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(d1 - d2)gr 2/9ρ, where d1 and d2 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.