# Erg

For other uses, see Erg (disambiguation).
"micro-erg" redirects here. For the micro-electroretinogram, see Micro-ERG.

The erg is a unit of energy and work equal to 10−7 joules. It originated in the centimetre–gram–second (CGS) system of units. It has the symbol erg. The erg is not an SI unit. Its name is derived from ergon (’έργον) a Greek word meaning work or task.[1]

An erg is the amount of work done by a force of one dyne exerted for a distance of one centimeter. In the CGS base units, it is equal to one gram centimeter-squared per second-squared (g·cm2/s2). It is thus equal to 10−7 joules or 100 nanojoules (nJ) in SI units. An erg is approximately the amount of work done (or energy consumed) by one common house fly performing one "push up", the leg-bending dip that brings its mouth to the surface on which it stands and back up.[2]

1 erg = 10−7 J = 100 nJ
1 erg = 10−10sn·m = 100 psn·m = 100 picosthène-metres
1 erg = 624.15 GeV = 6.2415×1011 eV
1 erg = 1 dyne cm = 1 g·cm2/s2

## History

In 1864, Rudolf Clausius proposed the Greek word (ἐργον) ergon for the unit of energy, work and heat.[3][4] In 1873, a committee of the British Association for the Advancement of Science, including British physicists James Clerk Maxwell and William Thomson defined the C.G.S. System of Units, and recommended the name erg or ergon for the C.G.S. unit of energy.[5]

In 1922, William Draper Harkins proposed the name micri-erg as a convenient unit to measure the surface energy of molecules[6] in surface chemistry.[7][8] It would equate to 10−14 erg,[6][9][10][11][12] the equivalent to 10−21 joule.

## References

1. Oxford English Dictionary
2. Filippenko, Alex, Understanding the Universe (of The Great Courses, on DVD), Lecture 44, time 24:30, The Teaching Company, Chantilly, VA, USA, 2007
3. Clausius, Rudolf (1867). "Appendices to Sixth Memoir [1864]. Appendix A. On Terminology.". In Hirst, T. Archer. The Mechanical Theory of Heat, With Its Applications to the Steam-engine and to the Physical Properties of Bodies. London: J. Van Voorst. p. 253. Retrieved 2014-03-17.
4. Howard, Irmgard K. (2001). "S is for Entropy. U is for Energy. What Was Clausius Thinking?" (PDF). Journal of Chemical Education. 78 (4): 505. Bibcode:2001JChEd..78..505H. doi:10.1021/ed078p505. Retrieved 2014-03-17.
5. Thomson, Sir W; Foster, Professor GC; Maxwell, Professor JC; Stoney, Mr GJ; Jenkin, Professor Fleeming; Siemens, Dr; Bramwell, Mr FJ (September 1873). Everett, Professor, ed. First Report of the Committee for the Selection and Nomenclature of Dynamical and Electrical Units. Forty-third Meeting of the British Association for the Advancement of Science. Bradford: John Murray. p. 224. Retrieved 2014-03-17.
6. Jerrard, H.G.; McNeill, D.B. (2012-06-12) [1963]. A Dictionary of Scientific Units - Including dimensionless numbers and scales (5 ed.). Chapman and Hall Ltd., reprint: Springer Science & Business Media. ISBN 9400941110. 9789400941113. Retrieved 2015-02-15.
7. Cardarelli, François (1999) [1966]. Scientific unit conversion: A practical guide to metrication (2 ed.). Springer-Verlag London Limited. doi:10.1007/978-1-4471-0805-4. ISBN 978-1-85233-043-9. 1447108051, 9781447108054. Retrieved 2015-08-25.
8. Cardarelli, François (2003). Encyclopaedia of Scientific Units, Weights and Measures. Springer-Verlag London Ltd. ISBN 978-1-4471-1122-1.
9. Roberts, Lathrop Emerson; Harkins, William Draper; Clark, George Lindenberg (2013-07-01) [1922]. 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. University of Chicago Digital Preservation Collection. University of Chicago. Retrieved 2015-08-25.
10. Holmes, Harry N. (1925). Colloid Symposium Monograph - Papers Presented at the Second National Symposium on Colloid Chemistry, Northwestern University, June, 1924. 2. The Chemical Catalog Company, Inc. Retrieved 2015-02-15.
11. Partington, James Riddick (2010-02-17) [1949]. An Advanced Treatise on Physical Chemistry: Fundamental principles. The properties of gases. 1. Longmans, Green. Retrieved 2015-08-25.
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