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 a ...

(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 pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. E ...

. 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 of ...

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 A base unit (also referred to as a fundamental unit) is a unit adopted for measurement of a '' base quantity''. A base quantity is one of a conventionally chosen subset of physical quantities, where no quantity in the subset can be expressed in ter ...

, it is equal to one

gram The gram (originally gramme; SI unit symbol g) is a Physical unit, 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 wate ...

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⋅cm²/s²). It is thus equal to 10⁻⁷

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 ligh ...

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 William Draper Harkins (December 28, 1873 – March 7, 1951) was an American physical chemist, noted for his contributions to surface chemistry and nuclear chemistry. Harkins researched the structure of the atomic nucleus and was the first to p ...

proposed the name

micri- ''Micri-'' (unit symbol ''mc-'') is an archaic non- SI decimal metric prefix for 10−14. It was proposed as a prefix for the CGS-unit of energy, the erg. The ''micrierg'' was proposed in 1922 by William Draper Harkins as a unit of energy equatin ...

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 ...

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 Surface science is the study of physical and chemical phenomena that occur at the interface of two phases, including solid–liquid interfaces, solid–gas interfaces, solid–vacuum interfaces, and liquid–gas interfaces. It includes the fiel ...

. 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 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 ...

References

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

History

See also

References