School of Physics Lecture Demonstration Manual

Fc-10 Viscosity (Stokes Law)

Published: Wednesday 06 June 2007 - Updated: Tuesday 29 March 2011


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.



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Stokes Law Pic 1

Stokes Law Pic 2


Stokes Law


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.

Safety notes

Chemical Safety 


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