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E = mc² — What Mass–Energy Equivalence Really Says - Leejohnston - 01-08-2026
## E = mc² — What Mass–Energy Equivalence Really Says
### 1. The Equation
E = m × c²
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### 2. What Each Symbol Means
- E = energy
- m = mass
- c = speed of light in a vacuum
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### 3. What the Equation Is Telling Us
Mass *is* energy.
Even a tiny amount of mass contains an enormous amount of energy because c² is so large.
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### 4. Where It Comes From (Intuition)
This equation emerges from special relativity.
It tells us that mass and energy are not separate things — they are two forms of the same physical quantity.
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### 5. Worked Example
If:
m = 0.001 kg (1 gram)
E = 0.001 × (3 × 10⁸)²
≈ **9 × 10¹³ joules**
That’s an enormous amount of energy.
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### 6. Real-World Applications
- Nuclear power
- Particle physics
- Stars and fusion
- Cosmology
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### 7. Common Misconceptions
- Mass is “destroyed” → false
- Only nuclear reactions use this → false
- Energy appears from nowhere → false
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### Try It Yourself
How much energy is stored in:
- 1 gram of matter?
- 1 kilogram?