The law refers to the frictional force — also called drag force — exerted on spherical objects with very small Reynolds numbers (e.g., very small particles) in a continuous viscous fluid.
Editors. "George Stokes proves Stokes Law". The Literary Encyclopedia. First published 01 May 2009
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6306, accessed 01 March 2015.]