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

Example:

- 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.

.