About 150 years ago a botanist, Robert Brown, observed pollen grains moving in a random way under his microscope. You can see the same effect with smoke today. We call it Brownian Motion.
Brown thought the movement of the grains may be explained by the fact that the pollen was alive! But in fact it was some years before it was explained that the movement was due to collisions between the pollen and millions of smaller (and therefore invisible) gas atoms.
The pollen was small enough to be knocked sideways when more air particles collided with one side of it than with the other. This was evidence of the continuous movement of gas atoms. Gas atoms have Ek.