Write stokes law.

Explanation

When a body moves through a viscous medium, the layer of the medium in contact with the body drift along with it. Hence relative velocity is produced between different layers of fluid and as a result a resistive force acts on the body moving through the medium. This resistance force is known as viscous force.
Viscous force (F) proportional to the velocity (v) and opposite to direction of motion . This force depend on the coefficient of viscosity `(eta)` and radius (r) of sphere.
Scientist Sir George G. Stokes enunciated the viscous drag force on body for viscosity of `eta`, large viscous medium , smooth ,small radius, spherical solid is `F_(v)=6pietarv`. This formula is known as Stokes . law.