Page 73 - Innovator's Science-8

• Troposphere : Most of the
atmospheric air is present in

troposphere.
Troposphere mainly consists of
nitrogen (78%), oxygen (20.9%),

argon 0.03%. Troposphere changes
from about 8 km over the poles to
about 16 km over the equator.

Clouds, rain and snow are seen in
troposphere.
• Stratosphere : The layer of

atmosphere above troposphere up
to a height of about 50 km is called
stratosphere.

In stratosphere, there is very little water vapour. Supersonic air craft
fly in this region. The temperature of stratosphere is higher than that
of troposphere and remains nearly constant up to a height of 25 km.

Ozone layer lies in the control zone of stratosphere. Ozone layer
protects all living organisms on the earth from the harmful ultraviolet
(UV) radiation coming from the sun.

• Mesosphere : Mesosphere extends from the height of 50 km to 80
km. In the mesosphere, air is very thin and the temperature falls to

about –85°C at a height of about 80 km from the earth.
• Thermosphere : Above mesosphere, thermosphere begins. In

thermosphere, temperature increases with altitude.

AIR EXERTS PRESSURE

We know air exerts pressure due to its own weight. We can experience
many activities to show that air exerts pressure. Some of them
Science are :
Bytes

1. It is easier to ride a bicycle in the direction of blowing wind because
Testimony
The air above us may the blowing wind exerts a pressure on us in the same direction in
seem light, but a column which our bicycle is moving and makes our bicycle move faster. On
of air just one square
cen metre wide weighs the other hand, we find it difficult to ride a bicycle against the
about 1 kilogram! That's direction of wind because in the case, the blowing wind exerts a
why air can press equally pressure on us in the opposite direction in which our bicycle is
on all objects in every
direc on. moving.

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Science-8