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Moments

Moments. Introduction. For stability or equilibrium we have already seen that:.

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Moments

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  1. Moments

  2. Introduction For stability or equilibrium we have already seen that: For rotational forces this means that the effect of the forces rotating the object clockwise must equal the forces rotating the object in an anticlockwise direction. A MOMENT is the measure of the turning effect of a force.

  3. What is a Moment? A moment is defined as: MOMENT (M) = force (f) x perpendicular distance from a pivot (d) So the units of a moment are: Newton metres or Nm

  4. There are two ways of increasing the size of a moment…….. • Increase the size of the force • Increase the distance from the pivot This can be seen in several everyday situations: • A long spanner undoes a nut easier then a short one • Its hard to open a door by pushing near the hinge • a large weight can be lifted using a large lever • A crane has a limited working radius

  5. Increasing the moment….

  6. For equilibrium (balance): The sum of the clockwise moments must be equal to the sum of the anticlockwise moments (moments may be taken about any point on a structure) This is known as ‘The principle of Moments’

  7. For Example…..

  8. Example 2 Unknown weight y=? yx0.1 +5x0.4=0.1y+2 Clockwise moments about fulcrum= • Anticlockwise moments about fulcrum= 20x0.3=6 • For Balance clockwise moments = Anticlockwise moments • 0.1y+2.0=6 0.1y=4 y=40N

  9. Example 3 • What are the sizes of the reactions X and Y at the trestles? Hints: • Take moments about any point • Total Upwards forces must equal total downwards forces • Moments through the point chosen as fulcrum=0 • Answers: Y=240N X=360N

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