Diffusion
is the name given to the movement of molecules from an area of higher concentration
to an area of lower concentration. In this animation, the molecules
start off bunched together in the form of a clump of salt. When they
get into the water they start to break away from each other, to dissolve.
Sometimes they collide which makes them move very rapidly in opposite directions.
The main purpose of diffusion is to distribute the molecules evenly throughout
the given space.