Page 93 - Science - 5

How air pressure is useful?How air pressure is useful?How air pressure is useful?
We use air pressure to drink juice from a straw. When

we suck on the straw the air is drawn out and no air is
left in the straw. The pressure inside the straw

becomes lower than the pressure in the air outside
the straw. It forces the liquid into the straw and the
juice comes into your mouth. A medicine dropper

works on the same principle.
What happens when we go on filling air into a

balloon? It bursts with a bang. Why does it burst?
The extra air exerts pressure on the walls of the

balloon. When the pressure becomes greater, the
balloon bursts. Air is compressed into smaller spaces.

Tyres filled with compressed air can support bicycles, cars, buses, trucks and
even aircraft.

WATER

Water is the most important liquid on the Earth. All
plants and animals need water to live. People have

many uses for water besides drinking. They use it for
washing and cooking. They use it to irrigate crops
and gardens, to clean streets and to operate air

coolers. They also use the power of flowing water to
generate electricity.

Water covers almost 75 per cent of the Earth's surface in the form of oceans,

rivers and lakes but very little of this water is fit for use. People throw garbage
and sewage into these water bodies. Factories also release oils, poisonous

chemicals and other wastes into the water. These substances, which make the
water dirty are called pollutants .

W
W
Water Impuritiesater Impuritiesater Impurities
We find two types of water impurities.

w Soluble Impurities :These are soluble in water,

e.g. salt, many chemicals etc.

w Insoluble Impurities : These are insoluble in

water, e.g. mud, oil etc.

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