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Homework Help: Sign convention of shear force and bending moment

  1. Jul 7, 2016 #1
    1. The problem statement, all variables and given/known data


    in the notes, the author define upward shear force as positive (LHS) , he take downward shear force as positive as positive (RHS)?

    2. Relevant equations

    3. The attempt at a solution
    why the author didnt fix downward shear force as positive , upward shear force as negative or vice versa
  2. jcsd
  3. Jul 7, 2016 #2
    If I had a beam, and applied a force acting upwards on the left, it would rotate clockwise.

    If I was to instead apply a force acting downwards, but on the right, the beam would still rotate clockwise.

    Sum of the clockwise moments = sum of the anti-clockwise moments. It is not about whether the force is acting up or down but whether the result of that force would cause it to rotate clockwise or anti-clockwise. :smile:
  4. Jul 7, 2016 #3
    move on to the lower part of note, i found that the author take the clockwise moment at LHS as positive while at RHS , the author take anticlockwise moment as positive,why is it so???
    why the author take different direction of moment as same sign??
  5. Jul 7, 2016 #4
    why the author take clockwise moment as positive at LHS, take anticlockwise moment as positive at RHS???
  6. Jul 7, 2016 #5
    So, the moment clockwise considered as positive in this case?
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