ScienceAir around us
What air is made of, how we know it is there, and why living things cannot do without it.
We cannot see air, yet it is all around us. We feel it when the wind blows, hear it rustle the leaves and see it lift a kite. The earth is wrapped in a thick blanket of air called the atmosphere. Without it, there would be no life, no weather and no sound.
What air is made of
Air is not one gas. It is a mixture of several gases:
- Nitrogen: about 78 parts in every 100. Plants need nitrogen to grow, though they take it from the soil.
- Oxygen: about 21 parts in every 100. Living things need it to breathe, and nothing can burn without it.
- Carbon dioxide: a very small part. Plants use it to make food.
- Other gases, such as argon, in tiny amounts.
Air also contains water vapour, which forms clouds and dew, and dust and smoke. The fine hairs inside our nose trap dust, which is why we should breathe through the nose and not the mouth.
Properties of air
- Air occupies space. Push an "empty" upturned glass straight down into a bucket of water. Water does not fill the glass, because the glass is already full of air.
- Air has weight. A football pumped full of air is slightly heavier than an empty one.
- Air presses in all directions. This is called air pressure. It is what holds a rubber sucker to a wall and lets us drink through a straw.
- Air expands when heated. Hot air is lighter than cold air and rises. This is how a hot-air balloon flies, and it is also what makes winds blow.
Why air matters
- Breathing: people and animals breathe in oxygen and breathe out carbon dioxide. Fish use the oxygen dissolved in water.
- Burning: a candle covered with a glass soon goes out, because the oxygen inside is used up.
- Plants: they take in carbon dioxide and give out oxygen during photosynthesis. In this way plants and animals keep the gases in the air balanced.
- Weather: moving air is wind. Winds carry clouds and bring rain. Windmills use wind to make electricity.
- Sound and flight: sound travels through air, and birds and aeroplanes fly in it.
Keeping air clean
Smoke from vehicles, factories and burning garbage pollutes the air and causes cough and breathing troubles. Planting trees, walking or cycling for short distances and not burning waste help to keep the air fit to breathe.
Key terms
- Atmosphere
- the blanket of air around the earth
- Mixture
- two or more substances mixed together
- Air pressure
- the push of air on everything it touches
- Wind
- moving air
Try it yourself
Stuff a dry paper napkin tightly into the bottom of a glass. Turn the glass upside down and push it straight down into a bucket of water, then lift it straight out. The napkin stays dry: air inside the glass kept the water out.
Quick questions
Answer in your head or on paper first, then tap to check.
Which gas forms the largest part of air?
Nitrogen, about 78 per cent.
Which gas in the air is needed for breathing and burning?
Oxygen.
Give one experiment to show that air occupies space.
An upturned glass pushed into water does not fill with water because air is inside it.
Why does hot air rise?
Air expands on heating and becomes lighter than cold air.
This is a simple explanation to help you understand. For examinations, read the same chapter in your prescribed textbook. Last checked: 11 November 2026.