Conservation of Angular momentum

  • Thread starter kyin01
  • Start date
  • #1
kyin01
47
0

Homework Statement


2-10.png


Why is angular momentum conserved?

Homework Equations


[tex]\vec{\tau}= \vec{r} x \vec{F}[/tex]
magnitude of [tex]\tau = I \alpha[/tex]

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:

Answers and Replies

  • #2
Dick
Science Advisor
Homework Helper
26,263
621
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.
 

Suggested for: Conservation of Angular momentum

Replies
23
Views
491
Replies
23
Views
134
Replies
8
Views
498
Replies
5
Views
143
  • Last Post
Replies
4
Views
461
Replies
4
Views
445
Replies
10
Views
611
  • Last Post
Replies
20
Views
788
Replies
13
Views
459
Top