# International System of Units

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## International System of Units

**International System of Units,**officially called the Système International d'Unités, or SI, system of units adopted by the 11th General Conference on Weights and Measures (1960). It is based on the metric system. The basic units of length, mass, and time are those of the mks system of metric units: the meter, kilogram, and second. Other basic units are the ampere of electric current, the kelvin of temperature (a degree of temperature measured on the Kelvin temperature scale), the candela, or candle, of luminous intensity, and the mole, used to measure the amount of a substance present. All other units are derived from these basic units.

### Bibliography

See U.S. National Bureau of Standards, Spec. Pub. 330, *International System of Units* (1971).

*The Great Soviet Encyclopedia*(1979). It might be outdated or ideologically biased.

## International System of Units

(Système International d’Unitées), a system of units of physical quantities, approved by the Eleventh General Conference of Weights and Measures (1960). The abbreviated designation of the system is SI. The International System of Units was developed to replace a complex set of systems of units and individual subsidiary units that had grown out of the metric system of measures and also to simplify the use of units. The advantages of the system include universality (it embraces all branches of science and technology) and coherence (that is, the consistency of derived units, which are found from equations without proportionality constants). As a result, if the magnitudes of all quantities are expressed in SI units, calculations may be carried out without introducing into the formulas any coefficients that depend on the choice of units.

The international and Russian names and symbols for base, supplementary, and some derived units of the International System of Units are given in Table 1. Russian symbols are given in accordance with the current GOST’s (All-Union State Standards); designations envisioned in the GOST Units of Physical Quantities Draft are also given. Definitions of base and supplementary units and their quantitative relationships are given in articles on the respective units.

The first three basic units (the meter, kilogram, and second) make possible the development of coherent derived units for quantities of a mechanical nature; the rest have been added to permit the formation of derived units for quantities that cannot be reduced to mechanical quantities (the ampere for electric and magnetic quantities, the kelvin for thermal quantities, the candela for quantities of light, and the mole for quantities in physical chemistry and molecular physics). The supplementary units radian and steradian are used in forming derived units of quantities depending on a plane angle or solid angle.

The International System of Units provides special prefixes to form the names of decimal multiple or fractional units: deci- (to form units equal to 10^{-1} of the original unit), centi- (10^{-2}), milH- (10^{-3}), micro- (10^{-6}), nano- (10^{-9}), pico- (10^{-12}), femto(10^{-15}), and atto- (l0^{-18}); and decca- (10^{1}), hecto- (10^{2}), kilo(10^{3}), mega- (10^{6}), giga- (10^{9}), and tera- (10^{12}).

### REFERENCES

Burdun, G. D.*Spravochnikpo Mezhdunarodnoisisteme edinits*. Moscow 1971.

Table 1. Base and derived units of the International System of Units | ||||
---|---|---|---|---|

Designation | ||||

Ouantity | Name of unit | international | Russian | |

Current | Planned | |||

* Formerly “degree Kelvin” (°K) | ||||

Base Units | ||||

Length ........ | meter | m | m | M |

Mass ........ | kilogram | kg | m | kr |

Time ........ | second | s | cek | c |

Electric current ........ | ampere | A | a | A |

Thermodynamic temperature ........ | kelvin* | K | K | K |

Luminous intensity ........ | candela | cd | k∂ | kд |

Amount of substance ........ | mole | mol | mojb | MOAb |

Suplimentary Units | ||||

Plane angle ........ | radian | rad | pa∂ | paд |

Solid angle ........ | steradian | sr | cmep | cp |

Derived units | ||||

Area ........ | square meter | m^{2} | M^{2} | M^{2} |

Volume, capacity ........ | cubic meter | m^{3} | M^{3} | M^{3} |

Frequency ........ | hertz | Hz | Гu | ѓЦ |

Velocity ........ | meter per second | m/s | M/cek | M/C |

Acceleration ........ | meter per second squared | m/s^{2} | M/cek^{2} | M/C^{2} |

Angular velocity ........ | radian per second | rad/s | pa∂/cek | paд/C |

Angular acceleration ........ | radian per second squared | rad/s^{2} | pa∂/cek^{2} | paд/C^{2} |

Density ........ | kilogram per cubic meter | kg/m^{3} | κǀ/M^{3} | kГ/m^{3} |

Force ........ | newton | N | ǀǀ | H |

Pressure, mechanical stress ........ | pascal | Pa | IIo(n/M^{2}) | Лa(H/M^{2}) |

Kinematic viscosity ........ | square meter per second | m^{2}/s | M^{2}/ceκ | M^{2}/C |

Dynamic viscosity ........ | pascal-second | Pa·sec | IIu·ceκ | Πa·C |

Work, energy, quantity of heat ........ | joule | J | ∂M | дж |

Power ........ | watt | W | BM | BT |

Quantity of electricity ........ | coulomb | C | κ | КA |

Voltage, electromotive force ........ | volt | V | B | B |

Electric field strength ........ | volt per meter | V/m | B/M | B/M |

Electric resistance ........ | ohm | Ω | OM | OM |

Electric conductance ........ | Siemens | S | cǀǀM | CM |

Electric capacitance ........ | farad | F | Ф | Ф |

Magnetic flux ........ | weber | Wb | Bõ | B6 |

Inductance ........ | henry | H | ǀǀǀ | Г |

Magnetic flux density ........ | tesla | T | MA | T |

Magnetic field strength ........ | ampere per meter | A/m | a/m | A/M |

Magnetomotive force ........ | ampere | A | a | A |

Entropy ........ | joule per kelvin | J/K | ∂M/К | дж/К |

Specific heat ........ | joule per kilogram-kelvin | J/(kg·K) | ∂M/(κi·К) | дж/(κГ·К) |

Thermal conductivity ........ | watt per meter-kelvin | W/(m·K) | 6m/(m·К) | BT/(M·К) |

Radiation intensity ........ | watt per steradian | W/sr | 6m/cmep | BT/cp |

Wave number ........ | unit per meter | m^{-1} | m^{-1} | M^{-1} |

Luminous flux ........ | lumen | Im | ǀm | AM |

Brightness ........ | candela per square meter | cd/m^{2} | κ∂/M^{2} | κд/M^{2} |

Illuminance ........ | lux | Ix | ǀκ | Aκ |

*Le Système International d’unitées (SI), Edition du Bureau International des poids et mesures*. Paris, 1970.

K. P. SHIROKOV