Moments and which direction they act

[weedannycool]

if i have a fixed x and y-axis and i have a few forcesin both negative and positive directions when i calculate the sum of the moments how am I meant to know which direction they act

M=Fd

 

[radou]

All you need is a convention, i.e. set one direction "of rotation" clockwise and the other counter clockwise - one set of vectors will then produce positive moments, and the other one negative.

 

[piner]

generally, if a force causes clockwise rotation it's considered negative. counter clockwise is positive, it depends on what your standards are.
if it's in 3D, the rxF will take negative forces and position vectors into consideration