SCIENTIST WORLD

The Doppler effect is when the frequency of a wave appears to change due to the relative motion between the source of the wave and the observer. For example, when a car with a horn passes by, the pitch of the sound seems to change as it approaches and then moves away from you. When it's coming towards you, the sound waves get compressed, making a higher pitch, and when it's moving away, the waves stretch, creating a lower pitch.