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

Angular momentum direction

  1. Nov 14, 2005 #1
    In 3-D dynamics why is the angular momentum not aligned with angular velocity?
    Does this mean H = Iw is wrong in 3-D ?
     
  2. jcsd
  3. Nov 14, 2005 #2

    Tide

    User Avatar
    Science Advisor
    Homework Helper

    How do you know the angular momentum is not aligned with the angular velocity?

    Generally, in 3D, the angular velocity is a vector and the moment of inertia is a tensor (matrix).
     
  4. Nov 14, 2005 #3

    BobG

    User Avatar
    Science Advisor
    Homework Helper

    The angular momentum vector can be aligned with the angular velocity vector. It's just not necessarily the case. If the two vectors are aligned, H=Iw is perfectly valid as a scalar equation.

    As Tide said, the moment of inertia is a matrix and the angular velocity is a vector. If the angular momentum vector and the angular velocity vector are aligned, all the elements of the matrix except the diagonals will be zero. As a result, the scalar equation can be used for each axis of rotation.

    Generally, if one were planning something, one would probably plan to have the geometric axes align with the object's principal axes (axes based on mass distribution) and would plan to keep the angular momentum vector and angular velocity vector aligned. In practice, the outside environment will cause the two vectors to become misaligned with each other (nutation).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Angular momentum direction
  1. Angular Momentum (Replies: 1)

  2. Angular momentum (Replies: 1)

Loading...