Definition of Doppler effect
The Doppler effect (also Doppler shift) is the change in the frequency or, equivalently, the period of a wave in relation to an observer who is moving relative to the source of the wave. It is named after the physicist Christian Doppler, who described the phenomenon in 1842. A common example of a Doppler shift is the change of pitch heard when a vehicle approaches and recedes from an observer. Compared to the emitted sound, the received sound has a higher pitch during the approach, identical at the instant of passing by, and lower pitch during the recession.
When the source of the sound wave is moving towards the observer, each successive cycle of the wave is emitted from a position closer to the observer than the previous cycle. Hence, from the observer's perspective, the period or time between cycles is reduced, meaning the frequency is increased. Conversely, if the source of the sound wave is moving away from the observer, each cycle of the wave is emitted from a position farther from the observer than the previous cycle, so the period or time between successive cycles is increased, thus reducing the frequency.
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Questions people ask
Real questions from the Stack Exchange community – follow a link to read the discussion.
- Is it possible to estimate the speed of a passing vehicle using a musical ear and the doppler effect? · Physics SE
- Will a marching band on the go sound out of tune to an observer due to the Doppler Effect? · Music SE
- Will moving a sound source in ATMOS just "blend" the sound, or will it create a Doppler-effect? · Video Production SE
Frequently asked questions
What is Doppler effect?
The Doppler effect (also Doppler shift) is the change in the frequency or, equivalently, the period of a wave in relation to an observer who is moving relative to the source of the wave.