# Erg

erg | |
---|---|

Unit system | CGS units |

Unit of | energy |

Symbol | erg |

Derivation | 1 erg = 1 dyn⋅cm |

Conversions | |

1 erg in ... | ... is equal to ... |

CGS base units | 1 cm^{2}⋅g⋅s^{−2} |

SI units | 10^{−7} J |

British Gravitational System | 7.375621×10^{−8} ft⋅lbf |

The **erg** is a unit of energy equal to 10^{−7} joules (100 nJ). 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'.^{[1]}

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⋅cm^{2}/s^{2}). It is thus equal to 10^{−7} joules or 100 nanojoules (nJ) in SI units.

## History

In 1864, Rudolf Clausius proposed the Greek word ἐργον (*ergon*) for the unit of energy, work and heat.^{[2]}^{[3]} 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*.^{[4]}

In 1922, chemist William Draper Harkins proposed the name micri-erg as a convenient unit to measure the surface energy of molecules^{[5]} in surface chemistry.^{[6]}^{[7]} It would equate to 10^{−14} erg,^{[5]}^{[8]}^{[9]}^{[10]}^{[11]} 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^{[12]} when the European Economic Community ratified a directive of 1971 that implemented SI as agreed by the General Conference of Weights and Measures.^{[13]} It is the unit of energy in Gaussian units, which are widely used in astrophysics^{[14]}^{[better source needed]}, applications involving microscopic problems and relativistic electrodynamics,^{[15]} and sometimes in mechanics^{[citation needed]}.

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