In this picture, the book says the father has a positive(+) torque with direction coming outside the paper, and the daughter has a negative(-) torque with direction ggoing inside the paper.
I knew torque's sign was determined by the direction of rotation. Clockwise – negative, Counter-clockwise – positive.
The thing is, the father and the daughter on the seesaw are moving both counter-clockwise. So aren't both supposed to have a positive torque value?
Best Answer
The direction of torque is determined by the direction of the acting force (and the direction of the corresponding lever arm), not the direction of rotation. Since the father's and daughter's weights are tending to move the see-saw in opposite directions, their torques are also in opposite directions.
Are you perhaps confusing torque with the similar concept of angular momentum, which does depend on the direction of rotation ?