Talk:Advanced Classical Mechanics/Constraints and Lagrange's Equations

The section on non-conservative forces is wrong. The final Hamiltonian still depends on the vector potential (obviously! What happened to it?) The form should be H = (p - qA)^2 / 2m + q Phi

Question on Virtual Work explanation

Here's a question (and a suggested edit) for the author(s) of the article or any other reader with similar knowledge:

I've been trying to get an intuitive understanding of why the concept of "virtual work," works in deriving Lagrange's equations. Its pretty easy to see how assuming that the system is frozen in time allows you to ignore moving constraint forces, but the question that I'm trying to answer is: why is this a legitimate assumption? I've read numerous derivations of Lagrange's Equations but none seem to explain why assuming delta t = 0 is an allowable move to make.

I'd appreciate if you could explain this in the context of the following example: A rigid, frictionless wire, rotating in a plane parallel to the earth's surface, along which a bead is constrained to move. No unbalanced applied forces are present.

Editing the text to include some sort of discussion of this issue might be quite helpful to readers, especially considering that other authors writing on Lagrange's equations have historically not addressed it. (The preceding unsigned comment was added by Ken924 (talk • contribs) 22:43, 27 August 2007)