Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025
Definition
The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer moving relative to the source of the wave. It is most commonly observed with sound waves.
The Doppler effect occurs when there is relative motion between a source of sound and an observer.
When the source of sound approaches the observer, the frequency appears higher (blue shift); when it moves away, the frequency appears lower (red shift).
The formula for the observed frequency $f' = f \left(\frac{v + v_o}{v - v_s}\right)$ where $f$ is the emitted frequency, $v$ is the speed of sound, $v_o$ is the velocity of the observer, and $v_s$ is the velocity of the source.
The Doppler effect has applications in radar and medical imaging technologies like ultrasound.
A sonic boom occurs when an object travels faster than the speed of sound, leading to a sudden change in pressure.