Activity 17.8.1. Exploring Pitch.
You hear a loud noise. Which wave property (frequency, wavelength, wave speed, amplitude, wave number, phase, etc.) do you think is related to the pitch?
Section 17.8 The Doppler Frequency Shift
Subsubsection Warm-up Activity
Video Lesson 17.8.1. Doppler.
Subsubsection Key Ideas
The frequency of a sound wave changes if there is relative motion between the emitter and the listener.
Definition 17.8.2. Doppler Frequency Shift.
The frequency of a sound wave heard by a listener is not always the same as the frequency created by the emitter:
\begin{equation*}
f_{\text{listener}} = f_{\text{emitter}}\frac{\nu_{\text{sound}} + v_{\text{listener}}}{\nu_{\text{sound}} - v_{\text{emitter}}}
\end{equation*}
Each velocity (of the source or the listener) is positive if it is moving in the direction of the other but negative if it is moving opposite the direction of the other, relative to the medium through which the wave is moving. As you saw previously, the speed of sound in air is about 343 m/s.
Subsubsection Activities
Activity 17.8.2. Sensemaking: Frequency Shift.
Use the equation to confirm your results from Representing Sound Waves about how the frequency changes if the listener is stationary and the emitter is moving either towards or away from the listener.
Activity 17.8.3. Explore Doppler Frequency Shifts.
How does the detected frequency change if the listener is moving away from a stationary emitter? How does the detected frequency change if the emitter is moving away from a stationary listener?
References References
[1]
Fire Engine Siren Demonstrates The Doppler Effect by davidrobert2007.
