The MKS system of units is a physical

system of measurement A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Systems of measurement i ...

that uses the

metre The metre (British spelling) or meter (American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its prefi ...

, kilogram, and second (MKS) as base units. It forms the base of the International System of Units (SI), though SI has since been redefined by different fundamental constants.

History

By the 19th century, there was a demand by scientists to define a

coherent system of units A coherent system of units is a system of units of measurement used to express physical quantities that are defined in such a way that the equations relating the numerical values expressed in the units of the system have exactly the same form, in ...

. A coherent system of units is a system of units where all units are directly derived from a set of base units, without the need of any conversion factors. The United States customary units are an example of a non-coherent set of units. In 1874, the British Association for the Advancement of Science (BAAS) introduced the CGS system, a coherent system based on the

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 ...

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 ...

and second. These units were inconvenient for electromagnetic applications, since

electromagnetic In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions o ...

units derived from these did not correspond to the commonly used ''practical units'', such as the

volt The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827). Defin ...

, ampere and ohm. After the

Metre Convention The Metre Convention (french: link=no, Convention du Mètre), also known as the Treaty of the Metre, is an international treaty that was signed in Paris on 20 May 1875 by representatives of 17 nations (Argentina, Austria-Hungary, Belgium, Brazi ...

of 1875, work started on international prototypes for the kilogram and the metre, which were formally sanctioned by the General Conference on Weights and Measures (CGPM) in 1889, thus formalizing the MKS system by using the kilogram and metre as base units. In 1901, Giovanni Giorgi proposed to the ''Associazione elettrotecnica italiana'' (AEI) that the MKS system, extended with a fourth unit to be taken from the practical units of

electromagnetism In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of ...

, such as the volt, ohm or ampere, be used to create a coherent system using practical units. This system was strongly promoted by electrical engineer George A. Campbell. The CGS and MKS systems were both widely used in the 20th century, with the MKS system being primarily used in practical areas, such as commerce and engineering. The International Electrotechnical Commission (IEC) adopted Giorgi's proposal as the ''M.K.S. System of Giorgi'' in 1935 without specifying which electromagnetic unit would be the fourth base unit. In 1939, the Consultative Committee for Electricity (CCE) recommended the adoption of Giorgi's proposal, using the ampere as the fourth base unit. This was subsequently approved by the CGPM in 1954. The rmks system (rationalized metre–kilogram–second) combines MKS with rationalization of electromagnetic equations. The MKS system with the ampere as a fourth base unit, is sometimes referred to as the MKSA system. This system was extended by adding the

kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phy ...

and

candela The candela ( or ; symbol: cd) is the unit of luminous intensity in the International System of Units (SI). It measures luminous power per unit solid angle emitted by a light source in a particular direction. Luminous intensity is analogous t ...

as base units in 1960, thus forming the International System of Units. The

mole Mole (or Molé) may refer to: Animals * Mole (animal) or "true mole", mammals in the family Talpidae, found in Eurasia and North America * Golden moles, southern African mammals in the family Chrysochloridae, similar to but unrelated to Talpida ...

was added as a seventh base unit in 1971.

Derived units

Mechanical units

Electromagnetic units

References

External links