Teaching Notes

Have the students share any experiences they have had with the Doppler Effect (attending auto races, listening on a moving train to railroad crossing bells). Ask the students to listen closely to the buzzer tone as they toss the Nerf ball back and forth. You can try making a harness of sturdy net material and whirling the Nerf ball around in a circle. Be sure the ball is securely mounted in the harness. If the students make a tape of the horn of a moving car, suggest that they put the waveform of the sound on an oscilloscope screen and measure the period. Incidentally, ask the students to listen
on the tape for the Doppler shift of the engine noise of cars passing by.

Enjoy tossing the Nerf ball.

SAFETY PRECAUTION: If you swing the Nerf ball in a circle, be sure it is securely mounted in the netting. Keep students back at a safe distance. If the students make the measurement of the car horn sounds, give them plenty of instruction on safety. The students doing the recording must stay well out of the road. The car must stay within the speed limit.

It can be difficult for students to make the connection between the Doppler Effect in sound and in light. Many students have very little sense of sound waves or wavefronts. Visualizing light as a wave is even more difficult. You may be able to help them visualize the Doppler Effect by suggesting that, as the source moves toward the observer, the wavefronts pile up in front of the source, so the frequency increases.