Stokes' law describes sedimentation of particles in liquids and can be used to measure viscosity. Particles in liquids achieve terminal velocity quickly. One can measure the time it takes for a particle to fall a certain distance and then use Stokes' law to calculate the viscosity of the liquid. Suppose a steel ball bearing (density 7.8 ? 103kg/m3, diameter 3.2 mm) is dropped in a container of motor oil. It takes 15 s to fall a distance of 0.45 m. Calculate the viscosity of the oil.