The brownian motion is the random movemement of microscopic particles suspended in a liquid or gas, caused by collisions with molecules of the surrounding medium.
If tiny particles like pollen are added to clear water and observed through a micrscope they will be seen to move about randomly. This was an early clue to the fact that matter is made of individual...
Molecules in a fluid move constantly, freely, randomly, in all directions and with all possible velocities. This erratic motion of the molecules causes them to collide with anything in their path....