The phenomenon of Brownian motion was first observed by Robert Brown in the form of random zig-zag motion of pollen grains suspended in water.

Colloidal particles show Brownian motion and it is responsible for the stability of the particle. Colloidal particles in a sol are continuously bombarded by the molecules of the dispersion medium on all sides due to which some impacts are created. These impacts are not equal in every direction. As a result, the sol particles show random or zig-zag movements. This random or zig-zag motion of the colloidal particles in a sol is called Brownian motion or Brownian motion.