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Moments - How are they actually calculated?

  1. Oct 9, 2013 #1
    Moments -- How are they actually calculated?

    Hello, I have a question.

    Is the moment calculated:

    Force times the distance or

    Force's perpendicular component (to axis) times the distance.

    For example, lets say I have a stick.

    Pulling on it is not moment.

    So if I push at the stick to an angle, the way I calculate the force that the other side is applying is by taking the perpendicular component of my Fa and multiplying it by the distance.

    Is that correct?
  2. jcsd
  3. Oct 9, 2013 #2


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    Homework Helper

    Yes, when you are calculating moments, you would use the perpendicular component. The parallel component will not produce any moment as the perpendicular distance is zero.
  4. Oct 9, 2013 #3


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    Gold Member

    Mathematically, a moment is ##\vec{l} = \vec{r} \times \vec{f}##. The magnitude comes out as ##l = rf\sin\theta##, where ##\theta## is the angle between the position vector and the force vector. This is equivalent to saying that it is the perpendicular component of the force.
  5. Oct 9, 2013 #4
    Thank you!
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