Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Can something moving linearly without rotation have anguar momentum?

  1. May 19, 2014 #1
    I was doing a question in Taylor book (example 3.3) where a sticky putty is thrown at a stationary wheel. To solve it we use conservation of angular momentum. What I am confused about is that the wheel is initially at rest and has no angular momentum initially. But when the putty is thrown at it the wheel starts spinning and gains angular momentum. Since angular momentum must be conserved (external torque is 0 so angular momentum conserved) there must be some inital angular momentum from the putty.

    So my question is even though the putty is thrown in a straight line and has no spin or rotational motion, it still posses angular momentum?
     
  2. jcsd
  3. May 19, 2014 #2

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    Yes.

    Even a point mass has angular momentum with respect to some reference frame. That essentially is how angular momentum is defined. The angular momentum of a system of particles is the sum of the angular momenta of the individual particles.
     
  4. May 19, 2014 #3
    Ok so with respect to some origin, a point mass will have angular momentum given by rxp where where r is the distance from the origin. Even if it appears to be going straight with no rotation correct? So angular momentum is always defined with respect to an origin
     
  5. May 19, 2014 #4

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

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