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 (), a
Greek word meaning 'work' or 'task'.
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
The second (symbol: s) is the unit of time in the International System of Units (SI), historically defined as of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds ...
-squared (g⋅cm
2/s
2). It is thus equal to 10
−7 joules or 100 nanojoules (
nJ) in
SI units.
* 1 erg = =
* 1 erg = = =
* 1 erg = =
* 1 erg = =
* 1 erg =
History
In 1864,
Rudolf Clausius proposed the Greek word () for the unit of energy, work and heat.
In 1873, a committee of the
British Association for the Advancement of Science
The British Science Association (BSA) is a charity and learned society founded in 1831 to aid in the promotion and development of science. Until 2009 it was known as the British Association for the Advancement of Science (BA). The current Chie ...
, 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
In surface science, surface free energy (also interfacial free energy or surface energy) quantifies the disruption of intermolecular bonds that occurs when a surface is created. In solid-state physics, surfaces must be intrinsically less energe ...
of
molecules
in
surface chemistry.
It would equate to 10
−14 erg,
the equivalent to 10
−21 joule.
The erg has not been a valid unit since 1 January 1978 when the
European Economic Community
The European Economic Community (EEC) was a regional organization created by the Treaty of Rome of 1957,Today the largely rewritten treaty continues in force as the ''Treaty on the functioning of the European Union'', as renamed by the Lisb ...
ratified a directive of 1971 that implemented the
International System (SI) as agreed by the
General Conference of Weights and Measures. It is still widely used in
astrophysics
Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline said, Astrophysics "seeks to ascertain the nature of the h ...
and sometimes in
mechanics.
See also
*
Foe (unit), relative measure for energy released by a supernova
*
Lumen second
In photometry, the lumen second (lm⋅s) is the unit of luminous energy in the International System of Units (SI). It is based on the lumen, the SI unit of luminous flux, and the second, the SI base unit of time.
The lumen second is sometime ...
, for the lumerg and lumberg units
*
Metre–tonne–second system of units
References
[
]
[
]
{{CGS units
Units of energy
Centimetre–gram–second system of units