[Leejohnston]

## Density — Why Things Float or Sink

### 1. The Equation

Density = Mass ÷ Volume

ρ = m ÷ V

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### 2. What Each Symbol Means

- ρ = density
- m = mass
- V = volume

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### 3. What the Equation Is Telling Us

Density describes **how tightly matter is packed**.

Objects float if their density is lower than the fluid they’re in.

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### 4. Where It Comes From (Intuition)

A heavy object can float if it spreads its mass over a large volume.

That’s why ships float but solid steel sinks.

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### 5. Worked Example

If:
- mass = 2 kg
- volume = 0.004 m³

Density = 2 ÷ 0.004
= **500 kg/m³**

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### 6. Real-World Applications

- Ships and submarines
- Hot air balloons
- Oil floating on water
- Planetary science

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### 7. Common Misconceptions

- Heavy things sink → false
- Floating depends on shape alone → false
- Density never changes → false

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### Try It Yourself

Why does ice float on water even though it’s solid?