Stokes' law

Statement

The viscous force exerted by a fluid on a spherical object flowing through it with a very small Reynolds number (so that we can apply the Stokes flow model) is given in magnitude by:

$F=6\pi \mu Rv$

where $v$ is the speed of flow, $R$ is the radius of the sphere, and $\mu$ is the dynamic viscosity for the fluid and the surface of the sphere.