The Doppler shift is a phenomenon that occurs when there is relative motion between a source of waves (such as sound or light) and an observer. It describes the change in frequency or wavelength of the waves as perceived by the observer due to this motion.
In the context of sound waves, the Doppler effect refers to the perceived change in frequency of sound when the source of the sound or the observer is in motion relative to each other. The Doppler effect can result in a shift towards higher frequencies, known as a "blueshift," or towards lower frequencies, known as a "redshift."
In everyday life, we experience the Doppler effect with sound in various situations. Here are a few examples:
Moving vehicles: When a vehicle with a siren (such as an ambulance or police car) approaches us, we initially hear a higher-pitched sound. As the vehicle passes and moves away, the pitch of the siren appears to decrease. This is due to the Doppler effect. The sound waves emitted by the siren get compressed as the vehicle approaches (blueshift), resulting in a higher perceived frequency. As the vehicle moves away, the sound waves get stretched (redshift), resulting in a lower perceived frequency.
Passing cars or motorcycles: When a vehicle passes us while accelerating or decelerating, we can hear the change in the engine sound. As the vehicle approaches, the engine sound may appear higher in pitch, and as it moves away, the sound seems lower in pitch. This is again due to the Doppler effect.
Train or airplane passing: Similar to the examples above, when a train or airplane passes by, we can observe changes in the pitch of the sound produced by the moving vehicle.
The Doppler effect is an important factor in our ability to perceive and locate sound sources in our environment. It helps us determine the relative motion of objects, such as the direction and speed of a moving vehicle, based on the changes in pitch we perceive. Additionally, the Doppler effect has applications in various fields, including astronomy (for analyzing light from celestial objects) and medical diagnostics (such as Doppler ultrasound for measuring blood flow).