Solids, Liquids and Gases

What is matter?

Everything around you is made of matter — your chair, your drink, even the air you breathe. Matter is anything that takes up space.

Matter usually comes in three forms, called states of matter: solids, liquids and gases.

Solids

A solid keeps its own shape. It does not flow or spread out. You can hold it and it stays the same.

• A rock, a toy brick, a pencil, an ice cube — all solids.
• The tiny bits inside a solid (we call them particles) are packed tightly together and hold still.

That is why a solid is firm and stays put when you pick it up.

Liquids

A liquid flows and takes the shape of whatever holds it. Pour it into a tall glass and it becomes tall; pour it into a flat dish and it spreads out.

• Water, milk, juice, and oil are liquids.
• The particles in a liquid are close together but can slide past each other, so a liquid can flow.

You cannot hold a liquid in your bare hand — it slips through your fingers!

Gases

A gas spreads out to fill all the space it can. It has no fixed shape and no fixed size.

• Air, steam, and the helium in a balloon are gases.
• The particles in a gas are far apart and zoom around freely, bouncing in every direction.

Most gases are invisible, but they are still real. Blow up a balloon and you can feel the gas pushing out the sides.

Changing state

Matter can change from one state to another when it is heated or cooled. Heat is one of the forms of energy, and adding or taking it away changes how the particles move.

• Melting: a solid warms up and turns into a liquid (ice → water).
• Freezing: a liquid cools down and turns into a solid (water → ice).
• Boiling / evaporating: a liquid heats up and turns into a gas (water → steam).
• Condensing: a gas cools and turns back into a liquid (steam → water drops on a cold window).

Water is the best example, because we see it as a solid (ice), a liquid (water), and a gas (steam).

Try it yourself! 🍫

Watch a solid turn into a liquid and back again.

1. Ask a grown-up to give you a few squares of chocolate or a small ice cube on a plate.
2. Place it on a warm windowsill or hold the plate (not the chocolate) in your warm hands.
3. Watch it slowly melt from a solid into a runny liquid.
4. Now put the plate in the fridge or freezer. The chocolate or water will freeze and become solid again.

You just changed the state of matter — twice!

Stay safe: Never heat anything on a stove or in a microwave without a grown-up. Warm sunlight or warm hands are all you need.