Length is defined as the straight-line distance between two points along an object. The SI unit of length is the meter, while the cgs system of units takes the centimeter as the base unit. In the British engineering system of units, lengths are measured in inches, feet, yards, and miles, with 1 mile = 5280 feet, 1 yard = 3 feet, and 1 foot = 12 inches.
In special relativity, the linear expansion of of bar of initial length is given by
where is the thermal expansion coefficient, is the temperature change.
Ångström, Arpent Length, Astronomical Unit
