Quantities, units and SI
Quantities, units and SI
In mechanics, a number without a unit is incomplete because 20 m20\,\mathrm{m}20m, 20 s20\,\mathrm{s}20s and 20 m s−120\,\mathrm{m}\,\mathrm{s}^{-1}20ms−1 describe different things. A quantity is something measurable, and a unit tells you the scale used.