# Stokes's law

From AMS Glossary

## Stokes's law

An approximate relation, valid at low Reynolds numbers, for the drag force on a sphere moving relative to a fluid.

According to this law the drag on a sphere of radius Stokes's law is a good approximation for the drag on cloud droplets falling in air, but not on raindrops.

*a*with speed*v*in a fluid with dynamic viscosity μ is