Materials
- Frisbee
- Duct Tape
- Buzzer
- 9 volt battery
Procedure
- Connect buzzer to 9.0 Volt Battery
- Tape buzzer and battery to the center of the Frisbee, leaving the plug to the 9.0 volt battery free so you can connect and disconnect the buzzer
- Toss the Frisbee back and forth between students (preferably outside)
Explanation
Sound waves travel out in three dimensions from the place where they were originally made. A simple two dimensional example of this is throwing a stone in a calm lake. A circular shaped wave will move out from the place that the stone made the disturbance in the water. If the spot that is making the wave moves with respect to someone observing or hearing that wave, then the frequency of the wave (number of wave fronts passing a point in one second) appears to change. As the source of the wave moves towards an observer, the waves get compressed together and the frequency is bigger. This gives the sound a higher pitch. If the object and the person observing the sound are moving away from each other, the waves spread out and the pitch is lower. The students can hear this as the Frisbee gets closer to them the pitch gets higher. As the Frisbee moves away from the students, the pitch gets lower.
Reinforcement Activities
Don’t want to go through the mess or hassle of making your own Doppler Effect experiment? Try some of the pre-made activities listed below.
For more fun with sound waves show students that sound doesn’t travel in a vacuum with a Bell in a Vacuum Jar. As the air evacuates the bell jar, the sound of the bell gets weaker and weaker until it is inaudible. A closer inspection of the apparatus shows that the ringer is still violently striking the jar, but no sound can be heard.
Have students determine the highest pitch that they can hear using a Galton’s Whistle.
Show that tubes of different lengths have different pitches by using fire. The singing tubes convert heat energy into sound energy using a Bunsen burner.
