# Stokes' law

Stokes' law is a formula that gives the terminal
velocity at which particles fall in a fluid (liquid or gas). For particles of radius *r* (less than 0.1millimeter) the
terminal velocity is 2(*d*_{1} - *d*_{2})*gr*^{ 2}/9ρ, where *d*_{1} and *d*_{2} are the densities of the particle and the fluid, *g* is the acceleration
due to gravity, and ρ is the viscosity of the fluid. It is named after
George Stokes.