levo

Forces

Moments, levers and gears

  • 2 things to know
  • Paper 2

Overview

Turning effects and how a spanner turns a nut, the moment of a force in words and symbols with its units and the perpendicular distance, why a force through the pivot has no turning effect, balancing about a pivot with seesaw and beam calculations, and how levers and gears transmit the rotational effects of forces.

What you need to know

Answer each one before you reveal it.

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Key term

State the equation for the moment of a force, in words.

Numbers

A force of 20 N acts at a perpendicular distance of 0.30 m from a pivot. Calculate the moment.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What can a force or a system of forces make an object do as well as move in a straight line?

    Model answer

    It can make the object rotate.

  2. 2

    Explain how a spanner makes a nut turn.

    Model answer

    The force applied at the end of the spanner acts at a distance from the nut, so it produces a turning effect about the nut.

  3. 3

    What is the moment of a force?

    Model answer

    It is the turning effect of that force.

  4. 4

    State the equation for the moment of a force, in words.

    Model answer

    Moment of a force = force × perpendicular distance from the pivot to the line of action of the force.

  5. 5

    A force of 20 N acts at a perpendicular distance of 0.30 m from a pivot. Calculate the moment.

    Model answer

    Moment = 20 × 0.30 = 6 N·m.

  6. 6

    Write the equation for the moment of a force using symbols.

    Model answer

    M = Fd, where M is the moment, F is the force and d is the perpendicular distance from the pivot.

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