Surprising Puppy Gift That Wags Its Tail

The Doppler effect refers to the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. It is commonly experienced with sound waves, such as when a car horn passes by: as the car approaches, the sound waves are compressed, causing the pitch to rise, and as it moves away, the waves are stretched, causing the pitch to drop. This effect also occurs with light waves, where the shift towards the blue end of the spectrum (blue shift) occurs wh