Page 76 - Innovator's Science-8

MOVEMENT OF AIR

Blowing or moving air is called wind. The speed of wind may vary from
5-10 km/h (gentle breeze) to 700-800 km/h (tornado).

The speed and direction of wind is affected by the following factors :
• Location on the earth • Rotation of the earth

• Local conditions • Height from the ground

EFFECTS OF AIR PRESSURE
Winds are caused due to difference in air pressure. Warm air is lighter. As
it rises, it cools and spreads. Once it is cooled, the air starts moving back

to the Earth. The region from where the air rises, an area of lower
pressure is created.

The region where the air sinks, an area of high pressure is created. Since
the atmosphere constantly works to restore a balance, air moves in from
an area of high pressure to an area of low pressure. The movement of air

Science is known as wind.
Bytes
Atmospheric pressure influences weather

Testimony Upward movement of air causes cloudy and the downward movement of
Winds do not blow in
straight lines because of air causes clear sky.
the Earth's rota on. This
deflec on of moving air is As air rises and creates an area of low pressure, water vapour in it
called the Coriolis Effect, condenses to form clouds. Conversely sinking air generally means that
and it makes winds curve condensation cannot take place.
to the right in the
Northern Hemisphere Low pressure is, therefore, associated with cloudy skies and wet
and to the le in the weather.
Southern Hemisphere.
High pressure is therefore associated with clear and sunny sky.

Generation of Wind
Wind currents are generated due to uneven heating on the earth.

Uneven heating on Earth
As you already know, the regions around the equator
are heated by the direct rays of the sun. The air in these

regions gets heated and rises and the cooler air from the
surrounding regions (0-30° latitude on either side of
equator) moves in. These winds blow from north and
south towards the equator as shown in the given figure.

The regions around the north and south poles are colder
as the sun rays slant the most in these regions. As a

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