[Leejohnston]

## E = mc² — What Mass–Energy Equivalence Really Says

### 1. The Equation

E = m × c²

---

### 2. What Each Symbol Means

- E = energy
- m = mass
- c = speed of light in a vacuum

---

### 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.

---

### 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.

---

### 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.

---

### 6. Real-World Applications

- Nuclear power
- Particle physics
- Stars and fusion
- Cosmology

---

### 7. Common Misconceptions

- Mass is “destroyed” → false
- Only nuclear reactions use this → false
- Energy appears from nowhere → false

---

### Try It Yourself

How much energy is stored in:
- 1 gram of matter?
- 1 kilogram?