Talk:Centrifugal force (rotating reference frame)/Archive 16

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Proposed replacement for wording

Present text:

This radial equation can be rearranged to represent the case of a co-rotating frame, that is, one rotating with the object so that the angular rate of the frame, $\Omega$, equals the ${\dot {\theta }}$ of the object in the inertial frame. In such a frame, the observed ${\dot {\theta }}$ is zero and ${\ddot {r}}$ alone is treated as the acceleration – so in the equation of motion, the $mr{\dot {\theta }}^{2}$ term is moved to the force side of the equation:

$F(r)+mr{\dot {\theta }}^{2}=m{\ddot {r}}$

Proposed replacement text:

In a co-rotating frame, that is, in a frame rotating with the object, the angular rate of the frame, $\Omega$, equals that of the object. Consequently, in the co-rotating frame the observed ${\dot {\theta }}$ is zero and ${\ddot {r}}$ alone becomes the acceleration. Observers in such a frame nonetheless arrive at the same equation, because they discover a need for a centrifugal force mr Ω² that must be added to the "force" side of the equation. Inasmuch as $\Omega ={\dot {\theta }}$ of the inertial frame, the equation of motion becomes:

$F(r)+mr{\dot {\theta }}^{2}=m{\ddot {r}}\ .$

It is as though the $mr{\dot {\theta }}^{2}$ term were simply moved from one side of the equation to the other.

The merit of the replacement is to emphasize the physical meaning of the mathematically trite movement of a term from one side to the other, which appears otherwise unmotivated. The replacement also segues better into the immediately subsequent text: "The centrifugal force term in this equation is called a "fictitious force", "apparent force", or "pseudo force" …". Brews ohare (talk) 13:51, 10 May 2009 (UTC)

It looks to me like the cited sources don't use your approach, but do it purely algebraically, motivated by getting an express that works in a frame where r-double-dot is the acceleration. They see no need to intoduce "observers" into the rotation frame and have them "discover" the centrifugal force, when it falls out easily from the equations of motion in the inertial frame. What source will you add to support your way? Dicklyon (talk) 14:52, 10 May 2009 (UTC)

You do not need to be tied to your sources so closely. Of course they do not introduce observers: they are simply doing the math and as mathematicians always do, proving the equivalence of a posed problem (the co-rotating one) to an already solved problem (the inertial one). That is not very helpful to the reader, who sees no need for a co-rotating frame anyway, and who I imagine, will be yawning over moving terms from left to right. Brews ohare (talk) 15:26, 10 May 2009 (UTC)

Here's some Newtonian discussion: Graneau Brews ohare (talk) 15:28, 10 May 2009 (UTC)

Brews ohare (talk) 15:48, 10 May 2009 (UTC)

As Wilhelm has pointed out, the way to move forward without fighting is to stick very close to sources. I wrote this section from sources, coming at it without any preconceived notions, expertise, or experience in this topic. I'm open to revisions based on sources, but not otherwise. I'm also not in favor of revisions that serve to complicate, or to exclude certain points of view in favor of others. For example, to say that these equations are arrived at by an observer in the frame is one, but only one, way of using them. It's equally valid to say that the equation is derived by an observer outside the frame, to get a simpler description in terms of an equivalent 1D problem; there's no reason we can't include both of these, if we have sources. But if the sources are not about the planetary motion problem, let's don't bother to connect their POV to it, OK? If the Graneau source says something you want to include, let's include it, but let's not change the derivation from what the other three cited sources use. Don't worry about your imagination of what readers will think; let the authors of the secondary sources be the judge of how it should go. Dicklyon (talk) 15:34, 10 May 2009 (UTC)

I understand your stance, which is very commonly used to control discussion. Of course, the debate then turns to whether the sources have been adequately interpreted, or are germane. This evolution already has begun. However, an important aspect of the discussion is the overall context, which is not restricted to this mathematical manipulation in a specific context. The larger picture is that of the role of centrifugal force. (I don't agree with your stance "But if the sources are not about the planetary motion problem, let's don't bother". The example is here only to illuminate the larger context, and is not an isolated stand-alone.) The introduction of observers is a common device, used for example, in most of the presentations of relativity and in describing the equivalence principle. It also is used in the context of centrifugal force, and I see no reason to limit the presentation of this example to that of some mathematicians trying to prove all problems are equivalent to an already solved problem. That equivalence is not excluded by use of the observer; rather, the observer simply motivates the sterile math manipulation. Brews ohare (talk) 15:43, 10 May 2009 (UTC) Here is an introduction to observers:Scientific American Serway Bueche Carmichael Takwale Datta Boleman KnudsenBatchelor Brews ohare (talk) 15:51, 10 May 2009 (UTC)

It appears that Taylor has been somewhat misconstrued, as he speaks of "reincarnation" rather than an "inference" of centrifugal force. A bit more flamboyant, eh? Brews ohare (talk) 23:54, 10 May 2009 (UTC)

Here's an interesting quote: Eddington "a relativity theory of translation is on a different footing from a relativity theory of rotation. The duty of the former is to explain facts; the duty of the latter is to explain away facts." Eddington refers to the Foucault pendulum. However, by the same reasoning, the rotating observer must invent centrifugal force to explain why his observations do not work out. Brews ohare (talk) 00:28, 11 May 2009 (UTC)

I'm familiar with the idea of an observer in a reference frame, but I don't see the relevance of all those sources about it. For example, in your Carmichael citatipn, which is one we can access online, the derivation of the fictitious force in the rotating frame is completed before the notion of an observer in frame without access to knowledge of how his frame relates to the outside is introduced. It's pretty clear that if he had stopped before that, it would still be useful and correct. I don't see how you think the Eddington thing applies here, either. And yes Taylor used some interesting language; on re-reading it, I agree it's not exaclty clear what he did between equations 9.70 and 9.71; instead of just doing algebra on the laws of motion, he brought in centrifugal force from some place then showed by algebra that it's the same laws of motion. He had worked out the same basic problem back on page 300, eq. 8.22, from Lagrange equation and there talked about moving the centripetal term from one side to the other and noticing it gives the equation of motion in a different frame. But it looks like he didn't derive it that way; he did more like Goldstein. Stommel and Moore just talk about moving the term across directly, but are perhaps not so clear that it's motivated by wanting to treat r-double-dot as acceleration. Maybe there's a better way to characterize what these various sources are doing, but none of them seem to be based on invoking an observer that has no knowledge of the frame's motion. Dicklyon (talk) 05:01, 11 May 2009 (UTC)

I'm afraid you understand the relevance of what supports your view and any other information or source is irrelevant or has no point Brews ohare (talk) 05:55, 11 May 2009 (UTC)

Rotation direction

the coriolis/centrifugal force rotates to the right in the northern hemisphere and to the left in the southern hemisphere. So, please change main picture in article to include both rotations

—Preceding unsigned comment added by KVDP (talk • contribs) 11:47, 15 September 2009

Radians per second

I always end up forgetting whether the formula is in radians per second or revolutions per second. I'm pretty sure it is the former here, but I don't want to screw up. Can someone confirm this is true throughout the text - and please sprinkle those units liberally so that people feel more comfortable working the equations? Also, the examples given include some mathematics, but they don't come down to concrete answers. I think that if you want to include an example, you should include something familiar like rotation of the earth at the equator and work it out to a plain number for the force.

N.B. the actual value for that is 1/289 of gravitational force [1], but their derivation leaves something to be desired (force measured in feet?). But to use their numbers, the radius is 20926202 feet, the period of revolution is 86164 seconds, and pi is 3.1415926. So the angular velocity is 2pi radians/86164 seconds = 7.2921 x 10^-5 radians/second. The centripetal acceleration is the angular velocity squared times the radius = 5.3175 x 10^-9 radians²/second² * 20926202 = 0.11128 radians² feet/second². Now at this point radians, rather magically to the uninitiated, make their disappearance, leaving 0.11128 ft/s² acceleration. The force experienced is this number times the mass of the object in pound-masses., which can then be converted to pound-force by dividing by standard gravity 32.174 feet/second² = 0.0034585 pound-force (per pound-mass). (Perhaps a sane metric version should also be given, but if you can follow this you can follow that! ;) ) Wnt (talk) 00:12, 11 December 2009 (UTC)

It's mentioned in a footnote, which I've made clearer. I've also added a wikilink to angular velocity which explains it further, tidying up a few other things in that section at the same time. In general though units are not given as the formulae are independent of units. Even the units for angular velocity would be wrong if you chose to work in e.g. Tonnes, Miles and Hours (you would need radians/hour) but seconds are almost always used even in non-SI systems so I think it's OK.

As for adding a concrete example, this is not appropriate to Wikipedia , as per WP:NOTHOW. Especially in a long article like this where there are a lot of examples, all quite different, as it would needed worked examples for all of them to fully cover the topic. But that would make the article a lot longer and just dilute the mathematical content. You perhaps want to look on Wikihow to see if that covers the topic in the way you want, or if you can add it there. --JohnBlackburne (talk) 10:10, 11 December 2009 (UTC)

Well, the article says that living on Earth is living in a rotating frame of reference, so the example is already used - just not explained. And the working of this precise example is sourced; I think it's one of the most common such questions asked. By comparison, several other examples such as the whirling table and the skywriter are not very informative, and the one about centrifugal force of the Universe is just plain bizarre. Wnt (talk) 13:11, 11 December 2009 (UTC)

Oh, and it doesn't matter whether you use radians per hour or radians per second, because the point is that the acceleration and force value you come up with is denominated in those units. The reason why clarifying radians or revolutions is particularly important is that those units don't exit the formula in as obvious a way. Wnt (talk) 13:29, 11 December 2009 (UTC)

I've rewritten the planet shape section - the galaxy stuff was pretty odd and unsourced, and there's a well written section on orbits later on so that serves much better so I removed it. There was also some Newtonian mechanics which duplicated something further up so I moved the reference then removed it.

The reason radians does not need clarifying is the formulae only work with radians: any other rotation measure introduces a scale factor. The need of radians in mathematics is pretty fundamental, and is considered background knowledge similar to e.g. the cross product and second derivative used in this article. None of these are explained but they are linked to where it makes sense, and readers can follow the links, including the category links at the bottom, for more information.

The links I've added include some such as flattening and rotation period with data. But again in general Wikipedia is not the place for detailed calculations of this data. Better to give the more interesting results and leave calculations it up to the reader, or to other sites like Wikibooks.--JohnBlackburne (talk) 14:59, 11 December 2009 (UTC)

I don't believe Wikipedia should be "dumbed down", but when possible an article should try to get at least some of the basic concepts across to laypersons and grade school students. People don't actually need to know calculus or trigonometry to run the numbers through the basic equation or to understand the general concept. This is the appropriate place to explain that radians are necessary, and for that matter why radians are necessary. Wnt (talk) 17:19, 11 December 2009 (UTC)

The problem is there are a lot of things going on "behind the scenes" in the few lines of algebra here. E.g. the fact that acceleration is a second derivative, or that the cross product is used to get from Ω to the derivative of Q, or what the cross product is, or that the magnitude of the final term is mΩ²r. All of it is explained, but it's explained elsewhere. That's how an encyclopaedia works: it covers everything but not all in one place. To include all or a significant portion of that into this article would result in considerable duplication and make an already long article longer and more difficult to read (and edit!). --JohnBlackburne (talk) 18:23, 11 December 2009 (UTC)

Removed Parachutist section again

With this edit user Brews ohare (talk · contribs) restored the Parachutist section he added in the version of 16 May 2009. The section was deleted on 22 dec 2009 by Wnt (talk · contribs), because "it has one reference that doesn't seem to talk about parachutes.". So I have removed the section again per wp:NOR and wp:UNSOURCED. DVdm (talk) 18:08, 6 August 2010 (UTC)

This section was rewritten, and not the same as the earlier version. To suggest that a source referring to parachutes be provided is strange. The section is not about parachutes, per se, but about straight-line motions as seen in a rotating frame. The notion of a parachutist is immaterial, just give a concrete picture. An arbitrary object could be chosen instead, obviously. Of course, straight-line motions require zero net force. As there is always a centrifugal force in a rotating frame, that means an agency is required to counteract this force if straight-line motion is to occur. I fail to see any OR here, nor any need to refer to a source on parachutes. Brews ohare (talk) 18:24, 6 August 2010 (UTC)

If this is not OR, then it will be easy to provide one or more good sources for the entire section. Please do so. DVdm (talk) 18:28, 6 August 2010 (UTC)

Um, perhaps you could provide some guidance that would illuminate for me just what in this section is OR? As I have pointed out, the point is simply that straight-line motion requires zero net force. Also, that centrifugal force is present in a rotating frame. These items hardly require further sourcing. Perhaps you are having difficulty with the way it is explained. Please advise. Brews ohare (talk) 18:31, 6 August 2010 (UTC)

Same case as before with this on Redefinition of the metre in 1983. Provide a source and you're in business. And please have a look at WP:BRD. It is not WP:BRDRD.... DVdm (talk) 18:35, 6 August 2010 (UTC)

Not helpful, DVdm. I guess there is some problem in being straightforward. However, here is a source for you: “Suppose that an object moves along a straight line in a rotating frame of reference. To an outside observer in an inertial frame the object's path is curved – thus there must be some force acting on the object to maintain the straight line motion as viewed by the rotating observer.” I would assume you would be very happy to work with me to apply this observation to the example of the parachutist to avoid any impression that this example involves complex logic or extrapolating conclusions implying OR? IMO it is a rather simple application of this principle, simple because the general case involves an apparent velocity and hence a Coriolis force, while this example does not. Brews ohare (talk) 18:45, 6 August 2010 (UTC)

It is not up to me to be helpful. It is up to you to provide sources when challenged. The source you just provided is sufficient for the sentence you quoted. It is not sufficient for the lecture you are trying to insert into the article. You really should know that by now. DVdm (talk) 19:18, 6 August 2010 (UTC)

You want a source for the parachute example? Do you have any objections to the physics, or are you just wikilawyering? /Pieter Kuiper (talk) 19:53, 6 August 2010 (UTC)

Pieter, the only thing I have is an objection to an unsourced, originally researched lecture. Wikipedia is wp:NOTTEXTBOOK. DVdm (talk) 20:29, 6 August 2010 (UTC)

Hi DVdm: I'm sorry that this example does not strike you as a useful addition to the article. I think it is, because it provides the flip side of the dropping ball example, and as such illuminates the concepts.

An invitation to help make the example meet your objections is not to say it is your obligation to do so. What it is, is an invitation to collaborate on building an encyclopaedia.

This example is obviously not OR in any sense of the word, and you have not made any effort to explain in any way the origin of your assessment. The above source provides the principle behind the example. The mathematics is given in the first paragraph of the WP subsection. This example follows not only qualitatively, as presented, but mathematically if one wants to follow through the provided math. If you really think this is my own idea or a projected conclusion beyond the principles, it is a commentary upon your understanding, or maybe your capacities.

That seems implausible. Brews ohare (talk) 20:08, 6 August 2010 (UTC)

I think you are in the same situation as here and here. Consider adding another RFC. I have nothing to add to my (4 times repeated) comments. DVdm (talk) 20:29, 6 August 2010 (UTC)

OK; I have made an RfC. Brews ohare (talk) 21:01, 6 August 2010 (UTC)

Is the following example a useful contribution to Centrifugal force (rotating reference frame)?

Is the following example a useful addition to the subsection Apparent motion of stationary objects?

Objections have been raised regarding an example, suggesting that it is WP:OR. The example is provided at this link. Please comment upon its suitability and, if possible, provide suggestions for its improvement. Brews ohare (talk) 21:00, 6 August 2010 (UTC)

• Here is the example; it is intended to follow the example Dropping ball, which is the contrasting case:

Dropping bird

A bird moving vertically parallel to the axis of rotation in a rotating frame appears to spiral downward in the inertial frame. The bird begins the drop with a horizontal component of velocity the same as the target site. The left panel shows a downward view in the inertial frame. The rate of rotation |Ω| = ω is assumed constant in time.

Let's look at a straight-line motion as seen in a rotating frame, rather than in one that is stationary. A bird drops onto a carousel, a flat platform rotating at a constant rate. The figure shows the vertical straight-line path of descent seen in the rotating frame. The bird drops at constant speed, occupying successively the vertically aligned positions one, two, three. Because the bird has zero horizontal velocity from the viewpoint of the rotating observer on the carousel, there is no Coriolis force in this example. There is, however, a centrifugal force.

In the stationary frame, the bird descends on the spiral path shown in the figure, because the target position on the carousel is rotating. The stationary observer sees a uniform circular motion of the bird when the spiral motion is projected downward, as in the left panel of the figure.

The stationary observer and the observer on the rotating carousel agree that there is no vertical force involved: the bird travels vertically at constant speed.

The horizontal motion is seen differently by the two observers. The rotating observer always sees a centrifugal force that tends to carry the bird away. It must be counteracted by a radial thrust to prevent a landing far off the mark. In contrast, the stationary observer, looking at the circular motion in the horizontal plane at the left of the figure, sees a centripetal force is necessary. Without a radial thrust, the bird would follow the dashed straight-line path in the left panel of the figure, obeying Newton's law of inertia.

Unlike the dropping ball case, where the fictitious Coriolis and centrifugal forces add together to produce the force necessary to cause the motion so an external agency is unnecessary, in this case the fictitious forces create a need for intervention. The basic rule is: if the inertial observer finds a situation demands action, the fictitious forces of the rotational frame will lead the rotational observer to the same conclusion, albeit by a different mechanism.

References

Comments upon RfC

• Please add your comments below, beginning with an asterisk *. It should be noted that this example is not in a vacuum; the mathematical background and another example precede it in the subsection. Brews ohare (talk) 21:05, 6 August 2010 (UTC)

• The fact that "the mathematical background and another example precede it in the subsection", is precicely what makes this section WP:OR. This is not a routine calculation. This section might belong in a textbook or in a lecture, but wikipedia is WP:NOT the place for this. DVdm (talk) 21:15, 6 August 2010 (UTC)

To the contrary, this is a completely trivial consequence of the material presented immediately preceding. If you have a problem making this connection, please point out what changes would fix that. Brews ohare (talk) 21:52, 6 August 2010 (UTC)

It belongs in a textbook or in a set of lecture notes. This is a request for comments. It is not a request for arguing whether Brews should be allowed to ignore all rules. DVdm (talk) 09:07, 7 August 2010 (UTC)

• There are only sources for the first paragraph, and not even all of that. Where are the sources for the rest of it? And the second link doesn't work: it gives me a "You have either reached a page that is unavailable for viewing or reached your viewing limit for this book" message. As I've not looked at the book (and can still look at other pages) it must just be outside the range of pages available for preview.--JohnBlackburne^words_deeds 21:21, 6 August 2010 (UTC)

I changed the source to one that still has a Google books access. As pointed out above, there is no need for further sources given the immediately preceding material. If you feel more is necessary, please be specific. Brews ohare (talk) 21:52, 6 August 2010 (UTC)

Yes there is: see WP:OR which is very clear on this: everything should come from sources, especially such a long and involved section which goes far beyond routine calculations.--JohnBlackburne^words_deeds 22:06, 6 August 2010 (UTC)

In fact, the presentation is qualitative. If the section appears involved, that may be a question of either your understanding of the topic (I don't claim any insight into this matter) or a question of clarity of exposition (which you could help me with by pointing out items you find are not obvious and so require sources or a better description). IMO the whole example is very straightforward, contains no logical complexity, is adequately sourced, and simply makes the basic ideas concrete. If that isn't working for you, please provide some specific guidance. That way, evolution can happen. Otherwise, you are in the position of making objections with no real intent of being constructive. Brews ohare (talk) 22:18, 6 August 2010 (UTC)

The constructive advice is "find sources for it". That's how Wikipedia works, content if challenged requires reliable sources, as it made clear at WP:OR. An exception is made for routine calculations that are easily checked and editors can agree on, but the unsourced content above consists of far more than routine calculations.--JohnBlackburne^words_deeds 22:34, 6 August 2010 (UTC)

John, you say "find sources for it". That is too vague. What exactly do you need sources for? The word it referring to everything is not specific. My feeling is that you haven't read this entire article and don't understand the concepts. That can make this particular example hard to follow, but is not my fault, and sources won't help. Brews ohare (talk) 23:28, 6 August 2010 (UTC)

BTW, there are no so-called routine calculations here, in fact, there are no calculations. The entire discussion is qualitative, needs no math at all (although math can be used if you prefer it), and falls into the regime of English discourse. Brews ohare (talk) 23:34, 6 August 2010 (UTC)

• This is routine reasoning, but rather wordy for a -pedia. The sourcing requirement leads to invocations of somewhat absurd references, like the robotics text. /Pieter Kuiper (talk) 21:44, 6 August 2010 (UTC)

Yes, insistence on verbatim sourcing means you have to look in strange places. Probably the example could be shortened, but even at its present length, DVdm and Blackburne have trouble understanding it. They think it is OR. Brews ohare (talk) 21:52, 6 August 2010 (UTC)

• My primary concern is that the edit in question completely fails WP:NOTTEXTBOOK. Specifically, "It is not appropriate to create or edit articles that read as textbooks, with leading questions and systematic problem solutions as examples." IMO, the example appears to be more to instruct rather to inform. As others have said above, it is more appropriate for a lecture or textbook, but not for a WP article (perhaps it could be used at Wikiversity). I believe the current examples in the article are more than sufficient to inform (in fact I'd recommend removing one or two based on the same WP:NOT argument) the reader. --FyzixFighter (talk) 22:24, 6 August 2010 (UTC)

This objection is both more germane and more difficult to support. The theses are: (i) Other examples accomplish the same thing. Please indicate which examples do that. And (ii) The example instructs rather than informs. If that has a meaning, I'd say that this objection means the example serves to teach skills (like exercises to master the mechanical details) more than it serves to sharpen understanding of the concepts. I can believe that opinion may vary on that judgment. My own is that this example, by treating a straight-line motion in a rotating frame, the flip side to treating a straight-line motion in a stationary frame, shows the following: in this case, centrifugal force has to be physically counteracted by a thruster, illustrating how real it is to the parachutist; on the other hand, in the dropped ball example, the centrifugal and Coriolis forces join up to produce exactly no need for any action. That illustrates the two faces of the fictitious forces, and is illustrative of the concept, not simply a teaching of manipulative skills.

Should we ultimately disagree about the impact of this example upon understanding, I'd opine that there is no need to drop the example inasmuch as it does have explanatory value, whether or not it has other benefits. Brews ohare (talk) 22:46, 6 August 2010 (UTC)

• Excellent text with a very nice illustration! I don't see what the problem here is. Sources are not needed when explaining a previously treated concept using an example. Examples and derivations are exempt from being challenged on the grounds of OR simply from lacking direct sourcing, unless a reasonable case is made that there is, (or that there can reasonable be), something wrong with the text. Also whether or not this fails WP:NOTTEXTBOOK is a matter of taste. Some Wikipedia articles by consent do read very much like textbooks (many of the articles I contributed to are of that nature), so this is not a blanket rule. What you probably don't want to do is rewrite a good encyclopedic FA class article into a dry textbook text that would lead to the article dropping from FA Class right back to Start Class :). Count Iblis (talk) 23:44, 6 August 2010 (UTC)

• As explanatory examples go, a long-winded explanation about a parachutist with a thruster seems overly complicated and confusing. The style is sort of text-booky, yet not very clear. The illustration is packed with info, yet not very clear. It's typical of Brews to defend this kind of article-bloating material that he likes to make up, and since he got kicked off of speed of light, he's attacking other topics now. Seems like a bad idea. Dicklyon (talk) 04:53, 7 August 2010 (UTC)

• This section should not be added to the article, because it is wrong. A parachutist falling at constant speed towards the center of Earth does experience a Coriolis force in the frame rotating with Earth, unless he falls straigt to one of the poles. Not over the poles his velocity is not parallel to rotation axis, and there will a Coriolis force East. This is called the Eötvös effect. −Woodstone (talk) 07:26, 7 August 2010 (UTC)

Don't you mean Buys Ballot's law? But this "parachutist" carries a litle thruster, keeping him above the target. So it is not wrong, but Dicklyon has a point, that this example can be confusing. /Pieter Kuiper (talk) 09:24, 7 August 2010 (UTC)

The problem's not that it's right or wrong, but that it's OR. One reason for disallowing OR is that if an editor is allowed to write what they want not based on any source it's very difficult to tell if it's correct, and editors can be tied up forever debating the correctness of an article, or even a section or paragraph. The rules on OR are in place to prevent that – you should always be able to point to a source for every argument and example.

What is clear on top of it being OR it fails [[WP:NOTTEXTBOOK], which says "It is not appropriate to create or edit articles that read as textbooks, with leading questions and systematic problem solutions as examples". The article already has a number of (sourced) examples, with a couple overlong already. It does not need another (unsourced) one.--JohnBlackburne^words_deeds 10:42, 7 August 2010 (UTC)

Woodstone: Thanks for your observations. Apparently the example is not sufficiently clear. The "Earth" is idealized, as is the parachutist falling at a uniform speed, and as the figure indicates is modeled as a rotating flat disk, not as a sphere. The problem is in cylindrical geometry. Its the same model used in the dropping ball example as well. So your objections are for the wrong situation. Brews ohare (talk) 12:49, 7 August 2010 (UTC)

I have added a disclaimer that the "Earth" is a flat disk, not a sphere. Brews ohare (talk) 13:10, 7 August 2010 (UTC)

Blackburne: Your objections are fully discussed above in response to FyzixFighter. You have replied to none of the points, and appear to be engaged in rhetoric, not useful discussion. Brews ohare (talk) 12:53, 7 August 2010 (UTC)

Dicklyon: Your comments are a bit confusing: the section is "bloated" yet it is "packed with information". It is "made up" and "unclear". It would be helpful, if instead of making gratuitous abrasive remarks about my being "kicked off" and "attacking other topics" that are violations of WP:Civil, you were to attempt to point out changes to make things shorter and clearer. Brews ohare (talk) 12:59, 7 August 2010 (UTC)

Pieter Kuiper: I appreciate your comments on the section. I see that the mention of "Earth" as a picturesque term for the rotating flat disk has derailed Woodstone, despite the figure showing a flat rotating disk. Of course, we all like to complicate our lives. Do you have any suggestions for improving the example? I like this example because it complements the preceding one that is very similar. The contrast is more illustrative than a totally new example. However, in view of the barrage of non-specific and nonconstructive complaints above, that make no effort to improve matters, maybe a different example would be better? Brews ohare (talk) 13:33, 7 August 2010 (UTC)

Maybe instead of a parachutist falling to "Earth", it should be phrased as a bird dropping onto a carousel? The dropping ball problem becomes the "dropping droppings" from the bird before it starts flight, and the second one is the descending bird problem. : ) Brews ohare (talk) 13:43, 7 August 2010 (UTC)

You see what happens (again), brews? Non of this would be necessary if you had sources for your lecture. The only thing that can improve matters, is sources, sources and sources. This is a request for comments on whether your lecture is OR or not. Consensus says that it is OR. It stops being OR when it is sourced. So please source it and stop disrupting this talk page? DVdm (talk) 13:48, 7 August 2010 (UTC)

DVdm: So now an RfC is a disruption of a Talk page? I thought it was about improving a proposed contribution. My requests for specifics about what is OR exactly, and what is unclear exactly, and what needs further sourcing exactly, are stonewalled by editors who dismiss this effort with no specific justification, but instead provide vague, nonconstructive assertions, apparently unmotivated by any interest in improving the exposition. Brews ohare (talk) 14:05, 7 August 2010 (UTC)

I have rewritten the example to refer to a bird and a carousel to avoid misinterpretation of the cylindrical geometry shown in the figure. Brews ohare (talk) 13:59, 7 August 2010 (UTC)

And your source for that is? Again, the point of WP is not for editors to write whatever they want but to write an encyclopaedia based on sources. You've been asked repeatedly for sources for what you've written, but you've yet to produce any. Repeatedly ignoring these requests, instead posting an RfC, for the second time in a few days, is certainly not a productive use of your time or anyone else's.--JohnBlackburne^words_deeds 14:19, 7 August 2010 (UTC)

This is not how WP:OR is used in practice on many math and physics articles. While WP:OR explicitely says that simple unsourced deductions are allowed (if the editors agree that it is valid), it does not say that more complex unsourced deductions can never be ok. Like I said before, I've added a quite a few far more complex unsourced derivations (for good reasons) to some Wiki articles without anyone giving a peep. WP:OR is in practice only invoked on such pages if there are real questions about the correctness of the proposed edits and a verification from sources is really needed. Count Iblis (talk) 14:46, 7 August 2010 (UTC)

Blackburne: OK, let's look at this in detail to assist you in becoming specific. Let's ask: What needs to be sourced?

• The first four paragraphs are simply describing the situation to be examined, setting up the discussion. As simply a set-up describing what is to be discussed, that hardly needs to be sourced.
• The statement about no vertical force can be sourced to Newton's law F=ma if you really need that.
• The next paragraph describes the horizontal motion in the rotating frame. There isn't any. I don't think we need a source here, that is simply the description of the vertical path.
• The assertion is made that there is a centrifugal force present in the rotating frame. That can be sourced if you insist, but of course that is the entire subject of this article and so hardly requires a new source. Rotating frames always have centrifugal force.
• The second from last paragraph describes the projection of a spiral path on the horizontal plane as a circular arc. I believe that to be an obvious point: do you want a source describing projection of a spiral down a cylinder as a circle in plane perpendicular to the cylinder?
• The next statement is that circular motion implies a centripetal force. Again, this connection is clear; a link to Centripetal force can be provided if you wish.
• The last paragraph is a summary.

Please go down this list and suggest where you have dissatisfaction. So far as I can see, there is nothing here of such import as to require an OR label or extensive sourcing. I find myself perplexed trying to understand specifically what you object to. Please try to clarify. Brews ohare (talk) 14:49, 7 August 2010 (UTC)

BTW, this RfC was introduced at the request of DVdm, who felt some additional input would be helpful. Please avoid maneuvering to create the appearance of disruption. Brews ohare (talk) 15:13, 7 August 2010 (UTC)

"By DVdm who felt some additional input would be helpful"? No, by DVdm who thought that other users might be able to help you understand the basics of WP:OR again. DVdm (talk) 21:36, 7 August 2010 (UTC)

Another way to deal with this

I've said that I support the inclusion of the text as it stands. However, if I had aded the text myself, I would read the comments as follows. OR is invoked simply because some editors don't like the text, not that there are any real concerns about OR. Then I would guess that the NOTTEXTBOOK objection is a better indication what they don't like about this and rewrite the text to take this into account. What you can do is to make the text shorter, do less detailed (mathematical) explaining. This then leads to the main point that the centripetal force is due to the centrigugal force plus the coriolis force becoming more visible, which isn't that bad. In fact. it could become quite similar to the paragraph I wrote some years ago in the fictitious force page:

In the case of distant objects and a rotating reference frame, what must be taken into account is the resultant force of centrifugal and Coriolis force. Consider a distant star observed from a rotating spacecraft. In the reference frame co-rotating with the spacecraft, the distant star appears to move along a circular trajectory around the spacecraft. The apparent motion of the star is an apparent centripetal acceleration. Just like in the example above of the car in circular motion, the centrifugal force has the same magnitude as the fictitious centripetal force, but is directed in the opposite, centrifugal direction. In this case the Coriolis force is twice the magnitude of the centrifugal force, and it points in centripetal direction. The vector sum of the centrifugal force and the Coriolis force is the total fictitious force, which in this case points in centripetal direction.

No sources were demanded for this at the time, so you should be in the clear if you write about the parachute jump in this way. Count Iblis (talk) 15:23, 7 August 2010 (UTC)

Note that if you take the faux objection of OR too serious, you would have to modify the text in a way that would make it to be disliked even more on the grounds on which it is really disliked. Count Iblis (talk) 15:27, 7 August 2010 (UTC)

Count: Your analysis is quite correct: there is no OR here, and DVdm , Blackburne, and DickLyon habitually use WP:OR or WP:RS as an excuse to malign contributions that they don't want to see included in an article, regardless of pertinence, and without regard for improving contributions or helping contributors. Their reasons for objection, inasmuch as the espoused guidelines are inapplicable, remain obscure. Brews ohare (talk) 15:35, 7 August 2010 (UTC)

I don't routinely use OR and RS where they don't apply. To me, the real issue, as I've stated, is bloat. It might be good to add a guideline some place to say that it's not cool for an editor to just add whatever long-winded examples and tangents that come to mind, to bloat an encyclopedic article into something so long and convoluted that nobody is likely to bother reading it. It baffles me that this kind of contribution, that Brews specializes in, can be seen by anyone as an improvement to the article. Particularly when it is being opposed by many good serious-minded editors, why does Brews continue to push so hard to get his creations included? It's very hard to fathom. And why does Count Iblis habitually back him up in this? Again, somewhat mysterious. Dicklyon (talk) 17:32, 7 August 2010 (UTC)

I'm not "backing Brews up", just explaining to him how to make better progress. You mention that the main issue is "bloat" and that is something concrete that Brews should be able to address. If Brews were to try to address an alleged OR issue that isn't really there, that would result in even more bloat and even more useless talk page discussions, and hence more irritation. So, it is perhaps better not to raise OR or RS as a veto and simply give an honest opinion, even is that's simply "I don't like it". Count Iblis (talk) 17:51, 7 August 2010 (UTC)

Why not raise OR and RS? They are core Wikipedia policies, which every editor should be familiar with. For example at WP:OR#Reliable sources is says "The only way you can show that your edit is not original research is to cite a reliable published source that contains the same material." So which source is this lengthy example from? And your assertion that "OR is invoked simply because some editors don't like the text", do you have any evidence of that?--JohnBlackburne^words_deeds 18:15, 7 August 2010 (UTC)

Upholding OR in this very strict way is not practical for math and physics articles that contain explanations at some detail. This problem has actually be discussed at length on the policy pages and the consensus was always that while the official rules won't be changed it is ok. for the math and physics editors to have a more liberal attitude. I.e. while OR is strictly forbidden, whether or not something is OR is left to the editors to decide; literal quotes from textbooks are not always necessary.

One obvious problem with very strictly sticking to the OR policy to the point of requiring that examples be literally quoted from textbooks, would be that it would be plagiarism to do so. Another issue is that an appropriate example or explanation for a Wikipedia article may not be found in textbooks, as the audience is different. The students who read university level textbooks are assumed to have a certan background knowledge on which the author builds, while Wikipedia is meant to be read by a wider audience with less knowledge. This is something I've frequently encountered when rewriting the thermodynamics articles. But that happened without editing disputes.

We have to keep in mind that the policy pages are edited mainly by people who are active on politics pages. There you'll find the most intractible editing disputes. The text of e.g. OR reflects what's best to manage pages like the one on e.g. Obama in order to prevent too much discussions/ editing disputes about whether his birt certificate is a forgery or not. In this light, it is quite understandable that the general rule is not to allow much more than computing age from birth date. Count Iblis (talk) 19:09, 7 August 2010 (UTC)

Count Iblis: Your remarks make sense, supposing that OR and RS are applied in earnest with a detailed description of the reasons behind their use to assist the contributor to build a better contribution. That hasn't happened here. In fact, my sentence-by-sentence outline requesting whether the designated OR policy applies to this sentence or to that, has been ignored by Blackburne. DickLyon has now no OR objection and has resorted to his customary "bloat" argument, which is, of course, at least partly subjective, and still without specifics. Brews ohare (talk) 19:25, 7 August 2010 (UTC)

(edit conflict)WP:OR is still policy - unless you can point to a page that says otherwise. There's no exception for any sort of article, especially not science where fringe theories and pseudoscience can easily masquerade as science, even with sources (though not reliable scientific ones). And I don't see the problem you mention in your second paragraph. Articles should be sourced, but that does not mean copied verbatim - unless the purpose is to quote. But this should not be a problem as an editor should only be writing about something they understand, so should never need to resort to copying. They should just write what's in the sources in their own words.--JohnBlackburne^words_deeds 19:36, 7 August 2010 (UTC)

John, nobody says OR is not a policy. What has been requested in this instance is evidence that it applies, rather than your own decision that it does apply, which frankly I disagree with. Moreover, if a policy is applied by you, given that I am as aware of this policy as are you, it follows that you and I are not on the same page. We don't interpret applicability to the present material the same way. And so, it behooves you to clarify why you have reached your conclusion. Believe it or not, people can disagree about applicability. The way to reach agreement is to explain yourself so that modification to meet the objection can be attempted. Saying a source is needed is insufficient: what is needed is what the source is supposed to establish, and perhaps why the statement is not obvious on its merits. Going a step further, you might explain what changes would assist your acceptance, in the spirit of crafting a better contribution. Brews ohare (talk) 20:07, 7 August 2010 (UTC)

No evidence that WP:OR applies is needed. Sources for your little textbook essay are needed. The way to reach agreement is that you provide sources, in the spirit of Wikipedia's policies. DVdm (talk)

High time to start writing WP:Ridiculous, I guess. Count Iblis (talk) 22:01, 7 August 2010 (UTC)

DVdm: You have misunderstood: No evidence is needed that WP:OR might apply; what is needed is the basis for saying that it does apply in this case. Sources can be provided if it is clear what exactly the sources are to be selected to establish. Brews ohare (talk) 04:50, 8 August 2010 (UTC)

You might indeed follow Count Iblis' excellent advice. The basis for saying that it does apply in this case is that you try insert a text without sources. It is not up to us to tell you "what exactly the sources are to be selected". It is up to you to provide sources: WP:PROVEIT. DVdm (talk) 10:35, 8 August 2010 (UTC)

DVdm: You say the proposed contribution attempts to “try insert a text without sources”. The two important points in this text are sourced: that there is no Coriolis force in such situations, and that a straight-line motion in a rotating frame requires forces to maintain it. The rest of the text is no more than description of these remarks as reduced to a very simplified situation. As such, there appears to me to be nothing identifiable as questionable, and so why are more sources needed? My effort to have you or Blackburne amplify your objections to point out what exactly you two find to be questionable, results in your above non-answer that it is "up to me" to read your minds. Brews ohare (talk) 15:12, 8 August 2010 (UTC)

It is not up to you to read our minds. It is up to you to provide sources. You continue to act like you have WP:NOCLUE about the meaning of WP:OR and nobody seemt to be able to help you understand it. That is not our problem. It is yours. DVdm (talk) 15:32, 8 August 2010 (UTC)

I conclude that in fact you cannot understand the material, and to avoid reaching this assessment, you invoke WP:OR. That is not my problem, it is yours. Brews ohare (talk) 15:44, 8 August 2010 (UTC)

Please try to avoid accusing people of dishonesty.

The material is not to be understood by anyone. It is to be sourced by the one who proposes it. Whether I understand it or not is irrelevant. Whether you can source it is relevant. Read the policy. DVdm (talk) 15:54, 8 August 2010 (UTC)

I would urge Brews to ignore DVdm and Blackburne's comments about OR from now on, as they are not being reasonable w.r.t. this issue. Count Iblis (talk) 15:57, 8 August 2010 (UTC)

Thank you for your advice, Count. No accusation of dishonesty was made. I do not think incapacity to understand the material is irrelevant: one cannot identify questionable text without understanding it. Brews ohare (talk) 16:00, 8 August 2010 (UTC)