As a sound source approaches or recedes, the frequency perceived by the observer increases or decreases. This is familiar with airplanes and cars and is used in a range of technologies.
NCEA & Science Curriculum
JNR SCI, SCI 3.6, PHYS 3.3
In the standard Doppler Ball demonstration a ball containing a buzzer is swung in a circle or is tossed between students. Unfortunately the volume increases while the ball approaches and decreases while the ball recedes. This can reinforce the misconception that many junior science students have that frequency is related to loudness. The Doppler Ball described here reduces changes in volume while the ball is swung in a circle by keeping the buzzer pointed in the same direction at all times during the motion.
Video and Audio
Download video (1 MB, right-click and save as): Dopplerball.m4v
Download audio file: (1.3 MB, right-click and save as): DopplerBall.wav
This demonstration uses the following gear; a soft projectile(available from $2 shop or similar), piezoelectric speaker, 9V battery, switch, connecting wire(available from electronics suppliers), two fishing swivels, paperclips, rope for handles and a hot glue gun.
Be sure nothing sharp nor hard projects from the Doppler Ball. Be sure it is securely fastened to the string and that students are well away from the region in which the ball travels.
Individual teachers are responsible for safety in their own classes. Even familiar demonstrations should be practised and safety-checked by individual teachers before they are used in a classroom.
Doppler Ball Frequency Shift
The Doppler Effect is named after the Austrian, Christian Doppler, who discovered this effect. Today the Doppler effect finds application in a range of technologies including medical ultrasound, speed detection and astronomy.
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Earlier work on this demonstration including a functioning model was completed by Victoria University student Kenese Lautusi as part of a summer internship though the Awhina program.
This teaching resource was developed in collaboration with Rory O’Keeffe, a New Zealand Science, Mathematics and Technology Teacher Fellow, 2007, hosted by Victoria University School of Chemical and Physical Sciences. Rory is a science teacher by training and is currently Deputy Principal at Lytton High School in Gisborne, New Zealand. He is also an amateur astronomer. See NZSMT Teacher Fellowships for more information about the Teacher Fellow Program.
Lytton High School students Ash King, William Shields and Sean Besseling participated in the development of this resource.
This teaching resource was developed with support from