Air takes up space — Chemistry, 4–6 years
Air is easy to miss because we cannot usually see it. We can still find it by watching what it pushes, fills or moves.
Air is there, even when we cannot see it
Air is a gas, and gases spread out to fill the space around them. An empty-looking cup is not truly empty: it contains air. We can notice air when it makes a balloon puff up, pushes a sail or moves our hair.
Why look for invisible air?
People needed to understand why a cup could stop water from entering, or why a tyre became firm when pumped. The useful problem was not naming air; it was knowing that unseen gas can push and fill space. That helps us explain wind, breathing and inflated objects.
A cup under water
Crumple a dry tissue and push it into the bottom of a cup. Turn the cup upside down and lower it straight into a bowl of water. Lift it out and check the tissue: it stays dry because the air inside the cup was taking up the space and kept water away.
The cup looked empty
A common thought is that the cup had nothing in it because air is invisible. That is a sensible guess: we usually decide what is there by looking. The test shows the missing thing was still present, because the tissue could not get wet until the air had a path to escape.
Balloons, tyres and breathing
This idea helps explain why a bicycle tyre supports you, why a balloon becomes round and why a paper bag can puff up. It also helps us understand breathing: your lungs fill with air, then push some air out. Air does not need to be seen to do useful work.
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