A man of mass m1 is standing at the edge of a disc of mass m2 which is pivoted about its CM. The man starts waling along the rim of the disc with a velocity μo. Find the angular velocity acquired by the disc by the motion of the man along the rim? I couldn't do this on my own so I turned to the solutions for the help. There it is written that since no external torque is present on the (man+disc) system therefore we can apply conservation of angular momentum about the axis of rotation, i.e the CM. But after that it is written that: ζman+ζdisc=0 Why is this?