joule, abbr. J, unit of work or energy in the mks system of units, which is based on the metric system; it is the work done or energy expended by a force of 1 newton acting through a distance of 1 meter. The joule is named for James P. Joule.

Joule, James Prescott, 1818-89, English physicist. His scientific researches began in his youth when he invented an electromagnetic engine. Joule made valuable contributions to the fields of heat, electricity, and thermodynamics. His work established the mechanical theory of heat, and he was the first to determine the relationship between heat energy and mechanical energy (the mechanical equivalent of heat). Joule discovered the first law of thermodynamics, which is a form of the law of conservation of energy (see conservation laws). He was one of the great experimental scientists of the 19th cent. The mechanical unit of work is named for him.

(born Dec. 24, 1818, Salford, Lancashire, Eng.—died Oct. 11, 1889, Sale, Cheshire) English physicist. After studying under John Dalton, in 1840 he described “Joule's law,” which stated that the heat produced in a wire by an electric current is proportional to the product of the resistance of the wire and the square of the current. In 1843 he published his value for the amount of work required to produce a unit of heat, called the mechanical equivalent of heat, and established that heat is a form of energy. He established that the various forms of energy are basically the same and can be changed from one into another, a discovery that formed the basis of the law of conservation of energy, the first law of thermodynamics. In his honour, the value of the mechanical equivalent of heat is usually represented by the letter math.J, and a standard unit of work is called the joule.

Learn more about Joule, James (Prescott) with a free trial on Britannica.com.

(born Dec. 24, 1818, Salford, Lancashire, Eng.—died Oct. 11, 1889, Sale, Cheshire) English physicist. After studying under John Dalton, in 1840 he described “Joule's law,” which stated that the heat produced in a wire by an electric current is proportional to the product of the resistance of the wire and the square of the current. In 1843 he published his value for the amount of work required to produce a unit of heat, called the mechanical equivalent of heat, and established that heat is a form of energy. He established that the various forms of energy are basically the same and can be changed from one into another, a discovery that formed the basis of the law of conservation of energy, the first law of thermodynamics. In his honour, the value of the mechanical equivalent of heat is usually represented by the letter math.J, and a standard unit of work is called the joule.

Learn more about Joule, James (Prescott) with a free trial on Britannica.com.