The Doppler Effect with Sound

Everyone is familiar with the effect of passing sirens, car horns and train whistles when the vehicle passes by. The increase in pitch as the source of the sound approaches, and the corresponding drop in pitch as it passes is due to the Doppler effect. The Doppler effect is defined as the apparent change in frequency of a wave, caused by the relative motion between the source of the wave and the observer. Our Doppler Effect experiment is grounded in the basic wave concepts of wavelength and frequency.
Using a free online mobile app called Phyphox, students use their mobile phone to measure how the frequency emitted from a stationary audio source changes with the frame of reference of a moving observer. The student experiment and teacher notes are available at the links below.
Student experiment; bit.ly/3ufTOrq
Teacher notes; bit.ly/3F6w5PF
Watch the companion video; bit.ly/3BrD4jH
Contact: Dr. David Sederberg, Purdue Physics and Astronomy Outreach [e-mail]
Timeline
0:00 Introduction
0:34 Explaining the Doppler effect with a slinky
1:11 Introducing the Phyphox app and requirements
1:56 Daniel introducing the Phyphox experiment
2:33 Making sense of the data
4:18 Daniel explains the car horn scenario
4:50 Relating the Doppler effect to astronomy