Question: What causes the doppler effect

Mossy answered on 9 Nov 2018:

Nice! The Doppler effect is when something is emitting a wave as it is travelling. The most obvious example is an ambulance driving past you. The ambulance is emitting a sound wave at a particular frequency. But as it’s driving toward you – the sound waves are catching up with each other and that makes it a higher pitch. As it drives away – the sound waves are further apart so it appears lower pitched.