rotating object
 

If you have a object rotating with constant angular velocity and without any translational velocity, and its moment of inertia changes, you can solve for its new angular velocity in the conservation of kinetic energy (since translational KE cancels out) equation, KE=1/2*m*v^2+1/2*I*w^2, v=0, KE=1/2*I*w^2 and in the conservation of momentum equation. P=I*w But, you do not get the same answer. Could somebody please explain why?

Re: rotating object
 

The usual picture is the ice skater who is turning with his arms wide open, and then as he closes his arms he rotates faster. THere is conservation of angular momentum but not of energy, since energy has been needed to change the position of his arms. Therefore, in this case, you should use the conservation of angular momentum rather than the conservation of energy.

PG