Conservation of angular momentum with energy

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Discussion Overview

The discussion revolves around the conservation of angular momentum and its relationship with energy during the motion of an ice skater who changes her moment of inertia by folding her arms. Participants explore the implications of this change on rotational speed and kinetic energy.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant describes the scenario of an ice skater folding her arms, leading to a decrease in moment of inertia and an increase in rotational speed, questioning the resulting energy change.
  • Another participant suggests that the skater does work when bringing her arms in, indicating that internal energy is converted into rotational kinetic energy.
  • A different participant notes that rotational kinetic energy is not conserved in this process.

Areas of Agreement / Disagreement

Participants express differing views on the conservation of energy in this context, with some agreeing that work is done and others emphasizing that rotational kinetic energy is not conserved. The discussion remains unresolved regarding the implications of these points.

Contextual Notes

There are assumptions regarding the definitions of energy and work in the context of the skater's motion that are not fully explored. The discussion does not resolve the mathematical steps involved in the energy calculations.

Who May Find This Useful

Readers interested in the principles of angular momentum, rotational dynamics, and energy transformations in physical systems may find this discussion relevant.

suhagsindur
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Ice sketar rotates with open arms & her moment of inertia is I, rotational speed W. So, angular momentum is I*W. Energy is (1/2)I*W*W
she folds her arms & her moment of inertia decreases to I/2. From conservation of angular momentum rotational speed became double say W*2.
Energy became (1/2)*I/2*W*W*4 = I*W*W ( Energy is doubled, How?)

Please tell me in this caculation where I am wrong?
 
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You're not wrong. The skater does work when she brings her arms in. She converts internal energy into rotational KE.
 
Rotational kinetic energy isn't conserved
 
OK, Very much Thanks for clearing my doubt.
 

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