Everything you touch is made of tiny bits far too small to see. The way those bits are packed decides whether something is a solid, a liquid or a gas — the three states of matter.
Why this matters: The same stuff can change state. Water can be hard ice, runny water, or invisible gas in the air. That explains a puddle drying up, or a cold glass 'sweating' on a hot day.
The three states
| State | Shape | Can you squash it? | Example |
|---|---|---|---|
| Solid | Keeps its own shape | No | A rock, an ice cube |
| Liquid | Takes the shape of its container | No | Water, milk, juice |
| Gas | Spreads out to fill all the space | Yes | The air, steam |
A solid keeps its shape, like a stone in a box. A liquid flows and takes the shape of its container, like juice in a cup. A gas spreads out to fill the whole space, like air filling a balloon.
Melting and freezing
- Melting is when a solid gets warm and turns into a liquid. Ice melts into water. Chocolate melts in your warm hand.
- Freezing is when a liquid gets cold and turns into a solid. Water freezes into ice in the freezer.
Worked example: An ice lolly is left in the sun. The sun's heat makes the solid ice melt into a runny liquid, so the lolly drips.
Evaporation and condensation
- Evaporation is when a liquid slowly turns into a gas. A puddle dries up because its water evaporates into the air as invisible water vapour.
- Condensation is when a gas cools and turns back into a liquid. Droplets form on a cold glass as water vapour in the air touches it and turns back to liquid.
The water cycle
Water goes round and round in a never-ending journey called the water cycle.
Put the journey of a raindrop in order:
- The sun heats the sea and water evaporates, rising as vapour
- High up it is cold, so the vapour condenses into droplets that make clouds
- The droplets join up and fall as rain (or snow)
- The water flows into rivers and back to the sea