Doppler ball
Doppler ball is a 90mm plastic ball with a PP3 battery powered tone generator and speaker inside. The ball can be safely whirled round in a large horizontal circle to demonstrate the Doppler effect.
You may have noticed that when an ambulance or police car goes past, its siren is high-pitched as it comes towards you, then becomes low-pitched as it goes away. This effect, where there is a change in frequency and wavelength, is called the Doppler effect.
When a source moves towards an observer, the observed wavelength decreases and the frequency increases. When a source moves away from an observer, the observed wavelength increases and the frequency decreases.
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