Stokes' Law
A mathematical law expressing viscous drag force experienced by small spherical particles moving at low speeds through a viscous fluid.
Governing formula
Fd = 6 π η r v
SI unit
N
In depth
Valid for laminar flow at low Reynolds numbers (Re < 1). Drag is directly proportional to fluid viscosity η, sphere radius r, and speed v.
Examples in the real world
Determining terminal falling speed of tiny fog water droplets in air or blood cells sedimenting in plasma.