BROWNIAN MOTION:
As
complicated as it may sound, it's not!
Brownian
Motion was first seen by a scientist called Robert Brown. He noticed
that when he looked at pollen grains in water through a microscope they were
moved around in a random way This was explained years later by another
scientist , who said that the strange movements were due to the much smaller
water particles hitting pollen grains and making the move. This odd movement
could only be explained by assuming that water (liquid) and pollen (solid)
were made of particles and that these particles were moving.
Thus, Brownian Motion proves the existence of particles and the fact that they have Kinetic Energy, which keeps them moving constantly (except in absolute zero conditions.)