Misplaced Pages

Revision as of 17:46, 2 February 2011

This page is not a forum for general discussion about centrifugal force. Any such comments may be removed or refactored. Please limit discussion to improvement of this article. You may wish to ask factual questions about centrifugal force at the Reference desk.

Physics Start‑class High‑importance

This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Misplaced Pages. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.PhysicsWikipedia:WikiProject PhysicsTemplate:WikiProject Physicsphysics Start This article has been rated as Start-class on Misplaced Pages's content assessment scale. High This article has been rated as High-importance on the project's importance scale.

This article may be too technical for most readers to understand. Please help improve it to make it understandable to non-experts, without removing the technical details. (September 2010) (Learn how and when to remove this message)

Archives

April 2004 June 2004 – January 2006 January 2005 – November 2006 February 2007 – April 2007 January 2007 – March 2008 April 2008 May 2008 June 2008 July 2008 – August 2008 September 2008 October 2008 August 2008 – May 2009 May 2009 – June 2009 June 2009 – ???

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_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_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_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_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 Misplaced Pages 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_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_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_deeds 20:23, 6 November 2010 (UTC)

See also this new entry at the Misplaced Pages: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 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_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 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,

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

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 ${\displaystyle {\ddot {r}}}$ 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 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 Misplaced Pages 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)

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 Misplaced Pages 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 Misplaced Pages. —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)

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 . 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. 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)

• Start-Class physics articles
• High-importance physics articles
• Start-Class physics articles of High-importance