Moments and Turning Forces

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Moments and Turning Forces
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The Lifting Challenge

• Who is strongest?

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What affects the turning force?

• Hold a rod horizontally and hang a weight on the
  rod near your hand.
• Have your partner move the weight away from your
  hand, try to keep the rod horizontal.
• What happens?
• Now try it with a heavier weight.

distance
Force
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What do you think?

• How is the turning force or moment affected by
  the distance from the pivot?
• As the perpendicular distance increases the
  turning force increases
• How is the moment affected by the force (effort)
  exerted?
• As the force increases the moment increases

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Can you be more quantitative?

• How is the moment affected by the distance from
  the pivot?
• As the perpendicular distance doubles the turning
  force doubles
• How is the moment affected by the force (effort)
  exerted?
• As the force doubles the moment doubles
• Therefore

Moment Force x perpendicular distance to pivot
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Unit for Moment

• Determine the unit for the moment of a force.
• Moment Force x perpendicular
• distance to pivot
• Newton metre (Nm)

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Is Moment a vector quantity?

• Does the direction matter?

• Calculate the moments below. In which direction
  are they acting? Clockwise or Anticlockwise?

Moments can either be clockwise or
anticlockwise.
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What if there is more than one force acting?

• Find the total moment acting on the bar above.
• When more than one force acts in the same
  direction, their overall turning effect is just
  the sum of their moments.

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Moments Circus

• There are six stations.
• Using the sheet provided record the effort used
  on each object and measure the perpendicular
  distance to the pivot
• Finally, calculate the moment.
• Do not forget units!!

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Experiment -Testing the principle of moments

• Using the apparatus given investigate the
  principle of moments.

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Experiment -Testing the principle of moments

• What did you notice about the anticlockwise
  moment and the clockwise moment?

• When forces act in a different direction, yet
  still balance, the total turning effect in each
  direction will be the same
• sum of clockwise moments sum of anticlockwise
  moments