What you need
Microscope, microscopic slide, cover slide, insulin syringe with needle, 5 ml fresh milk from a farmer
(Milk from the dairy is treated, its fat particles which are too small).

Experiment
*  Transfer one drop of water on the microscopic slide. * Add one micro drop of milk, mix with the needle.
* Place a cover slide on the diluted milk.
* Right: Watch the tiny  fat droplets through the microscope.
  (You have to wait until the droplets stop to flow).
Observations:   The samllest of the fat droplets tremble.
Explanation: Though the water molecules are too small to be seen under miscroscope they have a quick and strong movement. So they push the visible much bigger fat droplets.