Stokes’ Law

George Stokes gave an empirical law for the magnitude of the tangential backward viscous force F acting on a freely falling smooth spherical body of radius r in a highly viscous liquid of coefficient of viscosity η moving with velocity v. This is known as Stokes’ law.

According to Stokes’ law

F ∝ η r v

F = K η r v

where K is constant of proportionality. It has been found experimentally that K = 6π.

Hence Stokes’ law can be written as

F = 6π η r v