What causes Brownian motion in colloidal dispersion?

 
 
 Brownian movement may be defined as continuous zig-zag movement of colloidal particles in a colloidal sol. A state of continuous zig-zag motion of colloidal particles appears to be in view due to unbalanced bombardmentof the particles of dispersed phase by molecules of dispersion medium. This Brownian movementstabilises the sol.