Question: Do you know What the Doppler effect is

Stephen Rhatigan answered on 14 Nov 2017:

Imagine standing on the street and an ambulance with the siren on drives by. As it comes towards you the siren sounds high pitched. Once it passes you the sound changes and gets lower. This is the Doppler effect in action.
The Doppler effect is difficult to explain with out images but I’ll try.
Imagine a device that produces a loud beep once every second. That device would emit sound at a frequency of one beep per second.
You are standing at one end of a field and I’m standing still at the other end holding the beeper. While I’m standing still the sound of the beeper reaches you at a frequency of one beep per second.
Now imagine that immediately after the first beep I start running towards you as fast as I can (and imagine that I’m really fast). For me the second beep comes one second after the first beep but now the distance it travels to your ears is shorter so it arrives at your ears less than one second after the first.
If I keep the same speed, the beeps will reach you at a frequency greater than one beep per second.
The opposite would be true if I ran away from you – for you the time between beeps would be longer than one second as each beep would have to travel further to reach your ears. This means that the frequency would decrease.
So for a source of light or sound, if the source moves towards the observer the frequency of the emitted light or sound increases from the perspective of the observer. For sound this means a higher pitch and for light this means a “blue shift”.
If the source is moving away from the observer the frequency decreases from the perspective of the observer. For sound that means lower pitch and for light it’s called a “red shift”.
Hope that helped and if not: