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Re: [Phys-l] Landau on Lagrangian

I guess this statement illuminates the crux of my problem. When you say
that, at the start, you "have a Lagrangian formulation of the situation",
are you saying that you already know

1) the details of the Lagrangian for a particular problem, or
2) that the general definition of the Lagrangian is L = KE - PE, or
3) something else?

IE.; At the start, what is our a priori knowledge/definition of the

I doubt I'll be able to add much to this at this point, but my original post was essentially looking for a plausibility argument, as opposed to any formal proof, of what the Lagrangian of a *free* particle, ie L=T, would look like, without invoking N2. I think the thread, summarized well by DB, presents a reasonable plausibility argument.

As to what the form of V is, such that L = T-V, it seems unlikely that a plausibility argument other than "whatever is necessary to get N2," is to be found.

Stefan Jeglinski