Why does ice melt?

The longer answer

Ice, water and steam are the same stuff in three different forms. Scientists call these the three states of matter: solid, liquid and gas.

In a solid like ice, the particles are packed close and hold their places, so it keeps its shape. In a liquid like water, they stay close but slide around, so it pours and takes the shape of its cup. In a gas like steam, they spread far apart and zoom about, filling the air.

Warmth is what moves water from one state to the next. Take the warmth away and it goes back again: steam cools into drops, and water in the freezer turns 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. When steam meets a cold window, it turns back into drops.
• Ice takes up more room than the water it came from. Water's particles lock into a pattern with little gaps when it freezes, which is why ice cubes float in a drink.
• 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: an ice cube race

1. Put ice cubes of the same size on three plates.
2. Leave one in a sunny spot, one in a shady spot, and one in the fridge.
3. Guess which one will melt first.
4. Check every little while and see which turns into a puddle first.

Try sprinkling a pinch of salt on one cube too. Salt makes ice melt faster, which is why it is spread on icy roads.