Material Detail

Change a vehicle's speed and watch its sound waves bunch up in front and spread out behind; turn on Listen to hear the siren's note drop as it passes, and push past the speed of sound to see the waves pile into a shock cone. Further chapters show how big the drop is for a passing ambulance and how the same idea gives redshift in astronomy and wind speeds in weather radar. The page separates pitch from loudness, explains that the note stays high and then falls rather than rising as the siren nears, and says what is simplified: the waves are slowed hundreds of times and their spacing is schematic.

One plate of Laplace's Mini World, a free, non-commercial collection of 130 interactive 3D models in English and Chinese. No account or ads. Text, pictures and models are CC BY-NC 4.0.

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