Talk:Reactive centrifugal force/Archive 3

Archive 1

Archive 2

Archive 3

the curved path

Noting the recent changes in the introduction, it´s true that a curved path follws from a centripetal force. It´s also true that there will be no reactive centrifugal force without a centripetal force. However, the outward tendency on rotation due to the inertia presupposes the existence of a constraint which would cause a centripetal force and hence a curved path. Therefore, has the curved path not perhaps been introduced prematurely in the introduction? May I suggest that you maybe reverse the order of those two sentences and tweak accordingly? 89.140.133.201 (talk) 20:22, 8 September 2014 (UTC) As in perhaps, ´´´ When a constraint opposes the outward motion, a centripetal force will act inwards on the object causing it to follow a curved path.´´´89.140.133.201 (talk) 20:28, 8 September 2014 (UTC)

Except that the inertia isn't really strictly an outward tendency. It's a tendency to move in a straight line. If the source of the centripetal force is removed, the object doesn't just go radially outward but in a line tangent to the path it was following when the force is removed. For me, it's a more natural progression, similar to the ordering of the laws of motion, to say that the object is not following a straight line as inertia would have it do (1st law), therefore an external force is being applied (2nd law), therefore it is exerting a equal and opposite force on the source of the external force (3rd law). --FyzixFighter (talk) 01:45, 9 September 2014 (UTC)

I was examining the situation from the centrifugal clutch example. The inner shaft expands outwards under rotation. Curved paths and tangents don´t enter into it at this preliminary stage. Only the inertial effect is involved at this stage. The centriptal force comes into the picture only when the inner shaft makes contact with and is constrained by the outer shaft. Once centriptal force and reactive centrifugal force enter the picture, then we will have a curved (circular) path for each of the elements of the inner shaft, but the curved path is only incidental, whereas the causative mechanisms driving the device are rotation and the inertial effect. The tangent that ensues when the centripetal force is removed still involves an outward tendency, and the combined effect of the outward tendency of all elements around the rim of the inner shaft, is for the shaft to expand outwards. What you have written is technically correct, but people had been complaining about the top heavy wording. I could see that much of the top heavy wording centered around the involvement of the unnecessary term ´curved path´ so I attempted to illustrate the effect in question in more simple language using key terms such as inward, outward, center of rotation, constraint etc. As regards the clause about the directions being the same for both the reactive centrifugal force and the associated fictitious centrifugal force in the rotating frame, I was assuming as a matter of course that we were working around the same center of rotation, but I can see now that I should not have made that assumption for the reasons stated in the last paragraph of the inroduction. 141.105.106.140 (talk) 07:42, 9 September 2014 (UTC)

I'm all for simplicity, but not at the cost of being technically incorrect. The idea that inertia is a tendency to move in a straight line tangent to the curve is to me completely orthogonal to the idea that inertia is a tendency to move outward. I also think that it also doesn't work if we ever are dealing with non-circular rotation where the tangent line might correspond to decreasing radial distance. To only describe inertia in terms of the motion along the radius is to implicitly adopt a rotating, non-inertial frame (see EJ Aiton's, "The celestial mechanics of Leibniz in the light of Newtonian criticism" Annals of Science 18 (1):31-41 (2006)). Or, to quote Swetz, "Learn from the Masters!"

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

I don't think I've ever seen a description of inertia, either in general or in the particular case of rotation), in a reliable source that says that it is an outward tendency of the object. Do you have one? It would certainly clear up this apparent disagreement. --FyzixFighter (talk) 03:04, 10 September 2014 (UTC)

It's true that nobody specifically defines inertia as an outward tendency, but inertia gives rise to straight line motion, which in the examples that we are looking at gives rise to an outward tendency. Put in 'straight line' if you want, it's fine. The important thing is that you don't put in 'curved path' before the constraining centripetal force has been introduced. It's looking OK now apart from the last paragraph in the lead. I think that Mook and Vargish have dreadfully confused the reactive force with the fictitious force. 94.173.45.184 (talk) 20:27, 10 September 2014 (UTC)

Indeed, the "outward tendency" that people speak of only makes sense in a rotating reference frame; let's not conflate those. I took out the "one could" sentence that you didn't like, since it seems to have no direct relation to actual practice or sources. Dicklyon (talk) 20:53, 10 September 2014 (UTC)

action-reaction pair

´´the fictitious force is felt by ALL objects in the rotation frame, unrelated to the action–reaction pair´´. True. But the clause that was removed about acting on opposite bodies was presumed only to apply to cases where the fictitious force IS involved in an action-reaction pair, but best to leave it out now because it was only an unnecessary extra in the introduction. 141.105.106.140 (talk) 08:20, 9 September 2014 (UTC)

What does it mean for a fictitious force to be involved in an action–reaction pair? I thought a fictitious force never had a reaction. If it had a reaction it would be a real force. Or do you have a counter-example in mind? Dicklyon (talk) 20:57, 10 September 2014 (UTC)

Interesting point. I had to think about it. I would say that in cases of actual rotation, the fictitious centrifugal force always forms an action-reaction pair with another fictitious centrifugal force, but that the existence of a fictitious centrifugal force does not mean that an action-reaction pair involving a reactive centrifugal force and a centripetal force also has to exist. But where such an action-reaction pair, as between a reactive centrifugal force and a centripetal force does exist due to the introduction of a constraint, then there will always also be a fictitious centrifugal force involved in the process, observable only in the rotating frame of reference, but whose effects can be felt in any frame of reference. 94.173.45.184 (talk) 12:31, 11 September 2014 (UTC)

No Original Research

I couldn't find any original research in the article. Reference 4 in particular lays out this very simple concept quite clearly. 81.4.183.162 (talk) 09:40, 12 October 2014 (UTC)

reactive centrifugal force

reactive centrifugal force applies to a push or a pull that is directed away from the center of rotation and it only occurs in situations where one body is in physical contact with another body, such as in the examples given in the main body of the article. The planetary example at the end of the lead involves only fictitious centrifugal force. There is no reactive centrifugal force involved in the planetary example. There is an action-reaction pair when considered over the two centripetal forces in the planetary example but these can never be considered to be centrifugally directed and they are not what this article is about. Centri-Fugal means center fleeing. Please don't insert this paragraph again without discussing further on the talk page. 81.4.183.162 (talk) 09:08, 14 October 2014 (UTC)

Looking at the Mook reference, I see that he is talking about a different use of the term 'reactive centrifugal force'. It therefore starts to get very confusing so it's best to deal with Mook's usage as in a section of its own. 81.4.183.162 (talk) 09:24, 14 October 2014 (UTC)

Roche Reference

The Roche reference has been used in this article to argue that the fictitious force is more commonly used than the reactive force. Page 403 in the Roche reference however according to my reading says the complete opposite http://www.marco-learningsystems.com/pages/roche/Motion_in_a_circle_pdf.pdf I'm looking at the part halfway down the first column where it reads,

"This is the centrifugal force of physics, an entirely fictional force [19]. It has now virtually disappeared from school and undergraduate physics textbooks because it can be highly confusing. Indeed, it is not uncommon even for physics authors to confuse the language of inertial and rotating frameworks."

I will remove that sentence in the lead as it appears to be ambiguous. If anybody wishes to restore it, I won't object. 94.173.45.184 (talk) 10:01, 15 November 2014 (UTC)

Inertia?

This article connects the fictitious or pseudoforce with inertia, and not the real action/reaction pair. Of course that's backwards, and wrong. It is the real action/reaction pair of forces that are caused by overcoming a body's inertia, by exerting a "real" force on it (one that follows Newton's third law). Also, this relation is exactly the same in the linear acceleration case. A pair of forces caused by overcoming a body's inertia certainly would not disappear in a rotating frame (or in the linear case, a linearly accelerated frame), so they are not an artifact of the accelerated or nonaccelerated observer. Inertia is not an artifact of the observer! Fictitious forces are noninertial.

Likewise, g-force and weight, wherever they occur, tend to smash things to strawberry jam, and it matters not who the observer is (jam happens). They all produce real action/reaction force pairs, are not fictitious, and not artifacts of frame-choice. So (again) this article has the relation backwards. Inertia is the thing that is connected to real forces, not fictitious forces. Overcoming inertia causes the strawberry jam. SBHarris 00:42, 31 July 2015 (UTC)

Just what are you trying to say?

A) Are you trying to say that RCF is any real force that happens to be directed centrifugally?

OR

B) Are you trying to say that RCF is the negative of mass times acceleration of an object in an inertial frame? Meaning, if you will, the physical resistance a mass gives in response to its acceleration through space by unbalanced real forces.

So, which is it? Or is it something else? Every time I read this article I see something different. I added some explanatory text because I was so sure you meant (A), but I read it again and now (B) seems like it fits the scattered explanations better. The article is so strikingly unclear that there's really no way to tell. It's no wonder so many have thought it was quackery. The wordings are so confused and indecipherable that surely it looks like the confused (yet confidently proclaimed) mutterings of a crank.

Somebody please say what RCF is actually supposed to be and we can get to work clarifying it.

72.74.19.224 (talk) 04:25, 1 April 2015 (UTC)

I think it's somewhat something else. Yes, for an object in curvilinear motion, it is "the negative of mass times acceleration of an object in an inertial frame", but only for the part of the acceleration that is orthogonal to the velocity, I think. And that only gives the force vector; it's also relevant to know what that force acts on. For example, if the mass in question is a planet in circular orbit about a star, the force acts on the star (and as some have noted, is a centripetal force on the star even though it's the reactive centrifugal force of the planet; so it certainly can't be A). Dicklyon (talk) 05:20, 1 April 2015 (UTC)

Do you know what I mean by (A)? For a ball-on-massless-string, the string tension points petal and also fugal, The "fugal" part of tension is a "real" force". It's both "fugal" and it's a force (and a real force at that), but quite a different thing from the "centrifugal force" people commonly mean when they say "centrifugal force". By (A) I mean any real force in the system that just happens to be pointed fugally, it's almost trivial actually. I hope the article isn't about (A) because (A)'s notablity would be extremely tenuous, and it would be misleading to imply that (A) is somehow core to and essentially the same as the "centrifugal force" people commonly mean when they say "centrifugal force".

I think it's a good idea to forget gravity for now in this section of the talk page. Gravity's "equivalence" to pseudoforce is a distraction and makes for confusion. In the article(s), gravity and its confusing equivalence issues should be discussed only after explanations are given with examples using the other ("hard") forces (EM, strong, weak). That's just an opinion of mine about communicating on the subject more effectively. I'd like to go with it. :-) 72.74.19.224 (talk) 02:44, 4 April 2015 (UTC)

For more on this, it woud be best to study the sources and see what they're trying to say. Some seem a bit confused, like for a planet in elliptical order, is the gravitational force on the star the reactive centrifugal forces of the planet in orbit? Even though it's not quite in the direction from center of curvature toward planet? Sources seem to differ a bit on this, or are not careful in saying. Dicklyon (talk) 05:23, 1 April 2015 (UTC)

I think that illustrates my point well. If you will, readers shouldn't have to go to confused(!) sources to decipher what an article is about, it should be clear in the text of the article. If some sources are confused (as so many are on this subject), they should be written off as unreliable. If we can't explain what we're saying, and/or there isn't a reliable source out there saying whatever it is we're saying, the article should maybe be deleted for lack of notability?

Whether a "center" is meant to be the point pointed to by the radius of curvature or if it's something else is ultimately a matter of definition, and that is ultimately just a matter of being (again) clear about what's meant when one says "center". As a rule, if there's any way it can be confused as to what's meant by "center" (or anything else), it should be specified explicitly in situ. Though, I can't see how anyone would ever use a definition of "center" as anything other than the point pointed to by the radius of curvature at a given moment. Momentarily curved trajectories of bits of mass are a more general form of the problem, constant circular motion is just a simplification and a steady-state form of that. 72.74.19.224 (talk) 03:08, 4 April 2015 (UTC)

I have been having this same discussion with Dick for some years now and I remain puzzled to his attachment to the concept of RCF. It is described in a few sources but they are in a distinct minority and some of the sources that use the term are clearly very confused themselves. On the other hand, there are many good quality sources that are not the least bit confused or confusing because use the term only to refer to the inertial force. For this millennium at least, inertial CF is the only force used and taught by mathematicians, engineers, and physicists alike. Martin Hogbin (talk) 17:25, 10 April 2015 (UTC)

I think I get it now. I don't agree with it, and the article still communicates it badly, and is still rife with ambiguous unreliable refs, but I think I get it:

The "reactive centrifugal force" as discussed in this article is a vector of the same magnitude, direction, and units as the centrifugal pseudoforce vector. The view taken here focuses on the property of inertia which produces resistance to acceleration, i.e. the action opposing the net force on an object which causes it to be accelerating in the first place. That action (a vector) is the mass of the object times the negative of its acceleration (with acceleration being measured in an inertial frame of reference). This resistance to acceleration of an object is a commonly experienced and real physical phenomenon. In the most commonly discussed cases of centrifugal force, the net force is the centripetal force with the net acceleration being the centripetal acceleration.

The centrifugal pseudoforce vector by contrast is a mathematical construct. It is however, considered by the majority to have an actual physical reality, with that physical reality being the same physical thing as the reaction discussed above, the reaction produced by inertia opposing the acceleration of the object through space. The centrifugal pseudoforce construct indeed has the very same definition: mass of the object times the negative of acceleration -- with acceleration this time being the acceleration of the frame of reference as compared to an inertial frame. But, since the frame of reference is defined to be attached to the object, the acceleration of the frame is always exactly the same value as the acceleration of the object. Despite the sameness of the the two quantities and other factors suggesting actual sameness, this article takes the minority view that the pseudoforce vector is only mathematical, only exists in an (accelerating) frame of reference attached to the object, does not have a physical reality, and is not the same thing as the action produced by inertia opposing the acceleration of the object through space. With that view, "reactive centrifugal force" is the real physical action resisting an object's continuous centripetal acceleration, and is considered to be a same-valued but different thing from centrifugal pseudoforce.

Keep in mind though that "reactive centrifugal force" isn't and can not be viewed as a real force. RCF (as well as pseudoforce) has the effect of "connecting" to the net real force in order to be able to resist it, yes, but if it was a real force, then the sum of forces on the object would be zero and it could never accelerate. So, RCF should never be implied in the article as having all the nature of a real force. I think Newton used the word "action" carefully to be able to include these kinds of things in the 3rd law without calling them a force. That's why I say "action" above.

Cmwings (talk) 08:39, 17 April 2015 (UTC) (formerly IP 72.etc.etc.etc above)

I think most of what you say above is pedagogically correct. The centrifugal force of yore (of the texts) is a pseudoforce that you cannot ever feel, and which appears or disappears when you change frames. The (other) "centrifugal force" is real-- it is one-half of an action/reaction pair of overcoming a body's linear momentum and making it bend into a circular path. It is obviously a real force that follows Newton's third law, as it is part of an action/reaction pair, and doesn't go away (either member of the force-pair!) when you change frames. That's what MAKES it real.

Confusingly indeed, the two types of centrifugal force (real and pseudo/unreal) are in the same direction (centrifugal, obviously) and are of the same magnitude. Or at least, they are of identical direction and magnitude in the frame where the rotating object is motionless. [But not otherwise-- the fictitious CPF force goes up and down, depending on what rotating frame you choose and how fast it rotates; the real force pair including RCF never changes]. However, as pointed out below, this article's major error lies in connecting the pseudoforce (the fictitious force) to the process of overcoming the body's inertia. Wrong! The action/reaction force-pair (one of which is the RCF) is a real force changing the path of a real body with real inertia, according to Newton's first, second, and third laws. Fictitious forces don't care about Newton's third law, and ignore it. So inertia and its effects are connected ONLY to the real RCF, not the fictitous/pseudo CPF. IOW, you can make CPF go away by choice of frame, but not the real forces that are causing real mechanical stresses in the object (due to its inertia).

Changing subjects a bit, if you want to sprain your brain, I can easily give you an example of a fictitious pseudoforce which is CENTRIPETAL. Just consider an inertial body (floating in deep space), at a radius R from you, with no relative motion between you and the body. Then go to into an rotating frame. You will observe the (formerly motionless) object now unaccountably moving in a circle around you! So, how to explain this odd behavior in Newton's mechanics? Well, in Newton, the circular motion is caused by ONE and only one (new) centripetal force: but in this case, a centripetal pseudoforce. It goes away immediately when you stop spinning and change to a frame that isn't spinning at all. The object never notices either way, as the pseudoforce acting on it (as usual) was never felt by it, and didn't act according to Newton's third law. It was just a one-ended vector pointing inward, whose only purpose was to explain the circular motion imposed by your change to a rotating frame. This example, BTW, shows that pseudoforces generated by rotating frames aren't always centrifugal. Sometimes they are centripetal. SBHarris 01:01, 31 July 2015 (UTC)