brownian movement This phenomenon was first discovered by Botanist Brown, while observing aqueous suspension of fine spores under high power microscope. He found the spores moving to and fro, rapidly and continuously, in an totally haphazard fashion. This irregular motion is known as Brownian movement.

Experiments have shown that the motion of the suspended particles is not due to any chemical or electrical action. The motion becomes more vigorous when temperature is increased or less viscous fluid is chosen. Smaller particles are found to be more agitated than the bigger ones. No two particles are found to be executing the same motion, hence the motion cannot be due to any convection or eddy current.

The phenomenon can be explained if we imagine the suspended particles are like buoys in sea of molecules. Their wild movements are due to impacts of molecules of liquid from all sides, which give rise to resultant unbalanced force acting on the particle in a certain direction. The movements become more vigorous as temperature is raised as the molecules then have higher energy. If the size of the particles is very large, then no motion is observed. This is because then forces of impact almost completely balance.