Physics
Moving source, still observer
With a stationary listener the numerator is simply the speed of sound.
The Formula
f' = f x c / (c - vs)
With a stationary listener the numerator is simply the speed of sound.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| f' | Observed frequency | hertz | The frequency heard, in hertz. |
| vs | Source speed | m/s | Positive when approaching. |
| c | Speed of sound | m/s | About 343 metres per second in air. |
What Each Symbol Means
f'hertz
Observed frequency
The frequency heard, in hertz.
vsm/s
Source speed
Positive when approaching.
cm/s
Speed of sound
About 343 metres per second in air.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate the doppler effect page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate The Doppler Effect, filed under Science. Every number the guide produces comes from substituting into this one line.