The Doppler Effect

The Concept: A Shift in Frequency

The Doppler Effect is the change in frequency of a wave in relation to an observer. As the source moves towards an observer, the sound waves get compressed, leading to a higher perceived frequency (higher pitch). As it moves away, the waves stretch out, leading to a lower perceived frequency (lower pitch).

How to Use the Lab

• This simulation shows a "snapshot" of the wavefronts from a moving source.
• The source (speaker) is moving to the right.
• Use the slider to change the Source Velocity ($v_s$) and hear the immediate pitch shift.
• Select an observer perspective below to hear their specific perceived frequency.
• Observe how the wavefronts bunch up in front and spread out behind.
• Press "Simulate Pass By" to hear a full siren-like effect!
• The analysis panel shows the exact frequencies heard by each observer.