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SI units

the units of measurement generally accepted for all scientific and technical uses; together they make up the International System of Units. (See also metric system.) The abbreviation SI, from the French Système International d'Unités, is used in all languages. There are seven base SI units, defined by specified physical measurements, and two supplementary units. Units are derived for any other physical quantities by multiplication and division of the base and supplementary units. The derived units with special names are shown in the accompanying table.

SI is a coherent system. This means that units are always combined without conversion factors. The derived unit of velocity is the meter per second (m/s); the derived unit of volume is the cubic meter (m3). If you know that pressure is force per unit area, then you know that the SI unit of pressure (the pascal) is the unit of force divided by the unit of area and is therefore equal to 1 newton per square meter.

The metric prefixes can be attached to any unit in order to make a unit of a more convenient size. The symbol for the prefix is attached to the symbol for the unit, e.g., nanometer (nm) = 10−9 m. The units of mass are specified in terms of the gram, e.g., microgram (μg) = 10−9 kg.

Only one prefix is used with a unit; the use of units such as the millimicrometer is no longer acceptable. When a unit is raised to a power, the power applies to the prefix as well, e.g., a cubic millimeter (mm3) = 10−9 m3. When a prefix is used with a ratio unit, it should be in the numerator rather than in the denominator, e.g., kilometers/second (km/s) rather than meters/millisecond (m/ms). Only prefixes denoting powers of 103 are normally used. Hecto-, deka-, deci-, and centi- are usually attached only to the metric system units gram, meter, and liter.

Owing to the force of tradition, one noncoherent unit, the liter, equal to 10−3 m3, or 1 dm3, is generally accepted for use with SI. The internationally accepted abbreviation for liter is the letter l; however, this can be confused with the numeral 1, especially in typescript. For this reason, the capital letter L is also used as a symbol for liter. The lower case letter is generally used with prefixes, e.g., dl, ml, fl. The symbols for all other SI units begin with a capital letter if the unit is named after a person and with a lower case letter otherwise. The name of a unit is never capitalized.


Charles A. de, French physicist, 1736-1806. See: coulomb.

cou·lomb (C, Q),

The unit of electrical charge, equal to 3 × 109 electrostatic units; the quantity of electricity delivered by a current of 1 A in 1 s equal to 1/96,485 faraday.
[CA de Coulomb, Fr. physicist, 1736-1806]


/cou·lomb/ (C) (koo´lom) the SI unit of electric charge, defined as the quantity of electric charge transferred across a surface by 1 ampere in 1 second.

coulomb (C)

Etymology: Charles A. de Coulomb, French physicist, 1736-1806
the SI unit of electricity equal to the quantity of charge transferred in 1 second across a conductor in which there is a constant current of 1 ampere, or 1 ampere-second.


(C) (kū'lom)
The SI unit of electrical charge, equal to 3 × 109 electrostatic units; the quantity of electricity delivered by a current of 1 ampere in 1 sec; equal to 1/96,485 faraday; also used to measure radiation.
See also: roentgen
[CA de Coulomb, Fr. physicist, 1736-1806]


1. the unit of electrical charge, defined as the quantity of electrical charge transferred by 1 ampere in 1 second. Symbol C.
2. the SI unit of exposure to radiation. 1 coulomb per kilogram = 3876 roentgen; abbreviated C/kg.
References in periodicals archive ?
Columb wants to see the rules strengthened to allow stewards the power to fine riders up to a maximum of A$100,000 and ban them for up to six months.
Sentencing father-of-three Columb, Judge John Curran said: ``This was a dreadful robbery.
According to information gathered from Arabic-language social media, and our in-country source network, efforts to target the ISIL's sources of revenue are paying off," Columb Strack said, adding that "Tax revenues are much harder for the US-led coalition to target without having a substantial negative impact on the civilian population, and would most likely be counterproductive.
It did feel like we were starting all over again but there was a terrific feeling of community that we must not let this stop us," says Columb, a semi-retired engineer.
Barclays Plc (LSE: BARC) has announced a plan to close its St Columb Major branch before the end of the year.
Patrick Columb, 17, swiped PS40 which had been raised by the Society of St Vincent de Paul in West Lothian to help people in need.
After his scare against Ryan Vaughan, Vauxhall cruiserweight Wayne Adeniyi will look to start fast against former Novices champion Darryl Cullerton, while Kirkby super-heavy John Winters gets his 2010 campaign underway against Columb Henry.
Sian Columb, 37, of Appletree Avenue, Dinas, Tonypandy, was given a 12-month conditional discharge after pleading guilty to stealing 12 miscellaneous toiletries, a bra, a tub of butter, a box of chocolates and an MP3 player and pair of headphones from Asda.
44am after the celebration in St Columb Minor, near Newquay, a week ago.
Others en route to Manchester are: CLASS A: Ben Hughes (Hetton), Anthony Nelson (Horsley Hill), Keith Jones (Spennymoor), Michael McCormella (Hedfit, Jarrow), Simon Peverley (Lambton Street) Chris Bryan (Hylton Castle), Henry Columb (Silksworth).
Prominent Melbourne owner Nick Columb won a protracted duel to buy a daughter of the outstanding sire for AEUR400,000 (pounds 160,920/EUR237,120).
And at St Columb Minor Church, near Newquay, his widow, Helen, told mourners: "We had only just celebrated our 15th wedding anniversary and his last text read, '15 years and 1 day.