View source for Erg

{{Short description|CGS unit of energy and mechanical work}}
{{hatnote group|
{{other uses}}
{{redirect|Ergs}}
{{redirect-distinguish|Micro-erg|Micro ERG}}
}}
{{Use Oxford spelling|date=October 2019}}
{{Infobox unit
| name         = erg
| image        = 
| caption      = 
| standard     = [[CGS units]]
| quantity     = [[energy]]
| symbol       = erg
| symbol2      = 
| extralabel   = Derivation
| extradata    = 1 erg = 1 dyn⋅cm
| units1       = CGS base units
| inunits1     = 1 cm<sup>2</sup>⋅g⋅s<sup>−2</sup>
| units2       = [[SI units]]
| inunits2     = {{val|e=-7|u=J}}
| units3       = [[British Gravitational System]]
| inunits3     = {{cvt|1|erg|ftlbf|sigfig=7|disp=out}}
}}
The '''erg''' is a unit of energy equal to 10<sup>−7</sup>{{nbsp}}[[joule]]s (100{{nbsp}}[[Nano-|n]]J). It is not an [[SI unit]], instead originating from the [[centimetre–gram–second system of units]] (CGS). Its name is derived from {{Transliteration|grc|ergon}} ({{lang|grc|ἔργον}}), a [[Greek language|Greek]] word meaning 'work' or 'task'.<ref>{{cite book |url=https://books.google.com/books?id=0UkuAAAAYAAJ |title=The Greek in English |last=Goodell |first=Thomas Dwight |publisher = [[Henry Holt and Company]] |edition=2nd |year=1889 |page=40}}</ref>

An erg is the amount of work done by a force of one [[dyne]] exerted for a distance of one [[centimetre]]. In the CGS [[Unit of measurement#Base and derived units|base units]], it is equal to one [[gram]] centimetre-squared per [[second]]-squared (g⋅cm<sup>2</sup>/s<sup>2</sup>). It is thus equal to 10<sup>−7</sup> [[joule]]s or 100 nanojoules ([[nanojoule|nJ]]) in [[SI]] units.

* 1 erg = {{val|e=-7|ul=J}} = {{val|100|ul=nJ}}
* 1 erg = {{val|e=-10|u=sn⋅m}} = {{val|100|u=psn⋅m}} = {{val|100|u=pico[[sthène]]-metres}}
* 1 erg = {{val|624.15|u=GeV}} = {{val|6.2415|e=11|ul=eV}}
* 1 erg = {{val|1|u=[[dyne|dyn]]⋅cm}} = {{val|1|u=g⋅cm<sup>2</sup>/s<sup>2</sup>}}
* 1 erg = {{cvt|1.000000|erg|W.h|disp=out}}

==History==
In 1864, [[Rudolf Clausius]] proposed the Greek word {{lang|grc|ἐργον}} ({{Transliteration|grc|ergon}}) for the unit of energy, work and heat.<ref name="Clausius_1867"/><ref name="Howard_2002"/> In 1873, a committee of the [[British Association for the Advancement of Science]], including British physicists [[James Clerk Maxwell]] and [[William Thomson, 1st Baron Kelvin|William Thomson]] recommended the general adoption of the centimetre, the gramme, and the second as fundamental units ([[Centimetre–gram–second system of 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''.<ref name="BSAS_1873"/>

In 1922, chemist [[William Draper Harkins]] proposed the name [[micri-]]erg as a convenient unit to measure the [[surface energy]] of [[molecule]]s<ref name="Jerrard_2012"/> in [[surface chemistry]].<ref name="Cardarelli_1966"/><ref name="Cardarelli_2003"/> It would equate to 10<sup>−14</sup>&nbsp;erg,<ref name="Jerrard_2012"/><ref name="Harkins_1922"/><ref name="Colloid_1925"/><ref name="ACh_1922"/><ref name="Partington_1949"/> the equivalent to 10<sup>−21</sup>&nbsp;joule.

The erg is not a part of the [[International System of Units]] (SI), which has been recommended since 1 January 1978<ref>{{Cite book|url=https://books.google.com/books?id=6N68sMtqXSUC&q=1+January+1978%2C+erg&pg=PA3|title=Architects' Data|last1=Neufert|first1=Ernst|last2=Neufert|first2=Peter|last3=Kister|first3=Johannes|date=2012-03-26|publisher=John Wiley & Sons|isbn=9781405192538|language=en}}</ref> when the [[European Economic Community]] ratified a directive of 1971 that implemented SI as agreed by the [[General Conference on Weights and Measures|General Conference of Weights and Measures]].<ref>{{Cite journal|last=Jennings|first=W. A.|date=October 1972|title=SI units in radiation measurement|url=https://www.birpublications.org/doi/abs/10.1259/0007-1285-45-538-784?journalCode=bjr|journal=The British Journal of Radiology|language=en|volume=45|issue=538|pages=784–785|doi=10.1259/0007-1285-45-538-784|pmid=5078949|issn=0007-1285|url-access=subscription}}</ref> It is the unit of energy in [[Gaussian units]], which are widely used in [[astrophysics]]<ref>{{Cite web|url=https://physics.stackexchange.com/q/235581 |title=Are ergs commonly used in astrophysics? If so, is there a specific reason for it?|date=2016-02-12|website=Physics Stack Exchange|access-date=2018-09-15}}</ref>{{better source needed|reason=User-generated content|date=July 2021}}, applications involving microscopic problems and relativistic electrodynamics,<ref>{{cite book |last1=Jackson |first1=John David |title=Classical electrodynamics |date=2009 |publisher=Wiley |location=Hoboken, NY |isbn=978-0-471-30932-1 |page=784 |edition=3}}</ref> and sometimes in [[mechanics]]{{citation needed|date=November 2023}}.

==See also==
* [[Foe (unit)]], relative measure for energy released by a supernova
* [[Lumen second]], for the lumerg and lumberg units
* [[Metre–tonne–second system of units]]

==References==
<references>
<ref name="ACh_1922">{{cite journal | title=Journal of the American Chemical Society - Issues for 1898-1901 include Review of American chemical research, v. 4-7; 1879-1937, the society's Proceedings | journal=Journal of the American Chemical Society | publisher=[[American Chemical Society]] | volume=44 | year=1922 | issn=0002-7863 | url=https://books.google.com/books?id=nFE9AQAAMAAJ&pg=PA665 | access-date=2015-02-15 | page=665}}</ref>
<ref name="Colloid_1925">{{cite book | title=Colloid Symposium Monograph - Papers Presented at the Second National Symposium on Colloid Chemistry, Northwestern University, June, 1924 | first=Harry N. | last=Holmes | publisher=The Chemical Catalog Company, Inc. | volume=2 | issue=1 | year=1925 | url=https://books.google.com/books?id=g7u3AAAAIAAJ | access-date=2015-02-15}}</ref>
<ref name="Cardarelli_2003">{{cite book | title=Encyclopaedia of Scientific Units, Weights and Measures | url=https://archive.org/details/encyclopaediaofs0000card | url-access=registration | first=François | last=Cardarelli | date=2003 | publisher=[[Springer-Verlag London Ltd.]] | isbn=978-1-4471-1122-1}}</ref>
<ref name="Jerrard_2012">{{cite book|last1=Jerrard|first1=H. G.|last2=McNeill|first2=D. B.|date=1993|title=A Dictionary of Scientific Units - Including dimensionless numbers and scales|orig-year=1963 |edition=6 |location=London|publisher=Chapman and Hall|isbn=0412467208|oclc=803100353|ol=OL1351307M|author-link2=Donald Burgess McNeill|page=100}}</ref>
<ref name="Cardarelli_1966">{{cite book | title=Scientific unit conversion: A practical guide to metrication | first=François | last=Cardarelli | publisher=[[Springer-Verlag London Limited]] | date=1999 | orig-year=1966 | edition=2 | isbn=978-1-85233-043-9 | id=1447108051, 9781447108054 | doi=10.1007/978-1-4471-0805-4 | url=https://books.google.com/books?id=-ZveBwAAQBAJ | access-date=2015-08-25}}</ref>
<ref name="Harkins_1922">{{cite book|title=The Orientation of Molecules in Surfaces, Surface Energy, Adsorption, and Surface Catalysis. V. The Adhesional Work Between Organic Liquids and Water: Vaporization in Steps as Related to Surface Formation | publisher=University of Chicago | date=2013-07-01 | orig-year=1922 | first1=Lathrop Emerson | last1=Roberts | first2=William Draper | last2=Harkins | author-link2=William Draper Harkins | first3=George Lindenberg | last3=Clark | department=University of Chicago Digital Preservation Collection | url=https://books.google.com/books?id=j2Y6AQAAMAAJ | access-date=2015-08-25}}</ref>
<ref name="Partington_1949">{{cite book | title=An Advanced Treatise on Physical Chemistry: Fundamental principles. The properties of gases | first=James Riddick | last=Partington | author-link = James Riddick Partington | publisher=Longmans, Green | date=2010-02-17 | orig-year=1949 | volume=1 | url=https://books.google.com/books?id=aPzvAAAAMAAJ | access-date=2015-08-25}}</ref>

<!-- Not in use
<ref name="Filippenko_2007">Filippenko, Alex, ''Understanding the Universe'' (of ''The Great Courses'', on DVD), Lecture 44, time 24:30, The Teaching Company, Chantilly, VA, USA, 2007</ref>
Not in use-->

<ref name="Clausius_1867">{{cite book|last=Clausius|first=Rudolf|title=The Mechanical Theory of Heat, With Its Applications to the Steam-engine and to the Physical Properties of Bodies.|date=1867|publisher=J. Van Voorst|location=London|page=[https://archive.org/details/mechanicaltheor04claugoog/page/n274 253]|url=https://archive.org/details/mechanicaltheor04claugoog|quote=editions:PwR_Sbkwa8IC.|author-link=Rudolf Clausius|access-date=2014-03-17|chapter=Appendices to Sixth Memoir [1864]. Appendix A. On Terminology.|editor1-first=T. Archer|editor1-last=Hirst|editor1-link=Thomas Archer Hirst}}
</ref>
<ref name="Howard_2002">{{cite journal|last=Howard|first=Irmgard K.|title=S is for Entropy. U is for Energy. What Was Clausius Thinking?|journal=Journal of Chemical Education|date=2001|volume=78|issue=4|page=505|doi=10.1021/ed078p505|url=http://www.giovannibachelet.it/FG1-13-14/settimana_12/Howard_2001.pdf|access-date=2014-03-17|bibcode = 2001JChEd..78..505H }}
</ref>
<ref name="BSAS_1873">{{cite conference 
|url= https://www.biodiversitylibrary.org/item/94452#page/324/mode/1up
|title=First Report of the Committee for the Selection and Nomenclature of Dynamical and Electrical Units 
|date=September 1873
|conference= Forty-third Meeting of the British Association for the Advancement of Science
|editor-first= Professor |editor-last = Everett |editor-link = Joseph David Everett
|first1 = Sir W |last1 = Thomson |author1-link = William Thomson, 1st Baron Kelvin
|first2 = Professor GC |last2 = Foster |author2-link = Carey Foster
|first3 = Professor JC |last3 = Maxwell |author3-link = James Clerk Maxwell
|first4 = Mr GJ |last4 = Stoney |author4-link = George Johnstone Stoney
|first5 = Professor Fleeming |last5 = Jenkin |author5-link = Fleeming Jenkin
|first6 = Dr |last6 = Siemens |author6-link = Carl Wilhelm Siemens
|first7 = Mr FJ |last7 = Bramwell |author7-link = Frederick Bramwell
|publisher= John Murray
|location= Bradford
|page = 224
|access-date= 2014-03-17}}</ref>
</references>

{{CGS units}}
{{Ionising radiation related quantities}}

[[Category:Units of energy]]
[[Category:Centimetre–gram–second system of units]]