[Leejohnston]

## The Speed of Sound — How Fast Is It Really?

### 1. The Equation

The basic relationship is:

Speed = Distance ÷ Time

For sound in air (at room temperature):
v ≈ 343 m/s

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### 2. What Each Symbol Means

- v = speed of sound (metres per second)
- m = metres
- s = seconds

This value assumes:
- dry air
- about 20°C
- normal atmospheric pressure

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### 3. What the Equation Is Telling Us

Sound is not instantaneous.

It travels as a **pressure wave**, pushing energy through air molecule by molecule.
That process has a maximum speed.

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

Sound speed depends on:
- how stiff the medium is
- how dense it is

Air is light and compressible → moderate sound speed
Solids are stiff → sound travels much faster in them

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### 5. Worked Example

**How far does sound travel in 1 hour?**

1 hour = 3600 seconds

Distance = speed × time
= 343 × 3600
≈ 1,234,800 metres
≈ **1,235 km**

That’s roughly the distance from:
London → southern France

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### 6. Real-World Applications

- Thunder delay after lightning
- Sonic booms
- Aircraft design
- Acoustics and audio engineering

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### 7. Common Misconceptions

- Sound does **not** travel at the same speed in all materials
- Sound speed is **not** affected by loudness
- Sound cannot travel in a vacuum

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### Try It Yourself

How long would it take sound to travel:
- 1 km?
- across your town?
- from a nearby storm?