Did you know?

Air

Air is all around us - it surrounds the earth in a layer called the atmosphere.  All living things must have air in order to live.  Air is colourless and has no smell,  Yet it is really a mixture of a number of different gases. We can feel air when the wind blows, and we know air has weight.  Air carries sounds - without it we would not be able to hear because sounds cannot travel in a Vacuum.

The chief gas in air is nitrogen, which makes up nearly four-fifths of the air.   About one--fifth of the air is made up of Oxygen.  Air also holds some water particles called vapour.  We find the degree of Humidity in the air by measuring the amount of Vapour.

Air expands when it is heated, and when it expands it becomes lighter. This is why warm air rises.

The air that surrounds the earth gets thinner and higher you go.  All high-flying aircraft have to keep the air in their cabins at ground -  level pressure so that passengers can breathe normally.  In the same way,
mountaineers carry their own air supply because the air at the top of high mountains is too thin for normal breathing.