Moments, Couples and the Conditions for Equilibrium · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Turning forces and staying balanced

Science · Forces & Motion · ages 16-17
Name ______________________   Date ____________

  1. A force of 40 N pushes perpendicular to a door 0.8 m from the hinges. What is the moment?

    • 32 N m
    • 20 N m
    • 48 N m

  2. What is the unit of a moment?

    • newton
    • newton metre
    • joule

  3. A body in equilibrium has zero resultant force and zero total moment.

    Circle one:   True   False

  4. A person stands off centre on a plank resting on two supports. How do you find a support force?

    • Add both support forces to the person's weight
    • Divide the person's weight by the plank length
    • Set clockwise moments equal to anticlockwise moments about one support

  5. A force of 20 N acts perpendicular at 0.8 m from a pivot. Give the moment in newton metres.

    Answer: ______________

  6. Why does taking moments about the left support help?

    • It makes the answer larger
    • It removes the left support force from the equation
    • It removes the person's weight from the equation

  7. A couple is made of two 10 N forces 0.5 m apart. Give its moment in newton metres.

    Answer: ______________

  8. A pupil claims a pair of equal and opposite parallel forces has a resultant force. What should you tell them?

    • The pair gives a double push along the gap
    • The pair gives no moment at all
    • The pushes cancel, so only a turning effect remains
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Turning forces and staying balanced W1-mt_EDsdTZ0BNO-s1

  1. 32 N m · Multiply 40 by 0.8 to get 32 N m.
  2. newton metre · A moment is force times distance, so its unit combines the two.
  3. True · Both conditions must hold at once for balance.
  4. Set clockwise moments equal to anticlockwise moments about one support · Balance of moments about one support leaves one unknown to solve.
  5. 16 · Halving the force halves the moment: 20 times 0.8 is 16.
  6. It removes the left support force from the equation · The force at the pivot has zero distance, so its moment is zero.
  7. 5 · One force times the gap: 10 times 0.5 is 5.
  8. The pushes cancel, so only a turning effect remains · Equal and opposite forces sum to zero push, leaving pure turning.
Worksheet · LightMySky