Water changes form — Earth science, 4–6 years
Water can be liquid, solid ice or invisible water vapour, and warmth or cold can make it change.
Three forms of water
Water does not always look the same. It is liquid in a glass, solid as ice in a freezer and a gas called water vapour when it rises from warm water, although the vapour is usually too small to see.
Why does water change?
Water changes form because warmth makes its tiny parts move more, while cold slows them down and holds them together. This helps explain puddles disappearing, ice melting and drops forming on a cold window.
What happens to an ice cube?
Put one ice cube on a plate in a warm room. First it is hard and keeps its shape; then its outside becomes wet; after a while it is a small puddle. The solid ice took in warmth and became liquid water.
Steam is not always visible
The white cloud above a hot drink is often tiny water drops, not the invisible vapour itself. It is reasonable to call all of it steam because it appears when water is hot, but water vapour can be present without being seen.
Water changes around us
These changes help clothes dry, food cook, roads freeze and mirrors become misty after a bath. In clouds, water also changes between drops, invisible vapour and ice, then falls as rain, snow or hail.
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