# Pressure

## Pressure

Have you ever observed why the nails end with a sharp point, while sipping Cool drink from a straw, have you noticed that you actually suck the air out of the straw? Why and how does this happen? To answer all this questions lies in the concept of pressure. While you sip the Cool drink, you are actually applying pressure. What is a pressure?

What is a Pressure?

Pressure is the ratio of the force applied to the surface area over which force is applied. The amount of force exerted on a surface to the area.

When a force (Newton) is applied perpendicularly to a surface area (m²), then the pressure exerted on the surface by the force is equal to the ratio of F to A. Mathematically,

Pressure (P) = Force (F)/ Area (A).

SI unit of Pressure is “Pascal’s” (Pa).

A pascal can be defined as a force of one newton applied over a surface are of one meter square. Since the pressure is dependent on the area over which the force is acting. The pressure can be decreased and increased without any change in the force. The force applied being constant, if the surface becomes smaller the pressure increase, if the surface becomes larger the pressure decrease.

Atmospheric Pressure: Atmospheric pressure is a force in an area pushed against a surface by the weight of the atmosphere of Earth, a layer of air. The air is not distributed evenly around the globe. It moves, and at different times, the layer of air is thicker in some places than in others. Where the layer of air is thicker, there is more air. Since there is more air, there is a higher pressure in that spot. Where the layer of air is thinner, there is a lower atmospheric pressure.

The earth’s atmospheric air is surrounded by a layer of gases and so this air surrounding the earth exerts a pressure known as the ‘atmospheric pressure’. Its value at sea level is 101325 Pa. It is measured using a mercury barometer (hence atmospheric pressure is also known as barometric pressure), indicating the height of a column of mercury which exactly balances the weight of the column of atmosphere over the barometer.