Pressure is a fundamental physical quantity that describes the force applied perpendicular to the surface of an object per unit area. It's a crucial concept in physics, engineering, meteorology, and many other fields. In this guide, we'll explore different types of pressure, how it's measured, and its wide-ranging applications in science and everyday life.
What is Pressure?
Pressure (P) is defined as the force (F) applied perpendicular to the surface of an object per unit area (A) over which that force is distributed. The mathematical expression is P = F/A. The SI unit of pressure is the pascal (Pa), where 1 Pa = 1 N/m². Pressure is a scalar quantity, meaning it has magnitude but no specific direction.
Key Concept:
Pressure depends on both the magnitude of the force and the area over which it's distributed. This is why sharp knives cut better (same force over a smaller area creates higher pressure) and snowshoes prevent sinking (distribute weight over a larger area reduces pressure).
Types of Pressure
Atmospheric Pressure
Pressure exerted by the weight of the atmosphere.
~101.325 kPa at sea level
Gauge Pressure
Pressure relative to atmospheric pressure.
Used in tire pressure, blood pressure
Absolute Pressure
Total pressure including atmospheric pressure.
Used in scientific calculations
Differential Pressure
Difference between two pressures.
Used in flow measurement, filters
Units of Pressure
SI Units
- Pascal (Pa): 1 N/m²
- Kilopascal (kPa): 1,000 Pa
- Megapascal (MPa): 1,000,000 Pa
- Bar: 100,000 Pa
Other Common Units
- Atmosphere (atm): 101,325 Pa
- Millimeters of Mercury (mmHg): 133.322 Pa
- Pounds per Square Inch (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
Uses a column of liquid to measure pressure differences.
Common in laboratories
Bourdon Gauge
Mechanical device that uses a coiled tube that straightens under pressure.
Common in industrial applications
Piezoelectric Sensor
Generates an electrical signal proportional to applied pressure.
Used in electronic systems
Applications of Pressure
Meteorology
- Weather forecasting
- Storm tracking
- Altitude measurement
- Climate studies
Medical
- Blood pressure monitoring
- Ventilators
- Hyperbaric chambers
- Respiratory therapy
Industrial
- Hydraulic systems
- Pneumatic systems
- Process control
- Quality assurance
Transportation
- Tire pressure monitoring
- Aircraft cabin pressurization
- Submarine operations
- Fuel injection systems
Did You Know?
The deepest part of the ocean, the Mariana Trench, reaches depths of about 11,000 meters (36,000 feet). At these depths, the water pressure is approximately 1,100 atmospheres (111 MPa or 16,100 psi), equivalent to having about 50 jumbo jets stacked on top of you! Despite these extreme conditions, life still thrives in these deep-sea environments.
Pressure in Everyday Life
Common Pressures
- Atmospheric pressure at sea level: ~101.3 kPa (14.7 psi)
- Car tire pressure: ~200-250 kPa (29-36 psi)
- Bicycle tire pressure: ~350-700 kPa (50-100 psi)
- Blood pressure (normal): ~16 kPa (120 mmHg) systolic / ~11 kPa (80 mmHg) diastolic
- Scuba tank: ~20,700 kPa (3,000 psi) when full
Extreme Pressures
- Center of the Earth: ~360 GPa (52 million psi)
- Center of the Sun: ~265 billion kPa (38 billion psi)
- Highest man-made pressure: ~770 GPa (112 million psi) in diamond anvil cell experiments
- Space (interstellar medium): ~1.3 × 10⁻¹⁴ Pa (extremely low pressure)
Practical Tip:
When working with pressure systems, always follow proper safety procedures. Remember that pressure differences can be extremely dangerous. When inflating tires, never exceed the manufacturer's recommended pressure. When working with compressed gases, use appropriate regulators and safety equipment. And always release pressure from systems before performing maintenance. A good rule of thumb is to treat all pressure vessels as potentially dangerous and never take shortcuts with pressure-related safety measures.