Physical Quantities & Units

SI base and derived units, homogeneity of equations, prefixes, scalars and vectors, and the treatment of errors and uncertainties.

Physical quantities

Every physical quantity has a numerical magnitude and a unit. The seven SI base quantities and units are:

Base quantity	Symbol	SI unit
mass	$m$	kilogram (kg)
length	$l$	metre (m)
time	$t$	second (s)
electric current	$I$	ampere (A)
temperature	$T$	kelvin (K)
amount of substance	$n$	mole (mol)

Derived units are products/quotients of base units, e.g. the newton: $1\ \text{N} = 1\ \text{kg m s}^{-2}$ , and the joule: $1\ \text{J} = 1\ \text{kg m}^2\,\text{s}^{-2}$ .

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Physical quantities

Every physical quantity has a numerical magnitude and a unit. The seven SI base quantities and units are:

Base quantity	Symbol	SI unit
mass	$m$	kilogram (kg)
length	$l$	metre (m)
time	$t$	second (s)
electric current	$I$	ampere (A)
temperature	$T$	kelvin (K)
amount of substance	$n$	mole (mol)

Derived units are products/quotients of base units, e.g. the newton:

1\ \text{N} = 1\ \text{kg m s}^{-2}

, and the joule:

1\ \text{J} = 1\ \text{kg m}^2\,\text{s}^{-2}