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James Joule
In the history of thermodynamics, James Prescott Joule (1818-1889) was an English physicist noted for his experiments in the determination of the mechanical equivalent of heat, one of the precursors to the logic behind both the first and second law of thermodynamics. Joule was the son of a wealthy brewer who was tolerant enough of the scientific interests of his son to furnish him with a home laboratory, in which his elaborate experiments on the inter-conversion of forms of energy, from heat, gravitational, to mechanical, to electric, etc., were conducted. [1] Mechanical equilvalent of heat
See main: Mechanical equivalent of heatIn the early 1840s, Joule repeated British chemist and physicist Humphry Davy’s famous 1799 ice-rubbing experiments, which showed that ice cubes rubbed together in a room colder than the freezing point of water can be made to melt, a result which conflicted with the caloric theory, and began to extrapolate this principle to various other work-producing experiments, such as chemical, mechanical, and electrical.
The best known calculation for the mechanical equivalent of heat was that performed by Joule in 1843 wherein the falling weight was attached to wound rope to a wooden paddlewheel immersed in a tub of water. When the weight fell, the paddle wheel turned, causing agitation in the water and as a result a temperature increase. [2] The depiction shown adjacent is an engraving of Joule's apparatus for measuring the mechanical equivalent of heat. [3]In Joule's famous 1843 paper, entitled "The Mechanical Equivalent of Heat", he published the value A for the amount of work W required to produce a unit of heat Q. Joule contended that motion and heat were mutually interchangeable and that in every case, a given amount of work would generate the same amount of heat, regardless of the process. [2] In 1843, Joule summarized his overall objective and theory by stating that:
“I shall lose no time in repeating and extending these experiments, being satisfied that the grand agents of nature are … indestructible; and that wherever mechanical force is expended, an exact equivalent of heat is always obtained.”
References
1. Muller, Ingo. (2007). A History of Thermodynamics - the Doctrine of Energy and Entropy, (pgs. 21-24). New York: Springer.
2. Joule, James P. (1845). "On the Mechanical Equivalent of Heat", Brit. Assoc. Rep., trans. Chemical Sect, p.31, read before the British Association at Cambridge, June.
3. August 1869 issue of Harper's New Monthly Magazine, No. 231.
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