This pair of videos of waves in a ripple tank can be used to demonstrate the Doppler Effect. Ripple_Tank_Waves_1, shows ripples from a stationary source that students can analyze to find the frequency and wavelength of the waves. Ripple_Tank_Waves_2, shows the source moving at a constant velocity through the water. It may be used in class along with a movie of a moving sound source.
The movies were made using a Pasco ripple tank. A small 650W incandescent light source was mounted about one meter above the tank, and the ripples projected on the screen were photographed from the side (see lower picture on the right) using a high-speed video camera.