Page 87 - Journeys Through Society-7

has a hot climate and is influenced by the monsoon the more the lid is pressed
winds.
Elements of Weather
We will discuss here about some elements of the
weather.
Air Pressure
Air pressure is measured by an instrument called
barometer. Air has weight which presses down on the
Earth. The weight exerted by a column of air on the
surface of the Earth is known as air pressure.
Wow Fact
Air pressure decreases with increasing
altitude. It is higher at sea level and gets
lower with increase in altitude. At sea level,
2
air pressure is nearly 1.05 kg/cm .
Simple Mercury Barometer
It comprises of a tube with one end open and placed in
mercury. As air has weight, it exerts pressure on the
mercury making it rise in the tube. Normal
atmospheric pressure at sea level is 760 mm or 30
inches of mercury. When expressed in millibars, it is
1,013 millibars. If the mercury rises above this point,
we say that the air pressure is high but when it falls
below this point, the pressure is said to be low.
Mercury Barometer
Aneroid Barometer
It is made of a thin metal drum from which air has
been removed. The pressure of the outside air pushes
the lid of the drum inward. The higher the air pressure,
87
in. In an aneroid barometer,
the pressure on the lid is
shown by a needle on a dial.
Changes in air pressure
affect the weather. A rapid
drop in atmospheric
pressure marks the arrival Aneroid Barometer
of a low-pressure system. Low-pressure systems are
associated with cloudy, rainy or windy weather. A
rapid increase in atmospheric pressure pushes that
cloudy and rainy weather out, clearing the skies and
bringing in cool, dry air.
Wow Fact
China produces most of the wind energy in
the world. The United States closely follows
as the second largest wind energy producer.
Winds
Winds are the horizontal movements of air caused by
temperature changes, which, in turn, cause changes in
air pressure. Air pressure increases when
temperatures are low and decreases when
temperatures are high. Winds blow from regions of
low temperature and high pressure towards regions of
high temperature and low pressure. Coastal regions
enjoy cool sea breeze as air blows towards the hot
land during the day. At night, the cooler land breeze
blows out towards the sea. There are similar air flow
patterns along lake sides.
While studying the weather, it is necessary to learn
about the direction and speed of the winds. A wind is
described or named after the direction from which it
comes. A south wind blows from the south towards
the north. An east wind blows from the east towards
the west. Wind direction is determined by an
instrument called wind vane. Wind speed is measured
with an anemometer.
Wind vane Anemometer