Mks system of units

Mks system of units

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The MKS system of units is a physical system of units that expresses any given measurement using fundamental units of the metre
Metre
The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology...

, kilogram
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...

, and/or second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....

 (MKS).

Historically the MKS system of units succeeded the cgs system of units and laid the blueprint for the International System of Units
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

, which now serves as the international standard. Therefore the exact composition of the MKS system is a historical issue. As a matter of historical record the MKS system incorporated fundamental units other than the metre
Metre
The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology...

, kilogram
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...

, and second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....

 in addition to derived units. An incomplete list of the fundamental and derived units appears below. Since the MKS system of units never had a governing body to rule on a standard definition, the list of units depended on different conventions at different times.
  • cycle (This dimensionless quantity became synonymous with the term "cycle per second" as an abbreviation. This circumstance confused the exact definition of the term cycle. Therefore the term "cycle per metre" became ill-defined. The cycle did not become an SI unit.)
  • cycle per second
    Cycle per second
    The cycle per second was a once-common unit of frequency.With the organization of the International System of Units in 1960, the cycle per second was officially replaced by the hertz, or reciprocal second—i.e. the cycle in 'cycle per second' was dropped...

  • cycle per metre (This measure of wavenumber
    Wavenumber
    In the physical sciences, the wavenumber is a property of a wave, its spatial frequency, that is proportional to the reciprocal of the wavelength. It is also the magnitude of the wave vector...

    became ill-defined due to the abbreviation of "cycle per second" as "cycle".)

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