AP®PhysicsCollege BoardPhysics 1: Algebra-BasedStudy GuidesUnit 8: FluidsDensity & PressureDefinition of Pressure

Definition of Pressure (College Board AP® Physics 1: Algebra-Based)

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Dan Mitchell-Garnett

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What is pressure?

  • Pressure is defined as:

Pressure is the magnitude of the perpendicular force component exerted per unit area over a given surface area

  • Pressure can also be defined by the following equation:

P space equals space F subscript perpendicular over A

  • Where:

    • P = pressure, measured in Pa

    • F subscript perpendicular = component of force perpendicular to the surface, measured in straight N

    • A = surface of the area experiencing the force, measured in straight m squared

  • Pressure is a scalar quantity

    • It has magnitude only, no direction

  • A force acting on a surface produces a pressure

    • This force, however, may not act perpendicular to the surface

    • Only the force component which is perpendicular to the surface exerts a pressure on the surface

Force at an angle exerting pressure

Diagram showing a diagonal force F at an angle θ, with its perpendicular component exerting pressure on a vertical surface.
When a force is exerted on a surface at an angle, it is the perpendicular component of this force that produces a pressure on the surface.

Pressure in a fluid

  • The surface of an object submerged in a fluid experiences pressure

  • This pressure is the effect of all of the interactions between that surface and the particles of the fluid

    • This means objects in a fluid experience pressure on all sides in contact with the fluid

Examiner Tip

A single pascal is a very small amount of pressure, like the pressure exerted on a table by a 100 g piece of paper which has an area of 1 m2. Atmospheric pressure is roughly 100 000 Pa.

You do not need to memorize these quantities, but knowing their approximate sizes will help you sense-check answers in an exam.

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    Dan Mitchell-Garnett

    Author: Dan Mitchell-Garnett

    Expertise: Physics Content Creator

    Dan graduated with a First-class Masters degree in Physics at Durham University, specialising in cell membrane biophysics. After being awarded an Institute of Physics Teacher Training Scholarship, Dan taught physics in secondary schools in the North of England before moving to Save My Exams. Here, he carries on his passion for writing challenging physics questions and helping young people learn to love physics.