Question

What are the sign conventions for anticlockwise and clockwise rotations of moment?

Answer 1

Sign conventions are given for anticlockwise and clockwise rotations of moment. This is done so that the effect of the torque on an object can be properly expressed by expression of the sense of rotation of the body about an axis of rotation and also the magnitude of the torque.

Complete step-by-step answer:
Sign conventions are helpful in determining the sense of rotations of moment – either anticlockwise or clockwise. By writing the sign convention for the rotation of moment for an object, we get the complete information about the magnitude of the torque along with the sense of rotation about the axis of rotation which the torque tries to provide to the body.
Conventionally, an anticlockwise moment (one which tries to rotate the body in an anticlockwise sense about the axis of rotation) is considered to be a positive moment and the magnitude of the torque on the body is written along with a positive sign. On the other hand, a clockwise moment (one which tries to rotate the body in a clockwise manner about the axis of rotation) is considered to be a negative moment and the magnitude of the torque on the body is written along with a negative sign.

Note: The direction of rotation of the body and hence, the sign of the moment of rotation, that is, the torque depends upon the observer and his position with respect to the object. For example, a person facing one face of a rotating wheel sees the wheel rotating clockwise and hence judges the moment to be negative while the person who is facing the opposite face of the wheel sees the wheel rotating anticlockwise and hence, judges the moment to be positive.