The states of matter
Ice, water and steam are the same particles wearing three different disguises. The disguise depends on one thing: how much the particles are moving.
Everything is made of particles
Pick up anything — a metal spoon, a glass of water, the air in the room. Zoom in further than any microscope can go and you'd find the same thing: countless tiny particles packed together.
Water is the perfect example because you can meet it in all three states of matter: solid ice, liquid water, and the gas we call steam. Here's the key idea that surprises most people — the particles themselves are exactly the same in all three. A particle in an ice cube is identical to a particle in a puddle and identical to a particle in steam. Nothing about the particle changes.
What changes is how the particles are arranged, how they move, how far apart they sit, and how strongly they hold onto each other. And the thing that pushes a substance from one state to the next is heat: heating gives particles more energy to move, cooling takes it away.
Physical properties
Imagine pouring water from a jug into a glass. The water changes shape to fit the glass — it flows. Now try the same with an ice cube: it keeps its shape and just sits there. So "what shape is it, and can the shape change?" is a clue to whether something is solid, liquid or gas.
Things you can observe or measure without changing what the material is made of are called physical properties. Whether something flows, whether you can squash it, and whether its shape can change are all physical properties — and they depend on the state.
| State | Does it flow? | Can you squash it? | Can its shape change? |
|---|---|---|---|
| Solid | No | Only a tiny bit | Stays the same unless you push or break it |
| Liquid | Yes | Only a tiny bit | Takes the shape of the bottom of its container |
| Gas | Yes | Yes — a lot | Spreads out to fill the whole container |
Turn up the heat
What the particles are doing
In a solid
The particles are touching and locked into a neat, regular pattern. They can't travel — they can only vibrate on the spot. They hold together strongly. That's why a solid keeps its shape. Picture a packed lift where everyone is shoulder-to-shoulder: people can wobble and fidget, but nobody can actually walk anywhere.
In a liquid
The particles are still touching, but they've broken out of the pattern. They slide over each other, moving around randomly. They still hold together strongly — which is why a liquid stays in a puddle rather than flying apart, but flows to fit its container.
In a gas
The particles are far apart, in no pattern at all, zooming around very fast in every direction. They barely hold together — the attraction between them is very weak. That's why a gas spreads out to fill any space, and why you can squash it: there's so much empty room between the particles.
| State | How close? | Arranged how? | Moving how? | Hold together? |
|---|---|---|---|---|
| Solid | Touching | In a pattern | Vibrate on the spot | Strongly |
| Liquid | Touching | Random | Slide over each other, randomly | Strongly |
| Gas | Far apart | Random | Very fast, in all directions | Very weakly |
The colour that spreads on its own
- Fill a clear glass with water and let it go completely still.
- Gently add one drop of food colouring (or lower in a tea bag). Don't stir.
- Watch closely. The colour slowly creeps outward until the whole glass is tinted.
- Do it again with warm and cold water side by side. Which one spreads faster?
Completely safe — just water and food colouring. Warm tap water is plenty; nothing hot needed.
Four mind-benders
The book stops at three tidy states — but the real world is stranger and more wonderful than that. Here are four things that surprise most grown-ups.
Tinier than tiny
Particles are so small that you'd have to lay about 100,000 of them in a line just to match the width of a single hair. Nobody has ever seen one with their own eyes.
There's a fourth state
Heat a gas enough and its particles get torn into charged bits — a state called plasma. The Sun, lightning bolts and glowing neon signs are all plasma. In fact, most of the universe is.
Water breaks the rules
Almost everything shrinks when it freezes. Water does the opposite — it expands, so ice is lighter than water and floats. That's why ponds freeze from the top down and fish can survive the winter underneath.
You can't see steam
Real steam is an invisible gas. The white cloud above a kettle isn't gas at all — it's gas that has already cooled into tiny floating water droplets. You're watching condensation happen.
The goo that can't decide
- In a bowl, mix about 2 cups of cornflour with 1 cup of water. Add the water slowly.
- Stir until it's like thick honey. This goo is called oobleck.
- Punch or squeeze it fast — it feels hard, like a solid.
- Now let your hand rest on it — it oozes and drips through your fingers like a liquid.
Messy but safe. When you're done, let it dry and put it in the bin — don't wash it down the sink, as cornflour can clog the drain.
Key points
- There are three states of matter: solid, liquid and gas.
- The particles are the same in all three states — only their arrangement, movement and spacing change.
- Physical properties (like flowing, squashing and changing shape) are things you can observe or measure without changing the material.
- Particles are held together strongly in solids and liquids, but very weakly in gases.
- Heating gives particles more energy; cooling takes it away. This drives melting, freezing, boiling and condensing.