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Overview
Pressure describes how force is spread across an area. In fluids, pressure acts in all directions and plays a central role in fluid behavior. Pressure helps explain atmospheric effects, hydraulic systems, buoyancy, fluid flow, gas behavior, weather, and lift.
Force Over Area
Pressure increases when force increases or when the same force is applied over a smaller area. This is why sharp objects can pierce more easily than blunt objects under the same force.
Fluid Pressure
In a fluid at rest, pressure acts in all directions. At greater depths in a fluid, pressure increases because more fluid weight lies above.
Atmospheric Pressure
Atmospheric pressure is caused by the weight of air above a surface. It changes with altitude, weather, and atmospheric conditions.
Gauge and Absolute Pressure
Gauge pressure is measured relative to atmospheric pressure. Absolute pressure is measured relative to a vacuum.
Pascal's Principle
Pascal's principle states that pressure applied to an enclosed fluid is transmitted throughout the fluid. Hydraulic systems use this principle to multiply force.
Pressure and Phase Changes
Pressure can affect boiling point, melting point, and phase stability. Lower pressure can make liquids boil at lower temperatures.
Pressure in Gases
Gas pressure comes from particle collisions with container walls. Temperature, volume, and particle number affect gas pressure.
Common Mistakes
A common mistake is confusing force with pressure. A large force spread over a large area can produce less pressure than a smaller force concentrated over a tiny area.
Why This Matters in Physics
Pressure links mechanics to fluids, gases, weather, hydraulics, buoyancy, aerodynamics, medicine, and engineering systems.