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{{about|the history of the scientific concept of energy|the history of how humans use energy|Energy }}
The word '''''[[energy]]''''' derives from [[Greek language|Greek]] {{Lang|grc|ἐνέργεια}} ({{Lang|grc-latn|energeia}}), which appears for the first time{{When|date=June 2020}} in the 4th century BCE works of [[Aristotle]] (OUP V, 240, 1991) (including ''Physics'', ''Metaphysics'', ''[[Nicomachean Ethics]]''<ref>[https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.01.0053:bekker%20page=1098a&highlight=e%29ne%2Frgeia#note4 Aristotle, "Nicomachean Ethics", 1098a, at Perseus]</ref> and ''De Anima'').<ref>[[Potentiality and actuality]]</ref>

[[File:Thomas Young (scientist).jpg|thumb|right|[[Thomas Young (scientist)|Thomas Young]] - the first to use the term "energy" in the modern sense, in 1802.]]
The modern concept of energy emerged{{When|date=June 2020}} from the idea of ''[[vis viva]]'' (living force), which [[Gottfried Wilhelm Leibniz|Leibniz]] defined as the product of the mass of an object and its velocity squared,{{Full citation needed|date=June 2020}} he believed that total ''vis viva'' was conserved. To account for slowing due to friction, Leibniz claimed that heat consisted of the random motion of the constituent parts of matter — a view described by Bacon in ''[[Novum Organum|Novum Organon]]'' to illustrate [[inductive reasoning]] and shared by [[Isaac Newton]], although it would be more than a century until this was generally accepted.

[[Émilie du Châtelet|Émilie marquise du Châtelet]] in her book ''Institutions de Physique'' ("Lessons in Physics"), published in 1740, incorporated the idea of Leibniz with practical observations of Gravesande to show that the "quantity of motion" of a moving object is proportional to its mass and its velocity squared (not the velocity itself as Newton taught—what was later called [[momentum]]).

In 1802 lectures to the Royal Society, [[Thomas Young (scientist)|Thomas Young]] was the first to use the term ''energy'' in its modern sense, instead of ''[[vis viva]]''.<ref>{{cite book | last = Smith | first = Crosbie | title = The Science of Energy - a Cultural History of Energy Physics in Victorian Britain | publisher = [[The University of Chicago Press]] | year = 1998 | isbn = 0-226-76420-6}}</ref> In the 1807 publication of those lectures, he wrote,

{{quote|The product of the mass of a body into the square of its velocity may properly be termed its energy.<ref>Thomas Young (1807). ''A Course of Lectures on Natural Philosophy and the Mechanical Arts'', p. 52.</ref>}}

[[Gustave-Gaspard Coriolis]] described "[[kinetic energy]]" in 1829 in its modern sense, and in 1853, [[William John Macquorn Rankine|William Rankine]] coined the term "[[potential energy]]."

It was argued for some years whether energy was a substance (the [[caloric theory|caloric]]) or merely a physical quantity.{{Full citation needed|date=June 2020}}

==Thermodynamics==
{{Main|History of thermodynamics}}
The development of [[steam engines]] {{When|date=June 2020}} required engineers to develop concepts and formulas that would allow them to describe the [[mechanical efficiency|mechanical]] and [[thermal efficiency|thermal efficiencies]] of their systems. Engineers such as [[Nicolas Léonard Sadi Carnot|Sadi Carnot]], physicists such as [[James Prescott Joule]], mathematicians such as [[Émile Clapeyron]] and [[Hermann von Helmholtz]], and amateurs such as [[Julius Robert von Mayer]] all contributed to the notion that the ability to perform certain tasks, called work, was somehow related to the amount of energy in the system. In the 1850s, Glasgow professor of natural philosophy [[William Thomson, 1st Baron Kelvin|William Thomson]] and his ally in the engineering science [[William Rankine]] began to replace the older language of [[mechanics]] with terms such as ''actual energy'', ''[[kinetic energy]]'', and ''[[potential energy]]''.<ref name="Smith" >{{cite book | last = Smith | first = Crosbie | title = The Science of Energy - a Cultural History of Energy Physics in Victorian Britain | publisher = The University of Chicago Press | year = 1998 | isbn = 0-226-76421-4}}</ref>  William Thomson ([[Lord Kelvin]]) amalgamated all of these laws into the laws of [[thermodynamics]], which aided in the rapid development of explanations of chemical processes using the concept of energy by [[Rudolf Clausius]], [[Josiah Willard Gibbs]] and [[Walther Nernst]]. It also led to a mathematical formulation of the concept of [[entropy]] by Clausius, and to the introduction of laws of [[radiant energy]] by [[Jožef Stefan]].
Rankine coined the term ''potential energy''.<ref name="Smith"/>  In 1881, William Thomson stated before an audience that:<ref>Thomson, William. (1881). "On the sources of energy available to man for the production of mechanical effect." ''BAAS Rep''. 51: 513-18 (Quote: pg. 513); ''PL 2'': 433-50.</ref>

{{quote|The very name '''energy''', though first used in its present sense by Dr [[Thomas Young (scientist)|Thomas Young]] about the beginning of this century, has only come into use practically after the [[History of thermodynamics|doctrine]] which defines it had ... been raised from mere formula of mathematical dynamics to the position it now holds of a principle pervading all nature and guiding the investigator in the field of science.}}

Over the following thirty years or so this newly developing science went by various names, such as the dynamical [[theory of heat]] or ''energetics'', but after the 1920s generally came to be known as [[thermodynamics]], the science of energy transformations.

Stemming from the 1850s development of the first two [[laws of thermodynamics]], the science of energy have since branched off into a number of various fields, such as [[biological thermodynamics]] and [[thermoeconomics]], to name a couple; as well as related terms such as [[entropy]], a measure of the loss of useful energy, or [[Power (physics)|power]], an energy flow per unit time, etc. In the past two centuries, the use of the word energy in various "non-scientific" vocations, e.g. social studies, spirituality and psychology has proliferated the popular literature.

==Conservation of energy==
In 1918 it was proved that the law of [[conservation of energy]] is the direct mathematical consequence of the [[translational]] [[symmetry]] of the quantity [[conjugate quantities|conjugate]] to energy, namely [[time]].{{Citation needed|date=December 2010}}  That is, energy is conserved because the laws of physics do not distinguish between different moments of time (see [[Noether's theorem]]).

During a 1961 lecture<ref name="RPF1">{{cite book |first=Richard |last=Feynman|title=The Feynman Lectures on Physics; Volume 1|url=https://archive.org/details/feynmanlectureso0001feyn |url-access=registration |date=1964|publisher=[[Addison Wesley]]|location=U.S.A| isbn=0-201-02115-3}}</ref> for undergraduate students at the [[California Institute of Technology]], [[Richard Feynman]], a celebrated physics teacher and [[Nobel Laureate]], said this about the concept of energy:

{{quote|There is a fact, or if you wish, a law, governing natural phenomena that are known to date. There is no known exception to this law&mdash;it is exact so far we know. The law is called [[conservation of energy]]; it states that there is a certain quantity, which we call energy that does not change in manifold changes which nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity, which does not change when something happens. It is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number, and when we finish watching nature go through her tricks and calculate the number again, it is the same.|''The Feynman Lectures on Physics''}}

==See also==
* [[Timeline of thermodynamics]]
* [[History of physics]]
* [[Conservation of energy#History|History of the conservation of energy principle]]
* [[History of thermodynamics]]
* ''[[A Guide to the Scientific Knowledge of Things Familiar]]'', a book by Ebenezer Cobham Brewer, published around 1840, presenting explanations for common phenomena
* [[Caloric theory]]

==References==
{{Reflist|30em}}

==Further reading==
* Hecht, Eugene. "[http://scitation.aip.org/journals/doc/PHTEAH-ft/vol_41/iss_8/486_1.html An Historico-Critical Account of Potential Energy: Is PE Really Real?]" ''The Physics Teacher'' 41 (Nov 2003): 486–93.
* Hughes, Thomas. ''Networks of Power. Electrification in Western society, 1880-1930'' (Johns Hopkins UP, 1983).
* Martinás,  Katalin. "Aristotelian Thermodynamics," ''Thermodynamics: history and philosophy: facts, trends, debates'' (Veszprém, Hungary 23–28 July 1990), 285–303.
* Mendoza, E. "A sketch for a history of early thermodynamics." ''Physics Today'' 14.2 (1961): 32–42.
* Müller, Ingo. ''A history of thermodynamics'' (Berlin: Springer, 2007)
* Graf, Rüdiger. "[https://docupedia.de/zg/Graf_energy_history_v1_en_2023 Energy History and Histories of Energy]", ''[https://docupedia.de/ Docupedia-Zeitgeschichte]'' (Aug 2023).

==External links==
* [http://www.energyhistory.eu/en  ''The Journal of Energy History / Revue d'histoire de l'énergie'' (JEHRHE) ]
* [http://www.eia.doe.gov/kids/history/timelines/index.html Timeline of history of energy for children]
{{History of physics}}
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[[Category:History of energy| ]]
[[Category:History of science|Energy]]