Example - A child stands at the centre of a turntable with his two arms outstretched . The turntable is set rotating with an angular speed of 40 rev / min . How much is the angular speed of the child if he folds his hands back and thereby reduces his moment of inertia to 2 / 5 times the initial value ? Assume that the turntable rotates without friction .
Solution : When the child folds his hand back , there is no external torque involved , so the angular momentum is conserved in this case .
Rolling motion Rolling motion is a combination of rotation and translation .