This applet demonstrates Brownian motion. the big particle can be considered as a dust particle while the smaller particles can be considered as molecules of a gas. On the left is the view one would see through a microscope. To the right is the supposed explanation for the jittering of the dust particle.
© Michael Fowler, 22 September 1998
(http://galileoandeinstein.physics.virginia.edu/more_stuff/Applets/brownian/applet.html)
Used with permission.