Page 149 - Science Class 06

most commonest liquid on the earth. It is
found in the oceans, seas, lakes, ponds,
rivers and under the surface of earth as
ground water. A small amount of water is
also present as water vapour in the
atmosphere. About 74% of the earth
surface is covered with water. Water is also
present on the mountains in the form of ice.
Evapora on
Precipita on
Storage
Water Cycle
The water present on the surface of the
earth evaporates and moves upward. At
high al tude, it condenses and turns into
clouds. Finally, it returns to the earth as
rain, snow or hail. Most of the rain water
makes its way back to the oceans through
various streams and some trapped deep
into the earth’s crust. The process of
evapora on, condensa on and precipita on
are ever going processes. All these
processes help in con nuous circula on of
water on the earth. Water cycle is
par cularly ac ve in the region where heat
and moisture are abundant. In dry climate,
water cycle becomes slow and in very cold
climate, the water cycle is very limited. Low
ac vity of water cycle would naturally cause
low rainfall.
Science-6
1. Write the factors that may influence the
rate of evapora on.
2. What is the role of evapora on and
condensa on in the occurrence of rain?
3. How does climate affect water cycle?
THUNDER AND LIGHTNING
Thunder and lightning are natural pheno-
mena. They occur naturally and simulta-
neously on the days which are hot and
humid. Have you ever thought how do
thunder and lightning occur?
You know that warm air rises upward. At a
certain height, the water vapour present in
the air begins to condense to droplets of
liquid water. This condensa on releases
heat and warms the air further, giving added
impetus to rising air currents. The condense
moisture starts to fall. When these drops fall
through the mass rapidly rising air, fric on,
with the air tears some of the drops apart
into spray or mist. This results in the
forma on of electrical charges. The water
drops falling to the lower levels of the
clouds have a nega ve charge, the fine
spray that rises to the upper levels have
posi ve charge. When the large bodies of
two clouds with opposite charges come
near to each other, charges of the clouds
are transferred so as to become neutralised.
This causes spark called as lightning.
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