Increasing Spin: Ice Skater's Formula Revealed

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Discussion Overview

The discussion revolves around the physics of an ice skater increasing their spin rate, focusing on the relevant formulas and principles, particularly the conservation of angular momentum. Participants explore the factors that influence the rate of spin and the calculations involved.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants mention that the increase in spin rate is due to the skater pulling their limbs inwards, which affects angular inertia and angular kinetic energy.
  • One participant notes that to calculate the change in spin rate, one must consider the angular inertia with limbs extended versus pulled in, as well as mass and the distance pulled inwards.
  • Another participant emphasizes the conservation of angular momentum, stating that the initial angular momentum equals the final angular momentum, leading to an increase in spin rate when the moment of inertia decreases.
  • There is a reiteration that multiple parameters need to be known for precise calculations, indicating the complexity of the situation.

Areas of Agreement / Disagreement

Participants generally agree on the principle of conservation of angular momentum and its role in increasing spin rates, but the discussion includes varying levels of detail and complexity regarding the calculations and parameters involved.

Contextual Notes

Limitations include the need for specific values for mass, distances, and initial conditions, which are not fully addressed in the discussion.

phredbo
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any one know the formula for an ice skater in an increasing spin
 
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Increasing rate of spin?

Jim
 
It's complicated. Since the spinner does work by pulling a leg and arms inwards, the angular kinetic energy increases. You would need to know the angular inertia with leg and arms extended and then pulled in. Then you'd also need to know the amount of mass, the rate of spin, distance pulled inwards ..., to determine the work done (force times distance) while pulling the leg and arms inwards.

For a single point mass, if the radius is decreased by 1/2 the speed of the mass increases by 2, and the centripetal force increases by 8.
 
hi jeff many thanks for the quick reply. all the best phres
 
The formula, or the idea, which the OP perhaps wanted is the conservation of angular momentum. The initial ang mom =I1w1=final ang mom=I2w2.

As Jeff has said, a lot parameters have to be known for the actual calculation. But, as you must have noticed, if you pull in your arms and/or a leg, then I decreases, resulting in an increase of w, which means you are spinning faster. And vice versa.
 
reply to shooter

Shooting star said:
The formula, or the idea, which the OP perhaps wanted is the conservation of angular momentum. The initial ang mom =I1w1=final ang mom=I2w2.

As Jeff has said, a lot parameters have to be known for the actual calculation. But, as you must have noticed, if you pull in your arms and/or a leg, then I decreases, resulting in an increase of w, which means you are spinning faster. And vice versa.

hi shooter heaps of thanks for the help in the spin formula I am new to the physics forum. I am still finding my way around
the web site. all the best..phredbo
 

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