Ever wondered why a siren's pitch changes as it moves past you?
Doppler radar
Ever wondered why a siren's pitch changes as it moves past you?
Imagine you're listening to a speeding ambulance's siren as it rushes by. You notice the pitch of the siren goes higher as it approaches and lower as it moves away.
The pitch change is because the siren's sound waves are squished together as it moves toward you and stretched out as it moves away. This is the Doppler effect at work.
Example
If the ambulance is moving at 60 km/h and the siren's frequency is 700 Hz, you'll hear a higher frequency as it approaches and a lower frequency as it moves away.
Remember this
The Doppler effect explains why the pitch of a moving sound source changes for a stationary observer.
Text adapted from Wikipedia, licensed under CC BY-SA 4.0.
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