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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]


(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]
References in periodicals archive ?
Quantised inertia predicts that deuterons in cracks or defects less than 28 nm in width should heat up enough that, through mutual sheltering, they feel an attractive radiation recoil force that overcomes their Coulomb barrier, allowing fusion.
So, while there is a(n electromagnetic) field around the conductor, the definition of current is the movement of electrons through the conductor, driven typically by coulomb forces.
Zarrinkamar, "Exact solutions of the Dirac equation with Poschl--Teller doublering-shaped Coulomb potential via the Nikiforov--Uvarov method," Chinese Physics B, vol.
The coordinates [x.sub.j] of the negative charges, expressed in terms of these difference coordinates with primes by (4) for [eta] = [[xi].sup.*], satisfy the Coulomb equation of motion (3).
For the wall pressure of squat silos, the modified Coulomb theory is the most conservative.
The experiment started with an ideal Coulomb crystal and then the complexity was increased to match real life processes inside the stars.
Caption: Figure 8: Correlation graph between charge passed coulomb versus chloride diffusion coefficient: (a) GGBFS in HPC and (b) FA in HPC.
A Coulomb friction model used to simulate friction behaviour in this paper can be formulated as
Data on differences in spectra associated with different isotopes of heavy elements is being accumulated rapidly at present and may in the future prove an important source of knowledge about the nucleus, but at present not much more can be said than that reasonable assumed departures from the Coulomb law in the neighbourhood of the nucleus can account in order of magnitude for the observed effects.
Under low-temperature condition (such as 77 K), it was found that there was Coulomb blockade phenomenon in nanocrystalline metal with island structures [1, 2].