Talk:Action (physics)

From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Mathematics (Rated B-class, Mid-importance)
WikiProject Mathematics
This article is within the scope of WikiProject Mathematics, a collaborative effort to improve the coverage of Mathematics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Mathematics rating:
B Class
Mid Importance
 Field: Mathematical physics
WikiProject Physics (Rated C-class, High-importance)
WikiProject icon This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
C-Class article C  This article has been rated as C-Class on the project's quality scale.
 High  This article has been rated as High-importance on the project's importance scale.
 

Angular momentum and action units, integration by parts[edit]

I agree with this reinstatement by JRSpriggs, and do not agree with

  • this edit removing the fact that the units/dimensions of angular momentum and action are the same (torque and energy have nothing to do with the edit, so I don't know why the IP refers to these quantities), because sometimes its useful to illustrate same/similar units for very different quantities (in quantum mechanics, the angular momentum is quantized in units of hbar, but hbar has units of action, why not highlight this connection?)
  • also this edit, integration by parts is a specific way to integrate, and the reason is efficiency. Stating this way to integrate is a useful heads up. It is not a preference for the sake of it.

MŜc2ħεИτlk 17:17, 24 March 2016 (UTC)


Inclusion has many more requirements than just "useful information".
Removals of dubious uncited passages are subject to WP:burden before replacement.
Hello again Maschen and Hello Spriggs,
There are many more requirements for inclusion than just "it's useful". The material was removed for being largely incorrect and uncited. In addition, Torque#Units warns (with a citation!) against giving Torque as Joules (and by extension giving Angular Momentum as Joule-secs).
Like I said in the my last edit summary, if it's rewritten so it no longer implies that old fallacy, and *cited*, it can certainly be added back. But, this is not a vote. WP:burden is clear. If you want to replace material removed as dubious and uncited, you must find a reliable ref for it first. So, go do that. Please. Really. It could be interesting!  :-) If the material is so compelling and so useful, and if it's notable-enough and written so it's correct, then you should be able to easily find a reliable(!) ref for it. But, you're obliged to find the reliable ref first.
96.230.106.141 (talk) 08:29, 26 March 2016 (UTC)

Content without citations is also not necessarily a reason to delete (unless the topic cannot be cited reliably, is controversial, or whatever), and there are no obligations on anyone to immediately provide references. We (editors) know that references should be added eventually. For the trivial facts you insist on removing, I'll add a reference or two later today or tomorrow.
I have never known anyone who is stupid enough to think that torque and energy, or action and angular momentum, are the same or related just because their units are the same. Or that every quantity should have its unit expressed in a specific form that does not coincide with others. It should be obvious to look at the definitions of the quantities first.
It's very annoying when IPs randomly come along, invade and own pages, telling us what can and cannot be in the articles, what to do and not do, as if we didn't know, all the while insinuating us of screwing up. MŜc2ħεИτlk 08:51, 26 March 2016 (UTC)


If you take another look at WP:burden and other written policies, you'll find that dubious uncited content is absolutely removable. Often, to be nice and to maintain stability, uncited content that isn't dubious is sometimes left for a while with a "citation needed" tag with the idea that someday someone would get around to adding one. But, it's not at all traditional to just tag dubious content and leave it at that, especially for content as dubious as our present subject.

Regarding your "anyone who's stupid enough" commentary. What can I say about that? If you see the world and Wikipedia in those kinds of crass terms, maybe you shouldn't be doing this. Writing for lay-readers is what's being done here. Suggesting they're stupid because they don't understand a piece of writing is the wrong approach. It's our duty to write so it's understood, not the readers duty to understand what we write.

Regarding your "insinuating us of screwing up" paragraph. Well, again, I don't really know how to approach that. You must be very inexperienced in Wikipedia if you think one editor's removal of dubious content carries with it an implication that someone "screwed up". Telling people what can and cannot be in the articles is just the normal back-and-forth between good faith editors going about the business of editing WP. It seems you're very easily "annoyed" by that kind of normal good-faith exchange and numerous other things that are par for the course. I wish I could help give you peace in that regard, but you'll have to work on that personal issue yourself. :-)

Regarding "Random IP" comment. I understand your feelings believe it or not, lots of edits made at once (by anyone) are difficult to review and often a reversion is the right answer for a particular situation. But, you should review your attitude about "owning", you should know (by now) that IPs are full members with every status of logged in users and that no editor and no class of editors owns a WP page. Be careful to avoid automatically stereotyping. Give a little bit of review of the IP's (actually anyone's) editing history before jumping to conclusions about them. As they say, assume good faith. Read edit summaries carefully, judge edits by their content, not by the "color of the editor's skin".
96.230.106.141 (talk) 10:00, 26 March 2016 (UTC)

There you go again, deferring to policies, lecturing on obvious trivialities, and telling me that I suggest readers are stupid for misunderstanding (no) and do not read edit summaries (no again).
What I meant is anyone who does not know what energy, torque, angular momentum, action are, should have enough sense to look up their definitions. We can try to explain things correctly in the relevant context which I tried before you reverted branding it WP:OR. If you left it alone, maybe later I or someone else could add references. Building the content in stages is how things get done. Immediately deleting unsourced content because WP:THIS or WP:THAT said so is not.
Admittedly I can't find any sources saying explicitly that angular momentum also has units of J·s, instead using kg·m2·s−1, likewise for torque and angular momentum, and will not spend more time on this tiny issue of units anymore, have other things to do. MŜc2ħεИτlk 20:43, 28 March 2016 (UTC)
Hmmm. Interesting (that sources are hard to come by w/ units of "J·s" for AngularP). I'm actually arguing less for such a source (for "AngularP is in J·s") than for for being clear by not saying it because (like I've said) the two quantities are different. I'm mostly concerned that we shouldn't imply the sameness of (or a relationship between) two different "quantities" just because their "dimension" is the same. This is also in accord with BIPM (see next section). It might be possible to find a source saying "AngularP is in J·s" (or "Torque is in Joules", or whatever), but if so, it's very likely to be an unreliable source, or to be an unreliable passage in an otherwise reliable source. I wouldn't focus on finding that holy grail source because it really only allows the short term inclusion of a fact/implication that's still incorrect. The main point is to communicate clearly in a way that doesn't mislead. 96.230.106.141 (talk) 07:01, 30 March 2016 (UTC)
If not for its relationship with action (which is the basic thing that is quantized), angular momentum would not be quantized in quanta of h/4π. JRSpriggs (talk) 01:48, 29 March 2016 (UTC)
Neat. I'm unclear as to what the pronoun "its" refers to in "its relationship". I'm also unclear as to the specifics of what you mean by "relationship". I'm assuming for now you mean a relationship between angular-momentum and action. If there is such a relationship, and if it can be said in a way that doesn't imply that the two quantities are related just because their dimensions are the same, then it might be worthwhile to write that up with citations and include it. It does strike me as "something new" and possible WP:OR though. 96.230.106.141 (talk) 07:14, 30 March 2016 (UTC)

BIPM's take on the matter[edit]

Torque#Units cites BIPM at this link:
http://www.bipm.org/en/publications/si-brochure/section2-2-2.html

That page says:

  • "In practice, with certain quantities, preference is given to the use of certain special unit names, or combinations of unit names, to facilitate the distinction between different quantities having the same dimension. When using this freedom, one may recall the process by which the quantity is defined. For example, the quantity torque may be thought of as the cross product of force and distance, suggesting the unit newton metre, or it may be thought of as energy per angle, suggesting the unit joule per radian..."

The main point for us is to "facilitate the distinction between different quantities having the same dimension". We "facilitate the distinction" by not saying or implying that action is related to angular momentum. For this reason, I would even say that Angular Momentum is off-topic for the article -- unless it's to carefully say how it's not related to Action by mere virtue of their only-coincidental base units.

The passage says "...recall the process by which the quantity is defined..." which is apt here. Torque and Energy are defined by entirely different processes. Torque's process is a cross product of a force with a perpendicular length, while Energy's process is an integration of a force over a parallel length. To say that Torque is in Joules (or that Angular Momentum is in Joule-seconds) fails to "facilitate the distinction" between different processes.

Note that "Joule per radian" is correct for Torque, while "Joule" (in addition to being misleading regarding it somehow being energy) is off by a factor of Pi (maybe). "Joule-second" for angular momentum (in addition to it still being misleading which is the heart of our debate) might also be off by a factor of Pi, but I'd have to do some thinking on that. Hmmm...

96.230.106.141 (talk) 10:55, 26 March 2016 (UTC)

missing terminology[edit]

The present article doesn't provide sufficient clear context to make out the following concepts: classical action, quantum action, bare action. Would like to see article make these clear. 75.139.254.117 (talk) 01:24, 14 December 2016 (UTC)