Doppler effect
Move the source and observer toward each other and hear the frequency change.
When a source approaches an observer, the wavefronts ahead of it are compressed and the observed frequency rises; when it moves away, the frequency falls. An observer moving toward the source also meets more wavefronts per unit time.
Observed frequency vs. source speed
Positive speed means the source moves toward the observer; the observer's speed stays at the current setting.
Think about it
With the observer at rest, how does the pitch heard change as the source moves toward the observer faster?
The pitch rises. The wavelength ahead of the source becomes shorter while the speed of sound stays roughly the same, so the observed frequency increases.
Model assumptionsStill, uniform air · Speed of sound v = 340 m/s · Positive speeds mean moving toward each other · Speeds well below the speed of sound · No wind
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.