Solids, liquids and gases — Science, 7–10 years
Matter can look and behave differently depending on how its tiny particles are arranged and moving. This helps explain why ice, water and steam are three forms of the same substance.
The three familiar states
A solid keeps its own shape, like a spoon or an ice cube. A liquid takes the shape of its container but keeps its amount, like milk in a glass. A gas spreads out to fill the space around it, like air in a room.
Why this idea matters
People needed to describe why the same material could be hard, flowing or invisible. Looking at states of matter gives us a useful way to predict what will happen when something is cooled, warmed, poured or squeezed. It turns surprising changes into patterns we can test.
What happens to an ice cube?
Put one ice cube on a plate and leave it for an hour. First it is a solid and keeps its shape. Then heat from the room makes it melt into liquid water, which spreads on the plate. The water may later evaporate into a gas, even though you cannot see the gas itself.
A change is not disappearance
A common thought is that melted ice has vanished because the cube is no longer there. That seems sensible because the new water is spread out and looks different. Usually the material is still present: the ice has changed state, and careful measuring finds nearly the same amount of water.
States in everyday life
Bakers use solid butter, liquid oil and gases made by rising dough to change the texture of food. Refrigerators slow melting, while kettles help water become steam. These examples are useful because each state behaves differently, not because every material changes in exactly the same way.
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