Number density in physics is a subtle generalization of the concept of density and refers to the number of objects (particles, sound waves, galaxies, etc.) per volume.

Number density can be written as

$n\; =\; \backslash frac\{N\}\{V\}$

where n is the number density, N is the total number of entities and V is the volume.

Conversely, the total number of entities can be written as

$\backslash int\_V\; n\backslash ;d\backslash tau\; =\; N$

where $d\backslash tau$ is a volume element.

The number density of solutes in a solvent is called concentration.

Physical quantity

Nombre volumique de molécules