Illustration of Doppler Effect Introduction There are multiple articles and videos available on the internet which explain the Doppler effect, mostly using the fact that the waves get compressed when an object making sound approaches you and that the waves are stretched when the object moves away from you. These explanations are good enough, but don’t provide a deeper understanding. Also derivation of the formula for frequency change is left to the reader. This post is an attempt to explain in a layman’s terms the effects on the frequency of sound we hear. Subsonic & Mach 1 speeds In all the examples below, it’s assumed that the police car (Well, considering the speeds in the examples, it would be more like a jet!) running the siren is 12 seconds away initially, it approaches and subsequently passes you. You stop hearing the sound once it gets 12 seconds away from you. Approaching car Case 1 - Cop car traveling at 1/4th the speed of sound The initial sound emitte...