Pressure is force per unit area applied perpendicular to a surface. This guide covers definition, types, units, conversion, measurement, and applications.
What is Pressure?
P = F/A. SI unit: pascal (Pa) = N/m². Pressure is scalar.
Key Concept:
Higher force or smaller area → higher pressure; larger area spreads force → lower pressure.
Types of Pressure
Atmospheric
Due to the weight of air. ~101.325 kPa at sea level.
Gauge
Relative to atmosphere (e.g., tires, blood pressure).
Absolute
Includes atmospheric pressure.
Differential
Difference between two points (flow, filters).
Units of Pressure
SI Units
- Pa
- kPa
- MPa
- bar
Other Units
- atm: 101,325 Pa
- mmHg: 133.322 Pa
- psi: 6,894.76 Pa
- torr: 133.322 Pa
Pressure Conversion Table
| Unit | Pascal (Pa) | Bar | psi | atm |
|---|---|---|---|---|
| 1 Pa | 1 | 0.00001 | 0.000145 | 0.00000987 |
| 1 bar | 100,000 | 1 | 14.5038 | 0.9869 |
| 1 psi | 6,894.76 | 0.0689 | 1 | 0.0680 |
| 1 atm | 101,325 | 1.01325 | 14.6959 | 1 |
Measuring Pressure
Manometer
Liquid column to read pressure difference.
Bourdon gauge
Coiled tube straightens with pressure.
Piezo sensor
Generates signal ∝ pressure.
Applications of Pressure
Meteorology
- Forecasting
- Storm tracking
- Altitude
- Climate
Medical
- Blood pressure
- Ventilators
- Hyperbaric
- Respiratory therapy
Industrial
- Hydraulics
- Pneumatics
- Process control
- QA
Transportation
- Tire monitoring
- Cabin pressurization
- Submarines
- Fuel injection
Did You Know?
At ~11,000 m depth (Mariana Trench), pressure ≈ 1,100 atm (111 MPa, 16,100 psi).
Pressure in Everyday Life
Common pressures
- Sea‑level atmosphere ~101.3 kPa
- Car tires ~200–250 kPa
- Bike tires ~350–700 kPa
- Normal BP ~120/80 mmHg
- Scuba tank ~20,700 kPa
Extreme pressures
- Earth core ~360 GPa
- Sun core ~265 billion kPa
- Lab record ~770 GPa
- Space ISM ~1.3×10⁻¹⁴ Pa
Practical Tip:
Respect pressure safety. Use proper regulators, stay within ratings, and depressurize before maintenance.