Look around you. A wooden chair, the water in a glass, the air you are breathing right now — every single thing in the world is one of just three kinds of stuff. We call them a solid, a liquid or a gas. These are the three states of matter, and once you can spot them you can sort out almost anything in the room.

Here is the surprising part: the very same stuff can be a solid, a liquid and a gas at different times. Water is the champion of this. Freeze it and it becomes hard ice (a solid). Warm it up and it becomes runny water (a liquid). Heat it more and it turns into steam (a gas) that floats away.

Everything is built from tiny bits far too small to see. What makes a solid, a liquid or a gas is simply how those bits are arranged. Try each one. In a solid the bits are packed together and hold still. In a liquid they still touch but slide past each other. In a gas they fly apart to fill all the space they can.

Your journey through matter

Start by meeting each one properly in The Three States. Then discover how heating and cooling can turn one into another in Changing State, and follow water on its endless loop around the planet in The Water Cycle.