Page 68 - Science class 4

At night, this process reverses. Land

cools down faster than the sea. At this
Descending
Descending
Rising
Rising
point of time, the air above the sea is Descending Rising
cool air
cool air warm air
cool air
warm air
warm air
warmer than the air above the land. The
warm air rises and the cool air from the Land breeze
Land breeze
Land breeze
land now rushes towards the sea. This is
Land
Land
Land
known as land breeze . Ocean
Ocean
Ocean
Fact File
Cold air holds less water vapour than Sea breeze blows
hot air. in the morning.
MORE ABOUT WATER

More than 70 percent of the Earth's surface is covered with water.
Evaporation
Evaporation
Evaporation
Water exists in nature as snow, liquid water and water vapours. These
states are interchangeable.

The heat of the Sun transforms water to water

vapours by a process, called evaporation .
If we keep a beaker of water out in the Sun, the

level goes down by the evening. This is because
the heat of the Sun has evaporated some water.

Thus, when the weather is very hot, more water
gets evaporated increasing the water vapour

content in the air. The increase in water vapour
content of air makes the weather humid .

Condensation
Condensation
Condensation
Take a pan with water in it and cover it with lid. Keep it

for boiling. After some time we find tiny droplets of

water on the underside of the lid. These drops have
been formed because water vapours (steam) have

changed into water.

This process is called condensation . Clouds are formed

when water vapour condenses into tiny water droplets.