What is Atmospheric Pressure?

Just like liquids, the air is also pulled down by the earth’s gravitational force. This force applies pressure on the air in the downward direction. The pressure exerted by air is called Air pressure or Atmospheric pressure.

The atmospheric pressure is measured in Pascal (Pa).

Just like liquid pressure, atmospheric pressure too, works in all directions.

Atmospheric pressure at different layers of the Atmosphere

The atmosphere can be divided into 5 layers:

Troposphere
Stratosphere
Mesosphere
Thermosphere
Exosphere

The pressure exerted by air varies with every layer of the Atmosphere.

The atmospheric pressure in the Troposphere is greater than the other layers. This is because it experiences a downward force from the other layers as well.

Gradually as we move to the Stratosphere, the atmospheric pressure reduces, and reduces even further for the Mesosphere, then the Thermosphere, and is the least in the exosphere.

Now let us see how atmospheric pressure works.

How is the Atmospheric Pressure at a Given Point?

The pressure exerted at any given point above the earth’s surface is equal in all directions.

Also, equal pressures acting in opposite directions cancel each other out. Let us understand this with the help of 2 examples.

Atmospheric Pressure on a Table

The pressure exerted by the air on a table of dimensions 1 meter x 1 meter, in the downward direction is greater than 1,00,000 Pa. This is equivalent to ten cars being put on this table.

But the table is not crushed under such immense pressure. This is because the atmospheric pressure acting on the table in the upward direction is of the same magnitude as the downward pressure. This way equal and opposite atmospheric pressures cancel out.

Atmospheric pressure on a water bottle

Take a plastic bottle filled with water and place a cardboard paper on the open end of the bottle. Holding this paper, invert the bottle. Now, let go of the paper. We will see that due to the upward pressure, the cardboard paper sticks to the surface. It is held to the surface because of the air pressure that is pushing this paper in the upward direction! This upward air pressure is sufficient to counter the downward push exerted by the water.

Now, if we make a few holes in the bottle at its base, the atmospheric pressure forces air inside the bottle through them. The air from the top started exerting pressure on the water. The combined pressure of water and air from the top could easily overcome the pressure exerted by air from the bottom. Hence, there is a net force acting on the paper in a downward direction. That is, there is more pressure in the downward direction. This is the reason why the paper gets detached from the surface.

Summary

Atmospheric Pressure	Pressure exerted by air or atmosphere
Unit of Pressure	Pascal (Pa)
Direction of Pressure	Atmospheric pressure acts in all directions The pressure exerted at any given point above the earth’s surface is equal in all directions Equal pressures acting in opposite directions cancel each other out

Did you know?

The unit for measuring air pressure is Millibars, and the device used for measuring atmospheric pressure is a Barometer.

Also Check:

Atmospheric Pressure