Turning Effect of Forces

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  1. TURNING EFFECT OF FORCES MOMENTS
  2. Lesson Objectives
    • Identify what are the forces that will give rise to clockwise / anticlockwise moments
    • Calculate clockwise / anticlockwise moments
    • Use the principle of moments to solve problems.
  3. MOMENTS What is moments? A force can cause many things to move or stop. When a force causes an object to turn, this turning effect is called moments. Example: A person sitting on a see-saw.
  4. MOMENTS What is moments? A force can cause many things to move or stop. When a force causes an object to turn, this turning effect is called moments. Example: A person sitting on a see-saw.
  5. Types Of Moments
    • There are 2 types of moments:
    • Clockwise moment
    • Anticlockwise moment
  6. Types Of Moments
    • There are 2 types of moments:
    • Clockwise moment
    • Anticlockwise moment
  7. Clockwise Moment When a force causes an object to turn in a clockwise direction, it is called a CLOCKWISE MOMENT . To determine if the force causes a clockwise or anticlockwise moment, we have to ignore all other forces acting on the object. When the girl sits on the see-saw, her weight is the force exerted on the see-saw. weight
  8. Clockwise Moment When a force causes an object to turn in a clockwise direction, it is called a CLOCKWISE MOMENT . To determine if the force causes a clockwise or anticlockwise moment, we have to ignore all other forces acting on the object. When the girl sits on the see-saw, her weight is the force exerted on the see-saw. weight
  9. ANTI-Clockwise Moment When a force causes an object to turn in an anti-clockwise direction, it is called a ANTI-CLOCKWISE MOMENT . To determine if the force causes a clockwise or anticlockwise moment, we have to ignore all other forces acting on the object. When the girl sits on the see-saw, her weight is the force exerted on the see-saw. weight
  10. ANTI-Clockwise Moment When a force causes an object to turn in an anti-clockwise direction, it is called a ANTI-CLOCKWISE MOMENT . To determine if the force causes a clockwise or anticlockwise moment, we have to ignore all other forces acting on the object. When the girl sits on the see-saw, her weight is the force exerted on the see-saw. weight
  11. CALCULATING MOMENTS Moment = force ? perpendicular distance between force and pivot In symbols: Moments = F ? d Weight => F d Unit for moments: Newton-metre (Nm)
  12. Example 1: A cat of weight 20N stands on one end of a see-saw and the distance between the cat and the pivot is 3m, find the moment. Solution: In this case the cat is causing a clockwise moment. Clockwise moment = F x d = 20 x 3 = 60 Nm F = 20N d = 3m
  13. Example 2: A duck stands on one end of a see-saw, 5m away from the pivot. If the weight of the duck is 10N, find the moment. Solution: The duck’s weight is causing an anticlockwise moment. Anticlockwise moment = F x d = 10 x 5 = 50 Nm F = 10N d = 5m
  14. Examples which is the distance? Where is the force & pivot? F d d F F d d d F F
  15. weight weight Principle of Moments For an object to be in equilibrium(stable/not moving), the total clockwise moment must be equal to the anticlockwise moment about the same pivot point. pivot It is the fixed(non moving) point
  16. SOLVING PROBLEMS RELATED TO PRINCIPLE OF MOMENTS Step 1: Identify what are the forces that will give rise to clockwise / anticlockwise moment Step 2: Find the clockwise / anticlockwise moment Step 3: Equate the clockwise and anticlockwise moments
  17. Find the value of d.   WORKED EXAMPLE 10N 30N 6m d
  18. Step 1: Identify what are the forces that will give rise to clockwise / anticlockwise moment
  19. Find the value of d.   WORKED EXAMPLE Anticlockwise moment Clockwise moment 10N 30N 6m d
  20. Step 2: Find the clockwise / anticlockwise moment
  21.   Clockwise moment = Force x distance between force and pivot = 30 x d = 30d Nm     WORKED EXAMPLE Anticlockwise moment Clockwise moment Anticlockwise moment = Force x distance between force and pivot = 10 x 6 = 60 Nm Find the value of d.   Solution: 10N 30N 6m d
  22. Step 3: Equate the clockwise and anticlockwise moments
  23. Find the value of d.   Solution:   Clockwise moment = Force x distance between force and pivot = 30 x d = 30d Nm   Anticlockwise moment = Force x distance between force and pivot = 10 x 6 = 60 Nm   Using the principle of moments,   Clockwise moment = Anti-clockwise moment 30d = 60 d = 60 ? 30 d = 2 m WORKED EXAMPLE Anticlockwise moment Clockwise moment 10N 30N 6m d
  24. Points to note:
    • The unit for force must be in Newtons, the unit for distance must be in metres.
    • The distance must measured from the force to the pivot.
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