What Is a Physical Change?
A change in which the appearance, shape, or state of a substance changes, but its chemical composition stays exactly the same.
When something undergoes a physical change, you still have the same substance — it just looks or behaves differently. No new substance is created.
Some everyday examples of physical changes include:
- Ice melting into water
- Water freezing into ice
- A gold ring being melted and poured into a mould
- Steam condensing on a cold window
- A piece of paper being torn into smaller pieces
Think of a physical change like folding a piece of clay. You can squash it into a ball, flatten it into a pancake, or roll it into a sausage — but it's still the same clay! The substance hasn't changed, only its form.
The Moving Particle Theory
To understand physical changes, we first need to understand what matter is made of.
The idea that all matter is made up of extremely small particles that are always moving.
Here are the key ideas:
- All substances are made of tiny particles — too small to see with the naked eye.
- These particles are always moving.
- There are spaces between the particles.
- There are forces of attraction between particles that hold them together.
- When we heat a substance, we give its particles more energy, making them move faster.
The three states of matter — solid, liquid, and gas — all differ in how their particles are arranged and how fast they move.
| State | Particle arrangement | Particle movement | Spaces between particles |
|---|---|---|---|
| Solid | Regular, fixed positions | Vibrate in place | Very small |
| Liquid | Close but irregular | Flow and slide | Small |
| Gas | Far apart, random | Move very fast, freely | Very large |
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