Relative Frequency Equation
Reference from the original Physics I textbook.
- Relative Frequency Equation
For sound in a stationary medium: f′ = f(v ± v_D)/(v ∓ v_S), where v_D and v_S are nonnegative speeds along the source–detector line. Choose signs separately as described below.
[Hz]
1. If the detector is moving towards the source, then you use a + in the numerator.
2. If the source moves toward the detector, use v − v_S in the denominator.
3. If the detector is moving away from the source, then you use a - sign in the numerator.
4. If the source moves away from the detector, use v + v_S in the denominator.
5. If the detector or source is stationary relative to the medium, set that object’s speed to zero. This classical expression assumes source speed less than the sound speed.
- Related Glossary Terms
- Index
Chapter 9 - FFR - Wave-Particles
Reviewed physics notes (4)
These corrections keep the original lesson’s purpose while fixing errors in the source edition.
- The paired source sign is opposite to the detector sign when both approach or both recede. — Reference 1
- Approaching source raises frequency, so it reduces the denominator. — Reference 1
- Receding source lowers frequency, so it increases the denominator. — Reference 1
- Source mistakenly says numerator instead of source. — Reference 1
Glossary and deeper reading · 1 refreshers
These editorial refreshers supplement the reading. Definitions and examples are added guidance; original source wording and recorded answers remain in their original context.
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Doppler effect
The Doppler effect is a difference between emitted and observed frequency caused by relative motion of source and observer. For sound, both motions must be considered relative to the medium; motion changes the rate at which wavefronts are encountered. For example, a sound source approaching a stationary listener usually produces a higher observed frequency than the source’s rest frequency.