What is pressure?
Pressure is force normal to a surface divided by its area; the SI unit is the pascal.
How it works and key principles
Solids and fluids: Applying the same force over a smaller area increases pressure. In a still liquid it rises with depth; in a gas it arises from interactions of particles with surfaces. Atmospheric pressure reflects the air above and changes with altitude.
Evidence, examples and limits
Measurement and examples: A barometer measures atmospheric pressure, while a manometer can measure pressure differences. Hydraulic systems use pressure transmitted through a fluid. Pressure and force are not interchangeable; the area and the reference pressure also matter.
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