Needs of air is essential to live in. Air is all around us. Air is everywhere. Air is our basic need. All living things need air to live. We inhale and exhale air, during breathing. Air is a mixture of gases. We cannot see air, but we can only feel its presence. Moving air is called wind.
We can feel the presence of air by:
(i) When we switch on the fan, things like pages of book and curtains move.
(ii) When we sit in front of cooler, our clothes and hair move.
(iii) When we blow air into a balloon, its size increases.
Air has force:
Moving air has force. It can move things. Take some papers and put them on a table in a room. Switch on the fan. The air inside the room starts moving and makes the papers fly here and there.
Air has weight:
Weigh an empty football. Now pump air into the football and weigh it again. We will find that after pumping in air the football weighs more.
Air fills space:
Take an empty balloon. Blow air into the balloon. The balloon becomes bigger. The air takes up the space inside the balloon and gives it a shape. Thus air fills space.
Fresh air – Wind:
When the air moves fast, it is called wind. Wind can move things. Strong winds can uproot trees. It can make leaves, fruits, flowers and branches fall from trees. Clothes sway when the wind blows.
Uses of air:
Wind helps in running windmill. Aeroplane flies dues to the presence of air. Air helps in running of sailboat. Parachute and glider also fly due to the presence of air.
Living things need air to keep alive:
Needs of air is essential for all living things to keep alive. Human being and animals breathe air in and out. We cannot hold our breath for a long time because air is essential for breathing. Plants need air to make their food.
Air supports burning:
Needs of air is also necessary for burning. We can show this through the following activity.
Take a glass jar, two candles and a match-box. Light both of the candles. Cover one candle with a glass jar. Leave the other candle uncovered or open. After some time the candle covered with glass jar stops burning as it gets no air. The candle kept in open keeps on burning. So, air is necessary for burning. Air can be used for many other purposes.
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