The water cycle
Chemistry · Key Stage 2 · The School
One set of water, going round
Evaporation (liquid to gas, from seas and puddles), condensation (gas back to liquid, forming clouds), precipitation (rain, snow, hail), collection (rivers, lakes, groundwater) — and round again. No new water is made; the water in your glass has been through this cycle for billions of years.
Particles explain it
Heat gives water particles enough energy to break away and become gas. High in the sky it is cold, so they lose energy, slow down and clump back into droplets — condensation. Millions of droplets together are a cloud. When droplets join until they are too heavy for the air to hold, they fall.
Why it matters
The cycle is where all fresh water comes from. It also explains weather: warm wet air rising and cooling makes rain, which is why coasts and mountains are wetter. And it explains why pollution matters — what goes into rivers ends up in the sea, evaporates clean, but leaves the pollution behind to concentrate.
Put a bowl of warm water somewhere sunny with a small empty cup standing in the middle. Cover the bowl with cling film and put a coin on the film above the cup. Come back in a few hours. Water has EVAPORATED from the bowl, CONDENSED as droplets on the underside of the film, run down to the low point under the coin, and dripped into the cup — precipitation. Every stage, in one bowl.