SI units

An internationally agreed system of coherent metric units, increasingly used for all scientific and technical purposes. It was developed from the MKS system of units and replaces the CGS and Imperial systems of units. There are seven base units that are arbitrarily defined and dimensionally independent (see Table 1). These include the kelvin and the second. The meter has been redefined but is still a base unit. The base units can be combined by multiplication and/or division to derive other units, such as the watt or the newton (see Table 2). A set of prefixes, including kilo- and micro-, can be used to form decimal multiples or submultiples of the units (see Table 3). Any physical quantity may then be expressed in terms of a number multiplied by the appropriate SI unit for that quantity.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

International System of Units (SI)

A system of units based on the following fundamental quantities: metre, kilogram, second, ampere, kelvin, candela, and mole.

SI units

(Système International d'Unites; International System of Units) A system of standard units of measurement finalized at the 14th General Conference on Weights and Measures in 1971. It is based on seven units of measure, including three from the MKS system (meter-kilogram-second), the ampere for electrical current, the Kelvin for temperature, the candela for luminosity and the mole for molecular weight. See MKS system, amp, Kelvin, candela and mole.

BASIC SI UNITS Quantity        Unit of Measurement

 length (l)      meter (m)
 mass (m)        kilogram (kg)
 time (t)        second (s)
 current (I)     ampere (A)
 temperature     kelvin (K)
 atomic weight   mole (mol)
 luminosity      candela (cd) 


 DERIVED SI UNITS Quantity             Unit of Measurement

 force (f)            newton (N)
 work (W)             joule (J)
 power (P)            watt (W)
 pressure (P)         pascal (pa)
 frequency (f)        Hertz (Hz)
 electric charge (Q)  coulomb (C)
 potential (V)        volt (V)
 capacitance (C)      Farad (F)
 resistance (R)       ohm

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References in periodicals archive

In a historic decision on November 16, last year, more than 60 countries unanimously voted to redefine kilogram (SI unit of weight) along with three other units Kelvin (SI unit of temperature), mole (SI unit of amount of substance), and ampere (SI unit of current).

India adopts new measurement unit for Kilogram, Kelvin, mole, ampere

CVs in DCCT units are lower than CVs in SI units and therefore cannot be directly compared.

Biological variation of hemoglobin [A.sub.1c]: consequences for diagnosing diabetes mellitus

The value of 587 [m/sec] corresponds to one Volt in SI units, the value of 4n/5872 = 3.6 x [10.sup.-5] [kg] corresponds to one Farad in SI units etc.

On the uniform dimension system. Is there the necessity for Coulomb?

While SI units are very similar to metric units, there are subtle differences.

SI cube helps students learn SI units and volume

(1), that the reference constant whose numerical value is fixed when it is expressed in its SI unit Hz is [DELTA]v[([.sup.133]Cs).sub.hfs].

The current SI seen from the perspective of the proposed New SI

There are several other important SI units to become familiar with because they form part of the language soil scientists use in problem solving.

Chapter 3 Metric and International Scientific (SI) units

In deciding whether to provide individualized reports for clients using SI units, you must weigh several issues: Can your LIS do this automatically?

Absolute neutrophil critical values, clot activator tubes, no microscopic on trace blood, and reporting in SI units. (Tips From the Clinical Experts)

The intent of the guide is to convert the values to SI units without creating a need for manufacturers to retool their production facilities and to ensure that SI hardware can be used interchangeably with the hardware already in place on the nation's highways.

Metrication of roadside hardware

As a final note on SI units, it's surprising how often I have found that a letter "t" in a technical manuscript is still used to represent a short ton rather than the SI meaning of metric ton.

Short and sour

An influential decision was made to report IFCC results in SI units [millimoles of Hb [A.sub.1c] per mole of Hb [A.sub.0] (8)], and several countries, predominantly in Europe and the Antipodes, have adopted SI units for Hb [A.sub.1c] (9).

Reporting hemoglobin [A.sub.1c]: do the units matter?

I was under the impression that SI units were the norm throughout the engineering profession, except in the US.

SI should be obligatory