Air takes up space — Physics, 4–6 years
Air is invisible, but it is still there. It fills spaces, can move things and can stop water from entering a space that it already fills.
Air takes up space
You cannot usually see air, but you can see what happens when it moves or is trapped. An upside-down cup pushed into water keeps its inside dry because air is already there. Air may feel like nothing, yet it fills every open space around you.
Why notice air?
People needed to understand why an empty-looking cup could not fill with water, or why a bag became full when blown up. The answer was that “empty” places may contain air. This helps us design balloons, pumps and containers instead of treating invisible air as if it were nothing.
A dry tissue underwater
Push a small tissue into the bottom of a cup so it stays there. Turn the cup upside down and lower it straight into a bowl of water. Lift it out without tilting it: the tissue is dry. Water could not enter because the cup was filled with air; tilt the cup and bubbles escape, leaving room for water.
“There is nothing in the cup”
It is reasonable to call a cup empty when you cannot see anything inside it. But invisible does not mean absent: air is inside unless something else has taken its place. In the water test, tipping the cup makes the air visible as bubbles, which shows why the water can then enter.
Air in everyday things
A football, bicycle tyre and inflatable armband work because air fills their flexible skin. A syringe moves air or liquid when its plunger changes the space inside. We also breathe air from the spaces around us. These examples use air taking up space; they do not mean air can push every object by itself.
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