Stationary source - stationary observer
Moving source - stationary observer
Stationary source - moving observer
The change in pitch (frequency) that occurs where a moving source of sound (siren, train) passes you is known as the Doppler effect.
The difference between the actual frequency of the sound being emitted by the source and the frequency perceived by an observer is due to the relative motion of the source and the observer.
Irrespective of which of these is moving, the perceived frequency (pitch) is
For any source of sound, the wave emitted spreads from the source as a sphere.
For a moving source, the center of the sphere moves.
For a stationary source
The difference between the actual frequency of the sound being emitted by the source and the frequency perceived by an observer is due to the relative motion of the source and the observer.
Irrespective of which of these is moving, the perceived frequency (pitch) is
higher than the actual frequency when the source and the observer approach one another.
lower than the actual frequency when the source and the observer move away from one another.
lower than the actual frequency when the source and the observer move away from one another.
For any source of sound, the wave emitted spreads from the source as a sphere.
For a moving source, the center of the sphere moves.
The cartoon shows one crest from the wave at ten different positions.
The orange ring is from the orange source. The blue ring is from the blue source.
The green rings are from the source at intermediate positions.
If the source is moving
toward the observer, the frequency of the waves at the observer is higher than if the source were stationery.
away from the observer, the frequency of the waves at the observer is lower than if the source were stationery.
The orange ring is from the orange source. The blue ring is from the blue source.
The green rings are from the source at intermediate positions.
If the source is moving
toward the observer, the frequency of the waves at the observer is higher than if the source were stationery.
away from the observer, the frequency of the waves at the observer is lower than if the source were stationery.
For a stationary source
an observer moving
toward the source encounters crests of the sound wave at a higher frequency than a stationary observer
away from the source encounters crests of the sound wave at a lower frequency than a stationary observer
toward the source encounters crests of the sound wave at a higher frequency than a stationary observer
away from the source encounters crests of the sound wave at a lower frequency than a stationary observer