48-534: The erg is a unit of energy equal to 10 joules (100 n J). It originated in the Centimetre–gram–second system of units (CGS). It has the symbol erg . The erg is not an SI unit . Its name is derived from ergon ( ἔργον ), a Greek word meaning 'work' or 'task'. An erg is the amount of work done by a force of one dyne exerted for a distance of one centimetre . In the CGS base units , it
96-403: A conceptual leap: if heat was a form of molecular motion, why did the motion of the molecules not gradually die out? Joule's ideas required one to believe that the collisions of molecules were perfectly elastic. Importantly, the very existence of atoms and molecules was not widely accepted for another 50 years. Although it may be hard today to understand the allure of the caloric theory , at
144-409: A footnote signalled his first doubts about the caloric theory, referring to Joule's "very remarkable discoveries". Surprisingly, Thomson did not send Joule a copy of his paper but when Joule eventually read it he wrote to Thomson on 6 October, claiming that his studies had demonstrated conversion of heat into work but that he was planning further experiments. Thomson replied on the 27th, revealing that he
192-485: A force vector and a displacement vector. By contrast, torque is a vector – the cross product of a force vector and a distance vector. Torque and energy are related to one another by the equation E = τ θ , {\displaystyle E=\tau \theta \,,} where E is energy, τ is (the vector magnitude of) torque, and θ is the angle swept (in radians ). Since plane angles are dimensionless, it follows that torque and energy have
240-443: A perforated cylinder, he could measure the slight viscous heating of the fluid. He obtained a mechanical equivalent of 770 foot-pounds force per British thermal unit (4,140 J/Cal). The fact that the values obtained both by electrical and purely mechanical means were in agreement to at least two significant digits was, to Joule, compelling evidence of the reality of the convertibility of work into heat. Wherever mechanical force
288-492: A refined measurement of 772.692 foot-pounds force per British thermal unit (4,150 J/Cal), closer to twentieth century estimates. Much of the initial resistance to Joule's work stemmed from its dependence upon extremely precise measurements . He claimed to be able to measure temperatures to within 1 ⁄ 200 of a degree Fahrenheit (3 mK). Such precision was certainly uncommon in contemporary experimental physics but his doubters may have neglected his experience in
336-465: A value for the mechanical equivalent of heat of 1,034 foot-pound from Rumford's publications. Some modern writers have criticised this approach on the grounds that Rumford's experiments in no way represented systematic quantitative measurements. In one of his personal notes, Joule contends that Mayer's measurement was no more accurate than Rumford's, perhaps in the hope that Mayer had not anticipated his own work. Joule has been attributed with explaining
384-446: Is also equivalent to any of the following: The joule is named after James Prescott Joule . As with every SI unit named for a person, its symbol starts with an upper case letter (J), but when written in full, it follows the rules for capitalisation of a common noun ; i.e., joule becomes capitalised at the beginning of a sentence and in titles but is otherwise in lower case. The cgs system had been declared official in 1881, at
432-533: Is equal to (approximately unless otherwise stated): Units with exact equivalents in joules include: In mechanics , the concept of force (in some direction) has a close analogue in the concept of torque (about some angle): A result of this similarity is that the SI unit for torque is the newton-metre , which works out algebraically to have the same dimensions as the joule, but they are not interchangeable. The General Conference on Weights and Measures has given
480-654: Is equal to one gram centimetre-squared per second -squared (g⋅cm/s). It is thus equal to 10 joules or 100 nanojoules ( nJ ) in SI units. In 1864, Rudolf Clausius proposed the Greek word ἐργον ( ergon ) for the unit of energy, work and heat. In 1873, a committee of the British Association for the Advancement of Science , including British physicists James Clerk Maxwell and William Thomson recommended
528-450: Is expended, an exact equivalent of heat is always obtained. Joule now tried a third route. He measured the heat generated against the work done in compressing a gas. He obtained a mechanical equivalent of 798 foot-pounds force per British thermal unit (4,290 J/Cal). In many ways, this experiment offered the easiest target for Joule's critics but Joule disposed of the anticipated objections by clever experimentation. Joule read his paper to
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#1732772233772576-532: Is named "The J. P. Joule" after him. Joule's many honours and commendations include: There is a memorial to Joule in the north choir aisle of Westminster Abbey , though he is not buried there, contrary to what some biographies state. A statue of Joule by Alfred Gilbert stands in Manchester Town Hall , opposite that of Dalton. Joule married Amelia Grimes in 1847. She died in 1854, seven years after their wedding. They had three children together:
624-655: Is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of one newton displaces a mass through a distance of one metre in the direction of that force. It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889). In terms of SI base units and in terms of SI derived units with special names ,
672-553: The mechanical equivalent of heat as 4.1868 joules per calorie of work to raise the temperature of one gram of water by one kelvin. He announced his results at a meeting of the chemical section of the British Association for the Advancement of Science in Cork in August 1843 and was met by silence. Joule was undaunted and started to seek a purely mechanical demonstration of the conversion of work into heat. By forcing water through
720-522: The Cascade de Sallanches waterfall, though this subsequently proved impractical. Though Thomson felt that Joule's results demanded theoretical explanation, he retreated into a spirited defence of the Carnot – Clapeyron school. In his 1848 account of absolute temperature , Thomson wrote that "the conversion of heat (or caloric) into mechanical effect is probably impossible, certainly undiscovered" – but
768-609: The Kelvin scale. Joule also made observations of magnetostriction , and he found the relationship between the current through a resistor and the heat dissipated , which is also called Joule's first law . His experiments about energy transformations were first published in 1843. James Joule was born in 1818, the son of Benjamin Joule (1784–1858), a wealthy brewer , and his wife, Alice Prescott, on New Bailey Street in Salford . Joule
816-650: The Royal Society on 20 June 1844, but his paper was rejected for publication by the Royal Society and he had to be content with publishing in the Philosophical Magazine in 1845. In the paper he was forthright in his rejection of the caloric reasoning of Carnot and Émile Clapeyron , a rejection partly theologically driven: I conceive that this theory ... is opposed to the recognised principles of philosophy because it leads to
864-602: The conservation of energy credited them both. Also in 1847, another of Joule's presentations at the British Association in Oxford was attended by George Gabriel Stokes , Michael Faraday , and the precocious and maverick William Thomson , later to become Lord Kelvin, who had just been appointed professor of natural philosophy at the University of Glasgow . Stokes was "inclined to be a Joulite" and Faraday
912-492: The heat engine since 1824 ensured that the young Joule, working outside either academia or the engineering profession, had a difficult road ahead. Supporters of the caloric theory readily pointed to the symmetry of the Peltier–Seebeck effect to claim that heat and current were convertible in an, at least approximately, reversible process . Further experiments and measurements with his electric motor led Joule to estimate
960-439: The kinetic theory . Kinetics is the science of motion. Joule was a pupil of Dalton and it is no surprise that he had learned a firm belief in the atomic theory , even though there were many scientists of his time who were still skeptical. He had also been one of the few people receptive to the neglected work of John Herapath on the kinetic theory of gases . He was further profoundly influenced by Peter Ewart 's 1813 paper "On
1008-903: The surface energy of molecules in surface chemistry . It would equate to 10 erg, the equivalent to 10 joule. The erg is not a part of the International System of Units (SI), which has been recommended since 1 January 1978 when the European Economic Community ratified a directive of 1971 that implemented SI as agreed by the General Conference of Weights and Measures . It is the unit of energy in Gaussian units , which are widely used in astrophysics , applications involving microscopic problems and relativistic electrodynamics, and sometimes in mechanics . Joule The joule ( / dʒ uː l / JOOL , or / dʒ aʊ l / JOWL ; symbol: J )
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#17327722337721056-684: The annihilation of force, is necessarily erroneous. Joule here adopts the language of vis viva (energy), possibly because Hodgkinson had read a review of Ewart's On the measure of moving force to the Literary and Philosophical Society in April 1844. In June 1845, Joule read his paper On the Mechanical Equivalent of Heat to the British Association meeting in Cambridge . In this work, he reported his best-known experiment, involving
1104-504: The art of brewing and his access to its practical technologies. He was also ably supported by scientific instrument -maker John Benjamin Dancer . Joule's experiments complemented the theoretical work of Rudolf Clausius , who is considered by some to be the coinventor of the energy concept. Joule was proposing a kinetic theory of heat (he believed it to be a form of rotational, rather than translational, kinetic energy ), and this required
1152-519: The conclusion that vis viva may be destroyed by an improper disposition of the apparatus: Thus Mr Clapeyron draws the inference that 'the temperature of the fire being 1000 °C to 2000 °C higher than that of the boiler there is an enormous loss of vis viva in the passage of the heat from the furnace to the boiler.' Believing that the power to destroy belongs to the Creator alone I affirm ... that any theory which, when carried out, demands
1200-557: The feasibility of replacing the brewery's steam engines with the newly invented electric motor . His first scientific papers on the subject were contributed to William Sturgeon 's Annals of Electricity . Joule was a member of the London Electrical Society , established by Sturgeon and others. Motivated in part by a businessman's desire to quantify the economics of the choice, and in part by his scientific inquisitiveness, he set out to determine which prime mover
1248-402: The first International Electrical Congress . The erg was adopted as its unit of energy in 1882. Wilhelm Siemens , in his inauguration speech as chairman of the British Association for the Advancement of Science (23 August 1882) first proposed the joule as unit of heat , to be derived from the electromagnetic units ampere and ohm , in cgs units equivalent to 10 erg . The naming of
1296-412: The general adoption of the centimetre, the gramme, and the second as fundamental units ( C.G.S. System of Units ). To distinguish derived units, they recommended using the prefix "C.G.S. unit of ..." and requested that the word erg or ergon be strictly limited to refer to the C.G.S. unit of energy . In 1922, chemist William Draper Harkins proposed the name micri-erg as a convenient unit to measure
1344-457: The heating effect he had quantified in 1841 was due to generation of heat in the conductor and not its transfer from another part of the equipment. This was a direct challenge to the caloric theory which held that heat could neither be created nor destroyed. Caloric theory had dominated thinking in the science of heat since introduced by Antoine Lavoisier in 1783. Lavoisier's prestige and the practical success of Sadi Carnot 's caloric theory of
1392-743: The joule is defined as J = k g ⋅ m 2 ⋅ s − 2 = N ⋅ m = P a ⋅ m 3 = W ⋅ s = C ⋅ V {\displaystyle {\begin{alignedat}{3}\mathrm {J} \;&=~\mathrm {kg{\cdot }m^{2}{\cdot }s^{-2}} \\[0.7ex]&=~\mathrm {N{\cdot }m} \\[0.7ex]&=~\mathrm {Pa{\cdot }m^{3}} \\[0.7ex]&=~\mathrm {W{\cdot }s} \\[0.7ex]&=~\mathrm {C{\cdot }V} \\[0.7ex]\end{alignedat}}} One joule
1440-587: The measure of moving force". Joule perceived the relationship between his discoveries and the kinetic theory of heat. His laboratory notebooks reveal that he believed heat to be a form of rotational, rather than translational motion. Joule could not resist finding antecedents of his views in Francis Bacon , Sir Isaac Newton , John Locke , Benjamin Thompson (Count Rumford) and Sir Humphry Davy . Though such views are justified, Joule went on to estimate
1488-523: The mechanical equivalent of heat, in which he found that this amount of foot-pounds of work must be expended at sea level to raise the temperature of one pound of water from 60 °F to 61 °F . There is also a quotation from the Gospel of John : "I must work the work of him that sent me, while it is day: the night cometh, when no man can work". The Wetherspoon's pub in Sale , the town of his death,
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1536-414: The output of the alternative methods in terms of a common standard, the ability to raise a mass weighing one pound to a height of one foot, the foot-pound . However, Joule's interest diverted from the narrow financial question to that of how much work could be extracted from a given source, leading him to speculate about the convertibility of energy. In 1843 he published results of experiments showing that
1584-485: The paper he wrote to Thomson with his comments and questions. Thus began a fruitful, though largely epistolary, collaboration between the two men, Joule conducting experiments, Thomson analysing the results and suggesting further experiments. The collaboration lasted from 1852 to 1856, its discoveries including the Joule–Thomson effect , and the published results did much to bring about general acceptance of Joule's work and
1632-603: The same dimensions. A watt-second (symbol W s or W⋅s ) is a derived unit of energy equivalent to the joule. The watt-second is the energy equivalent to the power of one watt sustained for one second . While the watt-second is equivalent to the joule in both units and meaning, there are some contexts in which the term "watt-second" is used instead of "joule", such as in the rating of photographic electronic flash units . James Prescott Joule James Prescott Joule FRS FRSE ( / dʒ uː l / ; 24 December 1818 – 11 October 1889)
1680-611: The successor organisation of the International Electrical Congress) adopted the " Giorgi system", which by virtue of assuming a defined value for the magnetic constant also implied a redefinition of the joule. The Giorgi system was approved by the International Committee for Weights and Measures in 1946. The joule was now no longer defined based on electromagnetic unit, but instead as the unit of work performed by one unit of force (at
1728-543: The sunset green flash phenomenon in a letter to the Manchester Literary and Philosophical Society in 1869; actually, he merely noted (with a sketch) the last glimpse as bluish green, without attempting to explain the cause of the phenomenon. Joule died at home in Sale and is buried in Brooklands cemetery there. His gravestone is inscribed with the number "772.55", his climacteric 1878 measurement of
1776-570: The time it seemed to have some clear advantages. Carnot 's successful theory of heat engines had also been based on the caloric assumption, and only later was it proved by Lord Kelvin that Carnot's mathematics were equally valid without assuming a caloric fluid. However, in Germany, Hermann Helmholtz became aware both of Joule's work and the similar 1842 work of Julius Robert von Mayer . Though both men had been neglected since their respective publications, Helmholtz's definitive 1847 declaration of
1824-434: The time not yet named newton ) over the distance of 1 metre . The joule was explicitly intended as the unit of energy to be used in both electromagnetic and mechanical contexts. The ratification of the definition at the ninth General Conference on Weights and Measures , in 1948, added the specification that the joule was also to be preferred as the unit of heat in the context of calorimetry , thereby officially deprecating
1872-400: The unit in honour of James Prescott Joule (1818–1889), at the time retired but still living (aged 63), followed the recommendation of Siemens: Such a heat unit, if found acceptable, might with great propriety, I think, be called the Joule, after the man who has done so much to develop the dynamical theory of heat. At the second International Electrical Congress, on 31 August 1889, the joule
1920-414: The unit of energy the name joule , but has not given the unit of torque any special name, hence it is simply the newton-metre (N⋅m) – a compound name derived from its constituent parts. The use of newton-metres for torque but joules for energy is helpful to avoid misunderstandings and miscommunication. The distinction may be seen also in the fact that energy is a scalar quantity – the dot product of
1968-536: The use of a falling weight, in which gravity does the mechanical work, to spin a paddle wheel in an insulated barrel of water which increased the temperature. He now estimated a mechanical equivalent of 819 foot-pounds force per British thermal unit (4,404 J/Cal). He wrote a letter to the Philosophical Magazine, published in September 1845 describing his experiment. In 1850, Joule published
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2016-422: The use of the calorie . This is the definition declared in the modern International System of Units in 1960. The definition of the joule as J = kg⋅m ⋅s has remained unchanged since 1946, but the joule as a derived unit has inherited changes in the definitions of the second (in 1960 and 1967), the metre (in 1983) and the kilogram ( in 2019 ). One joule represents (approximately): 1 joule
2064-464: Was "much struck with it" though he harboured doubts. Thomson was intrigued but sceptical. Unanticipated, Thomson and Joule met later that year in Chamonix . Joule married Amelia Grimes on 18 August and the couple went on honeymoon. Marital enthusiasm notwithstanding, Joule and Thomson arranged to attempt an experiment a few days later to measure the temperature difference between the top and bottom of
2112-413: Was an English physicist . Joule studied the nature of heat and discovered its relationship to mechanical work . This led to the law of conservation of energy , which in turn led to the development of the first law of thermodynamics . The SI unit of energy , the joule (J), is named after him. He worked with Lord Kelvin to develop an absolute thermodynamic temperature scale, which came to be called
2160-444: Was more efficient. He discovered Joule's first law in 1841, that "the heat which is evolved by the proper action of any voltaic current is proportional to the square of the intensity of that current, multiplied by the resistance to conduction which it experiences". He went on to realize that burning a pound of coal in a steam engine was more economical than a costly pound of zinc consumed in an electric battery . Joule captured
2208-529: Was officially adopted alongside the watt and the quadrant (later renamed to henry ). Joule died in the same year, on 11 October 1889. At the fourth congress (1893), the "international ampere" and "international ohm" were defined, with slight changes in the specifications for their measurement, with the "international joule" being the unit derived from them. In 1935, the International Electrotechnical Commission (as
2256-482: Was planning his own experiments and hoping for a reconciliation of their two views. Though Thomson conducted no new experiments, over the next two years he became increasingly dissatisfied with Carnot's theory and convinced of Joule's. In his 1851 paper, Thomson was willing to go no further than a compromise and declared "the whole theory of the motive power of heat is founded on two propositions, due respectively to Joule, and to Carnot and Clausius". As soon as Joule read
2304-451: Was tutored as a young man by the famous scientist John Dalton and was strongly influenced by chemist William Henry and Manchester engineers Peter Ewart and Eaton Hodgkinson . He was fascinated by electricity, and he and his brother experimented by giving electric shocks to each other and to the family's servants. As an adult, Joule managed the brewery. Science was merely a serious hobby. Sometime around 1840, he started to investigate
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