Direct a laser beam through a beaker of water with a little bit of creamer added. The beam must be blocked after exiting the beaker, as the students must see the beam in forward scattering. The speckle pattern shimmers due to the motion of the fat particles in colloidal suspension.
The very small atomic induced motion of the milk fat drops causes a Doppler shift in the reflected light. This difference in frequency “beats” against the other reflected light from milk fat drops of different speed, Doppler shift, and frequency. This ties together several concepts we viewed separately.