Pressure = Force / Area. It describes how concentrated a force is over a surface.
Common Units
- 1 atm = 101,325 Pa = 14.696 psi = 1.01325 bar
- 1 bar = 100,000 Pa β 14.504 psi
- mmHg: 1 atm = 760 mmHg (used in medicine)
Types
- Atmospheric: Weight of air above a surface (14.7 psi at sea level)
- Gauge: Pressure above atmospheric (tire pressure)
- Absolute: Gauge + atmospheric (used in thermodynamics)
- Hydrostatic: P = Οgh (pressure from fluid depth)
Why Altitude Affects Cooking
Atmospheric pressure drops with altitude, which lowers water's boiling point (about 3β4Β°F lower per 1,000 ft of elevation). At high altitude, water boils at a lower temperature, so food takes longer to cook β the reason recipe instructions often include high-altitude adjustments for baking and boiling.
Pascal's Principle
Pressure applied to an enclosed fluid transmits equally in all directions β the working principle behind hydraulic systems (car lifts, brakes, excavator arms), where a small force on a small piston can generate a much larger force on a larger piston, multiplying force at the cost of distance moved.