Atmospheric Pressure

Air has a weight and it exert pressure on any surface. The earth is surrounded by air with height of about 80km. This Air exert a pressure on the surface or sea level. This pressure is called Atmospheric pressure. It is the pressure exerted by a column of air of height about 80km. The value of atmospheric pressure is about  . This pressure does not really affect human and other animal because the blood pressure is a little higher than the atmospheric pressure.

Evidence of Atmospheric Pressure.

1. When you drink a bottle (made from polymer) of coke . The bottle crushed inside if you don’t allow air to enter while drinking the coke. This is as a result of enormous atmospheric pressure outside the bottle.
2. A glass beaker inverted under the surface of water and raised up to the surface remain full of water. This is because of the air pressure holding the water up inside the beaker.

Since pressure  is directly proportional to height, Atmospheric pressure decreases with height or altitude(as you go up , the total air height decreases ).

Manometer

In the laboratory, the pressure of a gas in a container is measured with Manometer. All gases exert pressure . Gases moves from an area of high pressure to an area of low pressure. Manometer is a form of Pressure gauge.

The Manometer consist of a U-tube containing water in which the same atmospheric pressure is exerted to both arms which are at the same horizontal level.

Let the two arms be A and B, see fig 1 and 2 above.

Tube A is connected to a source of gas to measure its pressure. The gas exerted pressure on A causing the water level in B to rise up the tube.

The Pressure of Gas = Atmospheric Pressure + Pressure due to water column BC.

The Pressure of Gas = A.p + hpg

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