James Prescott Joule FRS (; 24 December 1818 – 11 October 1889) was an English physicist and brewer, born in Salford, Lancashire. Joule studied the nature of heat, and discovered its relationship to mechanical work (see energy). This led to the theory of conservation of energy, which led to the development of the first law of thermodynamics. The SI derived unit of energy, the joule, is named after him. He worked with Lord Kelvin to develop the absolute scale of temperature, made observations on magnetostriction, and found the relationship between the current through resistance and the heat dissipated, now called Joule's law.

James Prescott Joule (* 24. Dezember 1818 in Salford bei Manchester; † 11. Oktober 1889 in Sale (Greater Manchester)), Aussprache: dʒuːl war ein britischer Physiker.

James Prescott Joule (, Salford, près de Manchester, Angleterre – , Sale) est un physicien (et brasseur) britannique.

James Prescott Joule,född 24 december 1818, död  11 oktober 1889, var en brittisk fysiker som var verksam inom termodynamiken. Han har gett namn till SI-enheten för energi, Joule. Joule blev invald i Royal Society 1850 och bland erhållna utmärkelser märks bland andra Royal Medal (1852) och Copleymedaljen (1870).

James Prescott Joule (24 grudnia 1818 - 11 października 1889) - fizyk angielski, członek Towarzystwa Królewskiego (Royal Society).