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+--- Thread: The Doppler Effect — Why Sound and Light Shift (/showthread.php?tid=433)
The Doppler Effect — Why Sound and Light Shift - Leejohnston - 01-08-2026
## The Doppler Effect — Why Sound and Light Shift
### 1. The Equation (Sound)
Observed frequency:
f' = f (v ± v₀) ÷ (v ∓ v_s)
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### 2. What This Means
Motion changes how frequently waves arrive.
Approaching sources compress waves → higher pitch.
Receding sources stretch waves → lower pitch.
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### 3. Light Doppler Shift
For light, motion causes:
- redshift (moving away)
- blueshift (moving toward)
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### 4. Real-World Applications
- Ambulance sirens
- Astronomy (galaxies)
- Radar guns
- Medical imaging
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### 5. Common Misconceptions
- Doppler affects speed → false
- Only applies to sound → false
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### Try It Yourself
Why does a siren suddenly drop in pitch as it passes you?