Excess of pressure

Ever wondered why the edges of a knife are made sharp, why the nails that we use are made pointed. The answer to all these questions is based on the concept of pressure. It is generally defined as the amount of force applied to a certain area. It is a physical quantity. Its formula can be defined as the ratio of the force applied to the surface area over the object on which force is applied. 

p = F / A

In the upcoming section, we will study pressure in detail.

Define Pressure

Pressure can be defined as a physical force that is exerted on an object. This force applied is perpendicular to the surface area of the object per unit area. P = F/ A gives the basic formula of pressure, and its SI unit is defined in Pascal. 

Types of pressure:

The various types of pressure are;

• Atmospheric pressure
• Absolute pressure
• differential pressure
• gauge pressure

Atmospheric pressure: The Earth is surrounded by a layer of gasses, and the surroundings of the Earth exerts pressure which is defined as the Atmospheric pressure. The value of atmospheric pressure at sea level is 101325 Pa, and it can be measured using a mercury barometer.

Absolute pressure: It is the pressure that is detected above the absolute zero of pressure. It can be measured using a barometer and is equal to the atmospheric pressure plus the measuring pressure.

Gauge pressure: It is also defined as overpressure. It is the pressure of a system above the atmospheric pressure. 

Differential pressure: It is defined as the pressure difference between the two given points. Differential pressure has two variables. That is why it is more complex than gauge pressure or absolute pressure.

SI unit of pressure

There are various units of pressure to describe it. The SI Unit of pressure is Pascal represented by Pa, a pascal can be defined as a force of one Newton applied on the surface area of a one-meter square, or it can be written as N/m-² or kg m-¹ s-². Thus, the name was given in the year 1971. Before that, the SI unit of pressure was measured in newton per meter square. 

The formula of pascal can be given as

Pa = N/m² = kg/ ms²

Some other units of pressure are;

• The centimetres gram system or the CGS unit of pressure is Barye represented as Ba, which is equal to 1 dyn cm-2, or it is equal to 0.1 Pa.
• The other units of pressure are described as pounds per square inch and bar, unit of the atmospheric pressure is atm, millimetres of mercury or inches of mercury, torr, MSW and FSW.

The Reservoir/Excess pressure:

 A soap bubble has two liquid surfaces which are in contact with air, one inside the soap bubble and the other outside the soap bubble. At equilibrium conditions, the air pressure inside the soap bubble is increased than the outside pressure, and the extra pressure is called excess pressure.  

Let us consider a soap bubble which has radius R and surface tension T.  The excess pressure is exerted due to the surface tension of the soap solution. 

The force due to surface tension = 2 x 2πRT

At equilibrium, P πR2 = 2 x 2πRT

So, P = 4T/r

This shows that excess pressure inside the bubble soap is inversely proportional to the radius of the bubble.

Conclusion:

Pressure is defined as the force applied to an area in simple terms. There are many systems available to measure the pressure; absolute pressure and sealed gauge pressure are the two most common systems of pressure measurement. There are many differences between both of the systems that have significant effects on their measurement and uses.