Definition of Pressure: Classification, Units and Their Relations | New Topic

In this note, we are going to learn the Definition of Pressure, Classification of pressure, units, and Their Relations. Welcome to Poly Notes Hub, a leading destination for diploma and polytechnic engineering notes.

Author Name: Arun Paul.

Definition of Pressure

Pressure is defined as the force acting per unit area on a surface.

It means when a force is applied on a smaller area, pressure becomes higher.

Classification of Pressure

Pressure is mainly classified into the following types:

1. Atmospheric Pressure
   • The pressure exerted by the weight of air (atmosphere) on the earth’s surface.
   • Standard atmospheric pressure = 1 atm
2. Absolute Pressure
   • The total pressure measured from absolute vacuum (zero pressure reference).
   • Absolute Pressure = Atmospheric Pressure + Gauge Pressure
3. Gauge Pressure
   • The pressure measured above atmospheric pressure.
   • Most pressure measuring instruments show gauge pressure.
4. Vacuum Pressure
   • Pressure below atmospheric pressure.
   • Also called negative gauge pressure.
5. Static Pressure
   • Pressure exerted by a fluid at rest.
6. Dynamic Pressure
   • Pressure due to motion of fluid.

Units of Pressure

Relation Among Different Units of Pressure

• 1 atm = 101325 Pa
• 1 bar = 100000 Pa
• 1 atm = 1.013 bar
• 1 atm = 760 mmHg (Torr)
• 1 bar = 0.987 atm
• 1 kPa = 1000 Pa