Conservation of Angular momentum

AI Thread Summary
Angular momentum is conserved when there is no external torque acting on a system. The discussion highlights that changes in radius do affect torque, but if the force and radius are parallel, the torque remains zero. This means that even with a changing radius, angular momentum can still be conserved. The key point is that conservation applies in the absence of external influences, regardless of internal changes. Therefore, the conservation of angular momentum remains valid under these conditions.
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Homework Statement


2-10.png


Why is angular momentum conserved?

Homework Equations


\vec{\tau}= \vec{r} x \vec{F}
magnitude of \tau = I \alpha

The Attempt at a Solution



I first don't agree on why angular momentum is conserved, because if the radius change doesn't that change the torque?

And by definition angular momentum of a system is conserved when there are no external torque. While for particles, angular moment is conserved when there is no change in torque.

So the torque changes when radius is shortened, why is it that angular momentum is conserved?
 
Last edited:
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r and F are parallel. They are both directed towards the hole. The angle between them is zero so Fxr vanishes, regardless of the magnitude of r changing.
 

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