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Do now. Can you read the hydraulics pages of your books (p157)?. Today’s lesson. Know what the turning effect of a force is Know that the moment of a force depends on force and the distance from the pivot Know the principle of moments.

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Do now

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  1. Do now Can you read the hydraulics pages of your books (p157)?

  2. Today’s lesson • Know what the turning effect of a force is • Know that the moment of a force depends on force and the distance from the pivot • Know the principle of moments

  3. What happens when you try to open a door with one finger? Where do you push? Hi, my name is Mr Stick hinges

  4. Do you push near the hinges? I can’t do it!

  5. Do you push far from the hinges? That’s easier!

  6. Moments – Turning forces

  7. The turning effect of a force depends on two things; The size of the force Obviously!

  8. The turning effect of a force depends on two things; The distance from the pivot (axis of rotation) Not quite so obvious! Axis of rotation

  9. Turning effect of a force The turning effect of a force is called the moment of the force The moment is calculated by multiplying the force by the distance from the pivot

  10. Turning effect of a force – moment of a force Moment (Nm) = Force (N) x distance from pivot (m) Note the unit is Nm, not N/m!

  11. A simple example! 50 N 0.15 m nut spanner (wrench)

  12. A simple example! Moment = Force x distance from pivot Moment = 50 N x 0.15 m Moment = 7.5 Nm 50 N 0.15 m nut spanner (wrench)

  13. What do you do if the nut won’t move and you can’t push harder?! 50 N 0.15 m nut spanner (wrench)

  14. Get a longer spanner! Moment = Force x distance from pivot Moment = 50 N x 0.25 m Moment = 12.5 Nm 50 N 0.25 m nut spanner (wrench)

  15. More than one force Take an uneven see-saw for an example It’s not looking good! Do you think we’ll be safe in this power point? pivot

  16. If the see-saw is balanced, what must be the weight of the dog on the left? 1.2 m 2.2 m pivot ? N 110 N

  17. The force on the left is trying to turn the see-saw anticlockwise about the pivot 1.2 m 2.2 m pivot ? N 110 N

  18. The force on the right is trying to turn the see-saw clockwise about the pivot 1.2 m 2.2 m pivot ? N 110 N

  19. If the see-saw balances, the turning effect anticlockwise must equal the turning effect clockwise 1.2 m 2.2 m pivot ? N 110 N Anticlockwise moment = clockwise moment

  20. Anticlockwise moment = clockwise moment? X 1.2 = 110 x 2.2? X 1.2 = 242? = 242/1.2? = 201.7 N 1.2 m 2.2 m pivot ? N 110 N Anticlockwise moment = clockwise moment

  21. Rotational Equilibrium When there is no resultant moment on an object (when anticlockwise moments = clockwise moments) we say the object is in rotational equilibrium. YouTube - Alan Partridge's Apache office

  22. Whew! We seemed to have survived the power point pivot

  23. BOMB Don’t speak too soon! pivot

  24. BOMB pivot

  25. BOMB pivot

  26. BOMB pivot

  27. pivot

  28. Nice one! pivot

  29. You’ll have to do some questions now, or he’ll kill me too! pivot

  30. Read pages 162 and 163 and make notes. Then try the questions. pivot

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