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Archive 1Archive 2Archive 3

Nomination for deletion.

This article is beyond hope in my opinion. It can only be "fixed" by injecting a lot of weasel wording to talk around the outright scientific quackery it asserts. At some point, I will nominate for deletion based on the following concerns:

  • This article presents a long discredited view about the nature and origin of centrifugal force. The view is put forward as if it is another also-valid view on the subject, but it is not scientifically valid. It contains numerous fundamental errors. The material is presented as factual, when it is more historical in nature - as in the history of scientific ideas that are now in the dustbin. Attempts to find reliable and modern references have failed. See discussion for the long history of complaints about lack of validity. The subject is largely duplicated in the main Centrifugal Force article where its errors can be more readily corrected. The subject is notable for mention as a "Common Misunderstanding" in that main article, but it is not notable for its own article.

Consensus is needed of course, so please pipe in below. Remember, this subject requires some real knowledge, some real discernment, and some real head scratching to really really understand. I am a knowledgeable long-time practitioner, yet just a few years ago I felt it was a valid perspective and I preached it with bluster. I was wrong. The subject doesn't have to go away, just this article. The subject can remain in the "main" article and be modified there to correct its errors there.

User276 (talk) 01:19, 10 August 2012 (UTC)

Wait, you're a long time practitioner (of what?), and until a few years ago preached it with bluster? Now your eyes have been opened, you've cast out the lies, and want us to come along with you? Seems too much like religion to me. Dicklyon (talk) 04:21, 10 August 2012 (UTC)
My colorful language was irrelevant. Please focus on the subject at hand here. If you want to argue against deletion, please do that directly and with good evidence. Let's make the chit chat somewhere else or in some other section. User276 (talk) 05:35, 10 August 2012 (UTC)

Does the fictitious force supplant the reactive force?

The term "reactive centrifugal force" is not used for probably many reasons. The reaction to a centripetal force is often centripetal, not centrifugal. This is quite evident in the case in the moon and earth orbiting the barycentre, as pointed out by G. David Scott in the article that I have cited (added to the authorities listed in the first page). It is also very confusing.

The article as it stands is not bad but it really perpetuates the confusion. To suggest, for example, that the "reactive centrifugal force" has been "supplanted" by the fictitious centrifugal force is mindboggingly confusing. The article strives to make it clear that the reactive centrifugal force and the fictitious centrifugal force are very different phenomena. That would imply that one does not replace the other. So why confuse everyone by suggesting that the fictitious force has replaced (supplanted) the reactive force?

I am proposing that the first sentence of the second paragraph be changed as follows so that the intended meaning is clear:

from: "The concept of reactive centrifugal force is seldom used in modern physics and mechanics, having been largely supplanted by the concept of centrifugal force as a fictitious"...

to: ""The concept of reactive centrifugal force is seldom used in modern physics and mechanics. The term "centrifugal" is usually used in reference to the fictitious"....

Contrary to Dicklyon's contention that my proposals are mean-spirited I can assure you that my goal here, as in all my WP activity, is to improve the quality of the information for readers. AMSask (talk) 04:15, 12 January 2014 (UTC)

Where did I suggest your proposals are mean-spirited? I'm not loving this change, but I don't see the point of it. What was supplanted, as it said, was the concept; not the force. Dicklyon (talk) 06:31, 12 January 2014 (UTC)
You said my change was ill-motivated. Perhaps you meant ill-conceived. AMSask (talk) 07:05, 12 January 2014 (UTC)
Where you removed the text "is directed in the direction from the center of rotation to the rotating mass" you said "Removed reference to apparent direction". That removal is badly motivated since there is no mention of apparent direction in there anywhere; just an actual direction. Then you changed the discussion about the comparative concepts, reactive centrifugal force and the fictitious centrifugal force, to a statement about the usage of the word centrifugal: "The adjective 'centrifugal' is most often used in relation to a different phenomenon". But it is not so much a different phenomenon as it is a different conception of the same phenomenon, about forces involving rotation. This wording change seemed badly motivated, too, but I agree that maybe badly conceived would have been a better description of the problem. I don't mean that your motivations in editing are bad, just that this edit has no good reason. Dicklyon (talk) 19:33, 13 January 2014 (UTC)
They are NOT the same phenomenon nor are they a different conception of the same phenomenon!!! This is the problem. The reader of this article may well think that! It is not the case. See my response below to your other comment.AMSask (talk) 23:15, 13 January 2014 (UTC)
You are expecting the reader to discern what you perceive to be a difference between the concept of a force and the force itself? I don't think there is a difference, but if there is it is not going to be understood by the reader. CF does not replace or supplant RCF. It can't, of course, because it is an entirely different phenomenon. The article should say that. It says the opposite. AMSask (talk) 07:05, 12 January 2014 (UTC)
I don't understand you here. I am not expecting the reader to have anything to do with my perceptions. But there are historically different ways to conceptualize the forces in rotating systems, and this is what we're contrasting. Saying they are different forces might miss the point, as they can't both exist simultaneously, as they are in different systems. I think "entirely different phenomenon" goes too far in contrasting these concepts. Yes, they are different; but "entirely"? They are closely related. Dicklyon (talk) 19:33, 13 January 2014 (UTC)
How is the so-called reaction force to a centripetal force (RFTCPF) related at all to the fictitious centrifugal force (CFF)? The CFF is not even perceived as a reaction force to any force, real or fictitious. It has no physical source. It is not a Newtonian force. The RFTCPF is a real force that is in reaction to a real force and has a physical source (ie. originating in some body due to gravity or electromagnetic effect). Furthermore, the RFTCPF and the CFF act on different bodies and often in quite different directions (in relation to the direction from the center of mass of the bodies they act on, or are perceived to act on, and the center of rotation). What do they have in common?AMSask (talk) 23:15, 13 January 2014 (UTC)
The relationship is actually described in a table in the article. If the rotating reference frame is rotating about the center of rotation of the mass, then I think the two have identical formulas and magnitudes and directions (I'll have to check the conditions and verify when that's true; certainly when the motion is circular). They are different points of view on the same effect, the effect that relates rotation and inertia. Dicklyon (talk) 04:55, 14 January 2014 (UTC)
How are they just different points of view on the same effect!!?? There is a fundamental difference between the reaction force to the centripetal force and the centrifugal force: the reaction force has a physical cause (gravity, electromagnetic) whereas the centrifugal force does not. The reaction force does not arise because of rotation and inertia. It exists whether there is rotation or not. If two bodies in gravitational orbit stop rotating the forces between them do not disappear. The forces between the bodies do not change. As a result the bodies accelerate toward each other. The centrifugal force, however, disappears. So, again, what do they actually have in common?AMSask (talk) 06:51, 14 January 2014 (UTC)
Rotation. Two bodies falling toward each other without rotation don't have a force directed from a center of rotation. Seems pretty consistent. Dicklyon (talk) 07:25, 14 January 2014 (UTC)
That is true. Two bodies falling toward each other without rotation don't experience a force directed away from the center of rotation. But bodies falling toward each other with rotation don't experience a force directed away from the central point either. So the forces between the bodies do not change. The only thing that changes is your terminology? Is that your point? So you agree that without rotation it is correct to characterize the gravitational forces on each body as being directed toward the centre of mass of the two body system, but not when they are rotating? What changes with the rotation? AMSask (talk) 14:30, 14 January 2014 (UTC)
I think we agree that the gravitational force between two bodies is always along the vector between them. Each feels a force toward their center of mass. When there's circular rotation, that's the same point as the center of curvature of motion of either body. When elliptical or other non-circular orbit, the center of rotation moves and is not at the center of mass. Sometimes people do explicitly account for a "centrifugal" component that is less than the whole force of gravity, and is along that line. It does get a bit messier, and terminology is not always consistent about how that's done. Dicklyon (talk) 19:19, 15 January 2014 (UTC)
I would caution against putting that kind of statement into the article. There are two different centres of curvature for an elliptical orbit, one for each body. And they keep changing. Neither can be an inertial point. There is only one centre of rotation (i.e.located at the focus of the ellipse). The force on the bodies are directed to the centre of rotation, not the centre of curvature. AMSask (talk) 19:52, 15 January 2014 (UTC)

Please Reword

The first paragraph needs re-wording. It is not clear which force is on which object. It is the sentence: "In accordance with Newton's third law of motion, the rotating mass exerts an equal and opposite force on that object, which is directed from that object toward the rotating mass". Better would be something like "...the rotating mass exerts an equal and opposite force acting on that object and is directed towards the rotating mass". Also the use of "rotating mass" is confusing here; it suggests a spinning object like the "rotating earth". "object moving in a circular path" may be better. Can you please re-write? I like the "Jumping the Gun" comment. It clearly shows which force is on which object and outlines the action-reaction pairs. The same should be done here. Perhaps edits by various disagreeing writers has rendered this article confusing. It would be good to have a clean consistent approach. 

— Preceding unsigned comment added by 67.170.141.69 (talk) 21:29, 24 May 2014 (UTC)


Your best bet is to ignore the whole article. It's garbage. Perfectly pathological science.
Montyv (talk) 03:02, 31 May 2014 (UTC)

Jumping the Gun

As a college instructor in Physics, I am just as concerned about the potentially misleading term "centrifugal" as anyone else. However, this article does not contain any outspoken nonsense. The reader simply must take care to distinguish carefully what is and what is not said. Deleting the article at this point would be jumping the gun.

There is room for improvement. One could tabulate the forces acting on the various objects in a more systematic manner. Also, the statement that "the two forces upon the string are equal and opposite, exerting no net force upon the string, ..." is technically not quite true, since the string's center of mass is rotating and must have a non-zero net force acting on it. (But if the mass of the string is negligible, so is the net force on it.)

Let me try to vindicate the article as is, using basic Newtonian mechanics.

F1: Inward force by string on the spinning mass. ("Centripetal force")

F2: Outward force by the spinning mass on the string. ("Reactive centrifugal force")

F3: Inward force by the pole on the string. ("Post reaction force")

F4: Outward force by the string on the pole.

(F5: Inward force by something else on the pole, to keep it balanced.)

Forces F1 and F2 cannot exist without one another, due to Newton's third law. The same is true for forces F3 and F4.

In the inertial frame of reference, force F1 is the only force on the spinning mass, which is therefore not balanced. At this points many people incorrectly introduce a "centrifugal force" on the spinning mass, believing it should be balanced. This is the most common misconception, but it is not found in the article.

Forces F2 and F3 act in opposite directions on the string. If the string has negligible mass, F2 and F3 must balance to prevent the string from being pulled outward. The forces constitute the tension in the string.

Consider a hammer thrower. If the cable is not strong enough, it would break due to the tension in it; this proves the presence of F2 and F3. Toward the end of the swing, the hammer thrower has difficulty staying in place; this is due for force F4. — Preceding unsigned comment added by Arjenvreugd (talk • contribs) 02:12, 26 November 2012 (UTC)


"Centrifugal" is not misleading at all. It simply means "center fleeing". It just specifies a direction of something. "Centripetal" similarly only means in a direction toward a center. Too many people trying to "get it right" think there's something "fictional" about "fictitious force" (AKA pseudo or d'Alembert force). They've been told by their high school and college instructors that there's nothing fictional about "centripetal force", so they substitute "centripetal" when they're thinking "away from the center". They try to avoid looking dumb, but they underscore their ignorance instead.
The real way to "say it right" is to say "centrifugal pseudoforce". It's the "force" part of the term that's misleading, not the "centrifugal" part.
Montyv (talk) 03:52, 31 May 2014 (UTC)

Applications

I don't think the "applications" section should be here. All of the examples appear to have a closer connection to the fictitious force. Though they commonly also involve a reactive centrifugal force, it is either incidental or secondary to the mechanism being described. –Henning Makholm 03:00, 27 April 2008 (UTC)

I hope to check this later; I suspect that you are mistaken and that its removal is in fact promoting a POV. Harald88 (talk) 13:04, 28 September 2008 (UTC)
IN fact I immediately notice that it is exactly as I suspected. Thus I reintroduce that section, but keeping only the most appropriate examples. Harald88 (talk) 13:16, 28 September 2008 (UTC)
The "Applications" section has nothing to do with the reactive force that is the subject of this article. That is not a POV. It is a fundamental objection. The entire article should probably be deleted because it contains so many mistakes. But this section on "Applications" is simply misconceived and should be deleted now. The reactive (third law pair) force to a centripetal force never causes the body on which it acts to move outward. All parts of the rotating system are experiencing centripetal acceleration. All net forces are centripetal. So, if a body moves away from the centre it is due to inertia not a force. The outward movement is what is behind the "Applications" section. That is due to the pseudo "force" not the force that is the subject of this article.AMSask (talk) 20:29, 4 June 2014 (UTC)

Thesis hidden behind weasel words, vagueness, unclear refs.

Since this article is so fundamentally about calling such forces "real" (or "fundamental"), it needs to be much much more clear about that. If the arguments supporting "CF is fundamental/real" are so strong, they should be able to stand up to that light of day. As it stands now, the fundamental thesis of the article is hiding behind weasel words, vagueness, and unclear referencing. Montyv (talk) 14:44, 4 June 2014 (UTC)

I'd say the article is more about calling certain real forces "centrifugal" when they are applied by objects moving in curved paths (even when, with respect the object the force is applied to, it may be centripetal in some cases). I don't think there's anything fundamental about these forces. Dicklyon (talk) 04:06, 5 June 2014 (UTC)

There's no fundamental difference between the two situations of continuous circular motion vs. "curved path". The article is (incorrectly) alluding vaguely that there is. And then it again alludes vaguely with no explanation why that that presumed difference is somehow related to viewing centrifugal force as a fundamental force! (or as the also-vague "reactive CF"). Just more example of hiding behind non-specific fluff. Montyv (talk) 18:14, 5 June 2014 (UTC)

Pathological science: There's still no such thing as reactive centrifugal force.

Beware the authoritative, but unreliable reference. There is no subject that I know of more in need of the judgement of very knowledgeable editors than Centrifugal Force. I see many arguments above based on the "argument from authority" fallacy. It's our duty to reject the argument that "some prestigious institution published 'X' 50 years ago, therefore 'X' is includable". This even applies to more recent publications. 'X' is simply not includable if it's dubious, even more so if it's outright wrong. And, if 'X' is dubious or wrong by the judgement of knowledgeable editors, then references that say 'X' are unreliable and 'X' is not includable.

This includes Newton himself. Newton is not a reliable reference. We see farther than he did because we stand on his (and others') shoulders. Pseudoforce wasn't even a real concept until d'Alembert 100 years after Newton. There are too many good, modern perspectives and references debunking the view of Centrifugal (Pseudo)force which says it's a fundamental-force reaction "paired" to a centripetal force (as in the shoddy and ambiguous "forces come in pairs" - gag me). There is no excuse for repeating this pathological science as if it was reliable and real when we know damn well better.

This may appear to some to violate the infamous (and misleadingly simplistic) "WP:verifiability, not truth" maxim. But if you read it carefully, you will see that "verifiability" requires reliable references. And there is no way to determine reliability but by the judgement of knowledgeable editors.

Beware also, the difference between a "knowledgeable editor" and a merely "persistent" one. The idea of "reactive centrifugal force" has been perpetrated on Wikipedia largely by one particular persistent editor who is always around to push this pathology. He has a "sciency" degree, so he can speak with the feel of authority, but somehow he got this bad idea in his head and it won't go away. And somehow, he's always there.

This article is shameful. It needs to be deleted outright. Get it over and done.

Montyv (talk) 02:55, 31 May 2014 (UTC)

If you think the article is so shameful, then stop talking about it and put it up at WP:AFD. Let's see what happens.
With regards to your "dubious" tags, I don't think we are on the same page when we are talking about the "reactive centrifugal force". In my understanding the D'Alembert principle and Newton's Third Law are completely different. So that we can clear up the "dubious" tags and perhaps find better wording, I'm going to try identify where our difference of understanding is. Let's start by looking at where we have both principles present, but not looking at circular motion in particular for now: an object in an elevator going up. When the elevator first begins to accelerate upwards, from the perspective of the outside stationary frame their are two forces on the object - gravity (F_g) and the contact force of the floor on the object (F_1). Because the contact force on the floor is greater than the force of gravity (F_1>F_g), the net force is non-zero and upwards so according to Newton's 2nd law (F=ma) the object accelerates upward. If we instead wanted to look at this from the perspective of the accelerating frame of the object, D'Alembert says that we can transform an accelerating rigid body (the object here) into an equivalent static system by adding the so-called "inertial force" (F_i) acting on the object. The inertial force is given by F_i=-ma. This inertial force is why we say we feel "heavier" when an elevator starts going up. In the Newtonian definition of forces, there is no additional force pushing us down, but the feeling is an artifact of us describing the motion from an accelerated frame. Are we in agreement so far? If not, where do we disagree?
On to part 2 of the example. According to the Newton's 3rd law, the real forces all have to have equal but opposite pairs. The 3rd law counterpart of F_g is the force of gravity of the object on the earth, and the counterpart of F_1 is the contact force of the object on the floor (F_2). These forces exist regardless of whether we are describing motion in the stationary frame or the accelerating frame. F_2 is equal in magnitude to F_1, but points down in the opposite direction. Also F_1 acts on the object, but F_2 is acting on the elevator floor. So if we are applying F=ma to the object, or drawing a free-body diagram of the object, F_2 isn't part of that picture since it is not acting on F_2. We also can't talk about F_1 and F_2 "balancing", since again they are acting on different objects. In a lot of textbooks, they would say that F_1 and F_2 are an action-reaction pair, but trying to identify which one is the action or reaction, implying some kind of causality, is impossible since they occur simultaneously and are part of a single interaction (neither force exists without the other). Are we on the same page, and if not, where do we differ?
Taking this as an analogy to circular motion, F_1 is analogous to the centripetal force, F_i is analogous to the centrifugal (pseudo)force, and F_2 is analogous to the reactive centrifugal force. Like F_i, the centrifugal (pseudo)force acts on the object, is frame dependent, and vanishes in the stationary frame; like F_2, the reactive centrifugal force acts on the source of the centripetal force, is not frame dependent, and appears in the stationary frame. Some relatively modern sources that mention this distinction between the centrifugal (pseudo)force and the reactive centrifugal force are: John Roche (2001) "Introducing motion in a circle" Physics Education 43 (5), pp. 399-405; Yukio Kobayashi (2008) "Remarks on viewing situation in a rotating frame" Eur. J. Phys. 29, pp. 599-606. --FyzixFighter (talk) 16:00, 31 May 2014 (UTC)

Hi there FyzixFighter,

You're not the one I was alluding to by the way. I shouldn't have pointed a finger the way I did, it was uncivil. Sorry.

I like that you've decoupled rotation from acceleration. The essence of the centrifugal "force" question is indeed inside the linear acceleration example. After all, if a linearly accelerating object in free space (like a rocket with near-infinite Isp) is given a very very slight rotation rate (around an axis perpendicular to the acceleration), that acceleration becomes "centripetal". The "center" would likely be "moving", but that's easy to fix with a switch to a new (also non accelerated) reference frame. So, a linear acceleration caused by a non-zero net (fundamental) force* is really the same situation as a centripetal acceleration caused by a centripetal (fundamental) force when the radius is very long and/or omega is small. (*pretend it has a veeery slow rotation rate if you wish)

I also like how you've been careful say that a force is real or pseudo (if it wasn't clear by context). That's the kind of clarity the article needs more of.

I have more to say, but it's taking me a while to compose. I wanted to at least get some response out quickly. Thanks for your well ordered response. I'm optimistic.

Montyv (talk) 04:03, 1 June 2014 (UTC)


The first "dubious" marker I made can probably be resolved in large part by being specific about the type of force. To me, it implies (although it's not clear) that both are supposed to be "real". If so, then the article is calling CF "real" and I think you might agree that's a dubiousity problem. I called it OR because of lack of citation. Less importantly, it's also OR-ish because it interprets Newton - rather than paraphrasing a secondary source, it makes itself a secondary source.

The second "dubious" marker I made was again because of ambiguousness of what type of "force". Lack of clarity opens up for multiple interpretations, some of which are dubious.

By the way, I've been trying like crazy to download reference 5 from archive.org and I've been having trouble with Java on my browsers. Do you have it? Have you had any luck from archive.org? I'm really curious now what those refs actually have to say. I saw the 1884 book. The three remaining refs (other than ref 5 & the 1884 ref) were all behind a paywall. Do you or anyone else have copies of the pertinent pages of those refs to share in fair use so we can see what they say? Technically, a ref doesn't have to be internet-accessible and free of course, but it does help a lot in situations like this.

(More to come still.)

Montyv (talk) 04:50, 1 June 2014 (UTC)

That's odd that you're hitting a paywall. Do these links work for the first two references: Mook and Vargish, 1984, Brar and Bansal, 2004. I've relied on google books to get a look in most of these books. Ref #4 is behind a paywall, but you can at least get a preview of the first page of the article. Ref #1 and #2 are actually good cites for both of the comments you marked as dubious. I too can't seem to get access to ref #5.
I mentioned the linear acceleration example as merely an analogy. It's a purely linear case where you have a real force of the floor on the object, a fictitious/D'Alembert force in the opposite direction to make the accelerated frame look like a static frame, and a real force also in the opposite direction of the object on the floor. Let me take that analogy and be more explicit in how this looks for rotational motion. Imagine a space station that is rotating to simulate gravity (a la Space Odyssey 2001), so that the outer wall of the station is the "floor" of its inhabitants. From the perspective of an outside, stationary observer the wall/floor exerts a centripetal force, F_1, on an inhabitant. By Newton's 3rd law, there is also a force, F_2, that the inhabitant exerts on the wall/floor that is equal and opposite to F_1. In this case that means that F_2 is radially outward, and can be described as "centrifugal". From the perspective of the inhabitants, they see both F_1 and F_2, but because their observations are within an accelerated frame, they have to add a centrifugal (pseudo)force, F_c, acting on themselves to make the dynamics look like a stationary frame. This is the primary and most common usage of the term "centrifugal force" in physics, to refer to this fictitious/inertial/D'Alembert/pseudo-force. That's what the article centrifugal force (rotating reference frame) is meant to describe. The other two forces, F_1 and F_2 are real and form a action-reaction pair. F_1 is what we commonly call the "centripetal force". Physics texts generally don't spend a lot of time on F_2, usually just noting it as the 3rd law corresponding force to the centripetal force. But there are a few sources that call this a "centrifugal force" or the "reactive centrifugal force" since it points away from the axis of rotation (for example Acceleration and force in circular motion, which does the space station example). That's the force this article is meant to describe. Both F_2 and F_c are technically centrifugal. But we can describe their differences as follows: F_2 is a real force that both the stationary and rotating observers will see; F_c though is a pseudoforce since it vanishes in the stationary frame. F_2 acts on the wall/floor in the space station example; F_c acts on the inhabitants. F_2 has a 3rd law corresponding force (F_1); F_c has none.
Does this explanation make sense? If there's disagreement, where do we disagree in this example? --FyzixFighter (talk) 19:33, 1 June 2014 (UTC)


You agree that F_2 is a pseudoforce, right? All the evidence points to the idea that the term "action" (or "reaction") may indicate either a force or a pseudoforce. "Action" is a superset of the two "types" of force. Here's why: In the space station example, if F_2 isn't a pseudoforce, it must be a fundamental force, but then the object moving in a circle would have zero net fundamental force acting on it and would be moving in a circle by magic. So F_2 must be a pseudoforce, and if F_2 is called an "action" (or "reaction"), then "actions" must include both pseudoforces and forces.

F_2 is a result of (or even a "reaction to"(!)) the (centripetal) acceleration ma, which itself is a result of (or "reaction to") the nonzero net fundamental force (NZNFF) F_1 . So, the 3rd law's "action-reaction" phraseology must be talking about the superset of forces and pseudoforces. Call a pseudoforce a "reaction" if you wish, but it's still a pseudoforce, right?

Your idea that F_c is sitting there by itself is an interesting one. I'm skeptical of it, but I'll have to get back to you on it because it requires thinking.

Montyv (talk) 00:11, 4 June 2014 (UTC)

I just re-read your last response and noticed you did call F_2 a real force. That is a problem for the reasons I gave above. It's something the "pro reactive CF" and "anti reactive CF" camps need to resolve before making progress. Otherwise, the removers of text suggesting "real force" would surely be at edit war with those advocating elimination of such text.

I can certainly see how CF (which is really the same as the inertial response to a linear acceleration) can be considered as a "reaction" to a real force. It's an instantaneous (simultaneous) "reaction" indeed. Pseudoforce is (-ma) and becomes present as a "reaction" to the acceleration (ma/m). It's as if it's nature's way of implementing the 1st law. The acceleration itself is a simultaneous "reaction" to NZNFF. So, as long as the explanation is perfectly clear that that's why "reactive CF" is called "reactive", that would be technically correct. I have a feeling that's not the intended meaning though. I can't tell what the intended meaning is because the article is so gat-danged ambiguous and vague.

Anyway, as far as I can figure out, F_2 and F_c are one and the same things, both pseudoforces, both vectors pointing in the same direction and with the same magnitude. They both act at all points inside the object at once, and they both act as though they are through same point on the same object (its center of mass). Also, they aren't the same exact thing because they look and act alike, rather they are the same thing because they just really are the same thing, i.e. they're not twins occupying the same space at the same time.

Montyv (talk) 04:58, 4 June 2014 (UTC)

(after ec) No, F_2 is a real force. "Actions" or "Reactions" as the terms are used in Newton's 3rd law only describe real forces. The only pseudoforce here is F_c. The key flaw in your argument is when you say that F_2 balances F_1 (giving a zero net force on the object/inhabitant). However, this cannot happen because F_2 isn't acting on the object/inhabitant. That's why I tried to be very clear about what forces are acting on what objects. When we sum up the forces to get F_net, we only include to the forces on that object. Since F_2 does not act on the inhabitant, then it cannot balance the force of F_1 on the inhabitant. F_2 is the force that the inhabitant exerts on the wall/floor of the space station. As Roche points out (in the article I mentioned above) when talking about these forces, they "are equal and opposite here but do not balance because they act on different bodies." Only if we were doing the forces on the space station would we look at F_2, but then we would ignore F_1 which is a force on the inhabitants. F_2 is caused by the same fundamental phenomenon that causes F_1. We can source this relationship and qualities of an action-reaction pair of forces to pretty much any intro physics textbook (eg, Resnick; Halliday; Krane (1992). Physics, Volume 1 (4th ed.). p. 83). F_c is all by itself because it is a pseudoforce, therefore it has no 3rd Law pair. --FyzixFighter (talk) 05:21, 4 June 2014 (UTC)
Additionally, F_c and F_2 are only the same magnitude when the object/inhabitant is stationary in the rotating frame. F_1 and F_2 will always be equal and opposite (but acting on different objects) by the 3rd Law, but F_c depends on the frame I'm sitting in. I've got at least two sources that back up this distinction (Roche and Kobayashi), do you have sources that support your statements about F_2 and F_c? --FyzixFighter (talk) 05:26, 4 June 2014 (UTC)
The floor of the station is the path by which the (fundamental) centripetal force F_1 is imparted to the inhabitant, causing the (centripetal) acceleration (ma/m). F_2 does of course push back on the floor by way of the (fundamental) electrostatic forces within the inhabitant and between the inhabitant and the floor. The source of F_2 is pseudo however (the inertial "pushback" of mass against its acceleration by a NZNFF). Montyv (talk) 14:44, 4 June 2014 (UTC)

Given this discussion, and still seeing no logic behind Montyv's objections, I removed the dubious tags. We can follow up here if necessary. Dicklyon (talk) 05:31, 4 June 2014 (UTC)


I recognize that "dubious" gets (some) people's backs up. I had been thinking about replacing it with "vague", but replaced it with "clarification" which seems to be the same thing but it shows the note via hovering. The distinction between CF being "real" (aka "fundamental") and being "pseudo" is the main justification for the existence of this article. Agree? Part of the problem is that the article dances around the fact that it is calling CF "real". See weasel words. Try to clarify that if you will (either of you or anybody). If you don't, I'll give it a try, but I don't have the the same perspective as you so it will be hard to avoid doing what you view as damage. Montyv (talk) 14:28, 4 June 2014 (UTC)

This article is based on a flawed concept: that the reaction force to a centripetal force is centrifugal. It isn't. As Prof. Scott stated very succinctly in his 1957 article: "The reaction to a centripetal force is not a centrifugal force but another centripetal force". This was precisely the mistake made by Mook and Vargish in their text when they refer to the earth exerting a centrifugal force on the sun. In a two body rotation, both bodies rotate about a common central point (their centre of mass) so the third law pair to the centripetal force of the sun on the earht is the centripetal force of the earth on the sun. It is a little less clear when the system consists of a rotating tethered mass. A rotating ball exerts a force on the end of the tether that is directed toward the rotating ball. You can call that a centrifugal force if you want to really confuse everyone. But the fact is that the tether is experiencing a net centripetal, not a net centrifugal, force. AMSask (talk) 20:53, 4 June 2014 (UTC)

There is no argument as to whether CF is fictitious or real. Rather, there are two different things called CF, one a fictitious force and one a real force; they have separate articles, as well as being compared in the summary-style article centrifugal force. And the concept of the "earth exerting a centrifugal force on the sun" is not a "mistake"; it's a point of view; that is, the force is in the direction from the sun toward the earth, which is termed centrifugal because it is with respect to the POV of the earth, even though it acts on the sun, toward the center of rotation. These distinctions can be clarified if needed, but need not be called "mistakes". Dicklyon (talk) 04:03, 5 June 2014 (UTC)

No argument as to whether CF is fictitious or real?! NO!!! That's the crux of the argument!!! Montyv (talk) 18:27, 5 June 2014 (UTC)

The article is saying that there TWO(!) different kinds of centrifugal force? WHAT?!! Dicklyon, you are highly mistaken!!! You are pandering an outmoded (by 200 years!) pseudoscience that happens to be supported by a number of naive-but-seemingly-authoratative unreliable references. That's why I warned in the first place to beware that kind of argument from authority. Montyv (talk) 18:34, 5 June 2014 (UTC)

I removed the link to "Reaction_physics". That article is unreliable in that it refers to "forces" always having equal opposites when the term "action" allows for pseudoforces. The "Reaction_physics", would need to be clarified before it can be used as a ref or a link. Montyv (talk) 18:56, 5 June 2014 (UTC)

The removal of the link doesn't change the wording in any way. If you think the link should be in place, I think you can handle being without it while the matter is discussed (because there was no wording change). Also, according to WP:burden: Any material lacking a reliable source directly supporting it may be removed and should not be replaced without an inline citation to a reliable source. That means if you want to replace the link, you have to justify it. Now, to give you a hand with that, while you may not use a WP article as a ref, you may cut and paste a reliable ref from the linked article into this article. The emphasis of course is on reliable, merely "authoritative" doesn't cut the mustard. Montyv (talk) 19:04, 5 June 2014 (UTC)

If the Reaction_(physics) article was fixed to not be so vague (and also to be correct), the link to it would be perfectly fine. Montyv (talk) 19:14, 5 June 2014 (UTC)

Now to get down to the meat: As usual, it all depends on what's meant by "force". If "force" may mean "a fundamental force OR a pseudoforce" then it is okay to say "a force always has an equal-opp force opposing it". If "force" means only "fundamental force", then it is outright nonsense to say "a (fundamental) force always has an equal-opp (fundamental) force opposing it". It that were true, we would never get "F=ma", we would only ever get "F=ZERO(!)". Montyv (talk) 19:14, 5 June 2014 (UTC)

I've provided two sources, Roche and Koyabashi. some relevant quotes from the two sources that call the real (ie, not pseudo) centrifugal force a reaction force:
True centrifugal force exists only as a reaction to macroscopic contact or binding forces.
and
The term centrifugal force then has two meanings: one is the inertial force due to the rotation of the noninertial frame relative to the inertial frame and the other is the reaction force of the centripetal force to produce acceleration toward the center of rotation. The origins of these forces are different from each other.
The third law only applies to real/fundamental forces, and the error in your paraphrase of it is indicative of where your understanding is flawed. No one is saying that the 3rd law predicts "a (fundamental) force always has an equal-opp (fundamental) force opposing it", but what we the law does say is that "a (fundamental) force always has an equal-opp (fundamental) force". The forces in the pair are not opposing because they are not acting on the same object, hence the don't balance (result in F_net=0) even though they are real, equal and opposite. Again from those same references:
Centrifugal and centripetal force are equal and opposite here but do not balance because they act on different bodies.
and
The centrifugal force due to the rotation of the noninertial frame and the centripetal force act on the same point mass. The former force does not make a pair of action and reaction with any force, while the reaction of the latter force is the force exerted on the surroundings by the point mass.
A more general reference for this statement can be found in John Taylor's "Classical Mechanics" pg 17 (a fairly standard, modern physics text for classical mechanics)
According to the third law, the reaction force of object 2 on object 1 is always equal and opposite to the original force of 1 on 2.
Now, where are the references that support your view? --FyzixFighter (talk) 19:41, 5 June 2014 (UTC)


Thanks for your cool head in our reversion cycle. I see it as a sign of good will. I'll have to return the favor some day.  :-)
     So far, I've been able to look at the ref from PHYSNET MISN 0-17 by Signell. That ref is all well and good until it gets to saying "Newton's third law says that for every force there is an equal but opposite force". Then to clarify that it isn't talking about "F_1's pull on the post (or on the center of the space station)", it goes on to say "and the force equal but opposite to the centripetal force is called the centrifugal force". So, as so often the case, the way this source rephrases the 3rd law ambiqu-ifies the matter by being unclear about what "force" encompasses. That alone wouldn't make the source unreliable, but for the fact that one interpretation ("both FF and PF") is wholly correct and the other interpretation ("only FF") is wholly incorrect. Since the source can be interpreted either way, it is ambiguous and unreliable.
     We can disagree for the time being about ("only FF") being wholly incorrect, but that source also simply doesn't support your point (that CF is a FF) because it doesn't say "fundamental force" specifically. It just says "force" in a way that can also be read as "either fundamental or pseudo". It's ambiguous about the very point you would be trying to use it to support.
     I challenge you to find a reliable source that clearly and specifically says "CF is a fundamental force". That's what you need. Remember, the thesis of the article is that "CF is a FF". You (and supporters of that thesis) need to find (good) sources that support that. The burden is on you. If you can't find reliable refs that clearly support your thesis, well, you know what that means. To argue that your thesis is true because the other thesis is not proven true is Argument from ignorance, a logical fallacy. That is, I don't need to find refs to prove your thesis if false (particularly on a talk page), but you surely need (reliable) refs to support your thesis (particularly when you say it in the actual article). That said, I do find this all fascinating, and I am looking about for good refs myself.
     So, where are your reliable sources, eh? Like I said before, argument from authority doesn't cut the mustard. Ambiguous wording in sources doesn't cut it either. And neither does argument from ignorance. So, I am looking your sources over when I can find them. It is awesome fun!

Montyv (talk) 21:44, 5 June 2014 (UTC)

Quick question - what do you mean by "fundamental force"? Also, what is your definition of "pseudo force"? How do you distinguish between the two? For me one of the distinctions between real and fictitious forces is explained in this ref:
We call an apparent force such as this one a fictitious force because it is not a real force and is due only to observations made in an accelerated reference frame. A fictitious force appears to act on an object in the same way as a real force. Real forces are always interactions between two objects, however, and you cannot identify a second object for a fictitious force.
F_2 is the force on the outer wall/floor from the inhabitant (ie two objects), and F_1 is the force on the inhabitant from the outer wall/floor, therefore by this definition they are real forces. F_c on the other hand acts on the inhabitant but we cannot identify another object from which the force originates. --FyzixFighter (talk) 00:28, 6 June 2014 (UTC)

Reworded Reaction_(physics) article - the link is okay now

I reworded that "forces come in pairs" torquing of the 3rd law to allow for "rates of change of momentum", and added a citation for it. Now I'm okay with linking to it as long as it doesn't migrate back to that "force-only" wording. Montyv (talk) 00:27, 6 June 2014 (UTC)

Newton's Third Law of Motion: "Another corollary is that all forces in the Universe have corresponding reactions. The only exceptions to this rule are the fictitious fores which arise in non-inertial reference frames. Fictitious forces do not possess reactions." --FyzixFighter (talk) 04:11, 6 June 2014 (UTC)

Something missing

This article fails to make clear that the term 'reactive centrifugal force' in no longer in common use in physics mathematics or engineering and I am not sure that it ever has been. Using the term 'centrifugal force' to mean 'reactive centrifugal force' also not in common use and is extremely confusing.

It has been possible for some editors to find sources using 'reactive centrifugal force' or 'centrifugal force' with the same meaning and although this is sufficient to show that this terminology has been used. In modern (last 40 years or so) teaching and usage the concept of a reactive centrifugal force is deprecated as it is unnecessary and confusing. Not making this clear in this article makes it highly misleading. Martin Hogbin (talk) 16:48, 6 June 2014 (UTC)

The lead has said "The term 'reactive centrifugal force', in relation to the reaction force to a centripetal force, is seldom referred to in modern physics and mechanics" for some time now. And before that for a few years it was even more explicit in linking the article on the modern concept that supplanted this one. So it's not clear what you're saying. Dicklyon (talk) 01:26, 18 June 2014 (UTC)

"Applications" section is off-topic fluff.

The applications section lists a number of real-world situations where centrifugal force in general is applied, but it says nothing about how "reactive centrifugal force" [sic] in particular applies or is related to each example. It's a lot of generic "mom and apple pie". Its attempts to make a connection to "reactive centrifugal force" are weak and particularly vague. It merely substitutes "reactive centrifugal force" for "centrifugal force". Then in the end it bizarrely says "These devices are commonly analyzed in the frame of reference of the rotating mechanisms, using the fictitious force version of the concept of centrifugal force." which seems to be saying the examples have little to do with ""reactive centrifugal force".

A stronger connection needs to be made between the examples and the subject of the article (whatever that subject is given that it's currently so vague). Without a stronger connection (and one that doesn't contradict itself!), the section is highly deletable.

Montyv (talk) 15:08, 4 June 2014 (UTC)

Yeah I've never liked that applications section either. If we do add anything, we need to make sure we have a good source that says it is an application of the RCF. I might have one, but I need to think on it. --FyzixFighter (talk) 03:11, 5 June 2014 (UTC)
The governor as described is not a very good example, but the clutch is. Dicklyon (talk) 04:16, 5 June 2014 (UTC)
So perhaps you can explain why it is the "reactive centrifugal force" that makes it work and not the "fictitious centrifugal force". The authors of the Centrifugal force (rotating reference frame) seem to think the centrifugal governor or clutch operates on inertia or the fictitious centrifugal force. Your reference to Anthony G. Atkins, Tony Atkins and Marcel Escudier (2013). A Dictionary of Mechanical Engineering. Oxford University Press. p. 53. mentions nothing about a reactive centrifugal force. This is not an authority for the statements made in the article. Retrieved 5 June 2014. AMSask (talk) 06:36, 5 June 2014 (UTC)
I have to agree with AMSask here. I don't find the provided ref very convincing in supporting the argument that the centrifugal clutch is an application of the reactive centrifugal force. Perhaps I'm not seeing it though. Could you explain what parts of that reference you feel supports the inclusion in the applications section. In the meantime I'm going to be a bit bold and try summarizing a different application that is mentioned in a journal article. --FyzixFighter (talk) 01:22, 6 June 2014 (UTC)
As with other situations, you can analyze it various ways. The reason the centrifugal clutch seems like a good example for the reactive concept is that the force applied by the shoes on the inside of the drum, which creates the friction to engage the clutch, is most easily described this way. It's not a case of what force makes it work, but only of how one chooses to describe those forces. In the flyball governor, the reactive force is all just tension in the rods (and in the springs if it's not just a gravity-loaded device); this reactive force is not so interesting in that device. Dicklyon (talk) 15:59, 17 June 2014 (UTC)
If I understand you correctly, you agree that the "force" which causes the clutch shoes to move outward against the spring force is the fictitious centrifugal force. However, you are stating that once the clutch shoes reach the drum the force that causes the shoes to engage the drum and grip the drum by friction is the reactive centrifugal force. This distinction is not very clear in the article so it is very confusing to the reader. Can you find any authority that makes this distinction? AMSask (talk) 13:20, 19 June 2014 (UTC)
You do not understand me well. I said nothing about any force causing the clutch shoes to move outward against the spring forces; but if you want to look at it that way, you can, in the rotating frame, and then you can invoke a fictitious force to describe that. I'd rather just consider the fact that the shoes are being moved in a circle, via a centripetal force applied by the spring; the reactive centrifugal force then stretches the springs, until the shoes can't move out further, after which the drum supplies more centripetal force to keep the shoes going around, and the reaction to that force is a force of the shoes pressing against the drum, causing the friction that engages the clutch.
DickLyon: It seems to me that the real problem here is in trying to distinguish between the "pseudo force" that moves the shoes out and the "real reactive force" that you say stretches the springs. It is extremely difficult for the reader to discern a fundamental difference between what you insist are two distinct physical phenomena. Perhaps others will comment but I think you have captured the reason so many object to this article. By calling the reaction force to a centripetal force "centrifugal" you are simply confusing everyone including, possibly, yourself. In reality, all net forces are centripetal. All accelerations are centripetal. All outward motion is inertial (ie. due to the inability of the real forces to provide the centripetal acceleration needed in order to prescribe circular motion). AMSask (talk) 15:23, 20 June 2014 (UTC)
But this is the entire point of the set of articles on centrifugal force: to clearly distinguish these two different forces that people call centrifugal, one of which is a real reaction force and the other is a fictitious force, and how they relate to the centripetal force that makes an object move in a curved or circular path. If it is difficult to discern the difference, we need to work harder. I think the table in Centrifugal force is a good thing for you to review first. Dicklyon (talk) 16:09, 20 June 2014 (UTC)
You state: "The force of tension applied to the spring, and the outward force applied to the drum by the spinning shoes are the corresponding reactive centrifugal forces." What is the force of tension that is applied to the spring? The tension in the spring provides inward or centripetal forces to the shoes. There is no force pushing the shoes out. There is only the centripetal forces of the spring pulling the shoes in. The reaction to the force pulling one shoe in is the centripetal force pulling the other shoe in. There is no outward force. It is inertia that drives the shoes out. AMSask (talk) 05:16, 20 June 2014 (UTC)
Yes, that's more like it, except where you say "There is only the centripetal forces of the spring pulling the shoes in", that's true except for the "only", because there's also the corresponding reaction force that is stretching the springs. If not, what is stretching the springs? Your notion that "It is inertia that drives the shoes out" is fine, informally, but has no interpretation in terms of forces; in fact, the shoes are NOT being driven out; they only have centripetal forces on them. The reaction forces to those centripetal forces on the shoes are centrifugal on the springs and on the shoes. It's not that complicated. Dicklyon (talk) 06:04, 20 June 2014 (UTC)
DickLyon: The stretch of the spring is due to the masses on either end undergoing centripetal force. If you ignore the mass of the spring, which means essentially that the spring acts as a conduit of force between the two rotating shoes, then all forces are centripetal. This means that even the reaction forces are centripetal. AMSask (talk) 15:23, 20 June 2014 (UTC)
"The stretch of the spring is due to the masses on either end undergoing centripetal force" either means you agree, that the stretch of the springs is in reaction to the centripetal force that they apply to the masses, or you have some other notion of causality in mind. The spring would usually be said to cause the centripetal force that moves the masses in a circle, as opposed to "due to the masses on either end undergoing centripetal force", but in action–reaction pairs its not really very useful to try to say which is cause and which is effect. If you use an infinitely stiff spring, just a tight wire, it's the same: the mass pulls on the wire with the same, but oppositely directed, force that the wire pulls on the mass. At the other end of the wire, the reactive centrifugal force of the one mass is applied centripetally on the other, just like in the gravity two-body case. Not a problem except that you are bothered when the reactive centrifugal force is applied centripetally. Dicklyon (talk) 16:09, 20 June 2014 (UTC)
Your phrase: "when the reactive centrifugal force is applied centripetally" says it all. Clear as mud. AMSask (talk) 15:27, 21 June 2014 (UTC)
Yes, agreed, that's unclear; it is better to ignore the center-related direction at the place where to force is applied, and just go with reactive centrifugal force, which refers to the direction from center of rotation toward the body that is doing the pulling. Dicklyon (talk) 19:27, 21 June 2014 (UTC)
If that was the convention, then we should refer to both forces as centrifugal (i.e. in relation to the body that is doing the pulling). Who refers to the force of the earth on the moon (which is the reaction to the force of the moon on the earth) as centrifugal? AMSask (talk) 22:12, 21 June 2014 (UTC)
I don't know of anyone who would do that. Dicklyon (talk) 23:13, 21 June 2014 (UTC)
Why is that? It is the reaction force to a centripetal force. Why not call it a centrifugal reaction force then? AMSask (talk) 04:27, 22 June 2014 (UTC)
If the circular motion is uniform, the reaction force on the end of the spring to the centripetal force of the end of the spring on the shoe (which you want to call the reactive "centrifugal" force) is always less than the centripetal force on the end of the spring. It is equal only if the end of the spring is massless. It is never greater than the centripetal force on the end of the spring. It can't be because the end of the spring is always accelerating toward the centre. AMSask (talk) 15:27, 21 June 2014 (UTC)
Agreed. Dicklyon (talk) 19:27, 21 June 2014 (UTC)

Yes. Please explain that. That would be good. And better still, we should all not worry too much about this section. It's problems are just a symptom. Fixing this section is good, but it's also just nibbling around the edges. We don't want to fiddle with it too much at the expense of ignoring the pseudoscience at the core of the article. Montyv (talk) 18:47, 5 June 2014 (UTC)

The amended "applications" section is not really about an application of reactive centrifugal force. It is about the analysing tensions in a rotating rigid body. The tensions are in all directions. The net forces are all inward. The tensions within the body have to provide the centripetal force required to keep the body together as it rotates. But that hardly qualifies as an application, any more than a baseball, or a frisbee is an application of reactive centrifugal force. There are really no applications of the "reactive centrifugal force" because by its very nature it only exists as a tension and can never cause outward motion. This is in contrast to the application of the inertial centrifugal force. The centrifugal clutch is an application of the inertial centrifugal "force" because by spinning the shaft the clutch pads move outward (due to inertia, not force) and engage the surface of the cylinder and cause it to rotate. AMSask (talk) 19:58, 7 June 2014 (UTC)

Having just read the article on centrifugal clutch, I am drawing a picture of an inertial force making the inner shaft expand. When the inner shaft comes into contact with the outer shaft it exerts a centrifugal force on the outer shaft. The latter would be the reactive force, the subject of this article. Am I correct? But can we have a reactive centrifugal force in the absence of an inertial centrifugal force? The two act on different bodies, but are they really two different subjects? 83.42.238.255 (talk) 10:00, 5 September 2014 (UTC)

Introduction

I hope that nobody minds that I have removed a section from the introduction. I did so because in the moon planet example given, reactive centrifugal force does not exist. It only exists in contact situations like the centrifugal clutch. In the centrifugal clutch the inner shaft exerts a centrifugal force on the outer shaft while the outer shaft exerts a centripetal force on the inner shaft. In the moon planet example the centripetal force already exists in the form of gravity and not due to an interaction with the centrifugal force. The gravity would remain even if the rotation were to stop. In the clutch, the action reaction pair is centrifugal-centripetal but in the moon planet example there is no reactive centrifugal force and the action reaction pair is centripetal-centripetal. If you think I am wrong then feel free to revert. 95.23.221.174 (talk) 10:04, 6 September 2014 (UTC)

I would also like to remove this sentence from the introduction "A centripetal force is one that causes a body to follow a curved path (rotation)". My reason is that it is best to avoid going into detail about what centripetal force is in an article about centrifugal force. In this article centripetal force should be taken for granted to avoid a debate on whether centripetal force means a force directed towards a center or a force that acts at right angles to the direction of motion. 95.23.221.174 (talk) 10:12, 6 September 2014 (UTC)

Direction of force

I removed Dicklyon's references to the direction of the reaction force because it contained no authority in support and is simply a POV. The statement was:

from the point of view of the moon's rotation, it is still a reactive centrifugal force, applied in the direction from the center toward the moon, even though it is centripetal where it is applied to the planet.

The direction of a force in relation to the inertial centre of rotation is given by the acceleration of the body that the force acts on in relation to the inertial centre of rotation: F = ma. If the body is undergoing centripetal acceleration, then the force is centripetal. No one would say that the moon is undergoing centrifugal acceleration. Dicklyon has provided no authority for his statement. He is expressing a point of view that is not contained in any recognized physics authority in violation of the Wikipedia policy on NPOV. AMSask (talk) 17:32, 13 June 2014 (UTC)

There is no disagreement here about the direction of the force. And you are right that nobody would say that that the moon is undergoing centrifugal acceleration. The only point is to say why the force is called centrifugal. Dicklyon (talk) 06:22, 17 June 2014 (UTC)
It is amazing how many books are unable to express this simple concept clearly. Look at these; any good ones? The one that come close is this one, which follows a perfectly sensible explanation by an unexplained "But this concept is quite wrong" (and then proceeds with an even more strained attempt to convert to the pseudoforce concept, which is not in fact in conflict with the concept that they say is "quite wrong"). I suppose they are saying what AMSask is saying: that he doesn't like the fact that the reaction force of the moon on the planet is called a reactive centrifugal force, since it acts centripetally on the planet. Tough--that's what it's called. Dicklyon (talk) 06:45, 17 June 2014 (UTC)
Who, exactly, says that the direction force of the moon on the earth a centrifugal force? Unless you can provide some authority that gives the direction of a force on a body as anything other than the direction of the acceleration produced by that force (ie. the direction of the acceleration of the body on which the force acts), this is just your own personal POV. AMSask (talk) 23:12, 17 June 2014 (UTC)
Like I said, there's no disagreement that the direction of the moon's pull on the planet is toward the moon, which is the same direction as the acceleration, as you say. Do you need a source for that? Is your point of view on that physical fact in any way different from anyone else's? The text you objected to already notes specifically that "the forces on both bodies are centripetal." This is admittedly a special case, relative to the barycenter in a two-body problem. In a system like the Earth's pull on the Sun, the reactive centrifugal force in not generally centripetal, since Jupiter is moving the Sun more the Earth is; that's a case where trying to characterize the gravitational reactive centrifugal force as centripetal just leads to nonsense. Dicklyon (talk) 01:12, 18 June 2014 (UTC)
I added another ref to the Mook page that says, "the sun will feel such a reactive, centrifugal force from each of the planets...". Dicklyon (talk) 01:20, 18 June 2014 (UTC)
Your reference to Mook and Vargish does not support the statement:
"from the point of view of the moon's rotation, it is still known as a reactive centrifugal force,[3] applied in the direction from the planet toward the moon, even though it is centripetal with respect to the barycenter where it is applied to the planet."
In fact the Mook and Vargish reference contradicts the statement that everyone agrees is correct, which is that the reaction force of the planet's centripetal force on the moon is the moon's centripetal force on the planet. What we need is an authority for the statement that there exists a generally accepted convention that a force that provides centripetal acceleration is referred to nevertheless as centrifugal from the point of view of the moon's rotation. While you are at it, please explain what "from the point of view of the moon's rotation" means and why this is not your own POV. AMSask (talk) 13:03, 19 June 2014 (UTC)
Mook does not contradict the fact that in a two-body problem, the reactive centrifugal force of one body on the other via gravity is applied in a centripetal direction on the body that it is applied on. He says nothing at all about that, but instead talks about the more general n-body problem, where the small wobble of the big body that you use to define centripetal is irrelevant since most of the forces are in directions unrelated to it. Only the biggest planet (or the one with biggest gravitational force at its distance) is likely to have its reactive centrifugal force being applied approximately centripetally in the n-body case. This is one good reason why your wanting to call the reactive centrifugal force centripetal is something one seldom sees, and certainly not in situations more general than the 2-body case. Dicklyon (talk) 06:11, 20 June 2014 (UTC)
And the Mook reference does support that assertion that these forces are called reactive centrifugal forces, saying "the sun will feel such a reactive, centrifugal force from each of the planets..." at the end of the paragraph discussing "equal and opposite" forces like the pull of the ball on the string in reaction to the force of the string that keeps a ball going in circles. It's not that complicated. Dicklyon (talk) 06:16, 20 June 2014 (UTC)
The Mook reference says that the reaction force to the centripetal force of the sun on a planet is a centrifugal force on the sun ie. a force pulling the sun outward. But we all seem to agree that the centre of mass of the sun is undergoing centripetal acceleration, ie. toward the centre of rotation (assuming there are only two bodies). [If there are more than two bodies then it is complicated because the com of the sun could be between the centre of rotation and the planet, which I think is the point you were making]. Mook/Vargish do not say that it is centrifugal when it is viewed from the planet's position. They say it is centrifugal in relation to the sun. They make no reference to the location of the centre of rotation. What you need is an authority that says: 'Notwithstanding that all forces and accelerations are centripetal, if you consider the direction of the force not in relation to the body that experiences the force but in relation to the body that causes the force, the direction can be referred to as "centrifugal"'. That is what you are asserting. That is what is being objecting to. AMSask (talk) 20:24, 20 June 2014 (UTC)
But the center of rotation of the Sun is completely not the issue here, nor is the fact that the force on a body moving in a curved path is always centripetal, by definition of f = ma. Even if the Sun were an immovable anchor, it would be pulled on by reactive centrifugal force, that is, a force directed toward the rotating body. The "centrifugal" in the phrase describes the direction relative to the rotating body whose centripetal force we are describing to the reaction force to, that is, the orbiting planet. It has nothing to do with barycenter or wobble of the Sun. Mook says it right, in agreement with other sources that describe this way of looking at things. These are ordinary real forces that we all agree on. It's only the name "reactive centrifugal" that's bothering you, but it has a sensible meaning if you don't twist it into nonsense. Dicklyon (talk) 22:51, 20 June 2014 (UTC)
If Mook/Vargish was attempting to say that the force is centrifugal relative to the planet they would have said that. They didn't.AMSask (talk) 15:00, 21 June 2014 (UTC)
Is there any other possible interpretation of what he meant? We all agree on the direction. Mook is just pointing that this reaction force is sometimes called a "centrifugal force". Dicklyon (talk) 15:23, 21 June 2014 (UTC)
It´s only the fictitious centrifugal force in the rotating frame that is involved in the Sun-Earth problem which you are discussing. There is no reactive centrifugal force involved here. Yes, the centripetal force on the Sun (caused by the Earth´s gravity) is part of an action-reaction pair with the the centripetal force on the Earth (caused by the Sun´s gravity), but this is a non-sequitur to this article. In the centrifugal clutch, the centripetal force is a contact force and it does not form an action-reaction pair with itself as between point A on the outer shaft and another point B 180 degrees around the rim of the same shaft. In the centrifugal clutch, the action-reaction pair is the centripetal force exerted inwards by the outer shaft and the reactive centrifugal force exerted outwards by the inner shaft. 83.43.98.14 (talk) 11:54, 8 September 2014 (UTC)
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