# Absolute pressure, Gauge pressure, Atmospheric pressure Explained. Absolute pressure Gauge. English The Push or Pull applied on an object that causes the object to change its velocity is known as Force.

Forced applied on a unit area of a surface is known as pressure.

Pressure is equal to applied force / area on which the force acts. if the area is smaller the pressure on the surface will be greater and vice versa.

Pressure Exerted by Liquids

All the liquids have weight. The liquids exert pressure on the base and walls of the container in which they are stored.

when we pour a liquid into a vessel the weight of the liquid pushes down the base of the vessel producing a pressure.

The pressure exerted by a liquid is smaller just under the surface of the liquid but as we go deeper in a liquid the pressure of increases.

Pressure Exerted by Gas

Gases consist of molecules and these molecules move randomly.

In a sealed container they exert a force when they collide with each other and with the container walls and this applies a pressure to the container walls this pressure is equal throught the container.

if we connect a vacuum pump to this container,

The vacuum pump can remove almost all the molecules of the gas inside the container. As a result the pressure inside the container reduces to 0. This pressure is known as Absolute zero Pressure or Absolute Vacuum.

However practically a vacuum pump cannot remove all the gas molecules in a container.

What is Atmospheric Pressure.

Earth is surrounded by a layer of air called Atmosphere

and this atmosphere contains on everything it touches on the Earth. this pressure is known as Atmospheric Pressure.

As barometer is used to measure this atmospheric pressure, atmospheric pressure is also known as barometric pressure. The air or gases surrounding the earth becomes thinner and thinner as the altitude increases and so the atmospheric pressure decreases as we go up.

Standard Atmospheric pressure at sea level is 101325 Pascal.

What is Gauge pressure and Absolute Pressure

Usually pressure is measured using two references, one in which the Atmospheric pressure is used as Reference, that means we calculate the measured pressure is how much more than the Atmospheric Pressure and this pressure is known as Gauge Pressure.

In the second method Absolute Zero Pressure or Absolute Vacuum is taken as a Reference that means we calculate the measured pressure is how much more than the Absolute zero pressure or Absolute Vacuum and this pressure is known as Absolute Pressure.

Consider a normal pressure gauge ,before connecting the pressure gauge to any process, the reading in the gauge shows 0 PSI.

As we had discussed earlier every object on earth will undergo an Atmospheric pressure but that atmospheric pressure is not indicated in this gauge that is because this pressure gauge is designed to indicate the measured pressure is how much more than the atmospheric pressure that is here the Atmospheric pressure is taken as the reference standard.

Now lets connect this pressure gauge to a container filled with liquid.

the pressure gauge will indicate the pressure exerted by the liquid in the container this pressure is known as Gauge pressure.

The Atmospheric pressure varies from place to place depending upon the Altitude of the location and prevailing weather conditions.

when atmospheric pressure varies precise measurement can be achieved only if a fixed unchanging reference point is established. so here Absolute zero pressure is used as a reference.

Absolute zero pressure is the pressure of a perfect vacuum.

The measured pressure in which absolute zero pressure is used as a reference is known as Absolute pressure.

Consider that we need to measure the pressure of air in a tyre. if we use a pressure gauge, the gauge will indicate the pressure of air inside the tire only, which is the Gauge pressure.

if we use an absolute pressure gauge then this gauge will indicates the sum of pressure inside the tyre and the atmospheric pressure. that is absolute pressure is equal to gauge pressure plus atmospheric pressure.

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