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Forces

Pressure at a surface, and the equation p = F over A

  • 2 things to know
  • Paper 2

Overview

Fluids and why a gas counts as one, the force from fluid pressure acting at right angles to a surface, the pressure equation in words and symbols with calculations of pressure, force and area, why sharp knives cut and snowshoes stop sinking, and the units of pressure, force and area.

What you need to know

Answer each one before you reveal it.

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Key term

What is a fluid?

Key term

State the equation for the pressure at the surface of a fluid, in words.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is a fluid?

    Model answer

    A fluid is either a liquid or a gas.

  2. 2

    Explain why a gas counts as a fluid.

    Model answer

    Because a fluid is anything that can flow, and gases as well as liquids can flow.

  3. 3

    In what direction does the force caused by the pressure of a fluid act on a surface?

    Model answer

    It acts normal to the surface, meaning at right angles to it.

  4. 4

    A gas is sealed inside a rigid container. Describe the force its pressure exerts on the container walls.

    Model answer

    It exerts a force at right angles to each of the walls.

  5. 5

    State the equation for the pressure at the surface of a fluid, in words.

    Model answer

    Pressure = force normal to the surface ÷ area of that surface.

  6. 6

    Write the equation for pressure at a surface using symbols.

    Model answer

    p = F ÷ A, where p is pressure, F is the force normal to the surface and A is the area.

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