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Air surrounds the Earth just above the land and sea. It is often called the atmosphere. Air seems like nothing, but it is really several gases mixed together. Without air, there could be no living plants or animals on the earth. You are breathing air this very minute. You must breathe air to live. People have stayed alive more than a month without food, and more than a week without water. But a person can live only a few minutes without air.

Air has no colour, no smell, and no taste. Yet air is just as real as water or land. You do not usually see air, because it is transparent. The light rays pass straight through air. However, objects appear to be wavy if we look at them through a patch of warm air surrounded by cold air. For example, warm air rising above a hot radiator makes things behind it seem wavy. In this manner, you actually seem to see air.

You can feel air against your face when the wind blows. You can also see waves, clouds, and tree branches move as air pushes against them. Air can blow large sailboats across the widest oceans. It can turn windmills and pump water. Most sounds come to us through the air. If there were no air, the world would be silent, because sound cannot travel in a vacuum.

Air has weight, and it is this weight that keeps balloons that are lighter than air high above the earth. Air shows resistance to any motion. This air resistance keeps birds and airplanes up in the air, just as water resistance helps a water skier skim on the surface of the water. There is an “ocean” of air just as real as any ocean of water. When you walk, you push along the bottom of this ocean of air much as a crab crawls on the bottom of the sea. The ocean of air covers a larger area than all the oceans of water put together. It is many times deeper than the earth’s oceans and it covers all the earth.