# Sign convention of shear force and bending moment

1. Jul 7, 2016

1. The problem statement, all variables and given/known data

http://nptel.ac.in/courses/112107146/22

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. Jul 7, 2016

### Clever Penguin

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.

3. Jul 7, 2016

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??

4. Jul 7, 2016