Talk:Moment (physics)

Untitled
what does in discussions mean? "Moment of inertia (I = mω×r), which is analogous to mass in discussions of rotational motion."


 * You'd have to ask the author, but I took it to mean "when discussing". Gdlong (talk) 22:37, 19 May 2016 (UTC)

Bold text I found that this website is not very usefull for me --195.137.110.31 09:00, 18 September 2005 (UTC)

I came here from Pages needing attention, and clearly this one fit the bill. It basically consisted of two separate, independent articles that shared little relation to one another. I've attempted to clean it up, but I think it still needs some more work, particularly because I simply copied the parallel axis theorem more or less verbatim from the preexisting article. Some fact checking would be great.

Also, the previous article listed a few examples about physical moments, but I think this rather belongs in the Physics Study Guide. I've moved the examples to this talk page. --Diberri | Talk 06:02, Jul 14, 2004 (UTC)

Examples
Examples:

A force of 85 N is applied to the lever arm shown above left. The length of the moment arm is 0.6 m. The moment of force at the joint to the arm can be calculated as:

M = F x d = 85 x 0.6 = 51 Nm (clockwise)

This moment can then be applied at any point along the arm. For instance, if the object being moved was located 0.2 m from the pivot point, known as the fulcrum, the amount of force applied would be 51 Nm / 0.2 m = 255 N, considerably more force than was put into the arm. For this reason a suitable arm and pivot point can allow human muscle to move objects that would otherwise be immobile. This is the principle behind the crowbar (or a nutcracker), for instance, where the blade operates applies the entire force being applied at the far end of the bar. With a common 1 m bar with a blade of perhaps 5 cm (0.05 m) long, the crowbar multiplies the force by 1/0.05 = 20 times.

Distinguishing terminology, difference from torque?
Correct me if I'm wrong.
 * 1) The moment which is the main subject of this article is often called the moment of force to distinguish it from other moments used in physics, such as the moment of inertia, as well as from the more general moment (mathematics).
 * 2) This moment of force is the very same thing as torque
 * 3) The statement in this article that torque "is a force" is poorly worded at best.
 * 4) The proper symbol for newton-meters is "Nm".

I also have some nagging doubts about the relative priority of the mathematics meaning and this physics meaning, but that's all they are is doubts&mdash;it would be nice to have some backup for the claim that the physics usage came first. Gene Nygaard 14:44, 27 Jan 2005 (UTC)
 * Torque and moment are the same concept. It may make sense to merge this into Torque so that two pages on the same topic do not have to be maintained... Anyone else have a comment? - grubber 11:11, 2005 August 1 (UTC)
 * Looking 'moment' up in my dictionary to see its definition, I found this:
 * Physics a. The product of a quantity and its perpendicular distance from a reference point. b. The rotation produced in a body when a force is applied; torque.
 * Perhaps it would be best to leave these as separate articles with Moment (physics) dealing with sense a. (i.e., the more generic sense) and Torque dealing with sense b. (i.e., the more specific sense). &mdash;Mike 05:05, August 2, 2005 (UTC)


 * In my statics class and in my dynamics classes for engineering, "torque" and "moment" were used interchangably. If you decide that "moment" in physics refers not just to force, then the article should reflect that. The article, as written, is almost entirely about torque. I can see your point, that there is a more generic quantity here. But this article should reflect the distinction. - grubber 09:24, 2005 August 2 (UTC)

"Moment of a force" or just "moment" is the terminology typically used in physics. I've only ever heard engineers refer to it as torque. So if this it intended to be a physics article it should maintain the terminology. 68.148.191.243 22:18, 11 November 2007 (UTC)

I'm not completely convinced that this concept it studied apart from torque, although I can certainly see how it might be useful. What I'd really like to see is a reference, preferably from physics, that makes this distinction: not just a dictionary. Melchoir 09:18, 23 April 2006 (UTC)

Torque and moments are exaclty the same thing, so the articles should be merged, or at least a meantion of each in the others articles. The only difference between torque and moments are the occasions where the terms are used - 'torque' is usually used to descibe a rotational force down a shaft, for example a turning screw-driver, whereas moments are more often used to describe a bending force an a beam or some-such. This is the case in engineering at least. --LeakeyJee (talk) 15:27, 9 June 2008 (UTC)

Improvement Needed
This article needs to be rewritten. There is some very confusing notation used here. For example B is used both as the vector in the cross product and as the origin through which the second parallel axis passes.

This article also gives the impression that all of the parallel axis theorems are the same. It implies that the parallel axis theorem of the moment of force and the moment of inertial have the same form. Well they are similar but not the same. Parallel axes theorems should be stated explicitly. What about electric and magnetic dipole and quadrapole moments? The article also needs some reference to the moment of momentum (angular momentum) and the moment of velocity (angular velocity). What about the perpendicular axis theorem for moments of inertia of rigid bodies?

I do not find it hard to believe that the mathematical description of physics and mathematics co-developed. Was Newton a mathematician or a physcist? Your answer may depend on where you live. the fact that torque, electric dipole moment, and magnetic dipole moment depend on distance while moment of inertia depends on distance squared shows that the concept of higher order moments was used in physics as well as in mathematics.

The use of the term "moment" in Engilsh for the moment of force (troque) is not as prevalent as it is in other languages. Still the use of the term moment for torque should be mentioned in a quality article.

So this article needs major revision. It needs to use clearer notation (for example, talk about origin 1 and 2 instead of A and B. It also needs additional content. As it stands, it is doing a disservice to Wikipedia.

--F3meyer 07:09, 5 July 2006 (UTC)

Torque and moments are exaclty the same thing, so the articles should be merged, or at least a meantion of each in the others articles. The only difference between torque and moments are the occasions where the terms are used - 'torque' is usually used to descibe a rotational force down a shaft, for example a turning screw-driver, whereas moments are more often used to describe a bending force an a beam or some-such. This is the case in engineering at least. --LeakeyJee (talk) 15:26, 9 June 2008 (UTC)

Merger discussion -- moment (physics) and torque
See merger discussion at Talk:Torque. Gene Nygaard 10:10, 28 January 2007 (UTC)
 * Note: The Discuss links on the pages moment (physics) and torque should take you there. Nephron T|C
 * I would have thought so, though I don't know if it was always true. But everybody doesn't get to the discussion by using the "discuss" link, and this is one of those mergers that could go either direction as well.  Gene Nygaard 20:04, 16 February 2007 (UTC)


 * oppose, moment and torque are not the same. Rick Norwood 13:56, 28 March 2007 (UTC)

Merger discussion -- moment (physics) and bending moment
There are two different merge proposals. The proposed merge between moment (physics) and bending moment I think should be HERE, as moment (physics)'s merge proposal points here (and I made bending moment's merge tag point here). (If the proposal was to merge moment (physics), bending moment and torque -- I think the tags would have to be different -- see WP:Merge.) Nephron T|C 19:40, 16 February 2007 (UTC)


 * I was going to fix that after your message on my talk page (more on the templates there). What we need here are the two headers Question about the templates my talk page. If the other two are merged, bending moment should be merged into that article under whatever name; if there remains a separate torque article, bending moment should be merged into moment (physics).  Gene Nygaard 19:46, 16 February 2007 (UTC)

What about Bending Moment's relating to Structural Engineering?


 * oppose Rick Norwood 13:56, 28 March 2007 (UTC)


 * Oppose as well. Bending moments are a structural/mechanics of materials topic, and it is my opinion that such an topic is weighty enough to stand on its own, would get lost in a general moment article, and a full discussion would do the article for general moment itself more harm than good. Marimvibe 20:05, 22 April 2007 (UTC)


 * Oppose also, I agree with the above comments. --Chetvorno 02:39, 20 August 2007 (UTC)

I don't think that a full discussion of bending moment is what is proposed, but that you should treat moment without stating that an axis is necessary. I propose to merge the moment article with the one about Force, because in the Real world there are no Vectors, and that is what makes the people lose interest. You should state that moment is a false Vector used for calculations. And it really is Two parallel forces, one that you apply on an Object and one that appears due to the connections/support/inability to move of the body, or ability to move. I am going to do some changes about these in my native language, and add some 3d examples what do you say about Force and Moment? ThomCh —Preceding signed but undated comment was added at 17:15, 16 September 2007 (UTC)

technical
This article is incomprehensible to people without a college-level science background. Those who can understand it are those who have least need for the article. Can somebody please explain the concept for those with a non-mathematical background? 69.140.159.215 (talk) 03:19, 10 January 2008 (UTC)

whoever wrote that should know that he does not help any one —Preceding unsigned comment added by Alexandalexand3 (talk • contribs) 11:39, 21 August 2008 (UTC)

Request for article extension
I think this article should include moment of area and second moment of area.

Slughunter (talk) 20:21, 17 October 2010 (UTC)

Too technical?
This article has been tagged with the technical tag since 2007: The 2007 version was too hard to understand, but since then it has been completely rewritten. The current version is understandable, so I am removing the technical tag. Please discuss if you disagree. Guy Macon 02:47, 8 February 2011 (UTC)

Recent expansion of "Moment of Force" explanation...or disambiguation page?
User:MelissaSalsano-NJITWILL expanded this article here to explain in more detail what moment of force means and how to calculate it (including new images). I undid these edits, arguing that we want to avoid making this article redundant with the torque article. Here and here is our discussion. I have reinstated Melissa's text as long as I am the only one who has an objection to it. So, what do other people think? :-)

My "counter-proposal" is to make this page officially a disambiguation page linking to the articles moment of force/moment, principle of moments, pure moment, moment of inertia, dipole moment, etc. (I do like the new text and diagram, but I think they should be incorporated into torque instead of here.)

Does anyone have an opinion? The options are: Keep the expanded explanations and diagrams...Shrink to a disambiguation page...Or something else? :-) --Steve (talk) 08:10, 7 April 2011 (UTC)

Article References
Before I go on, I should note that my complaint here has more to do with a general 'feel' of the article than my familiarity with pertinent Wikipedia policies.

This article contains a lot of textual references to other articles; that is, it frequently uses the words "see article " in the text of the article. I'm not sure if there is a particular Manual of Style policy associated with this, but it feels very un-Wikipedian. It feels like rather than having direct references as prose, the text should be an indirect reference with a hyperlink.

I'm going to do what I can to remedy this, but I thought I'd drop a line into the talk page in the hopes that some editor more familiar with the concept would step in and make a sure change. Kierkkadon (talk) 16:31, 9 January 2013 (UTC)


 * I've gone ahead and just done a lot of editing on the 'Moment of Force' section of this article. Since the article title is Moment (physics) I've rearranged the section to deal only with the concept in pure physics, not necessarily the similarly-named concept in engineering. It would be nice to add a disambiguation note at the beginning of the section; I'll figure out how to do that if I can and add it. I've added a link to the main article, Torque, because really that's what this section needs. I removed the clumsy in-text references and generally made the section a tad smoother. Kierkkadon (talk) 16:48, 9 January 2013 (UTC)


 * The moment of force section doesn't belong here at all. I changed the text to reflect that using the term moment is just a short form for moment of force. There were many errors in the section at any rate, so readers should go to the full text article instead to eliminate confusion. Dger (talk) 18:30, 9 January 2013 (UTC)


 * Ah, this is much better. Thanks. Kierkkadon (talk) 18:34, 9 January 2013 (UTC)

When was the word 'moment' first used in physics and mathematics?
To understand the deeper meaning of the word moment it is necessary to find out when was the word 'moment' first used in physics and in what sense. Also, it is important to find out when it was first used in mathematics in the form such as in https://en.wikipedia.org/wiki/Moment_(mathematics). Maybe, historians of physics and mathematics would be able to better illustrate the matter. Bkpsusmitaa (talk) 16:18, 23 May 2014 (UTC)


 * Good idea. This looks relevant: http://physics.stackexchange.com/questions/44527/meaning-of-the-word-moment. —Ben FrantzDale (talk) 12:18, 30 May 2014 (UTC)

Missing a big part of the way 'moment' is used in physics
I came to this page hoping to refresh my memory on exactly how 'moment' is defined and used in physics, but I didn't see it. To be more precise, I was thinking of 'multipole moments'. These moments are the coefficients of the expansion of a (more-or-less) arbitrary potential in terms of spherical harmonic functions. Some of them have special names; for example, the 1st moment is the 'dipole moment' and the 2nd is the 'quadrupole moment'. The 'Nth multipole moment' is often referred to just as the 'Nth moment'. I was about to cite Jackson (E&M) as a reference, but it turns out a description already exists in the Multipole expansion page.

This use of 'moment' is common in physics (as a random example, it's key to the study of cosmic microwave background radiation). It is very similar to the usage described in the Moment_(mathematics) page but is a little more general. Because it's very common, I'm thinking this page should include that usage of the term.

As a related comment, the physics usage and the mathematics usage (as defined by the current wikipedia pages) are very much related, so much so that perhaps the two pages can be merged? When you look at it, each one of the physics moments is just a particular case of the x^n f(x) pattern described in the mathematics usage page. That might be a good way to organize this page.

Gdlong (talk) 22:27, 25 June 2014 (UTC)

I took my own advice and added a section on multipole moments, but in order to put it in context I ended up rewriting almost the entire article to portray a single, consistent way of thinking about moments, regardless of which particular moment it may be (e.g., moment of force, moment of inertia, various electric, magnetic, or gravitational moments, etc.) I'm hoping the rewrite makes things clearer. In that hope, I went ahead and removed the 'confusing' tag. I still think someone may want to look at eventually merging the mathematics and physics pages, but for now it's probably good to leave them separate. Gdlong (talk) 14:53, 23 July 2014 (UTC)

Assessment comment
Substituted at 00:20, 30 April 2016 (UTC)

Introduction needs rewording
I (again) rewrote the introduction for several reasons. First, a moment isn't a physical quantity; it's a mathematical expression involving the product of a distance (raised to some power) and a physical quantity. I think sometimes people struggle with the concept of moments because they want to think of them as a physical "thing", but that has limitations. For example, a quadrupole field can be thought of as a physical thing, and so in a sense can a moment of inertia. But trying to equate the two in terms of their physical characteristics (saying "they're both moments") can tax many people's intuition. To understand moments, you're better off looking at the mathematics. Second, there were a lot of examples in the first paragraph that served to confuse the definition rather than make it clear. Those examples are better presented later, after the elaboration where actual definition of a moment is given. Third, the nth moment is more easily understood after presenting the (r^n x q) expression; it is awkward to describe it in words in the introduction before that expression has been given. Fourth, you shouldn't confuse multipole moments with dipole, quadrupole, etc. moments. Multipole moments are the coefficients of the spherical harmonic expansion. Dipole, quadrupole, octupole, etc. moments are more simply defined, and in fact the definitions are presented later. Multipole moments are projections of the dipole (and quadrupole, etc.) moments, but that's not quite the same thing. And in any case, I'm not sure the introduction section, where we're trying to define the basic concept, is the right place to introduce the multipole expansion. Gdlong (talk) 22:37, 19 May 2016 (UTC)


 * note: moved this comment to conform to Wikipedia policy and keep chronological order. Gdlong (talk) 19:10, 1 March 2021 (UTC)

momentum
momentum is not a moment is wrong, since momentum p=vm=r¹I is the first moment of mass flow. Ra-raisch (talk) 17:54, 26 April 2018 (UTC)