The very thick layer of air which surrounds the Earth is called the atmosphere.
It is many miles thick. But beyond that, hundreds of kilometers up in space, there is no air at all.
At ground level there is plenty of air. As we climb higher and higher, there is less and less air. That is why climbers usually take oxygen with them when they climb high mountains.
Air that has been squeezed a lot is called compressed air.
E.g. – 1) When you blow up a balloon, you are squeezing air into a small space.
2) A tyre can be inflated (get filled with air). As you go on pumping more air into it the air gets squeezed or compressed.
Compressed air is very strong. It can hold the weight of a cycle, a car or any other vehicle and we don’t feel the bumps in the road. Compressed air also makes things fall slowly.
E.g. – Parachute
According to the above examples we can learn that the air occupies space and it has a weight. Air also has pressure.