# Stokes law

Stokes’ law. Stokes’ Law refers to the friction force experienced by spherical objects moving within a viscous fluid in a laminar regime of low Reynolds numbers. It was derived in 1851 by George Gabriel Stokes . In general Stokes’ law is valid in the motion of small spherical particles moving at low speeds.

## Summary

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• 1 Formula
• 2 Applications
• 1 Other applications
• 3 Sources

## Formula

For very small objects, the friction force dominates. Stokes’s law gives us this force for a sphere: Fr = 6πηvr, where r is the radius of the sphere. When a solution precipitates, the sedimentation rate is determined by Stokes’ law and is worth:

v = (2r2 (ρ0 − ρ) g) / 9η

## Applications

Knowing the densities of the sphere, the liquid and the rate of fall, the viscosity can be calculated from the Stokes law formula. Several balls are used to improve the precision of the experiment. The technique is used in industry to verify the viscosity of products, in cases such as glycerin. Stokes’ law is also important for the compression of the movement of microorganisms in a fluid, as well as sedimentation processes due to the gravity of small particles and organisms in aquatic environments.

### Other apps

• Settler design
• Crude oil desalination plant design (to remove the salt water that is emulsified)
• In the study of aerosols.
• In many types of characterization of materials such as solid catalysts, polymers, etc.