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equator and decreases pole wards. The amount of insolation received differs from season

to season and also between day and night. The earth has been broadly divided into three
heat zones depending upon the amount of insolation received. The temperature of any
place also depends upon its height above sea level and its distance from the sea. Places
located near the sea will experience moderate temperature, but those away from the sea,
will generally experience extreme temperature.

Of course, the temperature recordings are never solely dependent on
any one factor. Various factors affect the climate of a place. Winds,
ocean current, slope of land, vegetation cover are the many factors that
influence the temperature recordings. A thermometer is used to measure
the atmospheric temperature on a Fahrenheit or a Celsius scale.

Thermometer air or atmosphEriC prEssurE

Many of the forces within our atmosphere are easily recognised by
us like the temperature out side simply by stepping outside. We
immediately get to know whether it is cold, warm, or hot. Likewise, we
can feel the amount of wind, or see the level of windiness by looking
at how forcefully the trees are swaying back and forth. But we cannot
feel or see the atmospheric (Air) pressure. Atmospheric pressure is
the amount of force or pressure exerted by the atmosphere on the Barometer

objects located within it. It happens because the air presses us from all directions and our
body too exerts a counter pressure. Scientists (meteorologists) use a special instrument
called barometer to measure the pressure of the atmosphere.

The air always moves from high pressure areas to low pressure areas. When hot air rises, cold air
from surrounding area rushes there to fill in the gap. In this way, air circulation takes place.

Wind

Air in motion is called wind. Difference in atmospheric pressure helps wind to blow. Wind
direction is measured by an instrument known as the wind vane and its speed is measured
by anemometer.

There are broadly three types of winds—

1. Permanent or planetary winds

2. Seasonal winds

3. Local winds
Wind Vane and Anemometer
1. pErmaNENt or plaNEtary WiNds
These are winds which constantly blow in a particular direction throughout the year. Winds

which blow from subtropical high pressure belts to equatorial low pressure belts are called
Trade Winds.
Social Studies-7-7
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18 Social Studies