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Chlorina on

Chlorine is added to water to kill germs. This process of adding chlorine to water is
known as chlorina on.

Weather

The conditions of atmosphere around us keep on changing. Sometimes it is very hot
while sometimes very cold. Sometimes we see heavy rain. The change of the
condition of atmosphere around us at a particular time is called weather. The sun and
the earth play an important role in causing the change in weather.
Heat of the sun causes air to blow. When the air gets heated by the sun, it rises up. The
cool air then comes to occupy the space of warm air.
Heat of the sun also causes evaporation of water in rivers, lakes and oceans which
results in formation of clouds and rain.
The earth moves on its axis. This process is called rotation of the earth. It causes day
and night. The earth moves around the sun in its orbit. This motion is called revolution
which causes change in seasons.
As the earth is tilted on its axis, one half of the earth is closer to the sun than the other
half. The part close to the sun has longer and hotter days and thus has summer. The
part away from the sun has shorter and colder days and thus has winter.

Let’s
Revise

 Air is a mixture of different gases and water vapours.
 Moving air is known as wind.
 Air is needed by almost all the living things on the earth.
 Water is an invaluable resource; we absolutely cannot live without it.
 Evaporation happens when a liquid is heated.
 The simplest method to purify water is boiling.

Points to Remember

Chlorination : Method of purifying water by adding chlorine

Filtration : Method of cleaning water using a filter

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