1. The problem statement, all variables and given/known data http://web.mit.edu/course/16/16.unified/www/FALL/materials/documents/HO-M-6(Mohrs)(08).pdf I found this on the Internet . At there , the author defined positive as counterclockwise rotation . and also “ Positive shear would cause a clockwise rotation of the infinitesimal element about the element center. ” In the notes , the author defined positive shear axis as upwards , if I draw positive shear axis as downwards , will it make the difference ? Is it necessary to define clockwise rotation as positive now ? How about 2. Relevant equations 3. The attempt at a solution IMO , it 's necessary to define clockwise rotation as positive . Correct me if I'm wrong .