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+--- Thread: Work–Energy Theorem — Why Work Changes Speed (/showthread.php?tid=423)
Work–Energy Theorem — Why Work Changes Speed - Leejohnston - 01-08-2026
## Work–Energy Theorem — Why Work Changes Speed
### 1. The Equation
Work done = Change in kinetic energy
W = ΔKE
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### 2. What Each Symbol Means
- W = work (joules)
- ΔKE = change in kinetic energy
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### 3. What the Equation Is Telling Us
Whenever work is done on an object, its **speed must change** (unless energy is transferred elsewhere).
Work is the mechanism that changes motion.
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### 4. Where It Comes From (Intuition)
Pushing an object over a distance transfers energy into it.
More work → more kinetic energy → more speed.
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### 5. Worked Example
If a force does:
- 500 joules of work
Then the object’s kinetic energy increases by **500 joules**.
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### 6. Real-World Applications
- Braking systems
- Engine acceleration
- Sports performance
- Crash analysis
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### 7. Common Misconceptions
- Force alone changes speed → false
- Work always increases speed → false (can remove energy)
- Energy and momentum are interchangeable → false
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### Try It Yourself
Why does a longer stopping distance reduce injury in a crash?