a source (a police car) of sound waves with a constant frequency and amplitude. There are two observers, one on the left that will move away from the source and one on the right that will move towards the source. We have three diagrams:
shows the overall situation with the siren starting at time t1;shows the situation at time t2 when the observers are moving; andshows the situation at t3 after the observers have been moving for a time interval, Δt=t3−t2.
The crests and troughs are numbered so you can see how they move further away and so that we can track which ones an observer has measured.
The motion of the observer will alter the frequency of the measured sound from a stationary source:
An observer moving towards the source measures a higher frequency.An observer moving away from the source measures a lower frequency.
See on everythingscience.co.za