounced jool or pronounced jowl, a unit in the metric system of measurement, is used to measure work or energy. Its symbol is J. One joule is the amount of work done when a force of 1 newton acts on an object that moves 1 meter in the direction of the force.

The joule is used to measure all forms of energy, including heat, electrical energy, and mechanical energy. One joule equals about 0.239 calorie. A calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1 Celsius degree. One joule of energy per second is required to pass an electric current of 1 ampere through 1 ohm resistance. One joule per second equals one watt, a unit of electric and mechanical power (see Watt).

In the inch-pound system of measurement customarily used in the United States, work or energy is measured in foot-pounds. One joule equals about 0.738 foot-pound. The joule was named for the British physicist James P. Joule.

Contributor: Hugh D. Young, Ph.D., Prof. of Physics, Carnegie-Mellon Univ.

Joule

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