What are the states of matter?

The longer answer

The difference is how the tiny particles inside behave. In a solid they are packed tightly and stay in place, so it holds its shape. In a liquid they stay close but slide past each other, so it pours. In a gas they are far apart and zoom around freely.

Water is the easiest way to see all three. Ice is solid water. Warm it and it melts into liquid water. Heat it more and it boils into steam, which is water as a gas.

It works the other way too. Cool steam and it turns back into drops, which is called condensation. Cool water enough and it freezes back into ice.

Three things to know

• Steam is water too, just spread out thin in the air. When water gets hot enough, its particles let go of each other and fly off as steam, then turn back into drops on a cold window.
• Ice takes up more room than the water it came from. Water's particles lock into a pattern with gaps when it freezes, which is why ice cubes float.
• Snow is ice that grew in the sky. High in a cold cloud, water freezes onto tiny specks of dust and grows into a flake with six arms.

Try it at home: Watch water change state

1. Put an ice cube on a plate and watch it slowly melt into a puddle: solid to liquid.
2. With a grown-up, boil a little water in a pan and watch steam rise: liquid to gas.
3. Hold a cold plate above the steam, at a safe distance. Drops appear: gas back to liquid.
4. Put a cup of water in the freezer overnight: liquid back to solid.

Steam and boiling water burn, so a grown-up should handle the pan and the hot plate.