1. Limited time only! Sign up for a free 30min personal 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!

What happens when you rotate a rigid body

  1. Sep 11, 2015 #1
    Hi,

    I have a question about rigid body rotation. If I have a rod out in space in free float and I attach a battery powered fan to center of mass and then the fan is turned on to spin in a clockwise direction, then the rod should spin in a counterclockwise direction. This much I understand. But, what if, instead, the fan was attached to the end of the rod rather than to the center of mass? What would happen then?



    Any help would be greatly appreciated!
     
  2. jcsd
  3. Sep 11, 2015 #2
    As a more general question, what would happen if you attached the fan to anywhere on the rod other than the center of mass? how would the rod and the fan spin together? Is what happens similar to a clothes washer that is unbalanced? Thanks in advance for any insight into this question!
     
  4. Sep 11, 2015 #3

    Dale

    Staff: Mentor

    If you are rotating about an axis that is not an axis of symmetry then the moment of inertia is a tensor meaning that the angular momentum does not line up with the axis of rotation. This gives you a wobble which is called gyroscopic free precession or torque-free precession.
     
  5. Sep 11, 2015 #4
    Hi,

    Thanks for your answer, would the system wobble around a certain point? Like, center of mass of the system?
     
  6. Sep 11, 2015 #5

    Dale

    Staff: Mentor

    Yes. There is no external force so the center of mass must remain at rest (assuming it started at rest). The axis of rotation will wobble, but will always pass through the center of mass.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: What happens when you rotate a rigid body
Loading...