The Doppler Effect has two shifts. Red shift is the frequency of waves decreases as the distance between the wave source (passing car, plane, etc…) and observation point increases. Blue shift is the opposite of red shift. Blue shift is the frequency of waves increases as the distance between the wave source and observation point decreases. Imagine a car speeding past you… when you first hear the sound, it’s quiet. Then as the car gets closer, the sound gets louder. Then it passes you, it gets quiet all over again. You have just witnessed the Doppler Effect! I found this “Doppler Effect” amazing because the first time I ever heard of it was on “The Big Bang Theory”! (No copyright please…) Sheldon was apparently dressed as the Doppler Effect at Penny’s Halloween party. I thought he was a prisoner! I understand now what the Doppler Effect is thanks to him and my science teacher!