- Air is everywhere around us. No living being can survive without air.
- The air covers the whole Earth. This cover of air is called the atmosphere. We live within the atmosphere. It extends over hundreds of kilometres. Up to a height of 16 km, we find clouds, rain and snow. As we go up in the atmosphere, there is less and less air. Jet planes usually fly above the clouds.
- Air is matter. It occupies space and has mass. It has no colour and we can see through it. It fills all the space available to it.
- Air is a mixture of several gases. Nearly fourth-fifths (4/5) of it is nitrogen. About one-fifth (1/5) of it is oxygen. Air also has a small amount of carbon dioxide, argon, helium, water vapour and dust particles.
- At higher altitudes, air is thin and under the water, the available oxygen is less. Thus, breathing becomes difficult. Therefore, mountaineers and divers carry cylinders containing oxygen with them. Oxygen is also supplied to the patients who suffer from breathing difficulties.
- Oxygen is used by living organisms for respiration. During respiration, oxygen breaks down the food to release energy. During this process, carbon dioxide and water vapour are produced and released.
- Carbon dioxide along with water is used by the green plants in the presence of sunlight to make their food. This process is called photosynthesis. During this process, oxygen is released. In nature, the balance of oxygen and carbon dioxide is, thus, maintained.
AIR IS USEFUL TO HUMAN BEINGS
- Air is required by human beings for respiration.
- Air is necessary for burning. A chulha, sign or kerosene stove burn only when sufficient air is available.
- Vehicles such as bicycles, few kinds of carts, scooters, cars, trucks and aeroplanes have tyres filled with compressed air. Such tires make transport smooth and easier.
- Balls used for playing and balloons can be used only when they are inflated with air.
- Compressed air is used in machines for digging, mining and breaking stones. It is also used for lifting liquid substances from a mine.
- Compressed air is used in the brake systems of trains.
- Air helps in drying agricultural products such as grains, pulses, dry fruits and wet clothes.
- People feel cool in summer under a fan. The fan circulates air. This helps in rapid evaporation of sweat.
- Air helps in the movement of sail boats, gliders, parachutes and aircraft. Birds, bats and insects fly in the air.
- Air makes a windmill move. A windmill is used to draw water from tube wells and to operate flour mills. Along the coast, windmills are used to generate electricity.