Water can change its form — Physics, 4–6 years
The same water can be liquid, solid ice or invisible water vapour. Physics, 4–6 years.
Idea
Water does not always look the same. In a freezer it becomes hard ice; when ice warms, it melts into liquid water; when liquid water gets very warm, some becomes water vapour that mixes with the air.
Why it matters
People needed to know why puddles vanish, why ice melts and where mist comes from. The idea explains these changes without saying that the water has disappeared: it has moved into a different form, sometimes one we cannot see.
Try it step by step
Put three ice cubes in a cup and leave it on the table for one hour. At first the cubes are solid and keep their shape. Later they melt into liquid water, and drops appear on the outside because water vapour in the air cools there.
A common mistake
Many people think the drops outside a cold glass have leaked through the glass. That is a reasonable guess because the drops appear after the glass gets cold. They actually come from water vapour in the surrounding air, which turns liquid on the cold surface.
Where we see it
Freezers make ice for drinks, and ice packs keep food or injuries cool. Steam helps cook food, while clouds form when water vapour cools into tiny drops or ice pieces high in the sky. The water changes form again and again in nature.
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