Spinning on the stool with bicycle wheel Spin bicycle wheel

Spinning on the stool with bicycle wheel Spin bicycle wheel first, then get on stool Before sitting on the stool, hold the bicycle wheel with the handles vertical and get it spinning. In what direction is the wheel rotating? (As viewed from above, looking down from the ceiling. Clockwise (CW) or counterclockwise (CCW). With the wheel already spinning and the handles vertical, sit on the stool. With your feet off the floor, with one hand stop the wheel from rotating. In what direction do you spin after the wheel is stopped (CW or CCW)? Is the wheel actually stopped, or is it also spinning (with you)?

Solution

The interaction is in between the boy the cycle, i.e. internal. No external torque implies conservation of angular momentum. So if he rotates the wheel CW initially before sitting on the stool the angular momentum conservation says that if he stops the wheel w.r.t. him, the whole system (boy+wheel) will have the equal angular momentum, CW. So even if w.r.t. him wheel is stationary, the wholw system is rotating.

-Avi(IST-3:30am, 8/4/16)