Harry, I believe I understand what you are saying. The girl pulls her arms in rapidly, but the movement is along a single line to her side which does not generate a torque as far as I am aware. If no torque is produced, then there can be no change in angular momentum.
She does produce energy by moving her arms, but this would appear as heat once her arms come to a stop by her side. Dave -----Original Message----- From: H Veeder <[email protected]> To: vortex-l <[email protected]> Sent: Sun, Feb 9, 2014 2:38 pm Subject: Re: [Vo]:Linear and Angular Momentum Dave, I am saying if you carefully measured her final speed while considering losses due to friction and drag, her final speed would be slightly greater than could be explained by conservation of angular momentum alone. This is because she does some work in order to bring her arms inwards. In effect she has converted some internal chemical energy into angular momentum. Or is this wrong? Harry On Sun, Feb 9, 2014 at 1:33 PM, David Roberson <[email protected]> wrote: Harry, the skater pulls her arms inwards but that does not contribute to her rotating motion directly. The increased speed is due to the reduction of her moment of inertia and the conservation law requires for her to spin faster so that the product of her moment of inertia and angular velocity is constant. Dave -----Original Message----- From: H Veeder <[email protected]> To: vortex-l <[email protected]> Sent: Sun, Feb 9, 2014 1:05 pm Subject: Re: [Vo]:Linear and Angular Momentum A spinning figure skater is often used to demonstrate the principle of conservation of angular: https://www.youtube.com/watch?v=jeB4aAVQMug However, the skater also exerts some muscular energy to pull her arms inward, so doesn't this boost the angular momentum slightly? Harry
