Stokes law states that the retardation F, due to viscous drag, for a spherical body of radius r, moving with velocity v, in a medium of coefficient of viscosity η is given by

F = 6 π vr η

If ρ be the density of the spherical body and σ , the density of the liquid in which the body is moving, then its terminal velocity is given by

v =

For ρ > σ , the velocity will be downward and for ρ < σ , the velocity will be upwards.

(i) An iron ball is dropped in a long jar containing castor oil. How it will move?