 Stokes Law (laminar flow around a sphere)

Stokes Law, named after George Gabriel Stokes, describes the relationship between the frictional force of a sphere moving in a liquid and other quantities (such as particle radius and velocity of the particle). If a sphere or a body moves through a fluid, a friction force must be overcome.

Formula for the calculation of friction force, according to Stokes Law

Provided that the Reynolds number Re is less than 1 (laminar flow), Stokes Law applies:

FR=6*π*η*r*v

where

• FR: friction force to be overcome [N]
• V: Speed of the sphere relative to the liquid or particle velocity [m/s]
• R: Particle radius or radius of the sphere [m]
• Η: Dynamic viscosity [Pa*s=N*s/m²]

Based on the friction force formula, the sedimentation speed can be calculated using Stokes' equation.

Source: Horst Kuchling: Pocketbook of Physics; Published by Fachbuchverlag Leipzig, 16. Edition 1996

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