# Length (physics)

Physical size
Surname length
Formula symbol ${\ displaystyle l, s}$
Size and
unit system
unit dimension
SI m L.
cgs cm L.
Planck Planck length L.
Astronomic lj , AE , pc L.
diameter (d), circumference (u), wavelength (λ), u. v. a.

The length is a physical quantity that indicates the extent of physical objects and their distances from one another. The symbol for length is the lower case letter , its SI unit is the meter . A formula symbol is usually used for the length of paths and curves . In the SI system, the length is a basic quantity . ${\ displaystyle l}$ ${\ displaystyle \ mathrm {m}}$${\ displaystyle s}$

The length measurement is carried out by comparing the length to be measured with scales of known length. The length of the distances between two points or a scale is considered constant in classical physics. In the special theory of relativity , however, the length depends on the relative state of motion of the respective observer; one speaks of a relativistic length contraction .

## etymology

The noun mhd. Lenge , ahd. Lengī , like the adjective lang ( mhd. Lanc , ahd. Lang ), goes back to idg. Longho-s "lang".