Stokes' law can refer to:

• Stokes' law for friction force
• Stokes' law (sound attenuation) law describing attenuation of sound in Newtonian liquids

For integration, see Stokes' theorem.

In 1851, George Gabriel Stokes derived an expression, now known as Stokes' law, for the frictional force – also called drag force – exerted on spherical  objects with very small Reynolds numbers (i.e. very small particles) in a viscous fluid. Stokes' law is derived by solving the Stokes flow limit for small Reynolds numbers of the Navier–Stokes equations:

The force of viscosity on a small sphere moving through a viscous fluid is given by:

where F_d is the frictional force – known as Stokes' drag – acting on the interface between the fluid and the particle, µ is the dynamic viscosity, R is the radius of the spherical object, and V is the flow velocity relative to the object. In SI units, F_d is given in Newtons, µ in Pa·s, R in meters, and V in m/s.