Wikipedia is potentially like a supplemental textbook(adsbygoogle = window.adsbygoogle || []).push({});

which is online and instantly available

In another PF context someone was interested in getting

an intuitive layman's idea of topics in these Wikipedia articles:

http://en.wikipedia.org/wiki/Action_principle

http://en.wikipedia.org/wiki/Lagrangian

http://en.wikipedia.org/wiki/Lagrangian_mechanics

http://en.wikipedia.org/wiki/Gauge_theory

Prompted by this other PF member's interest, I looked at these articles and thought (just my personal take) that they are pretty good, for what they try to do. I have not compared what is available at Eric Weisstein's site "World of Physics" or "World of mathematics".

I would like to know what other people think about the Wikipedia treatment. Is there a better online resource for general audience that covers these topics?

A side issue-----things like gauge group and Lagrangian come up in quantum contexts, so why put this thread in Classical?

I think it belongs here because you first understand the ideas in a classical setting, and that makes it easier to apply them in other situations later.

Apparently the idea of "action" (which Euler called "effort" and which several of his contemporaries thought that Nature always chose to minimize) was first investigated by Maupertuis around 1750.

To understand how to get the Euler-Lagrange equation from differentiating the action integral and setting equal to zero the main thing seems to be

that you have to know something from Freshman Calculus called

"integration by parts". The Wikipedia treatment is way way basic and i think that is great----makes it seem accessible from Freshman Calculus

with maybe a little judicious handwaving. Like, if some Frenchman can do it in 1750 can it really be all that hard?

Anyway it's classical, so here's a classical forum thread if anyone wants to comment on the Wiki articles or on the action principle itself and anything related

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# Is Wikipedia good on the action principle? (Lagrangian etc.)

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