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The erg is a unit of energy equal to 10−7
joule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
s (100 nJ). It originated in the
Centimetre–gram–second system of units The centimetre–gram–second system of units (abbreviated CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. All CGS mechanical units ...
(CGS). It has the symbol ''erg''. The erg is not an
SI unit The International System of Units, known by the international abbreviation SI in all languages and sometimes Pleonasm#Acronyms and initialisms, pleonastically as the SI system, is the modern form of the metric system and the world's most wid ...
. Its name is derived from (), a
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
word meaning 'work' or 'task'. An erg is the amount of work done by a force of one
dyne The dyne (symbol: dyn; ) is a derived unit of force specified in the centimetre–gram–second (CGS) system of units, a predecessor of the modern SI. History The name dyne was first proposed as a CGS unit of force in 1873 by a Committee o ...
exerted for a distance of one
centimetre 330px, Different lengths as in respect to the Electromagnetic spectrum, measured by the Metre and its deriveds scales. The Microwave are in-between 1 meter to 1 millimeter. A centimetre (international spelling) or centimeter (American spellin ...
. In the CGS base units, it is equal to one
gram The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...
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 e ...
-squared (g⋅cm2/s2). It is thus equal to 10−7
joule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
s or 100 nanojoules ( nJ) in SI units. * 1 erg = = * 1 erg = = = * 1 erg = = * 1 erg = = * 1 erg =


History

In 1864,
Rudolf Clausius Rudolf Julius Emanuel Clausius (; 2 January 1822 – 24 August 1888) was a German physicist and mathematician and is considered one of the central founding fathers of the science of thermodynamics. By his restatement of Sadi Carnot's principle ...
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 James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish mathematician and scientist responsible for the classical theory of electromagnetic radiation, which was the first theory to describe electricity, magnetism and light ...
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
molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
s 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 Lisbo ...
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 he ...
and sometimes in
mechanics Mechanics (from Ancient Greek: μηχανική, ''mēkhanikḗ'', "of machines") is the area of mathematics and physics concerned with the relationships between force, matter, and motion among physical objects. Forces applied to objects r ...
.


See also

*
Foe (unit) A foe is a unit of energy equal to 1044 joules or 1051 ergs, used to express the large amount of energy released by a supernova. An acronym for "power of] fifty-one ergs", the term was introduced by Gerald E. Brown of Stony Brook University in his ...
, 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 sometimes c ...
, for the lumerg and lumberg units *
Metre–tonne–second system of units The metre–tonne–second or MTS system of units is a system of physical units. It was invented in France, hence the unit names ''sthène'' and ''pièze'', and became its legal system between 1919 and 1961 ("décret" 5 May 1961, "Journal Officiel ...


References

{{CGS units Units of energy Centimetre–gram–second system of units