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Homework Help: Verifying that the Euler-Lagrange equation uses generalized coordinates

  1. Apr 16, 2007 #1
    This is a question that I'm asking myself for my own understanding, not a homework question.

    I realize that in most derivations of the Euler-Lagrange equations the coordinate system is assumed to be general. However, just to make sure, I want to apply the "brute force" method (as Shankar calls it) to verify that the Euler-Lagrange equations indeed use generalized coordinates.

    So, here's the problem. Given the Euler-Lagrange equations in a Cartesian coordinate system [itex]x_1, x_2, ... x_n[/itex], show, by change of variables, that the equations retain the same form under a coordinate transformation.

    \frac{d}{dt} \left (\frac{\partial L}{\partial \dot{x_i}} \right ) = \frac{\partial L}{\partial x_i}

    I have no idea how to go about transforming coordinates. I created a coordinate system [itex]q_i[/itex] which could be written in terms of the [itex]x_i[/itex], but I wasn't sure how to use brute force methods to verify that the E-L equations use generalized coordinates. If someone could show me how to do it, I would appreciate it greatly.

    Thanks for helping me understand this!
    Last edited: Apr 16, 2007
  2. jcsd
  3. Apr 16, 2007 #2


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    http://www.uio.no/studier/emner/matnat/fys/FYS3120/v05/undervisningsmateriale/Symmetry.pdf [Broken] may be useful.
    Last edited by a moderator: May 2, 2017
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