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Atmospheric Pressure

The air surrounding the earth is called the atmosphere. Air has weight and therefore exerts pressure not only on the earth’s surface but on all objects on the earth.
The thrust on unit area due to the column of air on earth’s surface is called the atmospheric pressure.
Atmosphere exerts pressure in all the directions.

Effects of Atmospheric Pressure

It is due to atmospheric pressure that the ink gets sucked into a fountain pen.
Rubber suction pads are used to hang clothes and calendars on walls. When a suction pad is pressed against a flat surface, air is forced out of its sucker, reducing the pressure inside. The outside atmospheric pressure being greater, the sucker is pushed firmly and it adheres to the wall. Lizards are able to adhere to the wall because their feet function like suction pads. When you suck a liquid with a straw, the air in it is drawn into your mouth. The liquid is forced into the straw by the atmospheric pressure acting on the liquid.
Measurement of Atmospheric Pressure The atmospheric pressure may not be the same at all places. It is more at places at the sea-level and less on high mountains. The standard atmospheric pressure is considered at the sea-level. The instrument employed to measure atmospheric pressure is called a barometer. It was Torricelli, an Italian scientist, who invented a simple barometer in 1643.


It is found that air supports a water column 10 m high, i.e., the pressure of 10 m of water is equal to the atmospheric pressure. Thus, the atmospheric pressure (= water pressure) is equal to Pgh = 103 × 10 × 10 = 105 Nm−2. Since 10 m long tube is needed to make a barometer using water and it is not convenient, a high-density liquid like mercury is used to reduce the height of a barometer to nearly one metre.

Atmospheric pressure decreases as the altitude increases. This can be used to design Altimeter, which is used to measure the height of a place.


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