Class 11 Physics Rotational Motion Angular Momentum In Case of Rotation about a Fixed Axis

Angular Momentum In Case of Rotation about a Fixed Axis


  • When a person is rotating with hands stretched, so the moment of inertia will be more because distribution of mass is far from the axis of rotation.
  • As the person brings his arms close to body, moment of inertia decreases because the mass is now distributed close to axis.
  • In this situation no external torque is applied, means angular momentum is conserved.
  • Iω = constant.
  • As I decrease, angular velocity ω


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.


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