Why does ice float on water?

When you drop ice into a glass of water, it doesn't sink to the bottom; it stays at the surface. That may seem ordinary to you, but it's actually surprising: most substances are denser when solid than when liquid, so the solid sinks. Water is one of the most important exceptions to this rule, and it's thanks to this exception that lakes don't freeze all the way to the bottom in winter.

The journey starts with the particles that make up matter: in a solid, a liquid and a gas, how close together are the particles, and how much do they move? Then you'll see why heat and temperature aren't the same thing, and how particles behave when heat is transferred.

In the last two steps you'll look at melting, freezing and evaporation, and then at how substances expand when they're heated and contract when they're cooled. Once you've learnt why water expands as it freezes, you'll also be able to explain why water pipes burst in the winter months.