# Friction velocity (shear velocity)

## Description

Friction velocity, is a form by which a shear stress may be re-written in units of velocity. It is useful as a method in fluid mechanics to compare true velocities, such as the velocity of a flow in a stream, to a velocity that relates shear between layers of flow. Shear velocity is used to describe shear-related motion in moving fluids. A general rule is that the shear velocity is about 1/10 of the mean flow velocity.

Related formulas## Variables

u_τ | Friction velocity (m/s) |

τ | shear stress in an arbitrary layer of fluid (N/m^{2}) |

ρ | Density of the fluid (kg/m^{3}) |