The **MKS system of units** is a physical system of measurement that uses the metre, kilogram, and second (MKS) as base units.

Adopted in 1889, use of the MKS system of units succeeded the centimetre–gram–second system of units (CGS) in commerce and engineering. The metre and kilogram system served as the basis for the development of the International System of Units (abbreviated SI), which now serves as the international standard. Because of this, the standards of the CGS system were gradually replaced with metric standards incorporated from the MKS system.^{[1]}

An advantage of MKS units is that since the derived units (like joules) are based on MKS units, using MKS units naturally gives answers in the appropriate SI unit. For example, the kinetic energy of an object is defined by 1/2 × mass × velocity^{2}. If the calculation is done in MKS units of kilogram and meters per second then the result is in joules, the SI unit for energy. If the same calculation is done using CGS units the answer is in ergs (1 erg = 10^{−7} joules).

The exact list of units used in the MKS system changed over time. It incorporated base units other than the metre, kilogram, and second in addition to derived units. An incomplete list of the base 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 phrase "cycle per metre" became ill-defined. The cycle did not become an SI unit.)
- Cycle per second
^{[2]} - Cycle per metre (This measure of wavenumber became ill-defined due to the abbreviation of "cycle per second" as "cycle".)

In 1901, Giovanni Giorgi proposed to the Associazione elettrotecnica italiana (AEI) that this system, extended with a fourth unit to be taken from the units of electromagnetism, be used as an international system.^{[3]}
This system was strongly promoted by electrical engineer George A. Campbell.^{[4]}

- Metre–tonne–second system (MTS)
- Foot–pound–second system (FPS)

**^**"Units: CGS and MKS".*www.unc.edu*. Retrieved 2016-01-22.**^**"Proceedings of the American Philosophical Society".**76**(3). 1936: 343–377. JSTOR 984549.**^**Giovanni Giorgi (1901), "Unità Razionali de Elettromagnetismo", in*Atti dell' Associazione Elettrotecnica Italiana*.**^**Brainerd, John G. (1970). "Some Unanswered Questions".*Technology and Culture*. JSTOR.**11**(4): 601. doi:10.2307/3102695. ISSN 0040-165X.

The cycle per second was a once-common English name for the unit of frequency now known as the hertz (Hz). The plural form was typically used, often written cycles per second, cycles/second, c.p.s., c/s, ~, or, ambiguously, just cycles. The term comes from the fact that sound waves have a frequency measurable in their number of oscillations, or cycles, per second.With the organization of the International System of Units in 1960, the cycle per second was officially replaced by the hertz, or reciprocal second, "s−1" or "1/s". Symbolically, "cycle per second" units are "cycle/second", while hertz is "Hz" or "s−1".For higher frequencies, kilocycles (kc), as an abbreviation of kilocycles per second were often used on components or devices. Other higher units like megacycle (Mc) and less commonly kilomegacycle (kMc) were used before 1960

and in some later documents. These have modern equivalents such as kilohertz (kHz), megahertz (MHz), and gigahertz (GHz).

The rate at which aperiodic or stochastic events occur may be expressed in becquerels (as in the case of radioactive decay), not hertz, since although the two are mathematically similar, by convention hertz implies regularity where becquerels implies the requirement of a time averaging operation. Thus, one becquerel is one event per second on average, whereas one hertz is one event per second on a regular cycle.

Cycle can also be a unit for measuring usage of reciprocating machines, especially presses, in which cases cycle refers to one complete revolution of the mechanism being measured (i.e. the shaft of a reciprocating engine).

GramThe gram (alternative spelling: gramme; SI unit symbol: g) (Latin gramma, from Greek γράμμα, grámma) is a metric system unit of mass.

Originally defined as "the absolute weight of a volume of pure water equal to the cube of the hundredth part of a metre [1 cm3], and at the temperature of melting ice" (later at 4 °C, the temperature of maximum density of water). However, in a reversal of reference and defined units, a gram is now defined as one thousandth of the SI base unit, the kilogram, or 1×10−3 kg, which itself is now defined by the International Bureau of Weights and Measures, not in terms of grams, but by "the amount of electricity needed to counteract its force"

Gravitational metric systemThe gravitational metric system (original French term Système des Méchaniciens) is a non-standard system of units, which does not comply with the International System of Units (SI). It is built on the three base quantities length, time and force with base units metre, second and kilopond respectively. Internationally used abbreviations of the system are MKpS, MKfS or MKS (from French mètre–kilogramme-poids–seconde or mètre–kilogramme-force–seconde).

However, the abbreviation MKS is also used for the MKS system of units, which, like the SI, uses mass in kilogram as a base unit.

History of the metric systemThe history of the metric system began in the Age of Enlightenment with simple notions of length and weight taken from natural ones, and decimal multiples and fractions of them. The system was so useful it became the standard of France and Europe in half a century. Other dimensions with unity ratios were added, and it went on to be adopted by the world.

The first practical realisation of the metric system came in 1799, during the French Revolution, when the existing system of measures, which had become impractical for trade, was replaced by a decimal system based on the kilogram and the metre. In the pre-scientific era, the basic units were taken from the natural world: the unit of length, the metre, was based on the dimensions of the Earth, and the unit of mass, the kilogram, was based on the mass of water having a volume of one litre or a cubic decimetre. Reference copies for both units were manufactured in platinum and remained the standards of measure for the next 90 years. After a period of reversion to the mesures usuelles due to unpopularity of the metric system, the metrication of France as well as much of Europe was complete by mid-century.

In the middle of the 19th century, James Clerk Maxwell put forward the concept of a coherent system where a small number of units of measure were defined as base units, and all other units of measure, called derived units, were defined in terms of the base units. Maxwell proposed three base units: length, mass and time. Advances in electromagnetism in the 19th century necessitated new units to be defined, and multiple incompatible systems of such units came into usage; none could be reconciled with the existing system of mechanical units. This impasse was resolved by Giovanni Giorgi, who in 1901 proved that a coherent system that incorporated electromagnetic units had to have an electromagnetic unit as a fourth base unit.

The seminal 1875 Treaty of the Metre resulted in the fashioning and distribution of metre and kilogram artefacts, the standards of the future coherent system that became the SI, and the creation of an international body Conférence générale des poids et mesures or CGPM to oversee systems of weights and measures based on them.

In 1960, the CGPM launched the International System of Units (in French the Système international d'unités or SI) which had six "base units": the metre, kilogram, second, ampere, degree Kelvin (subsequently renamed the "kelvin") and candela; as well as 16 further units derived from the base units. A seventh base unit, the mole, and six additional derived units were added in succeeding years through the close of the twentieth century. During this period, the metre was redefined in terms of the speed of light, and the second was redefined in terms of the microwave frequency of a cesium atomic clock. Since the end of the 20th century, an effort has been undertaken to redefine the ampere, kilogram, mole and kelvin in terms of invariant constants of physics.

International System of UnitsThe International System of Units (SI, abbreviated from the French Système international (d'unités)) is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units, which are the ampere, kelvin, second, metre, kilogram, candela, mole, and a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system also specifies names for 22 derived units, such as lumen and watt, for other common physical quantities.

The base units are derived from invariant constants of nature, such as the speed of light in vacuum and the triple point of water, which can be observed and measured with great accuracy, and one physical artefact. The artefact is the international prototype kilogram, certified in 1889, and consisting of a cylinder of platinum-iridium, which nominally has the same mass as one litre of water at the freezing point. Its stability has been a matter of significant concern, culminating in a revision of the definition of the base units entirely in terms of constants of nature, scheduled to be put into effect on 20 May 2019.Derived units may be defined in terms of base units or other derived units. They are adopted to facilitate measurement of diverse quantities. The SI is intended to be an evolving system; units and prefixes are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves. The most recent derived unit, the katal, was defined in 1999.

The reliability of the SI depends not only on the precise measurement of standards for the base units in terms of various physical constants of nature, but also on precise definition of those constants. The set of underlying constants is modified as more stable constants are found, or may be more precisely measured. For example, in 1983 the metre was redefined as the distance that light propagates in vacuum in a given fraction of a second, thus making the value of the speed of light in terms of the defined units exact.

The motivation for the development of the SI was the diversity of units that had sprung up within the centimetre–gram–second (CGS) systems (specifically the inconsistency between the systems of electrostatic units and electromagnetic units) and the lack of coordination between the various disciplines that used them. The General Conference on Weights and Measures (French: Conférence générale des poids et mesures – CGPM), which was established by the Metre Convention of 1875, brought together many international organisations to establish the definitions and standards of a new system and standardise the rules for writing and presenting measurements. The system was published in 1960 as a result of an initiative that began in 1948. It is based on the metre–kilogram–second system of units (MKS) rather than any variant of the CGS. Since then, the SI has been adopted by all countries except the United States, Liberia and Myanmar.

MKSMKS may refer to:

MKS system of units of measurement based on the metre, kilogram, and second

MKS (Switzerland), a broker of precious metals

MKS Inc., a software vendor (formerly Mortice Kern Systems)

Lincoln MKS, an automobile produced by the Lincoln division of Ford Motor Company

Marks & Spencer, stock symbol MKS

McKusick–Kaufman syndrome, a rare human genetic condition

Moscow Korean School, a Korean international school in Moscow, Russia

Mutya Keisha Siobhan, an English girl group

Międzyzakładowy Komitet Strajkowy or Inter-Enterprise Strike Committee, formed in Gdańsk Shipyard, Poland in 1980

.mks, a file extension for the Matroska open standard free container format

Maxwell (unit)The maxwell (symbol: Mx) is the CGS (centimetre-gram-second) unit of magnetic flux (Φ).

Metre ConventionThe Metre Convention (French: 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, Brazil, Denmark, France, Germany, Italy, Peru, Portugal, Russia, Spain, Sweden and Norway, Switzerland, Ottoman Empire, United States of America, and Venezuela). The treaty created the International Bureau of Weights and Measures (BIPM), an intergovernmental organization under the authority of the General Conference on Weights and Measures (CGPM) and the supervision of the International Committee for Weights and Measures (CIPM), that coordinates international metrology and the development of the metric system.

As well as founding the BIPM and laying down the way in which the activities of the BIPM should be financed and managed, the Metre Convention established a permanent organizational structure for member governments to act in common accord on all matters relating to units of measurement.

The three organs of the BIPM are:

The General Conference on Weights and Measures (Conférence générale des poids et mesures or CGPM) – the plenary organ of the BIPM which consists of the delegates of all the contracting Governments;

The International Committee for Weights and Measures (Comité international des poids et mesures or CIPM) – the direction and supervision body of the BIPM that is made of 18 prominent metrologists from 18 different Member States;

The International Bureau of Weights and Measures (Bureau international des poids et mesures or BIPM) – the headquarters of the BIPM located at Sèvres, France that has custody of the International Prototype Kilogram and houses the secretariat for this organization and hosts its formal meetings.Only States can be Members as per the Metre Convention. In addition to Member status, the General Conference on Weights and Measures (CGPM) created in 1999 the status of Associate of the CGPM open to States and Economic Entities to enable them to participate in some activities of the BIPM through their National Metrology Institutes (NMIs). Membership of the convention requires payment of substantial fees. Failure to pay these over a span of years, without any expectation of a payment agreement, has caused a number of nations such as North Korea to be removed from the protocol. As of 7 August 2018, there are 60 Member States and 42 Associate State and Economies.

Initially the Metre Convention was only concerned with the units of mass and length but, in 1921, at the 6th meeting of the General Conference on Weights and Measures (CGPM), it was revised and it extended the scope and responsibilities of the BIPM to other fields in physics. In 1960, at the 11th meetings of the CGPM, the system of units it had established was named the International System of Units, with the abbreviation SI.

Metric engine (American expression)A metric engine is an American expression which refers to an internal combustion engine, often for automobiles, whose underlying engineering design is based on a metric system of units, particularly SI.

As American industry converted from traditional units to SI in the late 20th century, the automotive industry responded by transitioning its auto and engine designs to be "metric" rather than "English".

Newton (unit)The newton (symbol: N) is the International System of Units (SI) derived unit of force. It is named after Isaac Newton in recognition of his work on classical mechanics, specifically Newton's second law of motion.

See below for the conversion factors.

Otto cycleAn Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile engines.The Otto cycle is a description of what happens to a mass of gas as it is subjected to changes of pressure, temperature, volume, addition of heat, and removal of heat. The mass of gas that is subjected to those changes is called the system. The system, in this case, is defined to be the fluid (gas) within the cylinder. By describing the changes that take place within the system, it will also describe in inverse, the system's effect on the environment. In the case of the Otto cycle, the effect will be to produce enough net work from the system so as to propel an automobile and its occupants in the environment.

The Otto cycle is constructed from:

Top and bottom of the loop: a pair of quasi-parallel and isentropic processes (frictionless, adiabatic reversible).

Left and right sides of the loop: a pair of parallel isochoric processes (constant volume).The isentropic process of compression or expansion implies that there will be no inefficiency (loss of mechanical energy), and there be no transfer of heat into or out of the system during that process. Hence the cylinder, and piston are assumed impermeable to heat during that time. Work is performed on the system during the lower isentropic compression process. Heat flows into the Otto cycle through the left pressurizing process and some of it flows back out through the right depressurizing process. The summation of the work added to the system plus the heat added minus the heat removed yields the net mechanical work generated by the system.

Outline of the metric systemThe following outline is provided as an overview of and topical guide to the metric system:

Metric system – various loosely related systems of measurement that trace their origin to the decimal system of measurement introduced in France during the French Revolution.

Tesla (unit)The tesla (symbol T) is a derived unit of the magnetic induction (also, magnetic flux density) in the International System of Units.

One tesla is equal to one weber per square metre. The unit was announced during the General Conference on Weights and Measures in 1960 and is named in honour of Nikola Tesla, upon the proposal of the Slovenian electrical engineer France Avčin.

The strongest fields encountered from permanent magnets are from Halbach spheres and can be over 4.5 T. The record for the highest sustained pulsed magnetic field has been produced by scientists at the Los Alamos National Laboratory campus of the National High Magnetic Field Laboratory, the world's first 100-tesla non-destructive magnetic field. In September 2018 researchers at the University of Tokyo generated a field of 1200 T which lasted in the order of 100 microseconds using the electromagnetic flux-compression technique.

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