Suppose a point particle is undergoing circular motion about a fixed point such that a tangential force is accelerating its speed continuously. Now I believe that I can calculate the work done on this particle either by Force or by Torque.
However, for a rigid body, when I calculate work, I calculate it as:
- Work done by Torque in the frame of centre of mass to cause angular displacement added to the work done by the force in displacing the centre of mass.
- By work done by force in displacing its point of application
Now I understand that both of my methods 1 and 2 are equally valid for the circular motion case
But what I do not understand is that why isn't the work done by both force and torque (about point of rotation) added in the circular motion case? Why are these two works synonymous here, but not in method 1?
Is method 1 (as described above) applicable only only when torque is calculated about Centre of Mass and no other point?