1. IP1.30.3 Moving wave sources Moving wave sources

2. IP1.30.3 Moving wave sources When the car is approaching, the pitch sounds higher and higher. When the car has passed, the pitch gets lower. This is an example of the Doppler effect.

3. IP1.30.3 Moving wave sources Why does this happen?  When the source of waves is moving towards the observer, the waves it emits are all bunched up. This gives them a shorter wavelength and therefore a higher frequency  When the wave source is moving away, the wavelength is stretched, and the waves are more spread out and therefore the frequency is lower. The Doppler effect can be heard when a police car passes you with its siren sounding.

4. IP1.30.3 Moving wave sources The speed camera emits radio waves which reflect off a car. If the car is moving towards the camera the reflected waves are more bunched up which reduces their wavelength the faster the car.