Talk:Moment of inertia/GA1

GA Review

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Reviewer: TimothyRias (talk · contribs) 17:08, 4 January 2013 (UTC)

It this point this article quite clearly fails the good article criteria:

• 1b In particular, it does not comply with WP:NOTTEXTBOOK.
• 2b (and possibly 2c) There are many sections without in line citations. Even for sections that any physics student could reproduce, an inline citation (or two) should be given to a textbook supporting the treatment presented.
• 3a It is too narrowly focussed on the calculation of the moment of inertial, and hardly touches on the history of the subject or its applications.

It should not be hard to fix these, but it could involve quite a bit of work. I'll leave this review open for week or so, to see if there is any progress.TR 17:08, 4 January 2013 (UTC)

No do not leave it open. It is fine if it fails. I will work on these issues in the future. Prof McCarthy (talk) 17:41, 4 January 2013 (UTC)

The best I can do with the history is the citations presented to Huygens, Newton and Euler. As for applications, there is the tight-rope walker, compound pendulum and flywheels. The rest of the article shows how this material parameter appears in Newton's second law, angular momentum, and kinetic energy. Prof McCarthy (talk) 17:46, 5 January 2013 (UTC)

Added references to each section, though not each subsection. Prof McCarthy (talk) 18:27, 5 January 2013 (UTC)

This is my attempt to address concerns about 3a and 2b. I do not know how to address 2c. Finally, it is not clear to me what how to address 1b. As stated above, i am willing to accept that this article cannot achieve GA status. Prof McCarthy (talk) 18:33, 5 January 2013 (UTC)

I'm not disputing the review, but would like to understand how the article fails 1b. Is it too textbook like because some of the sections include derivations of equations? Thanks, Mark viking (talk) 19:47, 5 January 2013 (UTC)

I would like to know the answer to this question as well. Prof McCarthy (talk) 14:17, 11 January 2013 (UTC)

From WP:NOTTEXTBOOK " Textbooks and annotated texts. Wikipedia is an encyclopedic reference, not a textbook. The purpose of Wikipedia is to present facts, not to teach subject matter. It is not appropriate to create or edit articles that read as textbooks, with leading questions and systematic problem solutions as examples. These belong on our sister projects, such as Wikibooks, Wikisource, and Wikiversity. Some kinds of examples, specifically those intended to inform rather than to instruct, may be appropriate for inclusion in a Wikipedia article." Prof McCarthy (talk) 20:27, 28 January 2013 (UTC)

From good article criteria "1b. it complies with the manual of style guidelines for lead sections, layout, words to watch, fiction, and list incorporation." Failure of 1b. does not seem to be "lead sections, layout, words to watch, fiction or list interpretation." Failure of 1b. also does not seem to be "leading questions and systematic problem solutions as examples." It may be the regular use of mathematics to present the many and different ways that moment of inertia appears in Mechanics. Prof McCarthy (talk) 20:39, 28 January 2013 (UTC)

Reviewer:Arildnordby (talk) 23:56, 28 January 2013 (UTC)

Lead text should make clear that "moment of inertia" is a specific element from the inertial matrix.

In this article, that caveat comes too far down, in the "Overview" section in the well enough formulated sentence: "Moment of inertia around a fixed axis is a scalar, however the rotation of a body in space can occur around the three coordinate axes. In this case, the moments of inertia associated with the three coordinate axes define a matrix of scalars called the inertia matrix, also known as the inertia tensor."

At the very least, the first sentence should read: "In classical mechanics, moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass (SI units kg·m2, US units lbm ft2), is a property of a distribution of mass in space that measures its resistance to rotational acceleration about a fixed axis", rather than "..about an axis"Arildnordby (talk) 00:00, 29 January 2013 (UTC)

Thank you for this recommendation. I have added a brief discussion of the inertia matrix to the introductory sentence. Prof McCarthy (talk) 03:03, 29 January 2013 (UTC)

1. Would not the conceptual/logical flow from "special case" to "general case" improve if you end your first sentence with "..about a single axis", rather than "about an axis"? In this manner your first sentence advertises that your primary focus in this article will be simple rotation within a single plane (i.e, about a single, fixed axis), but where your second sentence duly notes that rotation in general will involve three axes of rotation, rather than just the one.

2. Is not, perhaps, the inertia matrix important enough to warrant its own article, so that in your article on "moment of inertia", you may sharpen its focus by merely linking to "inertial matrix" article, retaining only MoI-relevant stuff, rather than using sections 6++ to develop concepts predominantly useful for analyzing/handling general rotation (like inertia ellipsoid, body-frame coordinates, and so on), concepts that are of little need (although, of course, trivially applicable there as well) in the single axis rotation case?Arildnordby (talk) 07:03, 29 January 2013 (UTC)

Another (easily removable) defect. You really should specify in your very first paragraphs that "moment of inertia"/"inertia matrix" are concepts primarily useful for rigid body analysis, rather than general body/system analysis (in which cases "angular momentum" still might be said to be of relevance, but where localized vorticity analysis is generally more important). You sort of introduce the concept of the rigidity as you go along, you should rather declare at the very outset that "moment of inertia" is principally a concept within rigid body mechanics.Arildnordby (talk) 07:47, 29 January 2013 (UTC)

1. I believe this article is useful to readers who have heard of moment of inertia in high school physics and therefore assume it is a single number. This happens to also cover quite a bit of its practical applications. The fact that it becomes part of a matrix or tensor for movement in three dimensional space is important additional information that may broaden the readers understanding. While structuring the article so that planar movement is presented as a special case of spatial movement or separating the presentation into distinct planar and spatial articles, may be an interesting exercises, it is my opinion that the article may become less useful to the reader. I would note that this article regularly gets 4000 and as many as 7000 views per day with high ratings. 2. I believe the recent improvement to the lead paragraph includes a reference to rigid body dynamics. Prof McCarthy (talk) 08:39, 29 January 2013 (UTC)

It does, I didn't check properly. Sorry about that.Arildnordby (talk) 09:32, 29 January 2013 (UTC)

My apologies. Due to RL circumstances, I won't have time to continue this review. This is shame because there is lots of potential. Hopefully, Arildnordby can pick up my slack.TR 10:34, 29 January 2013 (UTC)

A possible point to include: Why does the spinning wheel more "easily" retain its instantaneous axis of rotation? This gyrational stability is an important feature for appliances, an everyday phenomenon, but I do not see you have touched upon it.Arildnordby (talk) 19:39, 29 January 2013 (UTC)

The movement of the axis of a spinning wheel is an important dynamic effect that results from the application of a torque perpendicular to the axis of the spinning wheel. This is discussed in detail in the article Gyroscopic precession. While this is an important phenomena, it is less an example the moment of inertia than it is the integration of the equations of motion for the spinning wheel. It would make sense to refer readers to this important effect, however, and I will include this link. Prof McCarthy (talk) 04:22, 30 January 2013 (UTC)

I agree a link addition is best here. In general, I happen to find your article very good (I have a Bachelor in Fluid Mechanics, btw), but I am very inexperienced at Wikipedia, so I'm not really the one who should be Okaying your article as good . I believe a request for a new review will be in order.Arildnordby (talk) 13:21, 30 January 2013 (UTC)

Placing this back in the review queue per above. Wizardman 17:51, 15 February 2013 (UTC)