This question probably has one of the best answers I have received on physics.stackexchange and I think the question itself was clear enough too.

The moderator who closed it for being "too localised", simply says it is because he received a flag. Is that reason enough? Surely flags are just there to get a moderator to look at it.

I would not consider it to be "localised" as it's quite a bog standard Lagrangian free particle problem. Perhaps I am wrong. What about this question is localised?

UPDATE: question is now open again.


2 Answers 2


Disclaimer: as the only person involved in answering the question so far, I may have some bias.

I think the question is a good one. It is asking how Lagrangians are actually applied to real problems, plain and simple, without all the clutter of conservation laws and phase spaces and other things that get theorists excited but don't always have a use.

I reworded the question to emphasize this interpretation and submitted it for reopening, which will require either a mod or (I think) a consensus of some low number of high rep users.

  • $\begingroup$ Yep, you need 4 other 3k+ users. $\endgroup$ Commented Apr 8, 2013 at 7:07
  • $\begingroup$ In this case your edits seem fine and I've reopened it :) Thanks! $\endgroup$ Commented Apr 8, 2013 at 7:11

Update: @ChrisWhite's edits make it much better, I reopened it. After all, closing is a temporary state that can usually be escaped by editing.

My opinion after skimming through it:

It looks like a homework-type problem1. You may want to see our homework policy.

You need to show what you have tried and your level of understanding before asking a homework problem. The "too localised" reason is just used as a proxy for "does not follow homework policy".

Opinion after reading it in full:

Looking closer, it seems like the question didn't make much sense. It was clear that you were confused about Lagrangian mechanics; but the question was not exactly answerable.

Here's an example of a question of a similar type where the problem is very, very accentuated: "How do I add numbers in General Relativity?"

That's a localized question; nobody else will ask that. It doesn't matter if the answer may contain a lot of conceptual details -- this counts as "accidental" learning. The bare minimum answer to the numbers question is "just like in normal arithmetic". Which isn't really useful to anyone. Similarly, the bare minimum answer to yours is "just like in Newtonian mechanics" -- not too helpful an answer. This is basically why it was too localized.

Note that since there's already a good answer, closing doesn't change much.

However, since your main goal is to understand how to replace NM with LM, asking that question (which @ChrisWhite did in his edit) may make it reopenable :)

Mods don't have to listen to flags. However, in this case, the flag was a sensible one that made the problem with the post clear. (Unfortunately I can't tell you the details of the flag itself, that's private information)

1. Note that it doesn't have to be homework, it's just the type that matters

  • 1
    $\begingroup$ Almost, apart from the fact I was not asking "how to add numbers". I was asking whether there was a lagrangian interpretation for the example I gave. $\endgroup$
    – Magpie
    Commented Apr 8, 2013 at 6:13
  • $\begingroup$ @mag it's an analogy :/ $\endgroup$ Commented Apr 8, 2013 at 6:15
  • $\begingroup$ analogy for rudeness. $\endgroup$
    – Magpie
    Commented Apr 8, 2013 at 6:16
  • $\begingroup$ @magpie ? How is that rude? I just compared your question to one which has a similar, more evident, problem. $\endgroup$ Commented Apr 8, 2013 at 6:19
  • $\begingroup$ If it came off as rude, I apologize for that :) $\endgroup$ Commented Apr 8, 2013 at 6:21
  • 1
    $\begingroup$ If that is how you like to present yourself to the world it's no skin off my nose. $\endgroup$
    – Magpie
    Commented Apr 8, 2013 at 6:24
  • 1
    $\begingroup$ @Magpie: I see now what you perceived as rude. I really wasn't trying to be rude, I just gave an example of a question where the same problem, in a very accentuated form, was there; which I thought would make the problem clearer :/ $\endgroup$ Commented Apr 8, 2013 at 8:15

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