Opening/Closing Arms on Rotating Stool Video Lessons

Example

# Problem: An ice skater is spinning with her arms extended out at her sides. She folds in her arms. Explain what happens to her total kinetic energy, moment of inertia, angular speed, and angular momentum in doing so.

###### FREE Expert Solution

Kinetic energy:

$\overline{){\mathbf{K}}{\mathbf{E}}{\mathbf{=}}\frac{\mathbf{1}}{\mathbf{2}}{\mathbf{I}}{{\mathbf{\omega }}}^{{\mathbf{2}}}}$

Angular momentum:

$\overline{){\mathbf{L}}{\mathbf{=}}{\mathbf{I}}{\mathbf{·}}{\mathbf{\omega }}}$

Moment of inertia will decrease.

From the conservation of momentum theory, Angular momentum is conserved if no external torque acts on the system.

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###### Problem Details

An ice skater is spinning with her arms extended out at her sides. She folds in her arms. Explain what happens to her total kinetic energy, moment of inertia, angular speed, and angular momentum in doing so.