On the basis of the Brownian motion, due to constant collisions of molecules of a liquid on dispersed particles, a purely random movement in arbitrary directions is set in motion. well.

The speed of motion depends directly on the particle size. This relationship is described by the Stokes-Einstein formula. More precisely, this formula actually addresses the diffusion coefficient rather than the speed of motion. In addition to the temperature, the viscosity of a liquid is an important constant in the Stokes-Einstein formula.