Fc-10 Viscosity (Stokes Law)

Aim

To demonstrate Stokes law. This states that when a body moves through a fluid the viscous resistive force is proportional to the radius a and its velocity v.

Apparatus

  • Stokes Apparatus
  • Glycerol

Stokes Law 1 Stokes Law 2

Stokes Law Apparatus.

Description

A series of steel ball bearings are arranged in the cradle shown in the diagram of Stokes apparatus. On turning the handle and releasing the balls simultaneously it is seen that the smaller balls take a longer time to fall through the fluid. As a consequence of Stokes law the terminal velocity is proportional to the square of the ball radius. Hence a ball of diameter a will take 4 times as long to fall a given distance than a ball of diameter 2a.