Using Stokes' Law show that the constant terminal velocity v of a sphere of radius r, density `rho` falling vertically under gravity through a viscous fluid of density `sigma` and co-efficient of viscosity `eta` is given by-
` v = (2/9).[{r^2g(rho - sigma)}/eta]`

A sphere of radius 0.25mm and of density 9000kg/m^3 falls through an oil of co-efficient of viscosity 0.2 Ns/m^2 and of density 800kg/m^3 . Find the terminal velocity of the sphere.

The terminal velocity of a copper ball of radius 2.0 mm falling through a tank of oil at 20^@C is 6.5 cm/s. Compute the viscosity of the oil at 20^@C . Given, rho_(oil) = 1.5 xx 10^3 kg//m^3, rho_(copper) = 8.9 xx 10^3 kg//m^3 .

Prove the result that the velocity v of translation of a rolling body (like a ring, disc, cylinder or sphere) at the bottom of an inclined plane of a height h is given by v^2=(2gh)/ (i+k^2^l R^3 Using dynamical consideration (i.e. by consideration of forces and torques). Note k is the radius of gyration of the body about its symmetry axis, and R is the radius of the body. The body starts from rest at the top of the plane.