The International System of Units (SI) specifies a set of seven base units from which all other SI units of measurement are derived. These SI derived units are either dimensionless, or can be expressed as a product of one or more of the base units, possibly scaled by an appropriate power of exponentiation.
Many derived units do not have special names. For example, the SI derived unit of area is the square metre (m2) and the SI derived unit of density is the kilogram per cubic metre (kg/m3 or kg m-3). However, 22 derived units are recognized by the SI with special names, which are written in lowercase. However, the symbols for units named after persons, are always written with an uppercase initial letter. For example, the symbol for the hertz is "Hz"; but the symbol for the metre is "m".
Video SI derived unit
Derived units with special names
The International System of Units assigns special names to 22 derived units, which includes two dimensionless derived units, the radian (rad) and the steradian (sr).
Maps SI derived unit
Examples of derived quantities and units
Other units used with SI
Some other units such as the hour, litre, tonne, bar and electronvolt are not SI units, but are widely used in conjunction with SI units.
Supplementary units
Until 1995, the SI classified the radian and the steradian as supplementary units, but this designation was abandoned and the units were grouped as derived units.
See also
- International System of Quantities (ISQ)
- International Vocabulary of Metrology
- Metric prefix
- Metric system
- Planck units
References
Bibliography
- I. Mills, Tomislav Cvitas, Klaus Homann, Nikola Kallay, IUPAC (June 1993). Quantities, Units and Symbols in Physical Chemistry (2nd ed.). Blackwell Science Inc. p. 72. CS1 maint: Multiple names: authors list (link)
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