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+--- Thread: Angular Momentum — Why Orbits Stay Stable (/showthread.php?tid=428)
Angular Momentum — Why Orbits Stay Stable - Leejohnston - 01-08-2026
## Angular Momentum — Why Orbits Stay Stable
### 1. The Equation
Angular momentum:
L = mvr
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### 2. What Each Symbol Means
- L = angular momentum
- m = mass
- v = velocity
- r = distance from rotation axis
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### 3. What the Equation Is Telling Us
Angular momentum is conserved unless acted on by an external torque.
When radius decreases, speed must increase.
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### 4. Where It Comes From (Intuition)
Rotational motion follows the same conservation logic as linear motion.
Nothing is lost — it shifts between speed and distance.
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### 5. Worked Example
A satellite moves closer to Earth →
it speeds up to conserve angular momentum.
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### 6. Real-World Applications
- Planetary orbits
- Ice skaters spinning
- Gyroscopes
- Accretion disks
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### 7. Common Misconceptions
- Objects slow naturally in orbit → false
- Rotation needs constant force → false
- Angular momentum depends on gravity → false
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### Try It Yourself
Why does an ice skater spin faster when pulling in their arms?