A joule
nA joule is the mechanical equivalent of heat meaning the number of units of work which the unit of heat can perform.
nIts value was found by James Prescott Joule in experiments that showed the mechanical energy which must be expended to raise the temperature of a unit weight of water by 1 degree F. was equivalent to 772 foot-pounds upon the Fahrenheit, thermometric scale, by reason of which it is often called Joule's equivalent, and represented by the symbol J.