1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Conservation of Angular momentum

  1. Apr 27, 2008 #1
    1. The problem statement, all variables and given/known data

    Why is angular momentum conserved?

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

    3. 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: Apr 27, 2008
  2. jcsd
  3. Apr 27, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    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.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?