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The table usually lists only one name and symbol that is most commonly used. The final column lists some special properties that some of the quantities have, such as their scaling behavior (i.e. whether the quantity is intensive or extensive ), their transformation properties (i.e. whether the quantity is a scalar , vector , matrix or tensor ...
The SI has special names for 22 of these coherent derived units (for example, hertz, the SI unit of measurement of frequency), but the rest merely reflect their derivation: for example, the square metre (m 2), the SI derived unit of area; and the kilogram per cubic metre (kg/m 3 or kg⋅m −3), the SI derived unit of density.
A quantity of dimension one is historically known as a dimensionless quantity (a term that is still commonly used); all its dimensional exponents are zero and its dimension symbol is . Such a quantity can be regarded as a derived quantity in the form of the ratio of two quantities of the same dimension.
These are called coherent derived units, which can always be represented as products of powers of the base units. Twenty-two coherent derived units have been provided with special names and symbols. The seven base units and the 22 coherent derived units with special names and symbols may be used in combination to express other coherent derived ...
Quantity name Definition In SI base units In other SI units SI: Physics: Basic: second [n 1] s: T: time: The duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. s: SI: Physics: Basic: metre: m: L: length: The distance travelled by light ...
New SI: Dependence of base unit definitions on physical constants with fixed numerical values and on other base units that are derived from the same set of constants. Arrows are shown in the opposite direction compared to typical dependency graphs , i.e. a → b {\displaystyle a\rightarrow b} in this chart means b {\displaystyle b} depends on a ...
A unit of measurement, or unit of measure, is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity. [1] Any other quantity of that kind can be expressed as a multiple of the unit of measurement. [2] For example, a length is a physical quantity.
Coherence may be restored, without changing the units, by choosing k = 3.6; then the kilometre per hour is a coherent derived unit, with 1 kmph = 1 m/s, and the metre per second is a non-coherent derived unit, with 1 m/s = 3.6 m/s. A definition of a physical quantity is a statement that determines the ratio of any two instances of the quantity.