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Moment about arbitary point

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Homework Statement


Why the moment isn't=15* 3Nm? Since we are taking moment about point O...it's 3m away from O

Homework Equations




The Attempt at a Solution

 

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  • #2
haruspex
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Homework Statement


Why the moment isn't=15* 3Nm? Since we are taking moment about point O...it's 3m away from O

Homework Equations




The Attempt at a Solution

Are you referring to the 15kNm moment that is applied? You don't multiply that by a distance. (It would give you something with units kNm2.) a force times a perpendicular distance gives a moment, but an applied moment is already a moment. Exactly where it is applied makes no difference, only its magnitude and direction matter.
 
  • #3
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Are you referring to the 15kNm moment that is applied? You don't multiply that by a distance. (It would give you something with units kNm2.) a force times a perpendicular distance gives a moment, but an applied moment is already a moment. Exactly where it is applied makes no difference, only its magnitude and direction matter.
ya , i knew that . But , how can be moment be applied? only force can be applied , right?
 
  • #4
haruspex
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ya , i knew that . But , how can be moment be applied? only force can be applied , right?
Are you asking as a practical matter how it is possible to apply a moment as opposed to a force? There does not need to be a way to do that. Consider turning a nut using a spanner. One can think of it as applying a torque, or as applying two equal and opposite forces along parallel but different lines of action. If you are told a moment of some specified magnitude and direction is applied, you do not need to care about how it is applied.
 
  • #5
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Are you asking as a practical matter how it is possible to apply a moment as opposed to a force? There does not need to be a way to do that. Consider turning a nut using a spanner. One can think of it as applying a torque, or as applying two equal and opposite forces along parallel but different lines of action. If you are told a moment of some specified magnitude and direction is applied, you do not need to care about how it is applied.
yes, this will only occur in the exercise , but not in daily life ?
 
  • #6
haruspex
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yes, this will only occur in the exercise , but not in daily life ?
I cannot think of a way to apply a torque to an object (in an inertial frame) other than by a combination of linear forces.
 

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