Talk:Centrifugal force

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Re-merging

Right now we have at least three separate pages (this page, a disambiguation page, and one specific to rotating reference frames) and a lot of overlap in material and in function. For example, this page and Centrifugal force (disambiguation) are performing nearly the same function. Perhaps someone knows the rational for why we have both of them? I'm wondering if we can't re-merge this page and Centrifugal force (rotating reference frame), since a good argument could be made (imo) that the rotating reference topic is the primary topic. That way the disambiguation page can still exist (to help distinguish between this and the Reactive centrifugal force). The only aspect that might not nicely fit is the Lagrangian formulation but which is (afaik) a very limited and slightly esoteric usage. I could very easily see that as a subsection. I could be wrong on this point, in which case it could be spun off into a separate article (Centrifugal force (Lagrangian mechanics) perhaps), but I still think the rotating reference frame should be the primary topic rather than the expanded faux disambiguation page we have now. Thoughts? --FyzixFighter (talk) 19:53, 13 September 2010 (UTC)

I would agree with a three way merge, between Centrifugal force, Reactive centrifugal force and Centrifugal force (rotating reference frame). The latter two seem far less encyclopaedic than they should be, with a surplus of examples and large, confusing diagrams needing overlong captions to explain them (and even then they are unclear). If the unencyclopaedic content were pared back it could be merged into the sections in Centrifugal force and I don't think the resulting article would be too large.

The DAB page I think should stay for now, though once the articles are merged this could be reassessed, as what would be left might be too trivial - there would only be one page on centrifugal force. But the page at Centrifugal force (disambiguation) has no content and would not get in the way of the merge, so need not be considered.--JohnBlackburne^words_deeds 20:23, 13 September 2010 (UTC)

For the most part I agree with you John, especially on the paring of surplus (imo, textbook-y) examples. The only difference in opinion I have is I would not advocate merging Reactive centrifugal force back in. The two are sufficiently distinct physical concepts (one's a fictitious force and frame dependent, the other a very real force that exists independent of frame; they will only equal in magnitude in a co-rotating frame) that I think separate articles are warranted. The concept of reactive centrifugal force is also a very common in engineering and one doesn't have to go searching for esoteric sources to find some that clearly make the distinction between the two. IIRC, one of the reasons for spinning it off was that one or two editors were constantly confusing the two and making the claim that they were the same thing. That isn't to say that Reactive centrifugal force couldn't use some paring and de-bloating, but I believe that there could still be enough information there to warrant its own article.

I should probably add some merger tags as a courtesy and to encourage others to chime in. --FyzixFighter (talk) 16:30, 14 September 2010 (UTC)

I think you should do away with the disambiguation page, since I can't see what it's for, but leave the summary-style centrifugal force article, and keep the other bloated articles separate (and separately work on de-bloating them). Dicklyon (talk) 04:18, 15 September 2010 (UTC)

I would support this merger idea. One single article is all that is required for the topic 'centrifugal force'. David Tombe (talk) 11:42, 21 October 2010 (UTC)

It wasn't a merger idea, so it's not clear what you're supporting. Dicklyon (talk) 20:51, 21 October 2010 (UTC)

Dick, the title of this section says re-merging, and from reading the lead that is what the author seems to be advocating, and I am supporting the re-merger. We only need one 'centrifugal force' article. The Germans don't have a multitude of articles on 'centrifugal force'. David Tombe (talk) 00:17, 22 October 2010 (UTC)

But your reply to me above seemed to say you were supporting me; sorry I misunderstood. Dicklyon (talk) 05:42, 22 December 2010 (UTC)

So everybody involved in this discussion supports the re-merge, but two months later it hasn't happened yet. Why not? (I support it too FWIW.) Alzarian16 (talk) 20:48, 21 December 2010 (UTC)

Well, not quite. I agreed with getting rid of the new disambiguation article, but keeping the summary-style article (this one) and keeping the bigger and more specific articles (the ones I called "bloated") separate. I went ahead and merged the disambig (by redirecting it here, since there was nothing else to do). Dicklyon (talk) 05:40, 22 December 2010 (UTC)

JohnBlackburne and FyzixFighter, do you have a merge plan that would get rid of some of the 48 KB of Brews ohare's bloat from Centrifugal force (rotating reference frame) as you merge? I might consider agreeing to a merge if I didn't think it would just add a lot of junk to what's currently not such a bad article. Dicklyon (talk) 05:46, 22 December 2010 (UTC)

My suggestion would be to merge only the first three sections of Centrifugal force (rotating reference frame) and drop the rest entirely, but I'd guess that others would probably disagree. Alzarian16 (talk) 18:26, 22 December 2010 (UTC)

I would just trim the article as it is now: it's something that I've thought of before but never got around too, but even as a standalone article there's too much bloat from Advantages of rotating frames onwards, and too many references for them to be useful. It should be easy to do now without Brews's disruptive objections.--JohnBlackburne^words_deeds 19:12, 22 December 2010 (UTC)

The Lagrangian section could do with considerable trimming also. I think this is a specialist and somewhat informal use of the term. Martin Hogbin (talk) 18:14, 22 December

I'm opposed to the merge. This article is the sister article of coriolis effect and shouldn't be merged with others. It's a completely different topic; the maths is different, and the equation that it comes out of is different one.Planetscared (talk) 17:00, 13 January 2011 (UTC)

I get the feeling that you have confused the merge here. The proposal entails a merge of Centrifugal force (rotating reference frame) into Centrifugal force. How are those a completely different topic? Yoenit (talk) 17:39, 13 January 2011 (UTC)

I'm opposed, too. I think this is a stale proposal, that we partially fulfilled by phasing out the disambig page. If someone still thinks that it's important to do more merging, they should speak up right away, or start a new proposal explaining why. Dicklyon (talk) 19:18, 13 January 2011 (UTC)

Dick, are you against merging Centrifugal force (rotating reference frame) into Centrifugal force? It seems like a good idea to me. ~~

Yes, I Oppose the merge, because, as I've explained before, Centrifugal force is a summary-style article that introduces the deeper treatments in Centrifugal force (rotating reference frame), Reactive centrifugal force, Absolute rotation, History of centrifugal and centripetal forces, and other articles. This seems like exactly the right place to have a summary-style article. Dicklyon (talk) 23:07, 13 January 2011 (UTC)

I do not believe that a disambiguation page is desirable. There is only one definition of centrifugal force in widespread modern use and that is Centrifugal force (rotating reference frame). A disambiguation page is in my opinion confusing to the general reader and gives undue weight to specialist, historical, or fringe meanings of the term. Martin Hogbin (talk) 12:45, 14 January 2011 (UTC)

I agree with you that a disambiguation page is not desirable here; that's why I eliminated it. I'm not sure why Wolfkeeper created it in the first place, or why Brews felt a need to bloat it to over 1600 bytes, but now it's gone. As for your assertion that "There is only one definition of centrifugal force in widespread modern use," that's sort of true, but a lot of disclaimers. Some dispatch to the other less modern, less widespread, and related points of view is still important, I think. A summary article is a good way to let the reader know what the different aspects are; for most, it's all they'll need. Or are you saying that some of the other articles are just junk that should be eliminated? Dicklyon (talk) 16:17, 14 January 2011 (UTC)

I am thinking of how this looks to an average reader who wants to know what centrifugal force is, or maybe a student needing some help on the subject. At the moment they see two articles, suggesting that the term has two, or more meanings. Personally, I would like to see one article on the standard modern meaning of the with short sections on historical or other meanings. Martin Hogbin (talk) 22:43, 14 January 2011 (UTC)

Dicklyon, anybody with a reasonable comprehension of the subject would know that there is only one 'centrifugal force', and that a single article could very easily accomodate all of the various perspectives on the matter. What you seem to have failed to grasp is that there is a big difference between,

(1) considering centrifugal force to be a fictitious force as viewed from a rotating frame of reference, and (2) considering centrifugal force to be a radially outward inertial force that arises in conjunction with absolute rotation, and which is revealed when Newton's laws are expressed in a rotating coordinate system such as polar coordinates.

The former involves the idea that centrifugal force even exists when an object is not co-rotating with the rotating frame, while the latter attributes centrifugal force specifically to absolute angular momentum. The two perspectives overlap in the co-rotating scenario, but it is unnecessary to involve a rotating frame of reference when doing planetary orbital analyis. David Tombe (talk) 11:44, 14 January 2011 (UTC)

David, a rotating coordinate system is the same as a rotating frame of reference. Fictitious forces and inertial forces are two terms for the same thing. In the context of a rotating frame of reference (or coordinate system) rotating refers to absolute rotation. The distinction you make simply does not exist. Martin Hogbin (talk) 22:43, 14 January 2011 (UTC)

Martin, Part of what you are saying is right. I agree with you that centrifugal force is a single topic. I also agree that most modern textbooks introduce it as a fictitious force that is observed in a rotating frame of reference. I also agree with you that that the words 'fictitious' and 'inertial' are used inter-changeably in the modern literature. But you are also overlooking some important factors. When an object is co-rotating with a rotating frame of reference, the centrifugal force will be an inertial effect which can actually be felt pushing outwards. However, within the context of the 'rotating frame of reference' perspective, if an object is stationary and not co-rotating with the rotating frame of reference, it is still deemed to be subjected to a centrifugal force based on the angular speed of the frame of reference. That is where this approach differs from the polar coordinates approach.

When we deal in polar coordinates, we are only concerned with the centrifugal force that arises in connection with absolute rotation, and which can be felt physically pushing outwards. And it is this perspective which is used in planetary orbital analysis where the rotation doesn't in general have a uniform angular speed. In other words, there is a branch of physics in which we consider centrifugal force as an outward radial force, and in which we don't normally invoke the concept of a rotating frame of reference, and in which the centrifugal force is induced by absolute rotation. This perspective needs to have a section of its own in the article.

What I would like to ask you is 'what category do you place this latter perspective in? Is it specialist? Or is it fringe? Or is it historical?' I would say that it is general and historical. It was originally devised by Leibniz, and it is used today in planetary orbital analysis. At any rate, we have identified two different perspectives on centrifugal force. We have one in which it is a fictitious force which is a function of the rotating frame of reference, whether the object is co-rotating or not. And we have another in which the centrifugal force is an inertial force which can be physically felt and which is a product of absolute rotation, and which doesn't require the concept of a rotating frame of reference. Both of these perspectives are sourced, although I admit that the former is currently much more widely sourced. David Tombe (talk) 23:17, 14 January 2011 (UTC)

It's essentially unsourced, idiosyncratic, and fringe. Goldstein made it clear enough that radial distance is a coordinate in a rotating coordinate system, not a concept different from the usual. Dicklyon (talk) 00:06, 15 January 2011 (UTC)

David, you seem completely confused, I suggest that we continue this discussion on your talk page. Martin Hogbin (talk) 02:19, 15 January 2011 (UTC)

OK. We'll go there. But based on what you have written above, I am guessing that you have done one of those university courses in applied maths entitled 'rotating frames of reference' in which the coordinate transformations are done, and where centrifugal force and Coriolis force emerge and are introduced as fictitious effects which are a product of observation from the rotating frame. That of course, despite being prolific in modern textbooks, is a specialist approach for advanced mathematicians and it is not the common understanding of centrifugal force amongst the public at large. The public at large think of centrifugal force as being the outward radial pressure which arises when something is spun. And the common understanding is the one that is used in planetary orbital analysis. Anyway, by all means carry on on my talk page. David Tombe (talk) 11:44, 15 January 2011 (UTC)

five different contexts?

I just reverted this edit which changed the description of the two types of centrifugal force, fictitious and reactive, into I'm not sure what. I had a look at the source for the 'five different contexts' but could not find it, and frankly the source is very poor one, a long and poorly written essay which is no substitute for the reliable academic sources already in the article. More generally if there is some source which introduces new material it should be worked into the article alongside existing material, not added to the lede in a way which disagrees with the rest of the article.--JohnBlackburne^words_deeds 17:31, 6 November 2010 (UTC)

John, it was in the paragraph third from the bottom. It read,

Thus Newton uses the term “centrifugal force” in the Principia to describe three very distinct concepts. First, he uses it to refer to a hypothetical repulsive force (such as the force between two electrons), which would result in a hyperbolic path, accelerating away from the source of the “central” repulsive force. Second, he uses the term to refer to the outward force exerted by a revolving object on some framework (such as the force exerted by a roulette marble on the housing). Third, he uses the term to refer to the “fictitious” outward force on a revolving object when viewed from a revolving frame of reference. A fourth context in which the concept of “centrifugal force” may arise is when phenomena are described in terms of curved coordinate systems, such as polar coordinates. Such non-linear coordinate systems are not inertial in the spatial sense, even though they may be static (i.e., not accelerating), as discussed in the note on Curved Coordinate Systems and Fictitious Forces. A fifth usage of the term “centrifugal force” occurs when the inertial forces on an object, relative to a momentarily co-moving inertial frame, are de-composed into tangent and normal components (in the osculating plane). The normal component is called centrifugal force. There is no Coriolis force with this convention, because the particle is always at rest with respect to the co-moving inertial coordinates. Needless to say, all these usages are very closely related, and differ only by context and convention.

You cannot leave the article lead stating that there are only two concepts of centrifugal force when there are clearly more. Polar coordinates is one such context. That is the context which is used in planetary orbital analysis. It is not something which is in any doubt. David Tombe (talk) 17:44, 6 November 2010 (UTC)

What Newton thought might be of interest historically but physics has moved on a long way since his time, in both what we know and how we describe it. From my reading of that he used it for more than we would today: e.g. the first example of repulsing electrons. But no, there are two concepts as expressed in the article and it summarises in the lede. And that essay hardly seems a reliable source: more a personal essay by someone with some odd views, on a web site created to push his self-published book.--JohnBlackburne^words_deeds 17:57, 6 November 2010 (UTC)

John, The article mentioned three concepts in connection with Newton. I had discounted the first concept in my count of five. Newton's other two concepts are exactly the same two concepts that you have already accepted. Ie. the reactive force and the inertial force in a rotating frame of reference. So you should have no problem with the bit about what Newton said. The article then went on to talk about polar coordinates. That is not in any doubt. We formulate the planetary orbital equation in polar coordinates and the radial equation has an outward centrifugal force term. Then he mentioned about normal and tangential resolutions of velocity. I found his remarks about 'no Coriolis force' in this system to be very interesting. I see no grounds for you to either doubt what the author has said, or to deem the source to be unreliable.

And for your information, in my own personal opinion, there is only one single concept of centrifugal force. In my view, four of the five mentioned in the source are one and the same thing. The so-called reactive force is merely a knock-on effect of the inertial force, just as a brick falling on somebody's head is a knock-on effect of gravity. David Tombe (talk) 18:12, 6 November 2010 (UTC)

None of this really matters. The Mathpages is a very intereresting work (- i.m.o. it is piece of art -) but it can never serve as an authoritative source as a basis for Wikipedia content. It is someone's personal (and, apart from one chapter, book-unpublished) view. It clearly is an ideal entry for the External links section, and perhaps even for the Further reading list, but the unpublished parts can never be used as a wp:RS, and can certainly never replace a solid textbook source. DVdm (talk) 18:37, 6 November 2010 (UTC)

Dvdm, Is your only concern about a solid textbook source which uses polar coordinates as an illustration of centrifugal force? Are you seriously doubting that centrifugal force is a polar coordinate term in the radial planetary orbital equation? David Tombe (talk) 19:07, 6 November 2010 (UTC)

Even if it were properly sourced the introduction is not the place to introduce sourced material. It should be introduced into the body of the article, properly integrated in what is a well established article. As for the content I still find what you added confusing and unclear, in particular what you mean by context. Polar coordinates are just another coordinate system, but there are an infinite number of them, any of which could be used to calculate the force, as they are largely interchangeable – Lagrangian mechanics is one way of approaching this. It's not clear what "normal and tangential resolutions of velocity" have to do with centrifugal force. And the others are what is there already, and in the article.--JohnBlackburne^words_deeds 19:45, 6 November 2010 (UTC)

John, It's a simple yes or no question. Do you accept the fact that centrifugal force is a term in polar coordinates which is used in the radial planetary orbital equation without involving rotating frames of reference? David Tombe (talk) 19:53, 6 November 2010 (UTC)

Take your questions to the ref desk if you don't understand the topic. If this is about the article I don't see how your question relates to it. Perhaps you could point to the section of the article you think is wrong and suggest a, reliably sourced, way to improve it.--JohnBlackburne^words_deeds 19:57, 6 November 2010 (UTC)

John, You didn't answer the question. The section in the article which you are asking about doesn't exist for the reason that some editors in the past have rejected the idea that centrifugal force is a term in the radial planetary orbital equation. I have supplied a source which states that centrifugal force is a term in polar coordinates outside of the context of rotating frames of reference. Do you have any objections to that material being put into the article on the basis of your own beliefs, or is it purely a matter of whether or not the source is reliable? David Tombe (talk) 20:08, 6 November 2010 (UTC)

Everything here needs a reliable source, and you have yet to supply one; it has nothing to do with "my beliefs".--JohnBlackburne^words_deeds 20:23, 6 November 2010 (UTC)

See also this new entry at the Wikipedia:Reliable sources/Noticeboard. DVdm (talk) 20:30, 6 November 2010 (UTC)

Didn't we have some of this discussion re: the radial equation of planetary orbits a little more than a year ago? "Introduction to Classical Mechanics" Atam P. Arya (1990), pg 231 is a reference that explicitly connects the moving the centripetal acceleration term to the force of the equation to get the radial equation as equivalent to viewing the physics from a non-inertial frame rotating with the planet. Jeremy B. Tatum "Celestial Mechanics" Chapter 16 [1] also clearly places the radial equation in a co-rotating, non-inertial frame. --FyzixFighter (talk) 20:44, 6 November 2010 (UTC)

Ah, I see. So this is nothing new, just reopening the same old arguments interrupted only by David Tombe's ban from physics. I suggest that if David Tombe has nothing new to bring to this discussion he stops it now, especially disrupting multiple venues with the same flawed arguments, in case he attracts the same sort of attention that got him banned a year ago.--JohnBlackburne^words_deeds 20:59, 6 November 2010 (UTC)

I agree. All input from David Tombe is best ignored; it was a large part of the reason for the massive bloat in these articles and for Brews ohare's problem and eventual banning. He is well known as a physics crank, and has done nothing to move away from that position in his year off. Dicklyon (talk) 18:37, 22 December 2010 (UTC)

Dicklyon, That is quite untrue. My input to the various centrifugal force articles has been negligible, and I have consistently advocated that we only need to have one very short article. As regards the 'crank' position which are are referring to, it is very well depicted by Bond's adversary in that cartoon that you seem so keen to include in these articles. David Tombe (talk) 19:47, 14 January 2011 (UTC)

Your several hundred article edits and several hundred talk-page edits in April–July 2008 kicked off and fueled the period of Brews hyper-inflation. Dicklyon (talk) 00:12, 15 January 2011 (UTC)

In the cartoon, when 'hat guy' says, "A laughable claim, Mister Bond, perpetuated by overzealous teachers of science. Simply construct Newton's laws into a rotating system and you will see a centrifugal force term appear as plain as day," he is indeed displaying some of your confusion. In one sense, he is entirely correct: "construct Newton's laws into a rotating system and you will see a centrifugal force term appear." That's what's called a "fictitious force", and I think we all agree that it arises from a rotating reference system. On the other hand, he is probably just confused about "overzealous teachers of science," likely because he doesn't know what to make of the term "fictitious"; this is the same problem you have exhibited many times. Mr Bond is also perhaps confused when he says "there's no such things as..."; you can interpret his position as meaning that he understands that he'll be crashed by the rim of wheel accelerating him along a curved path. Perhaps it's true that these "overzealous teachers" who deny "centrifugal force" actually exist; it would be interesting to find a sourced discussion of that if so. Dicklyon (talk) 00:26, 15 January 2011 (UTC)

Dick, The centrifugal force(rotating frame of reference) perspective is certainly the most prolific in the modern literature. But it is also specialist. It is for advanced mathematicians. It is a mathematical subject about describing how things are viewed from a rotating frame of reference. It is not about physical inertia. It involves using mutually cancelling fictitious forces in relation to stationary objects which have no inertia. That is not the perspective that Bond's adversary is invoking in the cartoon. Bond's adversary is invoking real physical inertia which crushes bones. Bonds adversary is talking about coordinates fixed in a physically rotating system which induces an outward inertial force. These are two distinct ideological perspectives on centrifugal force. They both need to be treated in separate sections within a single article on centrifugal force. The two perspectives overlap in the co-rotating scenario in which case the fictitious term is describing an actual inertial force.

Mr. Bond's perspective is yet a third perspective which is popular amongst high school students. And then of course there is Isaac Newton's perspective about centrifugal force being a reaction to centripetal force. You have your opinion on which is the correct perspective, and I have mine. But both need to be represented in a single article. And at least we are both agreed that neither Newton's nor Bond's opinions are correct. It seems to be a battle over whether it is the rotating frames of reference perspective or the Leibniz perspective, with myself supporting the latter. David Tombe (talk) 00:42, 15 January 2011 (UTC)

David, you seem to have a completely different understanding of this subject from physicists. I suggest that you continue on your talk page with those interested. Martin Hogbin (talk) 02:53, 15 January 2011 (UTC)

Martin, OK. See you there. David Tombe (talk) 11:48, 15 January 2011 (UTC)

Right, except nobody is interested. I'll go back to following my advice and ignoring David. Dicklyon (talk) 05:12, 15 January 2011 (UTC)

Dick, The problem would be greatly assisted if we could actually pin you down to a definite opinion in all of this. David Tombe (talk) 11:47, 15 January 2011 (UTC)

Single Centrifugal Force Article

I am proposing that there should be a single united article on centrifugal force to cater for all the perspectives on the topic. These perspectives are,

(1) That it is a radially outward inertial force that arises in connection with absolute rotation. It obeys the inverse cube law when angular momentum is conserved, and it is observed in planetary orbits and in the centrifuge device. It does not have to be equal to a centripetal force, but in the special case when it is equal to a centripetal force, we will have circular motion. (Leibniz/Lagrangian perspective)

(2) That it is a fictitious force which shows up in the transformation equations from an inertial to a rotating frame of reference, and which is observed to act on all objects from the perspective of the rotating frame of reference, whether such objects are co-rotating or not. (modern university perspective)

(3) That centrifugal force doesn't exist, and that circular motion arises when a centripetal force deflects an object from its straight line inertial path. (modern high school perspective)

(4) That centrifugal force is an equal and opposite reaction to a centripetal force. (Isaac Newton's perspective) David Tombe (talk) 11:57, 24 January 2011 (UTC)

I think the current article does a good job of clarifying the different perspectives, this way:

(1) No sources support this perspective, so we don't mention it. The inverse cube law comes up in (2).

(2) See Centrifugal force (rotating reference frame). We have a section with a main link.

(3) I don't see why we need to represent the opinion of someone who would say that something doesn't exist, when we have reliable sources on the thing. I think this "modern high school perspective" is essentially aprochryphal anyway; or it's a confused mixup between the two concepts (2) and (4), which do exist.

(4) See Reactive centrifugal force, which is not the same thing as what is most commonly called centrifugal force, but is related. We have a section with a main link.

Further, we have a section on historical conceptions, where the relationships of different conceptions can be compared.

I think a "unified" article would be an invitation for more of David's pushing of (1), and for other bloat. I'd rather see more effort put into tuning up the articles by trimming off unneeded junk and making them clear. There is stuff worth keeping in the other articles, and too much to merge into one, I think. Dicklyon (talk) 17:27, 24 January 2011 (UTC)

Dick, As regards your claim that persepective (1) is not sourced, that is where you are absolutely wrong. I supplied some sources recently at WT:PHYS. And then you claim that centrifugal force as an inverse cube law force is dealt with in perspective (2). No it is not. It is dealt with only when studying the planetary orbital problem as per perspective (1) which you seem to be very keen to sweep under the carpet even though it is represented in your favourite cartoon. Modern textbooks which deal with perspective (2) are dealing with the rotating frame transformation equations and they never look beyond the expression mrw^2 for centrifugal force. I have never seen the inverse cube law mentioned in a chapter about rotating frames of reference. And as for your claim that the reactive centrifugal force is something different, no it isn't. In fact, strictly speaking there is no such thing as a reactive centrifugal force because it is a pro-active effect. David Tombe (talk) 18:17, 24 January 2011 (UTC)

I agree with Dick's summary of (1)-(4). We have a number of references that show that (1) is the same as (2) (see Swetz, "Learn from the Masters!", pg 269; Linton, "From Eudoxus to Einstein", pg 413; Aiton, "The celestial mechanics of Leibniz in the light of Newtonian criticism"; Arya (1990), "Introduction to Classical Mechanics" (1990), pg 231) Perspective (1) is really only interesting historically, as these references show that (1), as a study of the motion along the radius vector (Leibniz's approach), is essentially a study of motion relative to a rotating frame of reference, ie perspective (2). We also have references that (4) is something different from (2) (see Roche, "Introducing motion in a circle").

I don't know if I agree though that there is too much to merge this article and Centrifugal force (rotating reference frame). I apologize for letting the merge discussion go stale - RL issues both fun and not so fun. But I do agree that both articles need extensive trimming - maybe after the trimming it will be clearer whether the two can be merged properly or not. --FyzixFighter (talk) 19:25, 24 January 2011 (UTC)

FyzixFighter, The point which you have overlooked is that (1) and (2) are only the same in the special case when the object is co-rotating with the rotating frame of reference. What perspective (2) does is, it uses maths to patch up the difference between the real inertial effect which can be felt as an outward push on an object that is in a state of absolute rotation, and the situation where an object is sitting stationary and being observed from a rotating frame of reference. In the latter, there is no inertial effect.

Perspective (1) concentrates on the actual inertial effect which can be felt and which can break bones and doesn't have to involve a rotating frame of reference, so we can hardly say that perspective (1) and perspective (2) are the same thing. Perspective (1) does not deal with stationary objects that are being viewed from a rotating frame of reference.

Your logic basically runs like this. There is an article on equines and it doesn't mention zebras. Dick argues that zebras don't exist and that there are no sources which say that zebras exist. You argue that zebras are just a kind of horse and don't need any specific mention as they are covered under horses. And despite the fact that what you are saying is not the same as what Dick is saying, you nevertheless claim to be saying the same thing as Dick. But between the two of you, you are both trying to make sure that zebras don't get mentioned. Then when a source is produced which proves that there is such a thing as a zebra, you produce another source showing that a zebra is an equine and that therefore it doesn't need any special mention within the article. Would we really need to have a source which specifically states that a zebra is a species distinct from a horse in order to be allowed to write an article on zebras? No. But we do have sources which treat planetary orbits without mentioning rotating frames of reference and in which the centrifugal force is an outward inertial inverse cube law force. Do we need to have a special source which states that this is a different perspective on centrifugal force from the perspective which ascribes a centrifugal force to a stationary object which doesn't actually possess any inertia and which merely appears to move in a circle? David Tombe (talk) 20:08, 24 January 2011 (UTC)

David, it is quite simple. You are wrong. Your argument is based on a bizarre conspiracy theory of physicists. This shows that not only do you not understand physics but you do not understand conspiracy theories. It is time to call it a day. Martin Hogbin (talk) 20:14, 24 January 2011 (UTC)

Martin, Which conspiracy theory are you talking about? Can you not see the difference between,

(a) An object with an absolute angular momentum that is pushing outwards from a centre due to its inertia, and

(b) An object that is sitting stationary with no inertia, but which is being observed to move in a circle from the perspective of somebody in a rotating frame of reference?

Those are two different physical situations. Can you not see the difference between them? Only situation (a) involves an inertial centrifugal force. I know that you think that situation (b) involves a centrifugal force and a radially inward Coriolis force, but this is just mathematical accountancy and doesn't involve any real inertial effects as such. David Tombe (talk) 20:24, 24 January 2011 (UTC)

@David - since we do have multiple reliable sources that say (1) is understood today as a specific application of the more general (2), then yes, we do need a reliable source that says (1) and (2) are distinct. Please remember WP:OR, WP:FRINGE, WP:BATTLE, and WP:SOAP, which you have previously been warned about. --FyzixFighter (talk) 20:43, 24 January 2011 (UTC)

FyzixFighter, There is a completely different emphasis. Perspective (1) is about actual motion along the radial vector. It's about actual inertia. It about a force which can be felt. Perspective (2) is about accounting for observations from a rotating frame of reference and it applies centrifugal force to situations in which there is no actual inertia. They are completely different perspectives on the subject, and I can show you multiple sources that deal with the orbital problem without using a rotating frame of reference. David Tombe (talk) 21:12, 24 January 2011 (UTC)

The merge proposed in its current form runs the risk of violating WP:SYNTHESIS. If each of the perspectives are so different, why is a joint article preferable? To justify a single article about all the perspectives listed, we would need a single source covering them all, as opposed to lots of sources each discussing one perspective. Details on each perspective could be filled in using other sources, but without the overarching source we wouldn't actually have any evidence that there is a single topic to cover. Alzarian16 (talk) 10:05, 25 January 2011 (UTC)

Confusion with Centripetal Force

Without a doubt, many people come to this page to understand the difference between centripetal and centrifugal force. The current explanation, while correct, is only understandable to people who already understand these concepts. Here are two external articles that do a significantly better job: physlink.com and www.suite101.com/content/centripetal-vs-centrifugal-a15865 (can't link directly because of a spam filter, but the article is good). —Preceding unsigned comment added by 90.231.129.170 (talk) 01:52, 28 January 2011 (UTC)

Anon 90.231.129.170, It's a pity that such confusion should exist between two quite different concepts, particularly when the very etymologies of the two words mean that one is an inward acting force whereas that other is an outward acting force. And alot of that confusion is down to Isaac Newton. Have a look at this very interesting web link [2] which explains Newton's reaction to Leibniz's views on centrifugal force.

The two web links which you have provided are very much based on the Newtonian concept of centrifugal force being an equal and opposite reaction to centripetal force. But the truth is that centrifugal force is a pro-active inverse cube law force which is not in general equal in magnitude to the centripetal force. It is generally agreed nowadays that even in the special case of circular motion, where the centripetal force will indeed be equal in magnitude to the centrifugal force, that the two will not form an action-reaction pair. Also, in case you are in any doubt as to whether or not centrifugal force is a reactive force or a pro-active force, then consider the simple case of a weight being swung on the end of a string in a horizontal plane. The centripetal force is caused by the tension in the string. But that tension is first of all caused by the tendency of the weight to move in a straight line, which in turn causes the radially outward inertial effect. The inward centripetal force doesn't kick in until the centrifugal force is already established. David Tombe (talk) 17:04, 28 January 2011 (UTC)

Nonsense. Dicklyon (talk) 00:01, 29 January 2011 (UTC)

This does indeed seem nonsense. Yoenit (talk) 00:20, 29 January 2011 (UTC)

Yoenit, Can you please elaborate on what you are claiming is nonsense. Are you saying that Leibniz's equation,

${\ddot {r}}=-k/r^{2}+l^{2}/r^{3}$

is nonsense, and that you think that centrifugal force and centripetal force do constitute an action-reaction pair? Are you taking the Newtonian view?

Leibniz's point of view is essentially the same as Lagrange's point of view, and it is the point of view which appears in Goldstein's 'Classical Mechanics'. Centrifugal force is an outward inverse cube law force when angular momentum is conserved. It is therefore not in general equal to the inward gravitational force. In an elliptical planetary orbit, at perihelion, the centrifugal force will be greater than the centripetal force, and the planet will be accelerating outwards. The reverse is the case at aphelion. The two different power laws, as between inverse square law for gravity and inverse cube law for centrifugal force provide the orbital stability. I suggest that you read up a bit on celestial mechanics before you start making blanket criticisms as you have just done above. David Tombe (talk) 01:07, 29 January 2011 (UTC)

The Leibniz equation is not nonsense. It's just a special case of the standard interpretation as a fictitious force, for the case of a reference frame co-rotating about the point of the central forces on an object, for example rotating about the Sun to follow a planet under the influence of gravity. In the co-rotating frame, orbital motion is simplified to motion only along R, so it reduces to a 1D problem. As you say, the inward (gravitational) and outward (fictitious) forces are not balanced when ${\ddot {r}}$ is nonzero. Goldstein explains all this, as we've discussed before. Nothing wrong with it, just with your interpretation that "the truth is that centrifugal force is a pro-active inverse cube law force" and your statement that for the weight on a string "The inward centripetal force doesn't kick in until the centrifugal force is already established." If you want to imagine the centripetal force as an "effect", it is the effect of stretching the string by having the weight move is a straight-line path that takes it to greater distances; once the string stretches, it applies the centripetal force that accelerates the weight into a curving path; the reaction force to that is felt by the guy in the middle who is holding the string; it's this force that is part of a balanced pair: string tension pulls equally on both ends. That's the reactive centrifugal force; the fictitious force on the weight seen by a rotating observer is different, not part of a reaction pair; not a real force at all when viewed from an inertial frame, which is whey they call it fictitious. But you know all that, so why do keep up the nonsense? Dicklyon (talk) 02:36, 29 January 2011 (UTC)

Dick, I'm glad you agree that Leibniz's equation is not nonsense. You will see that in Leibniz's equation, centrifugal force is not reactive. And you will see that it obeys an inverse cube law. So why are you maintaining that my assertion that "centrifugal force is a pro-active inverse cube law force" is nonsnese?

As regards your analysis of the weight on the end of the string, you left out one important link in the chain of logic. We're agreed that the tendency of the weight to move in a straight line causes the string to become taut. But you left out the final clause "due to centrifugal force". The full sentence should read "the tendency of the weight to move in a straight line will induce a centrifugal force which will pull the string taut". And this centrifugal force is the very same centrifugal force which appears in Leibniz's equation. The tension in the string is a consequence which then causes a centripetal force to act. The linear analogy to this is a person accelerating in an elevator. The pro-active force is the downward gravity, and the reactive force is the upward normal reaction of the floor of the elevator, and the two are not an action-reaction pair because they are only equal in magnitude in the special case when the lift is not accelerating. David Tombe (talk) 11:19, 29 January 2011 (UTC)

Um, no. The weight moves in a straight line and causes the string to become taut due to the weight's inertia (and because someone is holding the other end of the string). To quote from the page before in the Swetz reference you mentioned above (with emphasis mine):

In the case of a body rotating in a circle on the end of a string (ideally outside a gravitation field, or shall we say on a frictionless horizontal table), there is only one real force, namely the tension in the string. And in the case of the comet, the only real force is the attraction.

Additionally, regarding Leibniz's centrifugal force, Swetz says on the page you linked to (with emphasis mine):

The question arises whether the earlier [Liebniz's] concept can be interpreted meaningfully. Considered as an endeavor of the circulating body, or a force acting on the body itself, it does not exist. But if we consider a reference frame fixed in the body and rotating with it, the body will appear to have an endeavor to recede from the centre. This of course is a fictitious force reflecting the acceleration for the reference frame.

In a stationary, inertial frame watching what goes on, Leibniz's term appears as a term in the inertial part, m*a, of Newton's 2nd law, not as a contribution to the net force acting on the object. In a linear analogy, the centrifugal force is akin to the downward endeavor/force that an occupant would say they feel as the elevator accelerates upward (or the upward endeavor/force felt as the elevator slow down). This isn't a real force, but, just like Swetz explains the Leibniz's centrifugal force, is really just a "fictitious force reflecting the acceleration for the reference frame". --FyzixFighter (talk) 15:09, 29 January 2011 (UTC)

FyzixFighter, The key point in your argument is that we are working under a set of rules in which what Swetz says, takes priority over what Leibniz himself has said. So let's then consider what Swetz has said. As regards the weight being swung around on the end of the string, you will agree that,

(1) The string is being pulled taut, and

(2) That Swetz says words to the extent that in a frame of reference fixed in the string, the weight will appear to have an endeavor to recede from the centre, and that this endeavor is a fictitious centrifugal force reflecting the acceleration of the frame of reference.

(3) That this fictitious centrifugal force, being a co-rotating example is equivalent to the inverse cube law centrifugal force in the Leibniz equation.

But somewhere along the lines, you are trying to argue that this centrifugal force is not the cause of the string being pulled taut. You are arguing that the string is being pulled taut by the inertia. Correct, it is indeed being pulled taut by the inertia. But the centrifugal force is the inertial effect in question, because as you already know, centrifugal force is an effect of inertia, and so the string is being pulled taut by an inertial centrifugal force.

On your second point, the person in the elevator feels real forces which are caused by the normal reaction of the floor of the elevator. The person in the elevator never feels the force of gravity. Likewise when a motorbike rider is riding inside an elliptical wall of death, he will only ever feel the inward acting centripetal force. But it is the outward acting centrifugal force which is pressing him into the wall in the first place. And this centrifugal force is not in general equal to the centripetal force. And the analogy with the elevator is that the normal reaction of the wall in the wall of death is analogous with the normal reaction of the floor of the elevator, while the centrifugal force in the wall of death is analogous to the gravitational force in the elevator. David Tombe (talk) 15:53, 29 January 2011 (UTC)

I agree with the anon who started this thread. This article does a bad job of explaining the concept to the general public because it s has become bogged down with spurious discussions on different types of centrifugal force. There is only one meaning of the term in current widespread use and that is the meaning that should be properly and clearly described here and sitinguished from centripetal force. I think a much tougher line on spurious nonsense is needed here. Martin Hogbin (talk) 16:00, 29 January 2011 (UTC)

Martin, the main meaning that you're referring to is in the article that moved long ago Centrifugal force (rotating reference frame). The present article Centrifugal force was created as a summary style article to cover briefly the relationship of that main standard meaning in physics to other uses of the term. We don't need to deny the other uses to get this right. Dicklyon (talk) 19:39, 29 January 2011 (UTC)

But the current situation is crazy. Someone who wants to know what centrifugal force is has to know that the meaning they want is Centrifugal force (rotating reference frame). This is like having USA(North America) and a summary page to distinguish it from USA(the name of my dog) and USA(small town in Mongovia) on it. The primary meaning should be the main article, all the other meanings are historical, specialist, or fringe. Martin Hogbin (talk) 20:12, 29 January 2011 (UTC)

No, I think that's nutty. A person who wants to know what it is will come here and learn that it can mean some different but closely related things. Then they can decide which meaning they're looking for and either read the short version or follow the main links to the long versions. I added a bit to the lead to lead into them a little better. Dicklyon (talk) 20:18, 29 January 2011 (UTC)

But it does not mean some different but closely related things, except in historical, (very dubious) specialist, or fringe (being polite) contexts. I have no objection to a section on these at the end of the article. I really do not understand your objection to getting this subject in proper order so that the article is helpful to readers, as the anon suggests. Martin Hogbin (talk) 20:26, 29 January 2011 (UTC)

Reactive CF is what? Fringe? Only historical? Specialist? I don't think so. Dicklyon (talk) 20:33, 29 January 2011 (UTC)

It is somewhat specialist or maybe just an idiosyncratic or outdated use of the term. Note also that even in that book it is given the name 'reactive centrifugal force' to distinguish it from plain 'centrifugal force'. I have no objection to a section on'Reactive centrifugal force' or 'Alternative meanings' but there is no doubt whatever that the main meaning of the term is the Centrifugal force (rotating reference frame). It is this sort of thing that confuses readers and brings WP into disrepute. There is only one meaning in current widespread use and it is our job to make this clear to people who do not know. Martin Hogbin (talk) 20:53, 29 January 2011 (UTC)

I disagree – there is considerable doubt. What you call "the main meaning" or the "only one meaning in current widespread use" is really the meaning within the physics community; that's "specialist" compared to the meaning to the general population of people who feel a tug on a string when they swing a weight around, or who want to know how a centrifugal clutch works. Why can't we treat these in a coherent and comparative way that helps people with one perspective understand both better? Dicklyon (talk) 21:06, 29 January 2011 (UTC)

Both the examples you give are best explained using the standard (physics) definition of CF. Reactive centrifugal force is a confusing concept when trying to explain why things happen, that is why the reactive definition has become less used over the last half-century or so, particularly in education. Martin Hogbin (talk) 22:50, 29 January 2011 (UTC)

And what is that one meaning in widespread use Martin? The force that stops the water falling out of a bucket when you swing it over your head? I'd also have no objection to a united article to cater for centripetal force too. Although centripetal force is quite different from centrifugal force, it does rather seem that alot of people get the two confused, and therefore one single article could explain all the issues in separate sections. There's a problem at centripetal force too. I used to think that centripetal force was a force which acts towards a centre, such as in the case of gravity in an orbit. But apparently there is a school of thought over at the centripetal force article which teaches it as being a force which acts act right angles to the direction of motion. The two definitions of course diverge once we move outside of circular motion and into elliptical motion. David Tombe (talk) 17:07, 29 January 2011 (UTC)

David, you have already admitted that your opinion on centrifugal force is based on there being a conspiracy amongst physicist to mislead people. That makes your views fringe, to say the least, and think you would do yourself a favour by withdrawing from discussion of this subject. Martin Hogbin (talk) 18:36, 29 January 2011 (UTC)

Martin, I don't recall ever saying that my opinion on centrifugal force is based on there being a conspiracy amongst physicists to mislead people. My opinion on centrifugal force is the same as that of Leibniz and Maxwell, and I arrived at my conclusions from studying planetary orbital theory in Goldstein's 'Classical Mechanics'. Rather than anybody withdrawing from the discussion, it would be much more helpful if you would actually engage in the discussion. I want to see some evidence that you understand the topic. David Tombe (talk) 19:01, 29 January 2011 (UTC)

Maybe that is because you deleted it from your talk page. You said,'The only reason why anybody might oppose such a planetary orbital section is for ideological reasons. For example it might clash with a mindset based on relativism where everything is relative and in which there are no absolutes.' Martin Hogbin (talk) 20:22, 29 January 2011 (UTC)

Martin, I said that further up this talk page. It might be archived now. I was trying to speculate on why such an established topic was meeting with such strenuous resistance. David Tombe (talk) 21:44, 29 January 2011 (UTC)

Centrifugal force in engineering

There seems to be a suggestion here that engineers usually use the term 'centrifugal force' to refer to the reaction to the centripetal force and that this is desirable or necessary for the convenient understanding of things like centrifugal pumps, centrifugal clutches and stresses in turbine blades. I see little evidence that this is the case.

Consider a drawing of, say, a turbine blade with stresses and centrifugal forces marked on it. The engineer may consider the marked forces to be the reaction forces. On the other hand, they may well be considering themselves to be working in a frame of reference that is rotating with the blade, after all the blade does not rotate on the paper (or screen). If that is their understanding of what they are doing (and they probably have more important things to do that consider that subject in detail) then there is no problem with the marked forces being the standard inertial (I much prefer that term to' fictitious') forces that exist in a rotating reference frame.

Similarly, in the case of a centrifugal pump, it seems quite natural to use a reference frame rotating with the impeller, thus the water is pulled outwards by centrifugal force. Simple.

One case I can see where this approach is not so natural is that of water flowing round a curved pipe. Here the non-rotating frame of the pipe is the natural one. Martin Hogbin (talk) 10:55, 30 January 2011 (UTC)

Martin, if we are treating 'reactive centrifugal force' as a kind of 'apparent weight' concept, then a distinction does become relevant in non-circular motion. The 'reactive centrifugal force' will not in general be equal to the pure inertial force that causes it. The 'reactive centrifugal force' will always equate to the centripetal force, where such centripetal force has been induced by an inertial centrifugal force causing an object to press or pull against another object. See the comments below. David Tombe (talk) 14:17, 30 January 2011 (UTC)

The latest edits

Dick, Regarding your new paragraph, would it not have been better if you had said that these situations can be analyzed using either the 'rotating frames' approach or the Lagrangian approach, and in the special cases where circular motion is involved, the centrifugal force will be equal in magnitude to the centripetal force, and so we can used the 'reactive centrifugal force' approach? David Tombe (talk) 21:44, 29 January 2011 (UTC)

I think the Lagrangian approach is way too specialist to even mention at that point. Both approaches mentioned can be used, whether the motion is circular or not. Dicklyon (talk) 21:56, 29 January 2011 (UTC)

Dick, The reactive centrifugal force concept can only be used when the centrifugal force and the centripetal force are of equal magnitude. That is one of the reasons why I object to it. It seems that you have got confused about an already faulty concept. I don't think that the last lines of your new paragraph are very clear. Do you think the readers will get your point about these different centrifugal forces are not equal in general, especially when radial acceleration is involved? Also, where does the reactive centrifugal force enter the picture for somebody tied to an aeroplane propeller with the rotation origin right in their middle? David Tombe (talk) 23:47, 29 January 2011 (UTC)

When the reactive centrifugal force concept is used, it's equal ``by definition to the centripetal force, which is defined in terms of a center of osculation. It doesn't matter whether the motion is circular or not. I agree that "especially when radial acceleration is involved" is probably only going to confuse; I'll take it out. Dicklyon (talk) 00:41, 30 January 2011 (UTC)

Dick, If the two are equal I can't see how it wouldn't be circular motion. Anyway, what is meant by your statement these different centrifugal forces are not equal in general? Can you give me a scenario where they aren't equal. David Tombe (talk) 01:08, 30 January 2011 (UTC)

Consider a centrifugal railway with a non-circular loop. At each point, the centripetal force provided by the track is equal to the reaction force on the track by the rail car. If you need to resolve the forces to get rid of non-centripetal components, it's still true. Dicklyon (talk) 02:11, 30 January 2011 (UTC)

Dick, I've got your point, but you need to think very carefully about this. The non-circular situation which you have given is analogous to a person accelerating in an elevator. When the elevator is accelerating downwards, the force of gravity will be unaltered, but the upward normal reaction of the floor will be reduced. The person feels lighter because the upward normal reaction from the floor is less. Likewise in an elliptical centrifugal train, the centripetal force will be less as the train is moving further from the centre. But the centrifugal force as per the Leibniz equation, or as per the rotating frames approach, will still be calculated in the normal way.

But I can see that you are looking at the actual outward physical push on the floor of the train, and this will certainly be less than in the circular motion case if the train is moving outwards from the centre. It is this physical push which induces the inward centripetal force. I assume that it is this effect which you are taking to be the 'reactive centrifugal force'? And what would the equivalent be in the elevator? The person's weight doesn't change, but the degree to which gravity causes them to push against the floor does change as the elevator accelerates. We would tend to use the term 'apparent weight' for that situation, and so I suppose that your concept of reactive centrifugal force would bear an analogy with the concept of 'apparent weight'.

But is that what Newton had in mind for 'reactive centrifugal force'? Newton invoked the concept in relation to the Leibniz's planetary orbital equation, and in that situation we are not dealing with circumstances in which centrifugal force causes an object to press or to pull against another object such as to induce a centripetal force. In planetary orbits, the centripetal force is pro-active, so I'm not sure if your concept of reactive centrifugal force is the same as Newton's concept of reactive centrifugal force. Having said that, I think that Newton's concept of reactive centrifugal force in connection with planetary orbits was quite wrong. Your concept on the other hand, despite being driven by a pro-active centrifugal force, is in many ways a reactive concept. The centrifugal force pushes the person against the floor. The centripetal force then arises as a shared reaction between the person and the floor, and that's what gives the apparent weight.

This subject needs to be better explained in the article, and it definitely requires a section of its own. I don't think the readers are going to grasp what you mean by the centrifugal forces not being equal in general, unless there is some kind of demonstration such as the one you have mentioned about the centrifugal railway. Best to leave that line out of the introduction. David Tombe (talk) 14:07, 30 January 2011 (UTC)

I'll stay out of it for a while and see if others come up with a better lead or more explanation. Dicklyon (talk) 21:26, 30 January 2011 (UTC)

Dick, Likewise, I'll stay out of it for a while too and watch what other editors can suggest. But I do think that I have identified the 'reactive centrifugal force' as being an analogy with 'apparent weight'. And of course, apparent weight is not equal in general to the force of gravity. Apparent weight is only numerically equal to the force of gravity when the reaction surface is not accelerating towards or away from the object in question. For a better understanding of this subject in general, we might think about dividing examples into three categories,

(1) Examples involving centrifugal force in conjunction with push and pull interactions with strings, springs, and floors, which cause a centripetal force.

(2) The linear analogies to the above involving gravity in conjunction with push and pull interactions with strings, springs, and floors, which cause tensions and normal reactions. The accelerating elevator will give good analogies with elliptical motion at (1).

(3) Examples in which gravity and centrifugal force come face to face without any involvement of push or pull interactions. This is where the Leibniz equation comes in, pitting the inward inverse square law gravity force against the outward inverse cube law centrifugal force such as to lead to elliptical, hyperbolic, or parabolic orbits. David Tombe (talk) 22:28, 30 January 2011 (UTC)

Layman's terms

Can someone add an English version? Seriously, way too technical for a Wikipedia entry from paragraph one. --66.119.170.242 (talk) 00:53, 29 January 2011 (UTC)

I have to agree, this article starts with a confusion and then adds to it. I cannot see why we have to dive into rotating coordinates and the awful term fictional forces. In everyday fixed coordinates where we observe things as rotating, like a roulette wheel, there is a real force, in this case exerted by the ball on the constraining rim. Of course this is a real force experienced by the rim and it is equal and opposite to the centripetal force on the ball and of course we understand this force is rotating as we watch.Profstandwellback (talk) 17:33, 31 January 2011 (UTC)

Profstandwellback, I brought your comments down to here in order to better reflect the chronology of posting. Anyway, what you have just said is more or less what I have been saying all along. The subject can mostly be explained without recourse to mathematics. Even in the case where centrifugal force comes face to face with gravity in a planetary orbit, we could simply write in plain English that gravity is an inward inverse square law force and that centrifugal force is an outward inverse cube law force and that the combined effect leads to orbits which are circular, elliptical, parabolic, or hyperbolic. David Tombe (talk) 19:11, 31 January 2011 (UTC)

@Profstandwellback - what you're describing is the reactive centrifugal force, a force that the ball exerts on the constraining rim in accordance with Newton's 3rd law. It always exists (though in some cases it might not technically be "centrifugal") independent of the frame of the observer. The inertial/fictitious/pseudo/however-you-want-to-call-it force is a force that appears to be exerted on the ball - it only appears to exist inside a rotating frame, is determined by the rotation rate of the frame, has no third law partner, and is only an illusion of a force. In the inertial (stationary) frame there is no such force (force as defined in classical Newtonian mechanics, anything that contributes to F_net in Newton's 2nd law). I'd reccommend Roche's article "Introducing motion in a circle" which I think does a pretty good job of distinguishing the two. --FyzixFighter (talk) 00:02, 1 February 2011 (UTC)

In reply to FyzixFighter, I think I understand where you are coming from but it makes the simple seem complicated. Force is a real thing, it can be experienced by an observer or by an object , it can be felt as a real pressure (force divided by area), it can break real objects etc so why call it a fictional force? We can explain that it arises by the continual radial acceleration of a rotating object, which is a real acceleration inside our "normal" frame of reference. Students may find a continual acceleration hard to grasp when compared with a linear acceleration but it is sure to baffle them if you switch to rotating coordinates, a difficult intellectual leap, and then say the force is fictional. If you are inside the rotating frame, say on a fairground ride, you experience a very real force do you not? To call it fictional in order to use clever mathematics is perverse. Centrifugal force is simply the opposite of centripetal force, it is a real everyday force and simple to calculate from the angular rate. You can go on to explore the effects of alternate frames of reference for more advanced students, but Occams Razor tells us to choose the simpler explanation over the complex.Profstandwellback (talk) 14:00, 1 February 2011 (UTC) Can I dare to add a question about the point of WP? Is it to provide instruction to students? In which case we must at each step take the student from what they already understand to a new a deeper understanding. Therefore we begin with common everyday experience such as swinging a ball on a string and stuff like that. The forces involved need to be compared to other forces such as weight (this is a major step in understanding the world) and related to the origin of forces such as gravity and acceleration. The centrifugal/centripetal chestnut should not be allowed to become folklore like the story that "the bee can't really fly but no-one told him." When there is both rotation and radial acceleration or angular acceleration, the picture is significantly more complex and there is no hope of reaching understanding unless you have first grasped simple rotation examples. It is a huge mistake to approach the subject through maths rather than experience because this will turn many students off for life when a simple step by step explanation will bring those "AHA' moments. If WP is to have esoteric discussion about frames of reference, then fire away but don't expect to get converts from the people who are curious to understand but missed meeting Newton, I gather he was not a good teacher, just a cranky genius, there is a role for simple teaching.Profstandwellback (talk) 14:30, 1 February 2011 (UTC)

The goal of WP is to present what is verifiable, that is, what appears in reliable sources. I think there is a distinction, perhaps subtle, between it being a textbook (which it should not be) and it being an encyclopedia. One endeavors to teach while the other endeavors to inform. Again, I suggest if possible that you read the Roche article which sums up the other reliable sources and explains the two main and distinct uses of the term "centrifugal force" in science. Simple is good, but not if it makes something wrong. Let me be clear that I am not happy with the current state of the articles and that I feel that something could be done to clear up confusion, such as a merger, and I do feel that, when possible, a simple explanation should precede a mathematical derivation.

The term "fictitious" only applies to the centrifugal force that appears in rotating frames - reactive centrifugal force is very real and arises whenever you have a contact or binding centripetal force. Let me try an example to distinguish the two. A passenger is in a vehicle in the seat but not touching the wall yet and the vehicle rounds a corner. The passenger will say that she feels a force pushing her outward, and in fact relative to the seat she does accelerate outward until she meets the wall of the vehicle. So here are the two centrifugal forces: 1) from the perspective of the passenger, she feels a force exerted on her pushing her outwards, and 2) she exerts a centrifugal force on the wall when she reaches it (and the wall exerts a centripetal force on her). Now according to the passenger, there are three forces - two acting on her and one that she exerts on the wall. However, a stationary observer does not see the first one but merely sees the passenger moving in a straight line, and the vehicle and the seat moving out from under her until she comes into contact with the wall, at which point the contact force from the wall accelerates the passenger inward so that she follows a curved path. The stationary observer see only two forces - one that the wall exerts on the passenger and one that the passenger exerts on the wall. According to the stationary observer, what passenger perceives as an outward force on her is an illusion caused by her using the vehicle as her reference frame and neglecting to account for the frame's acceleration. In this example, the first centrifugal force is the typical usage of the phrase in modern physics. There are occurrences of the second, and the term centrifugal force does rightly apply to that force, but it is distinct form the first when you consider what the two forces are acting upon and whether the force is part of F_net in Newton's 2nd law in the inertial frame. Again, these are the uses as found in reliable sources. We can probably do better in giving a layman's explanation, but we should not sacrifice accurately relaying the information in reliable sources for the sake of perceived simplicity. --FyzixFighter (talk) 15:22, 1 February 2011 (UTC).

Thank you for a long explanation. I think a textbook and an encyclopedia share a didactic purpose and should still progress from sim ple to complex. I think the following is simple and rigorous, based on Newton. If a massive particle is constrained to rotate in a circle it will exert an outward radial force on the constraint. This is called centrifugal force. It is a real force with value found by multiplying the mass by the radius and by the square of the angular velocity. It remains the same value in rotating coordinates but the vector rotation can and must be reinterpreted. The constraint can take several forms (as has been discussed in previous posts). If the particle is constrained into a circular path with changing radius an interesting force is required acting at right angles to the trajectory called the Coriolis force. This is also a real force and very important in understanding many phemonena. Centrifugal force and Coriolis force along with Euler and gyroscopic forces can be called inertial forces because they arise from constraining a mass to follow any general path which is not a straight line. (Newtons first law) The constrained mass particle in the simple case of a circle experiences an inward radial force called the centripetal force which in this simple case is equal and opposite to the centrifugal force. Once the case is complex (non circular) the inertial forces cross couple depending on the three dimensional form of the constraint. This situation obtains in many real life examples as have been discussed as engineering examples.Profstandwellback (talk) 11:28, 2 February 2011 (UTC)

(I hope you don't mind me modifying the indenting to keep this a bet separate from the other discussion below) Again, what you're describing is the reactive centrifugal force and is not the way that the term is typically used in physics (when analyzing the motion of an object, I generally don't care about the forces that the object exerts on it's surroundings), nor how the lay person generally thinks about centrifugal force. I think that the lay person generally thinks about centrifugal force as the apparent force that pushes an object outwards in rotating frame, and not the force that the object exerts on a wall. Let me try another example, the Rotor (ride). People will usually say that it is the centrifugal force pushing them against the wall, but such a force is an illusion according to an inertial observer. There is an outward centrifugal force that the person exerts on the wall, but that is not the typical physics usage of the term and I don't think that the lay person is talking about that force when they use the term. Additionally, if people in the Rotor start throwing objects around, they will note that, from their perspective, objects follow curved paths and do not appear to obey Newton's 2nd law. In order to make Newton's 2nd law work from their perspective they must include the centrifugal force and the Coriolis force. These are the typical "fictitious" forces of physics, since to an inertial observer the objects do obey Newton's 2nd without invoking the apparent forces. Also note that there are no "constraining" forces for these objects so no reactive forces, so the usage of the concepts of centrifugal force and Coriolis force to describe their motion within the rotating frame is clearly distinct from the concept of reactive forces.

As I mentioned before, there are references that talk about the reactive centrifugal force, generally engineering sources talking about internal stress in solid rotating objects, which is distinct from how the term is generally used in physics. I don't think I have ever seen in any source how you've used the terms Coriolis force and Euler force. I have only ever seen those used for the apparent ("fictitious" or inertial) forces that arise from frame rotation and that are exerted on an object, not to describe the force exerted by the object on it's constraint. If you haven't yet read the Roche reference in the Physics Eduction journal, I highly recommend it because it does come at the concept from a pedagogical perspective. --FyzixFighter (talk) 15:23, 2 February 2011 (UTC)

thank you for the above argument, I think we agree that centripetal is the force on the particle while centrifugal is the force on the constraint and I agree the layman needs to be shown that centrifugal F. is not the force on the rotating mass. However I think the layman also appreciates that if you power up the rotation speed eventually the centrifugal forces will break the constraint, often dramatically in many engineering examples so she will be confused to be told the centrifugal force is imaginary or fictional. I appreciate the physics concentration on the trajectories of particles but in many engineering cases the forces on the constraints are important. So could we agree that the early part of the description in this article should clarify that the centrifugal force acts on the constraint in rotating systems with the usual examples and the maths treatment can be left till a later paragraph?Profstandwellback (talk) 14:57, 3 February 2011 (UTC)91.125.59.10 (talk) 14:35, 3 February 2011 (UTC)

The reactive centrifugal force is already mentioned in the first paragraph of the lead as one of the uses, and it is summarized in the third subsection, in about the same amount of space as the "fictitious" centrifugal force in the subsection above it. However the main usage of the term is in the context of rotating frames so, imo according to WP:UNDUE, that should be the position given the greatest emphasis. The reactive force has only limited usage and is not the common usage of the term, even if you or I or anyone else thinks that it should be (for the record, I don't) - the fact of the matter is that most reliable sources use "centrifugal force" to refer to the pseudo-force in rotating frames. We can and do mention both uses and should explain the difference between the two, but we should not try to "right great wrongs" by reversing the emphasis found in reliable sources and in mainstream science. --FyzixFighter (talk) 15:08, 3 February 2011 (UTC)

Gee. Gosh darn it. Just as soon as someone who knows what he is talking about begins to made a important and useful contribution to eliminating the idiotic nonsense of Wikipedia speak, along comes one of the lead fools, and tries to run the guy off. I suggest that you ignore this guy FyzixFighter, he is a know obstructionist, and get on with making some really needed changes to this article, so that really intelligent people can make sense of it. As it stands now, only those who speak physics nonsense can make sense of it. That may be rough going for you Prof Stand Well back, but it needs to be done. I hope sanity prevails since that is certainly absent in Wikipedia. —Preceding unsigned comment added by 72.64.47.126 (talk) 00:30, 1 February 2011 (UTC) —Preceding unsigned comment added by 72.64.51.3 (talk)

Quite the reverse. The use of the term 'centrifugal force' outside if its meaning as an inertail force in a rotating reference frame has proved so utterly confusing that it has been generally agreed that it is best not to use the term at all except in that context. If you work in an inertial reference frame there is no need for centrifugal force of any kind. Martin Hogbin (talk) 19:08, 1 February 2011 (UTC)

Hey double talk is what needs to be cleared up. You are not helping that effort. The idea of centrifugal force was pretty clear until physicists mucked it up. I dont see any clarity here that helps to explain it.72.64.51.3 (talk) 19:32, 1 February 2011 (UTC)

There is no need to use the term at all when working in an inertial frame. That seems simple enough to me. Martin Hogbin (talk) 19:37, 1 February 2011 (UTC)

Are you then saying that there's a need to deny that people do use the term to describe forces felt in an inertial frame, like the tug on the string that you're whirling around? Even some physics books have been pointed out that use it that way, so why should we go out of our way to pretend otherwise? Dicklyon (talk) 01:04, 2 February 2011 (UTC)

If some sources say that the term is sometimes used to describe the reaction to the centripetal force that we cannot deny that fact but I think to put that usage on equal terms with the inertial force would be giving undue weight to what is, I believe, an obsolete usage for physicists and engineers alike. The use of the term for a reaction force is spectacularly unhelpful in understanding the subject and is the cause of much confusion, probably including some on this talk page. The gist of one of the sources used to support that usage is that it is best not to use the term at all at an elementary level, something that I agree with. In other words there is not need to use the term when working in an inertial frame and no benefit from doing so. It is only when the more advanced subject of rotating frames is introduced that we need to introduce the term, or to put it another way, if you do not understand the inertial force necessitated by virtue applying Newton's laws unchanged in a rotating frame then it is best not to use the term at all. Martin Hogbin (talk) 22:49, 2 February 2011 (UTC)

I do have some sympathy for your POV about how people should use the term, like physicists do use it. But this section started by someone asking for an explanation in "layman's terms"; and laymen do use the term and do have explanations involving it; they talk about at outward force, and they do it without "rotating reference frames". I'm not asking to put it "on equal terms", but on reasonable terms at least. Dicklyon (talk) 04:39, 3 February 2011 (UTC)

Do laymen use the term without reference to rotating frames? I think that much of the time they are not quite sure what reference frame they are using. I have no objection to mentioning alternative uses of the term but I doubt very much that this will help laymen understand anything. The best advice to a layman or beginner is not to use the term at all if you want to understand what is going on. Martin Hogbin (talk) 00:04, 4 February 2011 (UTC)

can I refer you to my conversation a few paragraphs above?Profstandwellback (talk) 14:57, 3 February 2011 (UTC)91.125.59.10 (talk) 14:42, 3 February 2011 (UTC)91.125.59.10 (talk) 14:39, 3 February 2011 (UTC)

The problem with using the term 'centrifugal force' to refer to the reaction force on a constraint is that it gives no clue is to where the this mysterious force comes from. It is the reaction to the centripetal force so why not just call it this, no special name is needed, we do not have special names for the reaction to Coriolis force, for example. Martin Hogbin (talk) 00:04, 4 February 2011 (UTC)

Martin, In reactive situations, centripetal force only arises because a centrifugal force is either pulling on a string or a spring, or pushing on a surface. The centripetal force is not the prime mover in the situation. And so you ask where does this mysterious centrifugal force come from? It comes from physical inertia. As regards reactions to a Coriolis force, I can't imagine that within the context of your notion of a fictitious Coriolis force that there would ever be a reaction to one. You need to find a real Coriolis force where inertia is involved, and then you'll see how it reacts with constraints. David Tombe (talk) 00:41, 4 February 2011 (UTC)

FyzixFighter, I notice above that you are acknowledging the existence of the actual outward push against a constraining surface. But then you are making the disclaimer that this is merely 'reactive centrifugal force'. But you are overlooking the fact that this 'reactive centrifugal force' is actually caused by 'centrifugal force'. And the centrifugal force which causes it exists independently, whether or not we have a reaction with a string, spring, or surface. Have a look at this card here which you will find at number 12 in this web link [3]. Imagine that you are an observer standing on the tarmac. You will be in an inertial frame of reference. When the propeller spins, all the liquid and softer tissues inside Robin will move radially outwards from his middle. No centripetal force is involved in the destructive mechanism. This is a display of pure centrifugal force as observed from an inertial frame of reference, and it is very real. It will destroy Robin. And Robin can't make the smart remark which James Bond made in the other cartoon about the destructive effect being attributable to centripetal force. The centrifugal force alone is what will be destroying Robin in this case scenario. David Tombe (talk) 16:17, 2 February 2011 (UTC)

Nonsense. What's making Robin's body parts follow a curve path if there's no centripetal force? Dicklyon (talk) 17:46, 2 February 2011 (UTC)

Dick, Centripetal force will make a vain attempt to hold Robin together, but the damage will all be done by pure centrifugal force. I should have specified in the paragraph above that I was referring to centripetal force in relation to its absence in respect of the destructive mechanism. I have now corrected that.

In the James Bond cartoon however, the centrifugal force is pushing Bond against the rim, and so centripetal force is involved in the destructive mechanism. The Batman cartoon is an example of pure centrifugal force which doesn't involve a reaction, whereas the James Bond cartoon is an example of centrifugal force in which a reaction surface is involved. David Tombe (talk) 18:41, 2 February 2011 (UTC)

Nonsense. Dicklyon (talk) 04:39, 3 February 2011 (UTC)

Dick, Your response indicates that you have got no argument. The James Bond cartoon, which is here, [4], shows James Bond being pushed against the rim by centrifugal force. Centripetal force will then counteract the centrifugal force, and Bond will be crushed by the sandwich effect. Bond claims that only centripetal force is involved. However, put Bond into the position that Robin is in in this Batman cartoon at card 12 here [5] and Bond will not be able to use the argument about centripetal force. The destruction will be caused entirely by centrifugal force, because the centripetal force will be insufficient to hold Robin together. In fact if we were to watch three people in a row, each tied to a propeller, just like Robin, it would be a perfect triple display of centrifugal force as viewed from an inertial frame of reference. We would see centrifugal force radiating out from three centres. It would be very difficult to actually view the centrifugal force in this context from a single rotating frame of reference, because we wouldn't know which propeller to co-rotate from. David Tombe (talk) 12:54, 3 February 2011 (UTC)

Can I add yet another example? In conversation with FyzixFighter above, we agree that centripetal is the force on the rotating particle while centrifugal is the force on the constraint (which is forcing the particle into rotation). In many examples it is confusing which is which. Consider a spin drier, the drum is spinning but is also the constraint. The wet clothes rotate because of centripetal force but the water leaves the drum. We know the instantaneous motion of the water drops is tangential but that also looks like radial to a casual observer, no wonder people get confused. The water leaving is not fictional nor centripetal it is expelled by its inertia and until it breaks free of the drum we can call the force centrifugal.Profstandwellback (talk) 14:57, 3 February 2011 (UTC)91.125.59.10 (talk) 14:54, 3 February 2011 (UTC)

Prof, the case you give above is an excellent example of the confusion that arises from the misuse of the term 'centrifugal force'. In the non-rotating frame, the 'centrifugal force' acting radially outwards somehow makes the water leave tangentially?? Far better to say that the water continues its motion in a straight line but the drum moves round in a circle, thus the water leaves the drum. On the other hand, in a frame rotating with the drum, the radially acting centrifugal force makes the water leave radially. Perfectly logical. Martin Hogbin (talk) 00:04, 4 February 2011 (UTC)

Profstandwellback, Yes, the spin drier example is another example in which the centrifugal force flings the stuff outwards without being hindered by an inward centripetal force. In the James Bond cartoon, the normal reaction of the rim and the friction on the rim would be called dragging forces since they cause the object to co-rotate with the system. In the spin drier, we do have a transverse dragging force, but since we have no inward radial dragging force (ie. no centripetal force), then the outward centrifugal force prevails, and the water flies outwards beyond the rotating drum.

And in relation to what you said about it flying off tangentially, but that it looks as if it is flying off radially, it is actually doing both simultaneously. And that reminds me that there is a gaping ommission in this article. There is no section on 'centrifugal potential energy'. If we swing a weight in a vertical plane to a very high angular speed and then release it under arm, it will fly away an enormus distance. This will represent an huge radial expansion from the rotation origin. The tangential aspect will pale into insignificant. This is a classic display of centrifugal potential energy being unleashed. There used to be a section about this including the mathematical formula for centrifugal potential energy but it seems to have gone. David Tombe (talk) 17:27, 3 February 2011 (UTC)

My only argument is that if you don't back up your approaches with reliable sources, they are essentially nonsensical. David likes to point to Goldstein, but ignores what Goldstein says about how he got to the radial equation via a co-rotating system. There are no outward forces on the particles of water, and no radial motion of the particles away from the spinning drum, unless you are looking at it in a rotating system. The only outward forces in an inertial frame are on the "constraints"; these are the reactive centrifugal force. These are the only two interpretations I've seen in sources. Dicklyon (talk) 23:30, 3 February 2011 (UTC)

Dick, Goldstein doesn't mention rotating frames of reference in connection with planetary orbits. At least not in the 1950 and 1980 editions which are the editions which he personally wrote. And planetary orbits don't involve constraints. They involve centrifugal force coming face to face with gravity. Angular momentum will be conserved and the centrifugal force will obey an inverse cube law. In other situations where centrifugal force does get involved with constraints, then there will of course be a reaction which can be physically felt, but there is no reason to have this reaction dealt with in a separate article as we are doing at the moment. And if a centrifugal force breaks through any constraints, it will still be that same centrifugal force as in the planetray orbital equation. The object will continue in a straight line and it will have a constant angular momentum relative to the origin, and the radial expansion will obey the inverse cube law. The motion will be both radial and transverse to the origin, and there will still be inertia which will be felt as soon as any new constraint is put in its path. David Tombe (talk) 00:14, 4 February 2011 (UTC)

Martin, Regarding your reply to Profstandwellback, he didn't say that the centrifugal force makes the water leave tangentially. He said that it leaves tangentially. The tangential motion is due to the already existing tangential motion. This tangential motion causes a centrifugal force which deflects the tangential motion into the radial direction. The object flies outwards with both radial and tangential components of motion, and the tangential motion is constantly deflecting into the radial direction. Eventually the radial motion will become dominant. David Tombe (talk) 00:24, 4 February 2011 (UTC)

David, your erroneous assertion that "Goldstein doesn't mention rotating frames of reference in connection with planetary orbits" was answered in detail back in '09, here. Dicklyon (talk) 04:25, 5 February 2011 (UTC)

Reactive centrifugal force as a helpful concept

To respond to several replies above I ask anyone to give me an example where specifically naming the reaction to the centripetal force 'centrifugal force' is a helpful concept. Martin Hogbin (talk) 09:28, 4 February 2011 (UTC)

Martin, The reaction to a centripetal force is a particular manifestation of centrifugal force which can be physically felt. This article is about centrifugal force and therefore that manifestation needs to be dealt with in the article, as does 'centrifugal potential energy'. But the reaction to a centripetal (constraining) force is not the only manifestation of centrifugal force. Centrifugal force in general can be plotted mathematically by constructing Newton's laws in a rotating system and it will show up in any straight line motion relative to any arbitrarily chosen origin. And even when there are no radial constraining forces (radial dragging forces) involved, there are situations in which centrifugal force can still be physically felt and observed. Consider three propeller driven aircraft sitting on the tarmac. Tied to the three propellers are the Joker, the Riddler, and the Penguin. When the propellers are going full power, these three men will explode. Their molecules will accelerate radially outwards in all directions. We will witness three explosions from three epicentres and we will be standing in an inertial frame of reference. Is this a display of centrifugal force, or is it a display of the fact that particles continue to move in a straight line unless acted upon by a force? David Tombe (talk) 11:14, 4 February 2011 (UTC)

I was rather hoping that someone would try to give an example where the use of the concept of reactive centrifugal force was helpful in understanding some phenomenon, process, or equipment. How does that concept help explain your scenario? Martin Hogbin (talk) 12:11, 4 February 2011 (UTC)

Maybe this is an example; in a shell fuse there is a need for a timing and arming function to prevent the fuse being live until it has left the barrel. One method is to have ball bearings on a ramp constrained to move radially against a spring. The shell is spun during acceleration and the balls move outwards under centrifugal force, compressing the spring until it latches in the armed position. Another: in a rock crushing machine, rocks are dropped into a rotating drum with vanes which encourage the rocks to accelerate radially rather like a water pump. The lining of the drum is either hard or tough and the centrifugal energy smashes the rocks. In a conical pendulum governer, the weight(s) are constrained to move radially and reach an equilibrium displacement. The weights are centripetally constrained by gravity but the mechanism operated by the weights experiences centrifugal force.Profstandwellback (talk) 12:44, 4 February 2011 (UTC)

In a so called centrifugal clutch a set of friction pads lines a drum, held from contact by springs. When rotating the friction pads move radially outwards and exert a couple on the drum causing it to rotate; when the rotation is fast enough the pads and drum become locked together by friction caused by the high centrifugal force (and of course the corresponding centripetal force.)Profstandwellback (talk) 12:51, 4 February 2011 (UTC)

In another example from history, in about 1971 Rolls Royce (Aero engines) introduced carbon fibre turbine or compressor blades. Unfortunately the blades suffered radial creep due to centrifugal force and this problem after a while brought the company to insolvency; perhaps the most prominent case of corporate collapse due to centrifugal force ever recorded.Profstandwellback (talk) 13:03, 4 February 2011 (UTC)

Prof, your examples are just ones in which the term 'centrifugal force' is used in a casual way without specifying any reference frame. What makes the turbine blades creep? Centrifugal force. That is absolutely fine, I might have in mind an inertial force in the reference frame rotating with the blade and a layman probably will not have thought to consider the need for a reference frame at all. I have no objection to mentioning the informal use of the term to generally describe the force that pulls things outwards when you whirl them around, although I would point out that this terminology is now strongly discouraged as being confusing. It is fine for someone with no technical understanding or interest but for a budding engineer or physicist is is better not to use the term at all as it will sow the seeds of confusion that have blossomed all over this article.

What confuses things even more than the casual use of the term is the attempt to justify this by applying the term 'centrifugal force' to an outward going reaction to the centripetal force. That reaction force is just like any other reaction force, giving it a special name that is actually needed to describe a different concept helps no one. Martin Hogbin (talk) 13:43, 4 February 2011 (UTC)

Martin, The so-called 'reactive centrifugal force' is caused by centrifugal force. 'Reactive centrifugal force' stands in the same relationship to inertial centrifugal force, as apparent weight stands to gravity. But I have never approved of the name 'reactive centrifugal force', because in the situations where it is used, it is actually the inward centripetal force which is the reaction. The centripetal force can be a consequence of the pressure which a wall of death rider applies to the surface, or it can be a consequence of the tension which a swinging weight applies to the spring or the string. Either way, we need a primary centrifugal pressure to kick off the reaction.

I don't want to have a special article for reactive centrifugal force. I want those case scenarios dealt with in this article, with reference to non-circular scenarios such as the centrifugal train. And you still keep overlooking the fact that in celestial mechanics, we deal with pure inertial centrifugal force in a radial gravitational field in which no physical reaction is felt. Centrifugal force is a single topic, and the reason why it has been fragmented into so many articles has been due to a lack of comprehension of the topic on the part of those who fragmented it into five different articles. David Tombe (talk) 14:27, 4 February 2011 (UTC)

I do not want to confuse anybody. I agree that in the rotating mass on a string example it is important to explain the continual inward acceleration and you can call the force on your finger holding the string the reaction to the inward force experience as an outward radial force, so we could refer to the radial forces of rotating motion to explain the tension in the string. The diagram is static and I believe it was D'Alembert who suggested in the 18th Century that to turn the rotation to a statics calculation you IMAGINE an outward force arithmetically correct as the centrifugal force. In modern terms you call up a rotating frame and explain the tension in the string as a fictional force arithmetically correctly in the same way. So it's just a name for the force on the constraint equivalent to the correct name for the force on the rotating mass. However it is an often used name so it deserves a place in the WP. Trying to see rotating systems as a statics problem like d'Alembert or by switching to rotating frames is, I suggest, confusing for the layman but the answer surely is not to ban the use of the word but to explain without maths the physical situation. I find the celestial examples difficult for different reasons, the nature of the gravitational pull is, what can I say, complex? , because while Newton and Einstein give us the maths to compute it, the physical explanation is still more difficult than a piece of string, however it is true that the gravitational effect of a planet on the sun is as real an effect as the centripetal effect of the sun on the planet. I am just asking for an explanation that explains why the mass rotates without saying that centrifugal force is fictional.Profstandwellback (talk) 14:54, 4 February 2011 (UTC)

If a tensile force exists in a restraining chain or cable it has to be the result of a force differential between two counteracting force entities. If one of the forces is the so called centrifugal force of separation of a rotating body from a spacially fixed axis of rotation, and is due to a phenomenon called the conservation of angular momentum, then the negating so called centripetal force is rather obviously due to an additional occurring circumstance which acts to prevent the occurrence of this angular momentum conservation property. Since this stasis of counteracting forces can be maintained without significant system kinetic energy loss over appreciable periods of time, we are evidently not dealing with a problem of dynamics, but rather with a problem related to the relationships existing between 2 different physical systems of motion.69.154.109.190 (talk) 17:38, 4 February 2011 (UTC)

Anon 69.154.109.190, The equal and opposite forces pulling at each end of the chain, such as to cause the tensile stress, would both be centrifugal forces. As regards angular momentum, it will certainly be conserved if there is no net torque acting on the system. But conservation of angular momentum is not a cause of centrifugal force as such. However, when angular momentum is conserved, the centrifugal force acting on a particle will obey the inverse cube law. As regards your point about there being two physical systems of motion, I can see both a radial and a transverse aspect to the analysis. Is that what you are talking about? David Tombe (talk) 18:20, 4 February 2011 (UTC)

Yes. And with regard to the force components causing the tensile stress in the cable, I cant see how either one can be more unreal than the other.WFPM (talk) 23:31, 4 February 2011 (UTC)

WFPM, Actually, it makes a good case scenario for explanatory purposes. We have two bodies in linear motion. They are connected by a loose string. At one instant, the string will suddenly become taut due to the centrifugal force exerted at each end. These two centrifugal forces form an equal and opposite action-reaction pair. The tensile stress caused by the centrifugal forces acting at each end of the string then causes an inward centripetal force to act at each end, and the two bodies will then move in mutual circular motion about the centre of mass. When the circular motion arises, the centripetal forces will be equal in magnitude to the centrifugal forces, so we will have two action-reaction pairs and four forces all of equal magnitude. Angular momentum will be constant because there will be no net transverse force acting on the system. If we nip the string in the middle and pull it shorter, the angular momentum (r^2.w) will be conserved, but the angular speed (w) will increase. Hence the centrifugal forces (rw^2) and the centripetal forces will be increased. David Tombe (talk) 01:07, 5 February 2011 (UTC)

(edit conflict) Profstandwellback wrote:

"In modern terms you call up a rotating frame and explain the tension in the string as a fictional force arithmetically correctly in the same way."

Is this really what you meant to write? If so, you are confusing two distinct concepts. I know of no competent physicist or mathematician who would call the tension in the string a "fictional force". The force exerted by the string on the rotating ball, the reaction to that force exerted by the ball on the string, the tension in the string, the force exerted by the other end of the string on the finger holding it, and the reaction to that force exerted by the finger on the string are all proper forces—their magnitudes remain the same no matter what coordinate system you use to describe them.

If you use a rotating coordinate system in which the coordinates of the ball remain constant, then those coordinates will fail to satisfy the mathematical expression of Newton's second law, because they are not changing despite the fact that the string is exerting a (proper) net force on the ball. If you wish, you can salvage Newton's second law in this coordinate system (at the expense of violating his third) by introducing a pseudoforce field whose outward force on the ball will exactly balance the inward force exerted by the string. But there are no reaction forces to those exerted by this field. The inward (proper) force exerted on the ball by the string, for instance, is not a reaction force to the centrifugal force exerted on the ball by this pseudoforce field. It is rather the reaction force to the (proper) force exerted by the ball on the string. The forces exerted by this pseudoforce field are the ones which physicists refer to as "fictional" "pseudo-", or "inertial", and they are completely separate entities to any proper forces acting in the system. Like Martin Hogbin, I don't see how blurring this distinction will enable a layman to understand what's going on.

David Wilson (talk · cont) 01:58, 5 February 2011 (UTC)

This happens all the time in physics where a simple single dynamic physical process is interrupted and/or otherwise modified by another physical process with a different criteria of operational performance. sometimes the different processes are reactionary as in this case, and sometimes they are more independent of each other, like in a spring-powered mousetrap. but the physical forces are real in any case.WFPM (talk) 03:11, 5 February 2011 (UTC)

Reactive centrifugal force references

I am removing references which, when you actually read them, do support the use the term 'centrifugal force' to refer to the reaction to the centripetal force, except erroneously or in casual speech.

Can we assume that you meant "do not support"? Not that I agree with it, but that must be what you're trying to claim here, yes? Dicklyon (talk) 21:04, 5 February 2011 (UTC)

Mook

This reference actually talks about their being what is sometimes called a centrifugal force and describes this force as a 'reactive, centrifugal' [note the comma] force. In other words, the source does not support the use of either 'centrifugal force' or 'reactive centrifugal force' in the context being discussed but merely points out that the force in question a reaction force and is centrifugally directed. The source supports only casual or informal use of the term 'centrifugal force' to refer to the reaction to the centripetal force. Martin Hogbin (talk) 10:02, 5 February 2011 (UTC)

Roche

This is clearly an essay against what the author sees as misuse of the term 'centrifugal force', although it is admitted that the term is still misused is some modern books the source is soundly against such usage in a technical context.

Here are two quotes to give this source's opinion on alternative meanings of 'centrifugal force':

Huygens’ mistaken version of the concept of centrifugal force continues in use outside physics to this day, despite efforts to banish it by very distinguished physicists...

For example, many students are likely to have absorbed uncritically the statement that the Earth’s attraction on the Moon is balanced by a centrifugal force. The standard physics response to this is to point out that if the force of gravity on the Moon were balanced, then according to Newton’s second law there would be no lunar acceleration, since there would be no resultant force, and the Moon would fly off at a tangent. Martin Hogbin (talk) 10:21, 5 February 2011 (UTC)

Bowser

This source is nearly a century old and cannot be used as a guide to modern terminology.

Holton

This source explains that centrifugal force is an illusion and never uses the term 'reactive centrifugal force' or the term 'centrifugal force' with that meaning. Martin Hogbin (talk) 17:40, 5 February 2011 (UTC)

Discussion

Martin, The quote from the reference which reads,

Huygens’ mistaken version of the concept of centrifugal force continues in use outside physics to this day, despite efforts to banish it by very distinguished physicists...

is very revealing. And there was you only a few days ago ridiculing the notion that there is any conspiracy involved in all of this. We clearly have a situation now in which 'very distinguished physicists' have been making efforts to banish the concept of centrifugal force. Is that what accounts for the remarks of David J Wilson above where he agrees that it is a real outward force which causes the tension in the string, yet claims that the so-called fictitious centrifugal force has got absolutely nothing whatsoever to do with causing this tension? Are we now living in an era where the writings of the great masters such as Huygens, Leibniz, Maxwell etc. can be overridden by the opinions of the people who have been writing textbooks in the last twenty years? And does this account for dicklyon's latest posting where he attempts to undo my claim that Goldstein didn't use a rotating frame of reference in his treatment of planetary orbital theory? I recommend that you carefully read dicklyon's latest posting because you will find that rather than undermining what I had said, that it actually confirms what I had said. David Tombe (talk) 12:54, 5 February 2011 (UTC)

Roche

@Martin - I disagree on the assessment of Roche. Note the other quotes from Roche:

"I have identified at least three interpretations of centrifugal force in the literature: a valid meaning in physics, an entirely different but equally valid meaning in engineering, and a cluster of false meanings."

and later, discussing the engineering definition

"But we must leave the final word to the engineers. The stresses that develop in rapidly rotating turbine blades are thought of by mechanical engineers as being due to centrifugal forces [20]. To take a simple example, an object whirled on an elastic string pulls the string outwards, creating the tension in the string. Both the inertial centrifugal force acting on the string and the elastic centripetal force acting on the moving body are reaction forces—they call each other into existence. Centrifugal and centripetal force are equal and opposite here but do not balance because they act on different bodies (figure 3).

In a rotating turbine, for example, each outer section of the blade exerts an outwards pull on the portion between it and the shaft, while at the same time the latter exerts an elastic inwards pull on the former. It is the stresses in the blades and their causes that mainly interest engineers, rather than the centripetal forces. It follows that both elastic centripetal forces and inertial centrifugal forces act in a rotating solid body [21]."

I think Roche is a bit confusing because he does not use the phrase "reactive centrifugal force" but instead uses "inertial centrifugal force" to describe this concept of centrifugal force that is used by engineers. But he is clear that these two uses are different, distinct, and in current use by a section of the modern scientific community. --FyzixFighter (talk) 15:15, 5 February 2011 (UTC)

I think Roche is so confusing about what he calls 'an entirely different but equally valid meaning in engineering' that this claim is no help at all. What exactly is this meaning? Martin Hogbin (talk) 17:28, 5 February 2011 (UTC)

From my reading of Roche, it's for describing the internal stresses within a rotating solid object, as described in the latter quote I mention. The stress on a given section of the body are the result that originates from the inward force from the adjacent section closer to the axis of rotation and the real outward force from the adjacent section just outside of the given section (which is a reaction-action pair with the inward force that the given section exerts on that adjacent section just outside). To me that seems pretty clear, but then again I've been doing a lot of reading lately on internal and external stress and strain. I wonder if perhaps ref. 20 (Mabie and Reinholtz) in Roche is clearer - anyone have access to it at the moment? --FyzixFighter (talk) 17:43, 5 February 2011 (UTC)

FyzixFighter, Roche says,

To take a simple example, an object whirled on an elastic string pulls the string outwards, creating the tension in the string. Both the inertial centrifugal force acting on the string and the elastic centripetal force acting on the moving body are reaction forces—they call each other into existence. Centrifugal and centripetal force are equal and opposite here but do not balance because they act on different bodies (figure 3).

and he is perfectly correct in using the term inertial centrifugal force. And he is correct when he says that the centripetal force and the centrifugal force are acting on different bodies, in that in relation to the centrifugal force he is referring to the knock-on effect which the inertial centrifugal force acting on the weight transmits to the string. The inertial centrifugal force causes the reaction with the string, and the centripetal force is a measure of that reaction, but it is only equal to the centrifugal force in magnitude in the special case of circular motion. The centrifugal force and the centripetal force are not an action-reaction pair. The action-reaction pairs in this case scenario are (1) the two inward centripetal forces acting at each end of the string, and (2) the two outward centrifugal forces acting at each end of the string. Roche also makes an intersting statement which I don't fully agree with,

It must be admitted, nevertheless, that this subject is subtle and the least confusing strategy for most physics groups may be to teach them centripetal force only, and leave centrifugal force to the engineers.

I think that if taught properly, physics students should have no trouble in grasping the concept of centrifugal force. Anyway, I'm glad that you decided to retain the Roche reference. As regards the Mook reference, I think that we're all agreed that it was confusing and that Martin was correct to remove it. David Tombe (talk) 16:07, 5 February 2011 (UTC)

I honestly can say I'm amazed. I don't think you and I read the same article. Your summary of Roche's comments bear hardly any resemblance to what Roche actually said and is so badly mangled that I don't know where to begin. Let me just be content to correct your glaring mistakes in summarizing Roche: Roche is very clear that there is no real, or proper as another editor has said, centrifugal force acting on the weight on the end of the string. The motion of the weight requires no outward force acting on the weight, only an inward force. Roche is very clear that the centripetal force from the string on the weight and the real "inertial centrifugal force" from the weight on the string (what we've been calling the reactive CF) are a action-reaction pair, and so are always equal in magnitude (even if the path isn't circular). I could go on about the physics but we've all been down that road before of trying to explain to you proper physics that I doubt the results of another attempt would be any different. To any reasonable editor who looks at the article and David's summary, I hope that it is painfully obvious just how much David invented and injected to twist Roche around to support his fringe ideas. --FyzixFighter (talk) 17:29, 5 February 2011 (UTC)

The text to which Roche is a reference is The concept of the reactive centrifugal force is used often in mechanical engineering sources that deal with internal stresses in rotating solid bodies. Can anyone show me where Roche says this. Martin Hogbin (talk) 18:47, 5 February 2011 (UTC)

Martin, Roche doesn't say this anywhere. Roche talks about 'inertial centrifugal force'. FyzixFighter put the reference in as evidence of the use of the term 'reactive centrifugal force', and now FyzixFighter is arguing that Roche was wrong in using the term 'inertial centrifugal force'. So the reference obviously doesn't back up what it was intended to back up. David Tombe (talk) 19:50, 5 February 2011 (UTC)

@Martin - How is that not an accurate summary of the engineer's concept of reactive centrifugal force that Roche describes on pg 403 (which I quoted above)? --FyzixFighter (talk) 20:04, 5 February 2011 (UTC)

Roche refers to the 'the inertial centrifugal force acting on the string'. There is no inertial (as in fictitious) force acting on the string just the reaction to the centripetal force applied by the string to the weight. That may be what Roche actually means but I do not think such a confusingly worded statement should be used as a reference. It is not even clear what reference frame Roche or the engineers he describes are using. Maybe the engineers are thinking in terms of a rotating reference frame, who knows? Martin Hogbin (talk) 21:20, 5 February 2011 (UTC)

Martin, Roche is correct in his usage of the term 'inertial centrifugal force'. You seem to think that the only centrifugal force involved is a reaction to the centripetal force. But what causes the centripetal force? The centripetal force is caused by the tension in the string. And what causes the tension in the string? It's caused by the inertial effect of the weight tugging on the end of the string. Ie. the centripetal force is caused by the inertial centrifugal force. It's just as Roche says. It's a shared reaction. David Tombe (talk) 21:29, 5 February 2011 (UTC)

@Martin - Here is where I find it necessary to carefully read Roche. It seems clear to me that he using the adjective "inertial" to signify that the engineering CF is an inertial reaction, ie a reaction force due to the weight's inertia, and not to signify that it is a "fictitious" force. That's why he explains that this engineering CF is exerted by the weight on the string (or by an outer section of the turbine on an inner section), and not (like what Roche calls the "fictional CF" of rotating frames) on the weight itself. In the caption for figure 3, Roche calls it the "centrifugal inertial reaction". What frame is irrelevant, since the force and the internal stress exists independent of frame. I do agree that Roche's use of "inertial" to describe the engineering is confusing and probably not the best choice given that the rotating frame force is also called an inertial force in other sources, but it is clear that Roche sees the two as separate and distinct concepts. --FyzixFighter (talk) 21:49, 5 February 2011 (UTC)

FyzixFighter, An action-reaction pair have to act on the same body. Roche points out that the centrifugal force and the centripetal force are not acting on the same body. You say that Roche makes it very clear that the centrifugal force and the centripetal force are an action-reaction pair. Show me where he makes this claim? David Tombe (talk) 20:29, 5 February 2011 (UTC)

In the usual concept of a reaction force, a force of object A pushing on object B is accompanied by a force of object B pushing back on object A. A planet and its sun, for example; or two adjacent elements of string under tension. I've never heard of this "have to act on the same body" idea before. Dicklyon (talk) 21:02, 5 February 2011 (UTC)

Dick, I don't know where I got that idea either. I've striked it out. But nevertheless, a centrifugal force and a centripetal force are not an action-reaction pair. They are two independent forces. They only happen to have the same magnitude in the special case of circular motion. David Tombe (talk) 21:19, 5 February 2011 (UTC)

In the fictitious-force definition, as in Goldstein's planetary orbit equation, they are completely independent and unequal (except equal in circular orbits where they r is constant because they are equal), I agree. But the "reactive" CF is the equal and opposite reaction force by definition; to say they are not an action–reaction pair is just to say that you're talking about something different; that's OK, just don't confuse what you're talking about with the reactive CF. Dicklyon (talk) 21:30, 5 February 2011 (UTC)

Dick, OK, that's a good start. You acknowledge that the inertial centrifugal force is not in general equal to the centripetal force. But you are talking about something different. I suggested that this 'different' quantity which some of you are referring to as 'reactive centrifugal force' is maybe a centrifugal force analogue to apparent weight, in which case it will always be equal to the reactive centripetal force, just as apparent weight is always equal to the normal reaction in gravity problems. I can indeed see an action-reaction pair here. But I have never seen any sources which totally divorce 'reactive centrifugal force' from inertial centrifugal force. Roche certainly doesn't do it. He knows that the inertial centrifugal force is the driving force behind the tension in the string. There will never be a so-called 'reactive centrifugal force' unless there is also an inertial centrifugal force involved. David Tombe (talk) 21:51, 5 February 2011 (UTC)

At least two of the four removed refs support the usage discussed

Martin, I don't think your reasons justify the removal of most of those references. The fourth I agree does not support the usage of centrifugal force as a reaction force, even though it does discuss that reaction force. The fact that Bowser is 90 years old doesn't really detract from its value, since it's correct and pretty much in agreement with current usage. Roche discusses the "centrifugal inertial reaction of the mass M on the string", which is the same thing as what we're calling "reactive centrifugal force", so it could be used to describe the concept better, but not the support the term per se. Mook's "a reactive, centrifugal force" is exactly what we're calling "reactive centrifugal force", that is, a reactive force that is centrigually directed. We should definitely keep that one. So I think I'll restore Bowser and Mook, and maybe Roche as an alternative way to describe the concept. Dicklyon (talk) 21:02, 5 February 2011 (UTC)

Bowser

You use a circular argument with Bowser. Bowser shows that reactive centrifugal force is a current concept and current usage shows Bowser is right.

I don't claim that Bowser shows that reactive cf is a current concept. But it clearly is, given the number of people still trying to make it go away. Dicklyon (talk) 21:48, 5 February 2011 (UTC)

Mook

The argument is about whether the term 'reactive centrifugal force' is in current common use. There is no doubt that there is a centrifugally directed reaction force to the centripetal force but Mook specifically avoids calling it the reactive centrifugal force'.

General

Dick are you claiming that engineers still use the term 'reactive centrifugal force' (or just 'centrifugal force' to describe the same concept)? No one has yet shown how this concept is helpful to engineers or anyone else. Martin Hogbin (talk) 21:30, 5 February 2011 (UTC)

I'm not claiming that it's a major usage, but the sources do suggest that it's still out there. Particularly Angelo. You can just say he's wrong, but it's wishful thinking to say that everyone has come around to seeing CF the way physicists and most engineers see it. Dicklyon (talk) 21:33, 5 February 2011 (UTC)

And I am not claiming that nobody at all ever uses the term that way but it is definitely a minority usage and the article should therefore describe it that way. Can anyone give a modern example where the concept of 'reactive centrifugal force' is actually used to solve a problem? Martin Hogbin (talk) 21:38, 5 February 2011 (UTC)