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Forces and Their Effects

Turning forces and the moment of a force

  • 3 things to know
  • Paper 2

Overview

The turning effect of a force about a pivot on doors, taps and spanners, the moment of a force as force × distance normal to the direction of the force, its unit N m, and calculating moments, forces and distances.

What you need to know

Answer each one before you reveal it.

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Key term

Explain why pushing a door close to its hinge makes the door harder to open than pushing near the handle.

Key term

Explain why a spanner is used to loosen a tight nut rather than turning the nut by hand.

Key term

State the equation for the moment of a force.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Explain what is meant by the turning effect of a force.

    Model answer

    It is the tendency of the force to make an object rotate about a pivot.

  2. 2

    Describe a situation in which a force causes rotation.

    Model answer

    Pushing on a door handle makes the door swing round about its hinges.

  3. 3

    Name the fixed point about which an object turns when a force causes it to rotate.

    Model answer

    The pivot.

  4. 4

    Explain why pushing a door close to its hinge makes the door harder to open than pushing near the handle.

    Model answer

    The force acts a smaller distance from the pivot, so its turning effect is smaller.

  5. 5

    Give an example of a force causing rotation in a kitchen.

    Model answer

    Turning a tap handle rotates the tap about its axis.

  6. 6

    Explain why a spanner is used to loosen a tight nut rather than turning the nut by hand.

    Model answer

    The spanner lets the force act much further from the pivot, giving a larger turning effect.

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