Air Pressure

Air is a mixture of gases and molecules of these gases have weight due to gravity. Anything that has weight, pushes and presses against other objects. The envelop of air that surrounds earth (atmosphere) exerts a force which acts downwards on the surface of the earth.

The force of air column acting per unit area of a surface results in a pressure exerted by atmosphere. This pressure is called atmospheric pressure. The atmospheric pressure is about 1 kg cm² or 10 ton m².

In everyday life, atmospheric pressure plays an important role in the working of many things, for example, working of a straw, working of a syringe or ink dropper, working of a water pump.

Variation of Air Pressure with Height

The atoms and molecules of the gases in the atmosphere like those of all other matter are subject to earth’s gravitational pull. As a consequence, the atmosphere is much denser near the surface of earth than at higher altitudes. In fact, the density of air decreases very rapidly with increasing distance from earth. Therefore, atmospheric pressure also decreases with altitude. Often at higher altitudes, people find their nose bleeding because blood pressure of the body is much more than the pressure outside (atmospheric pressure).

Air pressure is measured by the instrument known as barometer.