Water on a windowsill

A glass of ice cubes, a puddle, a steaming cup and a cold window pane sit together in one scene. Water moves between solid, liquid and gas as heat comes in or goes out.

This picture is part of the full library

Every lesson is open to everyone for 7 days after it is published. This one came out on September 16, 2026: its text stays readable here, and its picture opens with a subscription.

See the plans

The app is free. A subscription opens every lesson, in every school year.

Age 12: open this week

Browse Age 12

In the picture

Ice cubes in the glass: solid water holding its own shape
Puddle on the windowsill: liquid water spreading out flat
Steam above the cup: warm water leaving as a gas
Droplets on the cold pane: gas turning back into liquid water

Examples

An ice lolly softening in the sun
A bathroom mirror fogging up after a hot shower

Key takeaways

Water changes state when it gains or loses heat, but it stays the same substance.
Melting and evaporation take heat in; freezing and condensation give heat out.