The Doppler effect
- It is a change in frequency or wavelength of a wave in relation to an observer who is moving relative to the source of the wave.
- It is named after Austrian physicist Christian Doppler.
- A common example of the Doppler effect is the change in pitch of a siren on a moving ambulance.
- As the ambulance approaches, the sound waves are compressed, causing the pitch to increase.
- As the ambulance moves away, the sound waves are stretched, causing the pitch to decrease.
In physics, the Doppler effect is used in a variety of applications, such as:
- Sonar and radar: to measure the speed of objects, such as ships or aircraft.
- Astronomy: to measure the velocity of stars and galaxies.
- Medical imaging: to study blood flow in the human body, using ultrasound.
- Weather forecasting: to track storms, by measuring the Doppler shift of the radar signals they reflect.