Re: [Phys-l] Landau on Lagrangian

[Stefan Jeglinski <jeglin@4pi.com>]

> 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
> Lagrangian?

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