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 cm2⋅g⋅s−2
| 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 10−7{{nbsp}}joules (100{{nbsp}}nJ). 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 word meaning 'work' or 'task'.{{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}}
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 is equal to one gram centimetre-squared per second-squared (g⋅cm2/s2). It is thus equal to 10−7 joules or 100 nanojoules (nJ) in SI units.
History
In 1864, Rudolf Clausius proposed the Greek word {{lang|grc|ἐργον}} ({{Transliteration|grc|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 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 the surface energy of molecules in surface chemistry. It would equate to 10−14 erg, the equivalent to 10−21 joule.
The erg is not a part of the International System of Units (SI), which has been recommended since 1 January 1978{{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}} when the European Economic Community ratified a directive of 1971 that implemented SI as agreed by the General Conference of Weights and Measures.{{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}} It is the unit of energy in Gaussian units, which are widely used in astrophysics{{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}}{{better source needed|reason=User-generated content|date=July 2021}}, applications involving microscopic problems and relativistic electrodynamics,{{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}} 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
{{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}}
{{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}}
{{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}}
|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}}
{{CGS units}}
{{Ionising radiation related quantities}}