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Generalized centrifugal forces

This reversion by DVdm seems unexplained to me. One reverted sentence is:

These generalized forces most accurately are called "generalized centrifugal forces" in this context, but the word generalized is sometimes omitted, causing some confusion. Generalized centrifugal forces are related to the square of the rate of change of generalized coordinates (for example, polar coordinates),

The only change here from the previous text is to break a sentence into two parts, and add the observation that omission of the word "generalized" to separate these forces from the Newtonian centrifugal force "causes confusion". The history of this WP article is evidence in itself that confusion results, and in the abstract it seems clear to me that failure to distinguish between different things by giving them the same name is a source of confusion.

The second change reverted is:

This usage is common in the field of robotics.

There is a link in the next sentence to the subsection below. This subsection contains several references from the field of robotics, which would seem to me to provide ample support for this simple observation.

Altogether, this reversion seems to me unwarranted, so I have undone it. Brews ohare (talk) 15:47, 25 March 2012 (UTC)

First, you'd better come to the talk page before you revert an undo - see wp:BRD.

Second, the removal was not unexplained. The edit summary said that it was unsourced, and it was. The phrases "most accurately", "but", "causing some confusion" are wp:POV if not wp:OR. I can live with the latter part of the edit, but the first part was definitely inappropriate. Please find a solid source for

These generalized forces most accurately are called "generalized centrifugal forces" in this context, but the word generalized is sometimes omitted, causing some confusion.

or kindly remove it. Thanks. - DVdm (talk) 16:00, 25 March 2012 (UTC)

Removed again: apart from the above unaddressed concerns it severely broke formatting, stripping out reference tags for no reason. And apart from obvious vandalism it is never acceptable to revert another editor without giving a reason, as you did in the change.--JohnBlackburne^words_deeds 16:23, 25 March 2012 (UTC)

Blackburne: A full discussion was provided on the Talk page prior to the reversion. Brews ohare (talk) 16:32, 25 March 2012 (UTC)

DVdm: I don't understand your comment above. Are you suggesting that the term "generalized centrifugal forces" does not arise in Lagrangian mechanics? Or are you objecting to the statement that the adjective "generalized" sometimes is omitted? The original text seems pretty close to the same thing:

The generalized forces that are called "generalized centrifugal forces" in this context (the word generalized is sometimes forgotten), are related to the square of the rate of change of generalized coordinates (for example, polar coordinates),"

Compare with the replacement:

These generalized forces most accurately are called "generalized centrifugal forces" in this context, but the word generalized is sometimes omitted, causing some confusion. Generalized centrifugal forces are related to the square of the rate of change of generalized coordinates (for example, polar coordinates),

Perhaps you object to the original text as well? Brews ohare (talk) 16:32, 25 March 2012 (UTC)

Find a source an you're in business. Otherwise it's wp:OR. You really should know that by now. - DVdm (talk) 16:37, 25 March 2012 (UTC)

All right, I'll do that later. I am traveling at the moment. However, it appears to me that my replacement text is virtually identical to the text I replaced, so that required a source as well. Please excuse me for not substantiating what already was accepted earlier from others. Apparently this entire section is objectionable to you and requires further sourcing. Sources are provided in the subsection referred to, and I'll just add footnotes to these same sources here, if that suits you. Brews ohare (talk) 16:50, 25 March 2012 (UTC)

Looking at this again, I actually see no difference between my suggestion and the present text aside from breaking a run-on sentence into two sentences. Inasmuch as that grammatical change is considered to be WP:OR. I see no point in arguing this ridiculous suggestion. I'll leave it the way it is. Brews ohare (talk) 03:18, 26 March 2012 (UTC)

Brews, I don't think the run-on was at issue. Rather, it's asserting what's "most accurate" and what "causes confusion". Such statements should never be made without a source. Dicklyon (talk) 05:46, 26 March 2012 (UTC)

Precisely. I assumed that was clear in my first reply. - DVdm (talk) 08:29, 26 March 2012 (UTC)

Dick: Thanks for the clarification. In response, I'd agree that occasions arise where "most accurate" requires substantiation. For example, in comparing two clocks. Or in comparing historical accounts. However, when the term "generalized centrifugal force" is abbreviated to "centrifugal force" by omission of the word "generalized" what happens is that one has failed to separate the technically correct Lagrangian terminology from the terminology used for the Newtonian force. Thus, the reader may confuse the meaning if they are not careful about definition by context. There is absolutely no need for a source to verify that in referring to the Lagrangian formulation, the terminology "generalized centrifugal force" is more accurate than "centrifugal force".

Nor is a source needed to suggest confusion is introduced when the clear descriptor "generalized centrifugal force" is replaced by the incomplete version "centrifugal force", the term commonly used to refer to Newtonian centrifugal force. Brews ohare (talk) 15:21, 26 March 2012 (UTC)

Perhaps DVdm is under the impression that "generalized centrifugal force" and Newtonian "centrifugal force" need no distinction, but that would be a misconception.

This very discussion may be an example of the confusion occasioned by dropping the adjective "generalized". Brews ohare (talk) 12:35, 26 March 2012 (UTC)

I have very carefully broken the sentence into two, with the least possible change in wording, so as not to upset anyone, for any reason whatsoever. Brews ohare (talk) 14:28, 26 March 2012 (UTC)

Brews, the only thing that I am under the impression of here, is that the phrases "most accurately", "but", "causing some confusion" are wp:POV if not wp:OR. I'm not even interested in the context. DVdm (talk) 15:29, 26 March 2012 (UTC)

DVdm: it is hardly WP:POV to say "cycle" when "unicycle" is meant, or "centrifugal force" when "generalized centrifugal force" is meant. Perhaps you just weren't careful in your remarks, and now are defending the indefensible result of hasty reaction. There is a POV for you, eh? It happens. Brews ohare (talk) 15:40, 26 March 2012 (UTC)

I'm not interested in "cycle" or "unicycle" or "centrifugal force" or "generalized centrifugal force". I'm interested in sources for phrases like "most accurately", "but", "causing some confusion". I have bolded the relevant parts of my first reply in this thread. - DVdm (talk) 15:55, 26 March 2012 (UTC)

DVdm: At the risk of becoming annoying, I think you're saying that some key words like "most accurately", and "causing confusion" are automatic flags regardless of where they arise and they always can be flagged as violations of WP:OR or WP:POV, no matter the context. Although that stance sounds simple, I don't think it really can handle every case. So, just as an example, suppose a term x has a particular meaning and a term y has another. Then if one says that a practice of calling x an y is "confusing", that is only a POV and should be sourced? If one says calling an x an x is more accurate than calling an x a y, that requires a source? Is that really how you think about this? Brews ohare (talk) 18:21, 26 March 2012 (UTC)

Of course I agree that it cannot "handle every case", but I'm sure that everyone (including you) will agree that it managed to handle all your cases up to now. Try learning from that, and you might survive here. Good luck. - DVdm (talk) 18:50, 26 March 2012 (UTC)

DVdm: You didn't assess my algorithm above. It corresponds to this case with x=generalized CF, and y=CF. It's survival, not a life, eh? Brews ohare (talk) 00:27, 27 March 2012 (UTC)

I still cannot work out what this use of CF is doing here at all. It is a very specialised, informal use of the term used only by experts. I would accept a short section near the end of the article entitled 'Other uses of the term CF' or the like but to give it such prominence in the article does our readers no favours. Martin Hogbin (talk) 08:58, 30 April 2012 (UTC)

I am confused. Please help.

I understand what centrifugal force is in everyday life, like on a merry-go-round you feel centrifugal force pushing you towards the outside of the merry-go-round. However what I don't follow is when people mention centrifugal force, are they referring to the 'fictious' force (like some magical force emitting from the centre of the spinning action) or the 'reactive' force (like on a ball tied to a string the reactive centrifugal force keeps the string taut)

I have never really heard of the fictious force example. I knew from a young age how true centrifugal force works, like on the wall of death the reason why the bikers don't fall off the wall is because as they go round, they keep wanting to travel in a straight line and it is this force (centrifugal force) that keeps them on the wall without them falling off it. I suppose one could say this is reactive centrifugal force as the wall provides the centripetal force to keep the bikers going round and the reactive centrifugal force keeps them cycling on the wall. But this is getting too scientific, as I have never ever heard anyone say centripetal force in everyday conversation. Please can someone help me on this. Thanks Diamondblade2008 (talk) 20:02, 11 March 2012 (UTC)

The force you think you feel when you are moving in a circle, such as on a merry-go-round, is a fictitious force usually described as centrifugal force. Wikipedia has a complete article about this fictitious force - see Centrifugal force (rotating reference frame).

There is also the force that is equal in magnitude and opposite in direction to any centripetal force. One group of people call this centrifugal force, or reactive centrifugal force. Wikipedia also has a complete article about this application of the expression centrifugal force - see Reactive centrifugal force. However, another group of people say this reactive force (equal in magnitude and opposite in direction to any centripetal force) should not be called a centrifugal force. They say it is just the opposite of a centripetal force and it doesn't have a special name. A debate has raged on Wikipedia for quite some time about whether the force that is equal in magnitude and opposite in direction to a centripetal force should ever be called a centrifugal force - to read the latest arguments in this debate see Talk:Reactive centrifugal force#There is no such thing as reactive centrifugal force (again). Dolphin (t) 06:14, 13 March 2012 (UTC)

That is the problem with Wikipedia. It is not 'another group of people' who deprecate the use of 'centrifugal force' to refer to the reactive force, it is all modern text books on the subject, written for engineers, mathematicians and physicists. Unfortunately, because the odd obsolete use of the term can still be found in published sources, this article is doomed to remain utterly confusing to anyone who does not already understand the subject. Martin Hogbin (talk) 09:47, 13 March 2012 (UTC)

@Martin: Wikipedia is an encyclopedia; it is not a textbook. I think it is tendentious to say this article is doomed to remain utterly confusing ... In the field of science, if an idea deserves to be rejected or criticised, the facts will be sufficient. Dolphin (t) 23:55, 13 March 2012 (UTC)

The article needs improving. We are not required to give equal weight to obsolete meanings of terms; we should be writing an up-to-date and easily-understandable encyclopedia article about the subject. At present we get a steady stream of readers telling us how unhelpful the article is. This article is a missed opportunity.

The has nothing to do with 'the field of science'; the physics has been understood for centuries and is not disputed. In science we can decide on what we wish terms to mean and it is quite common for usage of scientific terms to be restricted and clarified as time passes. Some decades ago the scientific community decided that using 'centrifugal force' to mean anything other than the inertial force found in rotating frames was to be discouraged as confusing and unnecessary. We should follow suit. Martin Hogbin (talk) 09:38, 14 March 2012 (UTC)

I would suggest that much of the confusion is a matter of semantics, and that by 'banning' the use of the term 'centrifugal force' MORE confusion is added! This poorly-worded article does not help. 99% of Engineers still refer to the reaction (to a centripetal force) force applied by an object when it is kept in a rotating motion as a Centrifugal force, and the thought-police aren't about to stop this!— Preceding unsigned comment added by 206.47.106.181 (talk) 16:29, 8 August 2012‎

No one is suggesting that the term 'centrifugal force' should be banned just that it would be more helpful to use it with the only meaning that is currently taught to mathematicians, physicists, and engineers alike. Martin Hogbin (talk) 08:40, 9 August 2012 (UTC)

Got your message on my talk page Martin. Thanks. Also thanks for the replies, it has been helpful. Diamondblade2008 (talk) 21:22, 13 March 2012 (UTC)

Overly technical language

I would like to improve the readability of this page. I am new however, so I thought before I made any changes, I would bring up the issue here. How do I go about editing a page that I believe needs major rewrites, rather than word substitutions and the addition of a few sentences? — Preceding unsigned comment added by Andrewrgross (talk • contribs) 02:26, 13 June 2012 (UTC)

My method is to use my personal sandbox. I copy everything except the categories at the bottom of the article and paste it all into my personal sandbox - see User:Dolphin51/Sandbox. There I can edit it at my convenience without offending anyone. When I have finished I can paste it back into the article. When relevant, before I paste back into the article I leave a message on the Talk page, alerting other interested Users to my changes on my personal sandbox, and inviting them to comment. Generally, others raise no significant objections so, after a few days or a week, I paste back into the article. Let me know if you want a personal sandbox and I will create one for you. Dolphin (t) 03:53, 13 June 2012 (UTC)

It would be better to start with smaller pieces, especially if you're new, so you can learn as you go. Try rewriting the lead, or a section. You can use the sandbox, or post a proposed change here, or just go ahead and be bold and edit the article (but don't get miffed if you get reverted: see WP:BRD). Keep in mind that this article was created as a WP:Summary style article, to lead people to the articles with more technical detail (see the "main" links in each section); but some editors have a hard time not adding tons of technical detail here, so it has crept a lot. Also keep in mind that CF is understood differently by different people, fields, and eras, and that we don't want to adopt one POV at the expense of the others (see WP:NPOV). Dicklyon (talk) 05:34, 13 June 2012 (UTC)

See also Talk:Gyroscope , idea to have simple demonstation(video) of the boiled egg(or other) which when spun quickly on a plate, goes from on its side to standing on end( unlike non-boiled egg).SignedJohnsonL623 (talk) 06:09, 21 October 2012 (UTC)

mass dependency in centrifuges

This article fails to explain why heavier bodies concentrate on at larger radii in centrifuges. — Preceding unsigned comment added by 173.25.54.191 (talk) 03:41, 6 October 2012 (UTC)

That is already covered in the Centrifuge article. -AndrewDressel (talk) 16:32, 21 October 2012 (UTC)

"Centrifugal" redirects here

IMHO, searching for "centrifugal" should redirect the user to a disambiguation page instead of this topic page. Some people might be looking for other topics, such as "centrifugal compressors." CheMechanical (talk) 17:28, 13 November 2012 (UTC)

I agree. Or make centrifugal a disambig page itself. Dicklyon (talk) 17:39, 13 November 2012 (UTC)

I also agree and I have made the change. Centrifugal is now a disambiguation page. Dolphin (t) 04:54, 28 January 2013 (UTC)

Example(s) needed.

It would be useful to have a numerical example for the computation of the "centrifugal" force, or "g" force, for the formula v^2/r. E.g., for a car going around a curve or a rotating pace station. — Preceding unsigned comment added by 75.57.187.51 (talk) 02:41, 28 January 2013 (UTC)

Centrifugal force is not a "reaction force"

I don't agree with the statement that the centrifugal force refers to two different concepts one of which is the reaction force. There really is no such thing as a reaction force. All forces occur in pairs. Assigning them the names action and reaction is arbitrary. Why not call the centrifugal force the action force? If you follow the link to reaction you will see this mentioned in that entry. The entry even mentions the common misconception about the centrifugal force as a reaction force. — Preceding unsigned comment added by 165.155.196.75 (talk) 12:14, 25 October 2013 (UTC)

You are entitled to your opinion, but I think you are forgetting the caveat in Newton's Third Law that action and reaction act on different bodies. I would suggest that it is the paragraph to which you refer in Reaction_(physics) that needs cleaning up and clarifying, rather than changing the article on centrifugal force. The reaction that is sometimes called "reaction centrifugal force" acts not on the body but on the constraint causing it to move in a circle. The latter (accelerating force) is usually best thought of as the "action", with the real outwards force on the constraint being the "reaction". (In a rotating frame of reference, such as the surface of the Earth, I agree that it is sometimes useful to consider the centrifugal force as an action force (reducing the force of gravity.) Dbfirs 20:57, 25 October 2013 (UTC)

165.155.196.75, you are absolutely correct. I have been trying to make this point for years. The 'reaction force' version of centrifugal force was created by people who did not understand the physics and who tried to dig themselves out of a hole caused by their own misunderstanding. It has never been a widely used or useful concept. Martin Hogbin (talk) 11:08, 29 December 2013 (UTC)

I agree that Reactive centrifugal force is not often a useful concept, and I'd never heard of it until I read the article, but it seems to be used in some texts (see the references). If you try holding a cannon ball whilst being whirled round in a circle, it certainly feels like a real force (which it is, but not a force on the cannon ball). Dbfirs 13:09, 29 December 2013 (UTC)

That is the problem, it is still possible to find the odd reference to reactive centrifugal some older sources and some online books. The reality is that for the vast majority of physicists, mathematicians, engineers, and teachers today only one concept of centrifugal force is in common use, that if the inertial (or fictitious) force. Presenting the two versions of the force on equal footings in this article is extremely confusing to readers who are trying to understand the subject. The reactive concept will almost certainly be at odds with what they have been taught elsewhere.

I have no objection to mentioning the reactive force as an alternative historical concept in some circles but it has no general legitimacy today. Martin Hogbin (talk) 14:13, 29 December 2013 (UTC)

The problem is in calling the force centrifugal. It is a real force, and it acts away from the centre, but not on the body being considered. Do you think it causes confusion in the minds of readers of the article? Dbfirs 07:35, 30 December 2013 (UTC)

Yes, I believe that it causes much confusion to use the same name for two different things. As 165.155.196.75 points out there is absolutely no need for a special name for the reaction force to the centripetal force. All forces have equal and opposite reaction forces and the centripetal force is no exception.

In the case of measurement in a rotating reference frame, we need to invent a new force and therefore giving it a special name is a good idea. Although it is sometimes called a fictitious force (I prefer inertial force) in a rotating frame it is perfectly real.

I am not alone in my opinion though. In modern practice (the last half-century or so) elementary physics is always done in inertial frames and rotating frames are left until a more advanced stage. The term 'centrifugal force' is never mentioned, simply because there is no need for it and it historically caused endless confusion to students. Once rotating frames are considered the new inertial forces are introduced. The problem is that the search capacity of the internet allows editors to search for terms like 'reactive centrifugal' and find the odd obscure reference to 'prove' that 'reactive centrifugal force' is still in common use. Martin Hogbin (talk) 10:24, 30 December 2013 (UTC)

I fully agree with you that there is no need for centrifugal force to be mentioned. I can remember long ago when it was acceptable to use the idea, and I occasionally switch to a rotating frame in my own thinking, but I never taught it (except to mention that it shouldn't be mentioned in elementary problems). The problem is that we can't abolish the term, or the various meanings that different people have given to it. Dbfirs 15:42, 30 December 2013 (UTC)

I am not trying to abolish anything but today 'centrifugal force' is used almost exclusively to refer to the inertial force required in rotating frames. It is hardly ever used to refer to the reaction force. The article should reflect this current usage by saying simply that centrifugal force is the inertial force. At the moment it is utterly confusing for someone who does not understand the term to be presented with two possible meanings, especially as one of them is obsolete.

I have no objection to a section later on in the article on alternative and historical uses of the term, which would discuss the reaction force meaning. Martin Hogbin (talk) 20:08, 30 December 2013 (UTC)

Yes, I agree that it would be better to remove the mention of the reactive force from the lead, and modify the later paragraph to make clear that using "centrifugal force" for the (real, when present) reactive force is non-standard (and potentially confusing). Is the Lagrangian usage essentially different? Could we re-phrase that sentence too? Dbfirs 21:20, 30 December 2013 (UTC)

The Lagrangian usage is a a rather specialist, and in my opinion somewhat informal, one. It is used mainly in the field of robotics. Martin Hogbin (talk) 10:05, 31 December 2013 (UTC)

Some reasonable science books do talk about the reactive version in preference to the fictitious version of CF, even though it's not the dominant way the term is used these days. Here's one. And some "practical" books, too, like this one and this one and this one. There's nothing wrong with this concept; I don't see why Martin claims it has "no legitimacy". Dicklyon (talk) 00:40, 31 December 2013 (UTC)

Dick, your response shows exactly the problems that I am concerned about. You have used the power of Google to find a handful of books which appear to use 'centrifugal force' to mean the reactive force. The problem with using this method is that WP will soon become Googlepedia; everything that I can find searching Google. There is still a vast volume of information that is not searchable online. How many sources do you think there are that use CF to mean the inertial force?

Let us now look at what your sources actually say:

Marion

This source consistently refers to the CF as the force exerted by the ball on the string.

Norfield

This uses the term to refer to the tension in the string acting in the hand in the centre of the picture. According to our definition here the reactive CF is the force felt by the string as a reaction to the centripetal force the string applies to the ball. Almost the same thing but not quite.

Later on it gets worse, it says that the riders on the carousel experience the CF. He is now using the same term to refer to the inertial CF but fails to mention rotating frames. Very confusing.

Burkett

It is hard to work out exactly what is being said here. The Newton's reaction law is mentioned but so is the term 'fictitious' used. This is a perfect example of the confusion that abounds by the use of one term to mean two different things.

Gardner

This source uses CF to mean the reactive CF as described in this article.

Discussion

We have four sources found by a Google term search. Two appear to use the term for the RCF as described in the article. Neither has any reviews and it is hard to see how they can be considered to represent any realistic fraction of the number of reliable sources on this subject.

The other terms are excellent example of the confusion that has historically been connected with centrifugal force. Many years ago physicists, mathematicians, and engineers decided to end this confusion by using the term CF to refer only to the fictitious/inertial force found in rotating frames. In inertial frames no such named force is necessary.

We are now dredging up chaos from the past and giving it a new lease of life. Martin Hogbin (talk) 10:43, 31 December 2013 (UTC)

Well done. I agree with what Martin has said. To call the reaction force to a centripetal force "centrifugal" is at best confusing and is simply wrong in many cases.

The example of the baseball player swinging a bat (or golfer swinging golf club) illustrates the problem. The force that is pulling on the hands of the player as the bat swings is the 3rd law pair force to the player supplying the centripetal force to the bat. But the centre of rotation of the player and bat (the centre of mass of the player/bat system, assuming it does not move during the swing) is between the centre of mass of the player and the centre of mass of the bat. Both centres of mass are accelerating toward that centre of rotation during the swing. So this force on the hands of the player is actually causing the centre of mass of the player to accelerate toward the centre of rotation (centre of mass of the system). It is not really centrifugal if it is looked at that way.

In any case in which a body experiences centripetal acceleration, the centripetal force on the body can be paired with another equal and opposite centripetal force. Although one may wish to characterize this real force as "centrifugal" (because, in the example, the force on the hands is in a direction away from the centre of rotation even though the centre of mass of the person as a whole is being pulled toward the centre of rotation and even though the hands accelerate toward that centre) that term only serves to confuse rather than illuminate. Consequently, the characterization of such a force as "centrifugal" is a bad idea. "Centrifugal reaction force" is not part of mainstream physics usage. In my view the term "centrifugal reaction force" should be avoided. The term "centrifugal force" should only be used in reference to the fictitious force.AMSask (talk) 20:19, 31 December 2013 (UTC)

... so why have you made the article even more confusing? Should we delete all reference to "reactive centrifugal force" and simply mention that a reaction to a contact force causing centripetal acceleration will be in a direction away from the centre? Dbfirs 13:40, 1 January 2014 (UTC)

Any confusion is caused by trying to use the same term "centrifugal" to describe two very different phenomena. The original stated categorically that the reaction to a centripetal force is always a centrifugal force. It would be less confusing to the student if that was true. But it isn't. AMSask (talk) 17:21, 1 January 2014 (UTC)

My suggestion would be simply to refer to the reaction to a contact centripetal force, rather than add more confusion by going on about opposing centripetal forces that have little connection with the topic. I think we are aiming to simplify this article, but we'll see how the rest of the discussion goes. I'd support reducing the prominence of this concept of "reaction centrifugal force". Dbfirs 20:18, 1 January 2014 (UTC)

A proposal

Can I suggest that the article is rewritten to conform to the more normal order for scientific topics, that is to say with the current mainstream view being presented first, without reference to other interpretations of the term.

Later on we can have sections on the history of the terminology and alternative and historical interpretations of CF. No important material should be lost but the article would be far more helpful to readers who actually want to know what CF is (as the term is currently used). Martin Hogbin (talk) 15:48, 1 January 2014 (UTC)

We do have an article already on centrifugal force (rotating reference frame), which is the mainstream interpretation you're talking about. The present article here was created as a summary-style article to help people understand if that's the article they want, and how it relates to other uses of the term. If you're proposing to rewrite this one to be like that one, then a merge would be more appropriate, and it we can go back to the era where we had all these arguments in that article instead of moving them to a (previously) short summary-style article. Dicklyon (talk) 17:27, 1 January 2014 (UTC)

Yes, I do know about the other centrifugal force articles and that does complicate the problem. The problem I see is that this is the first article that readers are likely to find and it is so utterly confusing that they will probably be put off pursuing their interest further.

As you can probably imagine, I would support merging this article with centrifugal force (rotating reference frame) and possibly with the reactive force article. As it is now we essentially have a POV fork, except that one POV is obsolete. Martin Hogbin (talk) 17:37, 1 January 2014 (UTC)

The intent when we did this was to fork the modern meaning from the old traditional meaning and other meanings, and leave a summary-style article help readers find the one they want and understand how they relate. This summary-style article has tended to get over-bloated with too much detail that duplicates the others, however, so yes it is more confusing than it should be. Why don't we fix that? Dicklyon (talk) 21:47, 1 January 2014 (UTC)

Why have three articles on one topic? One well written article would be much better. It would explain the subject, as it is currently used and taught, to our readers, and give a historical background, just like most other science articles. I do not think there ever was a single old traditional meaning for CF. Many older books are full of varied and confusing terminology. Martin Hogbin (talk) 22:39, 1 January 2014 (UTC)

I think we have at least four, but I wouldn't call them the same topic. Different concepts that are related and have the same name; that's what the summary style article is good for clarifying. Dicklyon (talk) 00:38, 2 January 2014 (UTC)

No clarification is necessary as there is only one meaning of CF in use today. One article with reference to the confused historical and alternative uses for the term is all that we need. Martin Hogbin (talk) 19:48, 6 January 2014 (UTC)

The centrifugal force is not fictitious in the literal sense, this should be made more clear

I run all the time into people who think that because beginner textbooks called the centrifugal force "fictitious", it must be just a figment of their imagination, like its some motion-induced hallucination. The centrifugal force is real, it's just not fundamental. A force meter in a rotating reference frame measures the centrifugal force just fine, independent of any human brain tricks. In my teaching, and I think the trend among scientists, is to call the centrifugal force an "inertial" force and avoid calling it "fictitious" as this leads to confusion. This article should make this distinction more clear. Any graduate level mechanics textbook makes clear the centrifugal force is a real effect, and not just something dreamed up by the masses. I will start to make some preliminary changes to the main article, but please help improve my changes without just blindly reverting them. 129.63.129.196 (talk) 16:13, 4 April 2013 (UTC)

I agree, 'inertial force' is the better term and probably the one used in more modern text books on the subject. The is a long history of keeping this article half way through the last century in terminology and understanding which I think should change. Dick, you once offered to discuss it with me. Martin Hogbin (talk) 18:06, 4 April 2013 (UTC)

Selecting the "best" of the modern terms isn't as important as clarifying in this article that it (whatever it's called) is a real thing, but just not a "fundamental" force. IMHO. Also best to do that clearly and obviously at the first use of the term. 108.7.9.153 (talk) 05:29, 10 May 2013 (UTC)

I'm not sure what "not fictitious in the literal sense" means, but we should be clear what "fictitious" means here (i.e. forces that do not appear in an inertial frame, but only in an accelerating frame). The lead already makes "fictitious" subsidiary to "inertial". And modern sources are pretty much a horrible mess, as older sources are. So, move carefully. Dicklyon (talk) 05:43, 10 May 2013 (UTC)

It means that fictitious, pseudo, D'Alembert, or inertial "force" is a real thing, not a made up thing, so it can't be said to be literally "fictitious" because it's literally "not fictitious".  :-)

It's a fascinating force-like "action", but it's not a fundamental force. It has the same units as force. It's "equivalent" to one of the fundamental forces (gravity) via the equivalence principle. It even helps call into question whether gravity is a fundamental force or a pseudo force. It has the same magnitude (and opposite direction) as the non-zero net of fundamental forces acting on an object (i.e. it's the negative of "ma" in F=ma). I'd say it's pretty real, whatever it is.  :-) Montyv (talk) 06:54, 10 May 2013 (UTC)

While I think "inertial force" is probably more informative than "fictitious force", I disagree when you say that it is a real thing. Classical Newtonian physics, ie F_net=ma, gives preferential treatment to inertial frames and that is what defines real vs fictitious force for classical mechanics. It's not a question of whether a force is "fundamental" or not. In the preferred frame of Newtonian mechanics, inertial forces vanish which is probably why they are described as "apparent" forces. The inertial "forces" that we think we see if we describe a particle's motion in an accelerated frame is really an artifact of the acceleration of the rotating frame and not indicative of an external force acting on the particle. Ultimately though we should rely on reliable sources - to quote a few:

Considered as an endeavor of the circulating body, or a force acting on the body itself, [the centrifugal force] 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. (Swetz, "Learn from the Masters!", pg 269)

and

Newton had realized crucially that it was much simpler to consider things from a frame of reference in which the point of attraction was fixed rather than from the point of view of the body in motion. In this way, centrifugal forces - which were not forces at all in Newton's new dynamics - were replaced by forces that acted continually toward a fixed point. (Linton, "From Eudoxus to Einstein", pg 413)

and

The planet experienced a centrifugal force in the same way that one experiences a centrifugal force when turning a corner in a vehicle. From the standpoint of an observer outside the vehicle the centrifugal force appears as an illusion arising from the failure of the traveller to take account of his acceleration towards the centre. (Aiton, "The celestial mechanics of Leibniz in the light of Newtonian criticism", pg 32)

That said, do you have any sources that would support or contextualize your claim that an inertial/fictitious force is just as real a thing as normal Newtonian forces? --FyzixFighter (talk) 21:24, 11 May 2013 (UTC)

I'm OK with "fictitious" because I know what it means. You can find sources that explain how real it is if you google for "centrifugal force" and "just as real" or "is as real" or something like that. They explain that it's real to observers in the rotating frame, but not present in an inertial frame. That's what it means. We can live with that. Dicklyon (talk) 03:01, 15 May 2013 (UTC)

I agree that keeping the "fictitious" part is important. What causes the tendency of a rotating body to move outward is not force but inertia - the tendency of a body to continue constant velocity in the absence of forces.

There is no outward acceleration experienced by any part of a rotating body or system. All parts of the system are being accelerated toward the centre. Since the notion of an outward or centrifugal acceleration is fictitious, the idea that there is a force tending to cause outward acceleration must also be fictitious. As a force, it is imagined. It is not real. It is false. I think it is very important to make this point to students.

Where the centripetal forces in the rotating system are supplied by gravity, there is not even a fictitious centrifugal effect. So to even talk about a centrifugal force, fictitious or real, where the forces are gravitational, serves no purpose.

The "reactive centrifugal force" is, I believe, also objectionable but for a slightly different reason. In a rotating body or system, there is no outward acceleration and no mechanism by which outward acceleration can occur. So there is no force tending to cause outward acceleration. The third law pair to a centripetal force on a portion of a rotating body or system is, ultimately, a force that contributes to the centripetal acceleration of the rest of the body or system since all accelerations are centripetal. A simple example would be two bodies in gravitational orbit about a common centre of mass. The third law pair to the force of gravity of the earth on the moon is the force of gravity of the moon on the earth. Each force causes the body on which it acts to accelerate toward the common centre of mass. I am surprised that Mook and Vargish would make this mistake (reference footnote 14 -^ Mook, Delo E. & Thomas Vargish (1987). Inside relativity. Princeton NJ: Princeton University Press. ISBN 0-691-02520-7, p. 47.) AMSask (talk) 04:21, 29 December 2013 (UTC)

You say "Where the centripetal forces in the rotating system are supplied by gravity, there is not even a fictitious centrifugal effect." But there is. In the case of a planet experiencing graviational attraction to its sun, the centrifugal force is the apparent force, in the frame rotating with the planet, that keeps it from from falling into the sun. In the rotating frame of a circular orbit, the centripetal and centrifugal forces balance, and the planet does not move (in the rotating frame). Dicklyon (talk) 05:53, 29 December 2013 (UTC)

It is different for gravity. Since the centripetal force is proportional to mass, the observer in gravitational orbit has no sense of a tendency to move outward. The orbiting observer feels/observes no force at all. Gravitational free-fall is, locally (i.e. ignoring tidal effects), physically equivalent to an inertial reference frame. AMSask (talk) 05:33, 30 December 2013 (UTC)

That is not inconsistent with what I said. The local free-fall is due to the balance or equilibrium of forces in the rotating frame. Gravity + Centrifugal = 0. Both terms are proportional to mass. Dicklyon (talk) 05:51, 30 December 2013 (UTC)

So when the centripetal force is supplied by gravity, there is no need to contemplate any forces at all in the rotating frame. There is no tendency for any body to flee outward, which is the centrifugal effect. This is not the case where the centripetal force is supplied by mechanical or electro-magnetic forces.AMSask (talk) 12:56, 30 December 2013 (UTC)

In a rotating frame there is always a centrifugal force acting on every mass (except for masses on the axis of rotation). Martin Hogbin (talk) 17:42, 1 January 2014 (UTC)

If you were orbiting the earth in a box that prevented you from making external observations, you would not need to invent the centrifugal force to make the laws of motion work. If you were in rotational motion due to a centripetal force supplied by anything other than gravity, you would have to invent centrifugal force to make the Newtonian laws work. That is all I was saying. AMSask (talk) 02:10, 2 January 2014 (UTC)

I don't see how gravity is special in this respect, unless you mean in the curved spacetime of GR where there is no gravity per se but other forces such as electromagnetic might still make things orbit. Dicklyon (talk) 02:16, 2 January 2014 (UTC)

AMSask, this article is about Newtonian mechanics. I do not know how centrifugal force is treated in GR but that is irrelevant for this article. In Newtonian mechanics, if you knew that you were working in a rotating frame then you would have to apply a centrifugal force to every (off-axis) mass in your box. If you then observed the mass to be stationary relative to the rotating frame you would then be able to deduce that there was an equal and opposite force of some kind acting. In your example this would be gravity. If you did not know that the frame of the box was rotating you would (erroneously) work in an inertial frame and wrongly conclude that there were no forces of any kind acting. This conclusion would be disproved as soon as you applied any other forces to your mass.

This is getting a bit off the main topic here. I overstated the original point - the CF can be used in the rotating frame of reference to explain why gravity does not appear to be working as you correctly point out. My point, clumsily stated, was that if you were in this box that was in gravitational orbit (ignoring tidal effects) you would not need to contemplate CF OR Gravity to explain any of the phenomena observed. However, if the box was rotating with a tether or electromagnetic force supplying the centripetal force, this would not be the case. With gravity, you never "feel" a centrifugal effect. Since it would not be apparent that there is any force acting at all, it is only if the rotating observer is informed that there IS a gravitational force that he would have to invent the CF in order to make Newton's laws work. There is no difference, locally, between an inertial frame and gravitational orbit (ignoring tidal effects) so I am not sure how you could do any experiment to determine that your free-falling box was not an inertial frame. AMSask (talk) 00:08, 7 January 2014 (UTC)

In Newtonian mechanics in an inertial frame the inertial CF is a mathematical certainty. Its value and direction and the body on which it acts is always clearly defined. That is why this concept of CF is now almost universal. Martin Hogbin (talk) 20:06, 6 January 2014 (UTC)

Did you mean to say "in a non-inertial frame", perhaps? Otherwise I don't understand the reference to "mathematical certainty". Why would CF be needed in the inertial frame? AMSask (talk) 00:08, 7 January 2014 (UTC)

Yes, my stupidity, I meant 'rotating frame'. The conversation is getting a bit off topic, as you say. It think that we agree that the inertial CF is a well-defined force that is used today in mathematics, physics, and engineering. I am happy to leave it as that.

From your conversation with Dick below I imagine that you agree with me that the reactive CF is an ill-defined, obsolete, and unhelpful concept. Martin Hogbin (talk) 10:07, 7 January 2014 (UTC)

Direction of the reaction to centripetal force. Correction needed.

The article as it is currently written contains a major error regarding the direction of the "reaction" force or third law pair force to centripetal force. The article states:

In accordance with Newton's third law of motion, the mass exerts an equal and opposite force on the object. This is the reactive centrifugal force. It is directed away from the center of rotation, and is exerted by the rotating mass on the object that originates the centripetal acceleration.

The error is in bold. The reaction force is not necessarily directed away from the centre of rotation. This needs to be corrected. I gather my attempt to correct it was not greeted with approval by Dicklyon. The fact is that the direction of the reaction force in relation to the centre of rotation depends on what you are dealing with. In many cases the reaction force is another centripetal force (eg. two bodies in gravitational orbit). The fact that it can be toward or away from the centre of rotation depending on the geometry of the rotating system, is also another reason that it should simply be referred to as the reaction force to centripetal acceleration rather than the centrifugal reaction force, but that is another issue.AMSask (talk) 04:12, 2 January 2014 (UTC)

I do understand your point. The force directed toward the rotating body may not be "outward" from the point of view of the other body if the other body in on the other side of the center. But to say so without a source with be what we call "original research". See WP:NOR. So find a source, and let's incorporate what it says. Dicklyon (talk) 04:16, 2 January 2014 (UTC)

I am not sure it qualifies as original research. It is basic first year mechanics. But this particular point is explained very clearly and nicely in by Scott, David, in Centrifugal Forces and Newton's Laws of Motion, Am. J. Physics, Vol. 25, 325 (1957) which can be found here: http://www.deepdyve.com/lp/american-association-of-physics-teachers/centrifugal-forces-and-newton-s-laws-of-motion-0bO8fgiEUy AMSask (talk) 06:54, 2 January 2014 (UTC)

The specific quote from Scott 25 Am. J. Phys. 325 that I was referring to reads:

"A mass A is moving in a circle; a centripetal force must therefore be acting on A. What is the reaction to this force? The reaction in general will be a force which causes a mass B to move in a circle. For example the reaction to the force which moves the electron around the proton in the hydrogen atom is the force which moves the proton around their common center of gravity. The same situation is revealed in the case of the moon and the earth, or the figure skater and her partner as they whirl about together. The reaction to a centripetal force is not a centrifugal force but another centripetal force. Though Newton's third law is used in statics, its real significance is in dynamics. When a force acts to accelerate one mass then there is always a reaction which is accelerating another mass in the opposite direction.". AMSask (talk) 22:37, 2 January 2014 (UTC)

What is conversation shows is how unhelpful the concept of reactive centrifugal force is. If people who understand the subject cannot agree what are newcomers to the subject to make of the concept? Martin Hogbin (talk) 10:15, 2 January 2014 (UTC)

In order to correct the erroneous suggestion that the reaction force to a centripetal force is always centrifugal, I would propose that the first part of the section entitled "Reactive centrifugal force" be changed to read as follows:

==Reactive centrifugal force==

Main article: Reactive centrifugal force

A mass undergoing curved motion, such as circular motion, constantly accelerates toward the axis of rotation. This centripetal acceleration is provided by a centripetal force, which is exerted on the mass by some other object. In accordance with Newton's third law of motion, the mass exerts an equal and opposite force on the object.

How one characterizes the direction of this reaction force depends on the geometry. In situations where reaction force is directed away from the centre of rotation at its point of application, it may be referred to as the "centrifugal reaction force". However, the reaction force to a centripetal force is often not centrifugal but is another centripetal force:

"A mass A is moving in a circle; a centripetal force must therefore be acting on A. What is the reaction to this force? The reaction in general will be a force which causes a mass B to move in a circle. For example the reaction to the force which moves the electron around the proton in the hydrogen atom is the force which moves the proton around their common center of gravity. The same situation is revealed in the case of the moon and the earth, or the figure skater and her partner as they whirl about together. The reaction to a centripetal force is not a centrifugal force but another centripetal force."

Comments? AMSask (talk) 03:47, 6 January 2014 (UTC)

Thanks for finding a source and quoting it. I'd make the lead-up to the quote a little more clear, and connect better with the concept of reactive centrifugal force, by pointing out that the reaction force is toward the rotating object in question. Such as "However, the reaction force to a centripetal force, while directed toward the rotating object, is often not centrifugal but is another centripetal force, when the object it affects is also rotating, on the other side of the center of rotation:" Dicklyon (talk) 04:21, 6 January 2014 (UTC)

Actually, the sentence before probably should be removed or modified, too, since the cited source, Signell, clearly defines the reactive cengtrifugal force: "centrifugal force: the reactive force to the centripetal force, to which it is equal but opposite." which doesn't depend on whether or not the "reaction force is directed away from the centre of rotation at its point of application." Dicklyon (talk) 04:26, 6 January 2014 (UTC)

I'd prefer to see the detailed discussion (of when a reactive force is and is not centrifugal) moved to the article of reactive centrifugal force, with just a brief mention in this article that the reaction can be away from the centre, and a link to the detailed article. Dbfirs 06:46, 6 January 2014 (UTC)

In response to Dicklyon's comment: re: the suggestion to add: "However, the reaction force to a centripetal force, while directed toward the rotating object,...". It gets tricky because the reactive force to the centripetal force can be directed away from the rotating object (ie. in cases where the centripetal force is toward the rotating object - eg. rollercoaster doing a loop). And re: "when the object it affects is also rotating, on the other side of the center of rotation". I don't want to be too picky, but since momentum is always conserved, there is always rotating mass on the other side of the inertial centre of rotation. Even where a single body is rotating by itself about a post fixed to the earth, the earth has a finite mass so the earth undergoes a very tiny rotation about an inertial centre of rotation (assuming there was nothing else going on). AMSask (talk) 17:48, 6 January 2014 (UTC)

In response to DBfirs comment: What is important, I think, is that there is always a reaction force to a centripetal force and that it is a real force whose direction is opposite to that of the centripetal force. As G. David Scott pointed out, where a body is undergoing centripetal acceleration due to a centripetal force, one can always point to some other collection of matter (i.e. the rest of the inertial system) that is (collectively) experiencing an equal and opposite centripetal force and (collectively) undergoing centripetal acceleration in the opposite direction. While it may be useful for engineers to analyse only the point of contact between the rotating body and a portion of the rest of the inertial system (eg. the end of a rope) rather than the collective rest of the rotating system, and to treat that as a centrifugal force, that can confuse the physics. It is really a matter of determining which conditions make it convenient to consider the reaction force direction as "centrifugal" (ie. when one wants to look at only a part of the rest of the rotating system). I don't know if we can make an exhaustive list of all the situations in which that would occur.AMSask (talk) 17:48, 6 January 2014 (UTC)

Again, I understand and appreciate your analysis. But you're proposing to replace a POV that has become a minority marginalized POV with an even more obscure POV based on a single 1957 source. Is this progress? Can't we just represent the concept of reactive centrifugal force simply, as it is usually presented, and as is easy to intuitively comprehend, rather than nit-picking it to death? Dicklyon (talk) 18:04, 6 January 2014 (UTC)

And you're right that what I said about the direction is not quite right. What I meant was that the force is directed along the vector from the center toward the rotating object; that is, it is always centrifugal with respect to the object whose centripetal force it is the reaction to; that's not complicated. Dicklyon (talk) 18:18, 6 January 2014 (UTC)

This discussion shows again how ill defined and unhelpful the concept of reactive centrifugal force is. There are no problems that require the use of the specific term reactive centrifugal force, we can always apply Newton's third law. There is no need to and no benefit in giving this force a special name.

When working in a rotating frame, the inertial CF is required. It is precisely defined and it is a new force that does not exist in an inertial frame. A specific name for it is necessary and helpful. Martin Hogbin (talk) 19:45, 6 January 2014 (UTC)

Reply to Dicklyon: The physics is either correct or not. It was an analysis made by a reputable and qualified physicist in a peer reviewed publication. Your statement that this analysis is only accepted by a marginalized minority seems, itself, to be POV. It is not supported by any evidence that I can see. Do you have any sources to support such an assertion?

The 3rd law reaction force acts on the body that applies the centripetal force to the first body. So the force vector originates with that body. It is directed toward the first. So I don't think you can say that it originates at the centre of rotation and points toward the rotating body. It is only if the force originates at a point that is on the same side of the center of rotation as the first body that it points away from the center.AMSask (talk) 20:29, 6 January 2014 (UTC)

The physics in the 1957 paper is fine. But the paper is about how the physics should be presented. It is perhaps unique in wanting to describe the reactive centrifugal force from the viewpoint of the object that it acts upon, rather than the viewpoint of the object whose centripetal force it is the reaction to. This is the POV I speak of. It makes many good points, but does not represent anything like a common viewpoints on CF. I do particularly agree with his opening paragraph. Dicklyon (talk) 06:00, 7 January 2014 (UTC)

I am not sure what you mean by "viewpoint". The direction of any force is the direction that the body on which the force acts will accelerate if there were no other forces acting. AMSask (talk) 06:34, 7 January 2014 (UTC)

Well the direction is not in question, I think, but how it is described is. The 1957 paper wants to call it another centripetal force when the object that it acts on is on the other side of the center; that's fine, it doesn't change the direction of what others call the reactive CF; it's still in the direction from center toward the rotating object, which is what centrifugal means in that context. Dicklyon (talk) 06:42, 7 January 2014 (UTC)

And I have said nothing about where the force "originates", as I don't know what that would mean; centrifugal is simply about the direction (from center toward the rotating object). Dicklyon (talk) 06:00, 7 January 2014 (UTC)

I was referring to the force vector representing the reaction force on the body (call it B) that is applying the centripetal force to the rotating body (A). The direction of the reaction force on B is given by an arrow pointing along a line from the center of mass of B to that of A. If that line passes through the center of rotation, the reaction force on B is centripetal, not centrifugal. This is the problem with calling it a "centrifugal reaction force".AMSask (talk) 06:34, 7 January 2014 (UTC)

Yes, I think we get that. But I don't see it as a real problem, since that direction is centrifugal in the usually understood sense, with respect to body A. Dicklyon (talk) 06:42, 7 January 2014 (UTC)

Even when the effect of the force on which the body acts is to accelerate that body TOWARD the center of rotation? This is exactly the problem! By that standard, we would call the force on the moon by the earth a centrifugal reaction force (ie. a reaction to the force of the moon on the earth that causes it to rotate about the earth-moon barycentre)! AMSask (talk) 12:41, 7 January 2014 (UTC)

Yes, of course, even then! We have agreed that a reactive centrifugal force often acts centripetally on another body; that's not a problem. The mutual gravitational force between Earth and Moon can be described as a centripetal force on each body; but also as a centrifugal reaction force to the gravitational pull on the other body. This may not be the typical way you want to talk about it, but can sometimes be useful. If you've got a massive star that doesn't wobble much, you can calculate the orbit of the planet by assuming a gravitational centripetal force based on the star position being fixed. But then maybe you want to estimate the error in the approximation, so you look at how much wobble the reactive CF would cause on the star; that reactive force would of course be centripetal if you want to look at its direction relative to the star in its wobble motion. Not a problem. Dicklyon (talk) 17:53, 7 January 2014 (UTC)

The reactive force is not directed centripetally in relation to just another body: it is directed centripetally in relation to the VERY BODY that it acts on! In other words, it provides the centripetal acceleration to the body that it acts on. Can you point to any authority that says that the force which causes centripetal acceleration to a body should be referred to as "centrifugal"? AMSask (talk) 20:54, 7 January 2014 (UTC)

With respect to your star/planet example, if you are trying to account for the wobble of the star relative to an inertial point (the centre of rotation of the whole star/planetary system) toward which the star and all its planets are accelerating, why would you want to call any of those forces "centrifugal"? What you are trying to measure, presumably, is the gravitational force between the star and planet. How does calling it "centrifugal" assist your analysis? Not only is it confusing, but there would appear to be no reason to consider the "wobble" to be anything but centripetal acceleration about an inertial point. AMSask (talk) 23:18, 7 January 2014 (UTC)

I think you're just being dense now. Reread what I said. I did not say that calling it centrifugal assists the analysis, and yes I already stipulated that you can consider the reactive CF to be centripetal in the sense that you mean. This is not complicated except as you make it so. Dicklyon (talk) 01:04, 8 January 2014 (UTC)

Keep it simple: Body A moving in a circle due to a centripetal force on it exerts a corresponding reaction force (whether through gravity or otherwise), sometimes called a reactive centrifugal force, on another body B. The direction of this force is aligned with the vector from center toward body A, which is why it's called centrifugal. End of story. Some authorities go on, as you do, and point out that sometimes the force is on a body B on the other side of the center, and that the reactive CF is felt as a centripetal force by body B. That's all good. Not a problem. Not a contradiction. Not a reason to ignore completely the minority usage of those who refer to reactive CF, which is, after all, what everyone feels when they swing a weight around on a rope. Dicklyon (talk) 01:11, 8 January 2014 (UTC)

And yes I understand that many physicists, along with you and Martin, would love for this minor usage to go away entirely, or to have never existed. But that's not the reality of the situation. At least it makes physical sense, even if you don't like the logic of the terminology or find it confusing, compared to other sometimes-seen layman's interpretations. Dicklyon (talk) 01:15, 8 January 2014 (UTC)

The concept of a centrifugal non-Newtonian force a perfectly legitimate concept in physics. The fact that it is not a real force in the Newtonian sense does not mean that it is not a real phenomenon. The reactive force to a centripetal force is both a real phenomenon and a real force in the Newtonian sense. But the term "centifugal" in relation to the reaction force is misleading at best and erroneous and confusing at worst. It is particularly misleading where the ONLY force on the body in question is a centripetal one. To call it "centrifugal" to satisfy some intuitive notion about how the direction "feels" is not physics.

Assigning a direction to a force based on something other than the direction in which the body on which it acts accelerates (or would accelerate if no other forces were acting on it) is not something physicists do. Using your standard we could give it any direction at all. We could call it tangential because in some cases a tension force on a body that arises in reaction to the centripetal acceleration of a body is tangential to a line from the body through the centre of mass. (This occurs, for example, with two steel bars tethered by a thin wire at each end, rotating about an axis through their centre of mass and perpendicular to the rectangular plane. The tension in those wires is a force that is not directed through the centre of rotation but is, in fact, along the wire which is at right angles to the radial direction). So, while the term "centrifugal" may satisfy some intuitive concept, it is NOT a part of mainstream physics teaching. If you can find even ONE reputable physics text used for first year university mechanics that endorses the term, I would be very surprised. If you can't, I don't think that an article on CF should give more than a passing mention of it.AMSask (talk) 19:12, 8 January 2014 (UTC)

I don't really see what you're going on about. We mostly agree. But you seem to be suggesting that we disagree on what's real, or the direction, or something, which we don't. And you seem to think that I have an opinion about whether it's a good idea to call the reaction force to a centripetal force a reactive centrifugal force. But I don't have an opinion about whether it's a good idea that people call it that. I just note that that's what it's called in a lot of books and papers, especially older ones. So we need to represent that. But I do disagree with your strawman "Using your standard we could give it any direction at all." I don't have a standard, just an explanation that if you describe the direction (which we agree on) in terms of where the original rotating body is, that direction is centrifugal (along the line from center of rotation to the body in question), even when it is centripetal with respect to the body that it acts on. It's not complicated. Dicklyon (talk) 01:24, 9 January 2014 (UTC)

I agree that there should be no more than a passing mention in this article, and not in the lead. It was your addition that gave it greater prominence! Just a brief mention, as suggested by Dicklyon, would be best, with any long discussion of when it exists and when it is useful being relegated to the linked article on the exact topic. My suggestion would be something on the lines of: "When a reaction to a centripetal force acts on another body in a direction away from the centre, this is sometimes called a Reactive centrifugal force. In an inertial frame, this is a reaction to the centripetal accelerating force and should not be confused with the inertial force more commonly called the centrifugal force." Dbfirs 21:05, 8 January 2014 (UTC)

Perhaps the lead could be modified to read: "In Newtonian mechanics, the term centrifugal force usually is used to refer to an inertial force (also called a "fictitious" force) observed in a non-inertial reference frame." I'd prefer to see other uses just mentioned under an appropriate heading lower down in the article. "The term centrifugal force is also sometimes used in Lagrangian mechanics to describe certain terms in the generalized force that depend on the choice of generalized coordinates, and reactive centrifugal force is occasionally used to refer to a reaction force corresponding to a centripetal force." plus perhaps my suggestion above? I think it's time that we stopped arguing and moved towards an improvement to the article. The long discussion about when the force exists and when it is useful can all go in the sub-article on the minority usage. Dbfirs 21:38, 8 January 2014 (UTC)

Keeping it brief is a great idea. But keeping the descriptions of the other uses of the term CF correspondingly brief is also a great idea, since this is intended to be a summary-style article to get people to the article on the concept that they care about. It has to explain more than a disambig page does, so that people will be able to figure out which concept that they want, when they come in with the typical misconceptions that don't fit any physical meanings at all. Dicklyon (talk) 01:24, 9 January 2014 (UTC)

But this section was about a proposed "correction" where no correction is necessary. Dicklyon (talk) 01:24, 9 January 2014 (UTC)

So where you have two bodies in gravitational orbit about their common center of mass, you do think it is correct to still call the force on one body centrifugal even though there is ONLY one force on each and each force causes the body on which it acts to undergo centripetal acceleration? How does one determine which force to call centripetal and which to call centrifugal?AMSask (talk) 06:03, 9 January 2014 (UTC)

It's mutual and symmetric. The reactive centrifugal force of each is centripetal on the other. It's not complicated. Dicklyon (talk) 06:12, 9 January 2014 (UTC)

!!Ok. Let's put that quote in the article: "The reactive centrifugal force of each is centripetal on the other." That sure clears everything up. Sorry I was so dense.AMSask (talk) 06:59, 9 January 2014 (UTC)

Let's not. This is pure OR. Martin Hogbin (talk) 15:05, 9 January 2014 (UTC)

Agreed, let's don't. Though the source does say "The reaction to a centripetal force is ... another centripetal force." (in the context of two objects orbitting a mutual center). I think we can all agree when it's stated that way. I understand that you prefer not to call it a "reactive centrifugal force", as that describes its direction with respect to the object on the other side of center, the one that the reaction is to, as opposed to the one the reaction acts on. That's life. Dicklyon (talk) 04:14, 11 January 2014 (UTC)

Well, it is good to see that we all agree on something!

We appear to be using different naming conventions for force direction. One could argue that we should call a north wind a south wind because it provides a southward force. But the convention is to name the direction of the wind as the direction opposite to the direction of the force it provides (i.e opposite to the compass direction toward which the air flows). We just have to know that and everything is clear.

For forces, the direction is established by Newton's second law of motion F = ma. That is to say that the direction of the force on m is the same as the direction of the acceleration of m, (m being the mass on which the force acts). It is about 300 years too late to replace this with another convention. If you want to talk about the direction of a force in relation to something other than the direction given by F = ma you can do that, I suppose. We could call it the anti-Newton convention. But I question the wisdom of trying to do that and I don't see the place for that convention in a WP article, even if such usage may be found in some obscure publications. There has been confusion in writing about centrifugal force since pre-Newton times. Even Newton's views changed significantly during his lifetime. Our purpose should not be to perpetuate the confusion. AMSask (talk) 19:57, 11 January 2014 (UTC)

Is that not where we started. One definition is ill-defined, obsolete, and confusing whilst the other is well defined, current, and useful. We should not be giving them equal treatment in WP. Martin Hogbin (talk) 23:49, 11 January 2014 (UTC)

One has a 9 KB article, the other 35 KB. Seems OK. Dicklyon (talk) 02:57, 12 January 2014 (UTC)

It is not the volume of text that matters, it is the confusion caused by this article that is the problem. I would have no objection to increasing the volume of text in the RCF article (once you can agree on what exactly it is). What would you say to merging this article with the FCF article but leaving the RCF article? Martin Hogbin (talk) 23:20, 12 January 2014 (UTC)

You're not saying we have a disagreement on the direction of any Newtonian force, are you? Or that we get to change the terminology used to describe that direction? See my latest edit to your edit to Reactive centrifugal force. Is there anything ambiguous, unclear, or controversial about that? Dicklyon (talk) 02:54, 12 January 2014 (UTC)

Take the two-body gravitational orbit rotation. We are in agreement that the direction of the centripetal force on body A is the direction of the centripetal acceleration of body A. But you seem to want to label the reactive force, the force that is causing body B to undergo centripetal acceleration, a centrifugal force. Why on earth anyone would think that makes anything clear is beyond me. You seem to be trying to introduce a new convention for the direction of the reaction force that is different than the convention for all other forces. AMSask (talk) 21:29, 12 January 2014 (UTC)

Or perhaps you do disagree, since you reverted? Please say why. Dicklyon (talk) 03:51, 12 January 2014 (UTC)

I don't follow what you are asking.AMSask (talk) 21:29, 12 January 2014 (UTC)

Plug-holes

is it true dat centripetal force only happens in de southern hemisphere. I read dat before and in Europe the direction changes and dats we we have centrifugal force 109.152.255.99 (talk) 21:25, 29 August 2014 (UTC)

I've moved your question to the end and given it a title on the assumption that it was a genuine question.

You seem to have mis-read something because centrifugal force, if it exists, happens wherever something is turning.

You have probably read that the Coriolis force from the rotation of the Earth acts in the opposite direction in the southern hemisphere. This is true, and accounts for the direction of winds round a depression, but this force is negligible on the scale of the rotation of water down a plug-hole. It is swamped by remaining rotation of water from the way the sink or bath was filled. Dbfirs 22:44, 29 August 2014 (UTC)

Lagrangian mechanics

Does the mention of Langrangian mechanics refer to the inertial force or the equal and opposite reaction force, or can it be to either? This is a strange sentence in an introduction. Lagrangian mechanics in mathematics is an alternative way to treat the same physical effects that are treated in classical mechanics. 83.43.96.185 (talk) 09:52, 4 September 2014 (UTC) Sorry I didn´t see the final section. But I think this is just the inertial force. 83.43.96.185 (talk) 09:58, 4 September 2014 (UTC)

...and a reaction force corresponding to a centripetal force.

The last phrase in the opening paragraph calls centrifugal force both a "reaction" and a "force". It's a reaction to the nonzero net fundamental force's attempt to change the motion of an object. It could be said that a mass "reacts" to the nonzero net fundamental force on it by simultaneously 1) accelerating and 2) generating the resistive pseudoforce (with magnitude equal to the magnitude of the nonzero net fundamental force).

As far as calling it a "force" goes, we're intermingling talk about both fundamental forces and pseudo forces in the article and being ambiguous about it. In an article on this topic, distinguishing between them clearly is of vital importance. We should be careful to be specific when we use the word "force". We should always be clear about whether we mean a fundamental force or pseudoforce. Otherwise, we confuse readers and ourselves.

So, what does the phrase mean by "force"? Should the phrase be "...and a reaction (fundamental) force corresponding to a centripetal force"? Or should it be "...and a reaction (pseudo) force corresponding to a centripetal force"?

Montyv (talk) 04:43, 11 May 2013 (UTC)

Sorry, but I think you are confusing two uses of the phrase "centrifugal force". The centrifugal force that is a reaction force to a centripetal force is categorically different from the centrifugal force that is a pseudo-/inertial/fictitious force. Note that the sentence states clearly that these are two distinct concepts. The first does not vanish in an inertial frame and acts on a different object than the centripetal force, whereas the second does vanish in an inertial frame and appears to act (but only in the rotating frame) on the same object acted upon by the centripetal force. Also, if you follow the wlink for "reaction", you'll see that it goes to Reaction (physics) which means we are talking about the classical Newtonian definition of force, which pseudo-forces do not satisfy. Pseudo-forces only arise when we try to bootstrap Newton's 2nd law of motion to accelerating frames. --FyzixFighter (talk) 20:44, 11 May 2013 (UTC)

'...I think you are confusing two uses of the phrase "centrifugal force"'. This is going to happen all the time as long as the article mentions more than one type of CF as mainstream. Martin Hogbin (talk) 20:17, 6 January 2014 (UTC)

Two "categorically" different forces? Reading the centrifugal clutch page I can see the two different effects in question. The inertial force acts on the inner shaft and when the inner shaft makes contact with the outer shaft a centrifugal force then acts on the outer shaft. But is that a different force? Technically yes, as it acts on a different body. But can we have the reactive centrifugal force acting on the outer shaft without first having the inertial force acting on the inner shaft? 83.42.238.255 (talk) 10:31, 5 September 2014 (UTC)

Reverted

"centrifugal and reactive centripetal forces are opposite in direction to the centripetal force." This is how the lede now reads after I fixed it, and is exactly correct. Clearly centrifugal and centripetal force point in opposite directions. Clearly centripetal and reactive centripetal force point in opposite direction (as they are an action-reaction force pair). Hence, the sentence as I corrected it, was wrong. It is now right. SBHarris 04:30, 13 September 2014 (UTC)

Certainly the centripetal force and the reaction to it point in opposite drections, which is why the reaction force is call centrifugal. The fictitious centrifugal force, however, is unrelated to any centripetal forces. It is directed outward from the center of rotation of the rotating reference frame, which need not be related to any centripetal effects going on. And where you wrote "reactive centripetal force" I think you meant the reaction to the centripetal force, which is what's call a reactive centrifugal force. Anyway, that sentence trying to describe the directions of not-very-related forces had no chance of being right in general, so I just removed it. It could be put back if qualified to frames rotating with the moving object, about the center of rotation, but hopefully such detail can be omitted from the lead. Dicklyon (talk) 05:03, 13 September 2014 (UTC)

Yes, I think the safest thing to do is to remove the sentence. SBHarris and I were obviously interpreting it differently, and each of us knew we were correct. Dbfirs 08:11, 13 September 2014 (UTC)

Okay, I had to go and read the unfortunate Wiki article reactive centrifugal force to figure out what in the world you were talking about. Somebody (not clear who) has decided that good old centrifugal force should get a new name "reactive centrifugal force" if it is provided by a contact force like in a centrifuge. Or by the pull of a tether or rope in a tether-ball. And yes, I think it's best to just remove reference to this in the lede. It's not only not a common term, but it's a bad one for several reasons.

1) However fictitious centrifugal force sometimes is, it is necessary in a rotating frame (such as on Earth while going around the Sun) to "explain" why the Earth is not pulled into the Sun by the gravity which we know is pulling them straight together. Giving that force a new name once it is provided by mechanical stress (say a tether on a whirling tetherball) would be sort of like saying that in Newton's mechanics an apple falls because it is pulled downward by gravitational force, but once it hits the ground and stops, that force in the same direction now becomes a "reaction force weight" (in opposition to a primary push upward by the ground, which provides an action force that wasn't applied to the apple before). It's a lot easier to just assume the gravitational force on the apple doesn't change through fall and at rest, though of course the stresses do. But we should not rename gravitational force because it now helps to cause stress in an object that has stopped falling because it is opposed by a contact force.

2) The other reason not to say some force is "reactive" is that it takes the third-law concept of an "action-reaction" force pair (to which I don't object) and pushes it farther into pretending that we can even identify which end of the force-pair is the "action" force and which the "reaction" force. Of course we cannot. You can chose any side you like for these terms. Standing on the ground, I would be justified in considering my weight to be an "action force" or "primary force", and the upward push from the ground to be the "reaction force." Who is say that is wrong? Similarly, I demand that this "reactive centrifugal force" of yours be renamed to "active centrifugal force", and let us then have it opposed by a "reactive centripetal force" that is provided in the inward direction, due to the reaction of the stressed tether (or stressed centrifuge wall) in response to the primary "force action" of the ball pushed by primary centrifugal force outward, and against it. Why not? SBHarris 03:57, 14 September 2014 (UTC)

I agree that "reactive centrifugal force" is not usually a helpful term, especially when it is confused with "fictitious" centrifugal force that we are all familiar with. I wouldn't use it at all, but, unfortunately, some texts do. I agree that the distinction between action and reaction depends on the frame of reference, though your last scenario leads to error when pushed too far. Dbfirs 07:54, 14 September 2014 (UTC)

What error? I stand on the ground and regard my weight as the primary force, and the ground pushing back as REaction. In my rotating space station, I'm entitled to view my centrifugal weight on the deck as primary, and the deck's centripetally directed force pushing back against my feet as REactive to it. But you insist it's the other way, with my centrifugal weight as REactive. Sorry, but there's no physics to make me view the force-pair that way. All THAT does, is implicitly require me to view the problem from the non rotating frame, and (since I'm on the space station) I refuse to. SBHarris 17:49, 14 September 2014 (UTC)

I was referring to the error in your last scenario, not your first. I'm quite happy with use of "fictitious" centrifugal force in a space station or reducing your weight at the equator, provided that you make clear that the analysis is valid only within limits. In those cases, the limits are fairly obvious. You scenario of a ball rotating on a tether is problematic because it is normally viewed from outside the reference frame. Dbfirs 19:45, 14 September 2014 (UTC)

Dbfirs, you say that some texts do use the term,"reactive centrifugal force" but they are very few and far between and becoming increasingly less common. The policy of WP:due weight should be applied here and the concept of reactive centrifugal force relegated to the history section. The only centrifugal force taught and used today, in physics, mathematics, and engineering is the inertial (fictitious) one. Martin Hogbin (talk) 12:39, 14 September 2014 (UTC)

No. Recall that this is the summary-style article to help people find which concept they're looking for. And even though the fictitious force is the main way it's taught in physics, the other is still around and used in various places, sometimes only implicitly, as in the centrifugal force you feel from the tension of a rope when you swing a weight around, which is very often called centrifugal force. Here is another modern physics book that calls the reaction force the centrifugal force. Dicklyon (talk) 14:26, 14 September 2014 (UTC)

So you may have found a book (can you quote the relevant section please) but you have to weigh that against the vast majority of, physics, engineering, and mathematics books which only use the modern concept of the term. There are probably more books which use the term incorrectly to refer to a supposed force acting on rotating bodies, but that do not mention a rotating reference frame. There are books which say that the Moon landings were fake but we have to weigh those against the currently accepted view that they were not. The generally accepted view regarding centrifugal force is that the term should only be used to describe the inertial force, to avoid the confusion of having one name for two different things. It can be a confusing subject for beginners to understand and that last thing that we want to do is to add to that confusion.

Note that I am not saying that we should not mention reactive centrifugal force in this article, just that it should be put into its scientific and historical context, along with phlogiston. I am puzzled by your attachment to an outdated, pointless, and confusing concept.

I would never use the term "reactive centrifugal force" (and never did when I was teaching the subject), but some texts do seem to use this term for what I would call a force acting away from a centre of rotation and exerted by a body on its restraint. I agree that the term is confusing. In my own thinking, I do sometimes use centrifugal force as an action force because it can provide an alternative analysis and sometimes a short cut to an answer, but in my teaching I never used the word centrifugal (except to explain the meaning of the word just for interest and in case students met it elsewhere). Dbfirs 20:13, 14 September 2014 (UTC)

I agree that thinking informally in terms of a centrifugal force can be useful for people who understand the subject already but in an encyclopedia we need to be more careful about what we say and consider who our readers might be. There would be many people who want to find out what CF is, that is to say people who do not already understand the subject. For them, giving two answers, including one that is rarely used today, is most confusing and unhelpful. When you look something up, the last thing you want to hear is that it might be this or it might be that. In some cases that might be unavoidable, but not in this case, where there is a clearly preferred meaning.

More expert readers might be interested in the history of the term, or in possible alternative meanings. That is fine, we can talk about other uses in an appropriate section. Martin Hogbin (talk) 20:43, 14 September 2014 (UTC)

The "reactive centrifugal force" concept is not wrong or informal or unphysical; it's just not the usual thing that's call centrifugal force these days. But enough books still do use it this way that to pretend otherwise would be silly. That's why we have this summary-style article to help people understand the difference and find the detailed article on the one they're interested in. I object to the characterization of reactive centrifugal force as "outdated, pointless, and confusing concept"; it is perhaps outdated, or at least out of favor, but it's no more pointless or confusing than the fictitious force in a rotating reference frame. Probably much less confusing to many readers. Dicklyon (talk) 20:51, 14 September 2014 (UTC)

From a point of view of WP Policy we have to give WP:due weight to the opinions of reliable sources. I am sure that the vast majority of reliable sources do not use the concept of reactive centrifugal force. When we discussed this before, I found that some of the references you gave did not actually support the concept of reactive centrifugal force at all. Can you please quote the section from the book you cited that you think uses the term as I am unable to access it.

Regarding the physics, reactive centrifugal force is outdated because it is very rarely used any more (if it ever was). It is pointless because all forces have an equal and opposite reaction and we do not give special names to them all. There is no benefit in giving the reaction to the centripetal force a special name, in fact doing so complicates things by suggesting that there is something special or unusual about centripetal force. This is not the case, the centripetal force a force like any other, it can be the tension in a string or electrostatic, magnetic, or gravitational in origin, the kind of force that most students are already familiar with.

Use of the term 'centrifugal force' to mean anything other than the inertial force is deprecated in most educational establishments. Dbfirs states above that he never used it when teaching. Experience has shown that the best way to teach elementary physics and engineering is to work in an inertial frame and apply Newton's laws; the introduction of a special force, created because things rotate, just confuses people. (Rotating reference frames are a different thing, in such frames centrifugal force is anew and necessary force). Martin Hogbin (talk) 14:59, 15 September 2014 (UTC)

SBharris, Your argument would seem to be upheld by Roche. See page 403 in the Roche reference. http://www.marco-learningsystems.com/pages/roche/Motion_in_a_circle_pdf.pdf There is no priority over which is the action and which is the reaction. They both call each other into existence. 94.173.45.184 (talk) 10:27, 15 November 2014 (UTC)

I'm sure I can find an old book that mentions the phlogiston theory. That doesn't mean that we should put it forward as a current theory in Wikipedia. The Roche viewpoint is OK provided that we remain in the rotating frame. Dbfirs 12:14, 15 November 2014 (UTC)

DBfirs, My mistake was in not making it clear from the outset that the reactive centrifugal force pre-supposes a rotating system. I will correct that now. 94.173.45.184 (talk) 17:52, 15 November 2014 (UTC)

How do you feel about that now? It's more than just a matter of point of view. The physical interaction is not frame dependent, but the rotation does have a distinct point of origin.94.173.45.184 (talk) 18:10, 15 November 2014 (UTC)

I would have preferred to retain the emphasis on the rotating frame of reference. Such a point of view is strongly deprecated in modern rotational dynamics at elementary level where real forces in an inertial frame are normally considered. Dbfirs 21:34, 15 November 2014 (UTC)

DBfirs, Remember, the section in question is about the reactive centrifugal force, a real physical effect which is frame independent. I appreciate what you are saying and I had to think about it. The Roche article mentions how the inertial centrifugal force is the cause of the interaction with the constraint. If we were to emphasize that the inertial force is only observed from the point of view of the rotating frame, people might then ask 'how does it then cause a real effect which can be viewed from any frame of reference?'. I do know however what you are saying. You are saying that the physical effect which is described in the rotating frame of reference as an inertial centrifugal force is the effect which pushes or pulls on the constraint, calling into existence the action-reaction pair. You are saying that the physical effect is there in any frame but that it can only be called an inertial centrifugal force in the rotating frame. I tried to avoid dealing with that in the section for fear that it would become top heavy. If you were to reintroduce the term 'rotating frame of reference' you would have to explain that the action-reaction pair is called into existence because of an interaction between the constraint and an inertial effect which is known as 'centrifugal force' in the rotating frame of reference. I try to avoid that level of detail, knowing how most readers intuitively understand the concept of inertial centrifugal force anyway. But by all means have a try. 94.173.45.184 (talk) 21:57, 15 November 2014 (UTC)

No, it's the interpretation that is restricted to a rotating frame of reference. In an inertial frame only Newton's laws are needed, with no mention of the word "centrifugal". Dbfirs 22:07, 15 November 2014 (UTC)

So what would you prefer to say is causing the push or pull on the constraint?

When it occurs, it's just the reaction to the centripetal force which is a real force in both an inertial frame and a rotating frame. Dbfirs 23:02, 15 November 2014 (UTC)

But what causes the interaction with the constraint? 94.173.45.184 (talk) 23:58, 15 November 2014 (UTC)

I have reverted to before the introduction of the too-narrow concept of a "constraint" two days ago. This would seem to be trying to remove things like gravitational force as a mechanism for a reactive centrifugal force, yet that is an important case often found in books. Dicklyon (talk) 22:07, 15 November 2014 (UTC)

The reactive centrifugal force does not exist in conjunction with gravity. The reactive centrifugal force arises when a body in a rotating system physically contacts and pushes or pulls on a constraint. In gravity situations, only the inertial centrifugal force is involved and it is not an equal and opposite reaction to gravity. In gravity situations the reaction force to gravity is another centripetal force on the other side of the centre of rotation, connected with another planet. You should undo your reverts otherwise readers will think that the reactive force can arise in conjunction with gravity, and this will confuse them totally since it doesn't make any sense. 94.173.45.184 (talk) 22:23, 15 November 2014 (UTC)

That's wrong. Gravity is not special in this sense. Neither are contact forces. Read some of the cited sources (e.g. this one). In a two-body situation, the reactive centrifual force is centripetal from the point of the view of the other body, but it still points in the direction that is outward with respect to the body that the first centripetal force acts on, and is still referred to as a reactive centrifugal force. In a multi-body problem interpreting the reactive centrifugal force as centrifugal doesn't make much sense. Dicklyon (talk) 23:19, 15 November 2014 (UTC)

Mook's concept is nothing like Roche's concept, and therein lies a large part of the problem. Mook's concept is not about centrifugal force in any shape or form. Mook has got it all wrong. 94.173.45.184 (talk) 23:57, 15 November 2014 (UTC)

Perhaps it's time to refer to centrifugal force by its truer name - centrifugal inertia

Being that 'centrifugal force' is not a true force, and instead is a reaction to centripetal forces, the name is a misnomer and creates much confusion, and many arguments, between those who do not fully understand the mechanics thereof. I propose that changing the name will help to alleviate some of the confusion and make centrifugal inertia an easier concept to understand.

Perhaps it is time to start calling it, more correctly, 'centrifugal inertia'.

--Seschenburg (talk) 14:20, 25 October 2014 (UTC)

Unfortunately, we don't get to decide what things are called. The article attempts to explain what most other people, and many text books, mean by the term. Our article on the Coriolis force has been renamed "Coriolis effect", so I suppose we could rename this article "Centrifugal effect", but we would still have to mention that is it commonly called a force. Dbfirs 16:22, 25 October 2014 (UTC)

Besides, not all forces in an accelerated frame are reaction forces from contact that produce G-force acceleration, and stress. In Newtonian mechanics, the man weightless in the falling elevator is kept in his accelerated frame by the force of gravity on him, which, as usual, he can't feel (he doesn't feel it on the ground either, but instead, the reaction force of weight).

"Inertia" is not a force, but a property of mass that requires a force if it is to be accelerated. In the frame of the falling elevator there is no acceleration, so no force is required (that force only arises in the ground frame). Likewise contact forces causing weight (or relative accelerated motion) in a linearly accelerated or rotating spaceship need explaining in the ship frame, so inertia and a "fictitious force" is how we do it. But fictious forces aren't always fictitious. They can be thought of that way when causing relative motion-- you can invoke a fictious force causing your fall toward the back of your accelerated ship. But these forces result in real contact forces when you hit the ship wall, and are then, in your new frame, half the action-reaction pair employed in overcoming inertia. Interestingly we have names for centrifugal and Coriolis and even Euler forces, but in linear systems the best we do for a name is "g-force", by which we mean reaction force to g-force accceleration. Sticking "inertia" into the names of these things isn't all that helpful, though it is useful in expaining their origin.SBHarris 18:31, 25 October 2014 (UTC)

Another pesron is utterly confused by this unhelpful article. It is time to change it. Martin Hogbin (talk) 12:46, 15 November 2014 (UTC)

It would be more awkward to call it the "Reactive force known as centifugal force", or "Centrigual force in reaction to a centripetal force". We do in general have to decide what to call things, and this particular centrifugal force is often found with "reaction" or "reactive" in some such construct. Do you have a better idea what to call it? Further, your premise that 'centrifugal force' is not a true force, and instead is a reaction to centripetal forces is fucked up. The reaction force to a centripetal force is a true real force, as true and real as the centripetal force that it is the reaction to. The other CF is the fictitious one. The article should strive to make this clear if it is not already. Dicklyon (talk) 22:27, 15 November 2014 (UTC)

Dicklyon, And your premise that the reactive centrifugal force concept applies to gravity is also dead wrong. It doesn't. It only applies to contact forces. While I agree with you that we need to use some kind of name to describe the concept, you are causing confusion here by mixing the concept in question up with orbital mechanics. It has got nothing to do with orbital mechanics. That's why Martin Hogbin has a point. If we were to scrap the name reactive centrifugal force altogether, then we could at least discuss the effect in question in isolation, without messing it all up by getting it all confused with gravity and orbital mechanics.94.173.45.184 (talk) 22:39, 15 November 2014 (UTC)

Wrong; see my response in the section above, and read the cited sources. It applies equally to gravitational forces. Dicklyon (talk) 23:27, 15 November 2014 (UTC)

And I do realize the Martin has a point, but you seem to be missing it. His point is that the traditional "reactive" viewpoint on CF is no longer the viewpoint favored by physicists. I don't disagree. Yet it is still a valid physically meaningful concept that is commonly used. We need to help readers understand the difference. Dicklyon (talk) 23:31, 15 November 2014 (UTC)

Dicklyon, The problem is that the term 'reactive centrifugal force' was invented by wikipedians in order to artificially segregate the real physical effects from their inertial sources, and that was because of a clash between those editors who saw importance in the real physical effects and those editors who wanted to think of centrifugal force as only being an artifact in a rotating frame of reference. I agree with your argument that it is very helpful to have a name for the purpose of discussions, but then editor Amsask came along with Mook trying to argue that reactive centrifugal force doesn't even exist as a concept, never mind as a name. Mook was of course talking about something completely different. He wasn't talking about the reactive concept relating to constraints, which is what Roche was talking about. It's one thing to invent a name to cover a particular concept, but once we can't even agree on what that concept is, then it's time to scrap the name and go back to the drawing board. I would have agreed with you on 'reactive centrifugal force' until you started to get it all mixed up with Mook. And neither is this anything to do with history. Reduce it all to one single article on centrifugal force and treat all the facets in separate sections. A section on physical constraints, a section on rotating frames, a section on orbits, polar coordinates, and Lagrangian. In fact, this article alone would be sufficient. You could scrap the reactive force article and the rotating frames article because both of them are particular facets of the subject. You could import stuff from those articles to this article. Have a look at my comments on FyzixFighter's talk page. 94.173.45.184 (talk) 09:54, 16 November 2014 (UTC)

94.173.45.184, I do not agree that the term 'reactive centrifugal force' was invented by wikipedians but is certainly is very rarely used these days and it is the cause of endless confusion. That is why it is not used. There is general agreement in teaching the subject that it is best to start explaining circular motion in an inertial frame only. When we do this, there is no need to invent a new force called 'centrifugal force' we need only have centrpetal force to explain everything that happens. Of course there is, as always, a reaction force to the centripetal force but giving this a special name serves no useful purpose.

When we start to work in rotating frames, we have to invent some new forces unless we want to change the laws of physics. At that stage only should we mention centrifugal force. You can see on this page how having two meanings for one term (one of which is unnecssary and pointless) continues to cause confusion. Martin Hogbin (talk) 11:38, 16 November 2014 (UTC)

Certainly the Mook meaning is unnecessary and pointless. Mook seems to think that the centripetal force caused by the Earth's gravity acting on the Moon is a centrifugal force from the perspective of the Earth because it acts away from the Moon on our side of the origin. How wrong could anybody be? Centrifugal force is always considered outwards from the origin, not across the origin. That's a side issue though. The main problem as I see it comes down to the fact that there is a real centrifugal force acting in physical constraint situations, whereas most books nowadays say that centrifugal force is only an artifact of a rotating frame of reference. So rather than trying to rationalize with and reconcile this dilemma, they chose to split the wikipedia article into two. I can't see a way out, because every time the thorny question arises as to what causes the string to stretch in the first place, agreement breaks down. Roche put it nicely on page 403. But in answer to Roche's explanation, one editor mentions phlogiston and another editor muddies the waters by turning up with Mook along with a whole new meaning for the term 'reactive centrifugal force'. I think the first priority is to focus the discussion on what stretches the string in reactive centrifugal force cases. If a consensus can be reached on what stretches the string, then I think that should bring the discussion to a satisfactory conclusion. I think the cause of the stretching is the main sticking point. 94.173.45.184 (talk) 13:01, 16 November 2014 (UTC)

94.173.45.184, the physics of the subject is perferctly well understood and there is no mystery what stretches a string in a rotating system whem measured in an inertial frame or in a rotating frame. I agree with your point abour RCF in gravitational systems. It just adds to the reasons for not using RCF. As well as being unhelpful and confusing, it is now ill-defined.

However bad and unhelpful RCF may be though it is mentioned in a few text books so we should not expunge it completely from WP. Martin Hogbin (talk) 09:39, 17 November 2014 (UTC)

Straw poll on removing 'reactive centrifugal force' as a current alternative meaning

Just to be clear I have no objection to keeping a historical section on this usage, with a link to the main article on it, but I do not think it should be treated as a current meaning of the term. Martin Hogbin (talk) 12:46, 15 November 2014 (UTC)

• Remove Martin Hogbin (talk) 12:46, 15 November 2014 (UTC)
• Remove The concept is confusing and, at least in the case of forces acting between two bodies at a distance, wrong. Mook's example that is cited is just wrong. In the two body gravitational rotation example of the sun and earth that Mook uses, all forces are centripetal. The reaction to the force on the earth by the sun is the gravitational force on the sun by the earth. The direction of each force is determined by the direction of the acceleration of the centre of mass of each body relative to the centre of rotation of the two-body system (the inertial point). The acceleration of the centre of mass of each body is toward the centre of rotation - ie. centripetal. To even suggest that either of these forces is centrifugal is absurd. Dicklyon is the only one who seems to think that one should be able to call the direction of each of the two forces "centrifugal".AMSask (talk) 14:23, 16 November 2014 (UTC)

• Remove and Merge Removing that means that this article then becomes nearly indistinguishable in function as the Centrifugal force (rotating reference frame) page. Merging the two (that article into this one) would then be in accordance with WP:PRIMARYTOPIC since in the technical world the term "centrifugal force" 99% of the time refers to the fictitious force of rotating frames. --FyzixFighter (talk) 16:31, 15 November 2014 (UTC)

To clarify, what I'm suggesting is only merging centrifugal force and centrifugal force (rotating reference frame) and leaving Reactive centrifugal force off by itself. --FyzixFighter (talk) 22:25, 15 November 2014 (UTC)

To see what life might be like with one merged article, just skim the 20 archive pages of Talk:Centrifugal force (rotating reference frame), especially around 2008 before I sorted it out as a summary-style article and several more specialized articles. Dicklyon (talk) 22:20, 15 November 2014 (UTC)

See my suggestion below. We first remove/downgrade then look at the case for merging. Martin Hogbin (talk) 10:08, 18 November 2014 (UTC)

• Keep – there is already an article without the reactive force: Centrifugal force (rotating reference frame). The present article is supposed to be a summary-style article to help the reader find the more specific content that they are interested in. That can't be done by removing one of the concepts. Dicklyon (talk) 22:09, 15 November 2014 (UTC)

In view of the existence of separate articles giving fuller details of the separate concepts, I'm inclined to agree that this article should be just a summary, perhaps with even clearer links to the separate detailed articles. Dbfirs 22:40, 15 November 2014 (UTC)

Please note that I said above, 'Just to be clear I have no objection to keeping a historical section on this usage, with a link to the main article on it'. Martin Hogbin (talk) 01:25, 16 November 2014 (UTC)

• Scrap Initially I said merge. That's because I was taking my concept of reactive centrifugal force from Roche. But there's no point in having a special article on reactive centrifugal force if we can't even agree on what it is. Roche has one concept of reactive centrifugal force. Mook on the other hand has a totally different concept of it. Mook's concept of reactive centrifugal force is nothing like Roche's concept of it. Mook talks about the the centripetal force that the Earth exerts on the Moon due to gravity as being the equal and opposite reaction to the centripetal force that the Moon exerts on the Earth. It's a completely different concept nothing to do with the Roche concept, and not even anything to do with centrifugal force. And let's be honest about it, there's not a single source that specifically uses the term 'reactive centrifugal force'. The term was invented by wikipedians. I would have been happy enough to play along, so long as we knew what situations we were treating, and I thought I had pretty well got it explained in terms of stretched strings and normal reactions on surfaces acting as constraints. But Dicklyon then comes along and muddies the waters with the totally unrelated Mook interpretation that lies in the field of orbital mechanics. So Martin Hogbin is right. We need to treat the planetary situations and the constraint situations in their own place, within a single centrifugal force article, and not have this chalk and cheese mixed up together in a special article under an umbrella name invented by wikipedians. Even then there will be problems to surmount, because there is a reluctance on the part of some editors to acknowledge the primary cause of the interaction with the constraint that gives rise to the Roche concept of the reactive centrifugal force. How can an inertial force that only exists in a rotating frame cause a real effect that is observable in all frames? That dilemma seems to have been the primary reason why the article was split in the first place, accompanied by the misinformed belief that the two aspects of centrifugal force in question aren't related to each other. But of course they are related. Ultimately centrifugal force is centrifugal force. So good luck to anybody who knows how to sort this mess out. 94.173.45.184 (talk) 00:03, 16 November 2014 (UTC)

94.173.45.184, could you remove one of your replies please. Martin Hogbin (talk) 01:23, 16 November 2014 (UTC)

Thanks.

A proposal

How about we start by editing this article to make clear that inertial CF is the currently accpted meaning ofthe term with a link to the main article on that subject. We could give a brief description of what it is, for the non-technical reader, here. The main article should give more of the mathematical details.

We then have a section called, 'Alternative and historical uses of the term'. This could start with a paragraph of the history of the term and then have sub sections mentioning RCF and the specialist Lagrangian use of the term in robotics.

If, when this is complete, if there is a consensus that the article is still confusing, we should look at merging all three articles into one, or maybe two. Martin Hogbin (talk) 09:47, 17 November 2014 (UTC)

There seems to be a consensus to do something so I will start by mainly reorganising this article to give greater prominence to the inertial force. Some wording changes may be needed. Martin Hogbin (talk) 10:16, 18 November 2014 (UTC)

On looking through the article I think wording changes are needed to properly describe inertial CF. Much of the current word seems to be aimed at detracting from the actual meaning of the term Martin Hogbin (talk) 18:15, 18 November 2014 (UTC)

I would be careful drawing too much conclusion from a discussion promoted as a "straw poll". Dicklyon (talk) 05:03, 19 November 2014 (UTC)

Discussion

Dick, do you appreciate the differentce in character between inertial CF and reactive CF?

Reactive CF is a name given to the reaction to the centripetal force. All forces have a reaction and, although we are free to give forces any names that we like, there is no reason that we must give the reaction to the centripetal force a special name. Not only is there no reason to do this but I have never seen a case where giving this force a special name has made anything clearer or helped understanding in any way. On the other hand there are many cases (these talk pages being just one) where giving the reaction to cetripetal force the name 'centrifugal force' has confused people. If the term 'centrifugal force', referring to the RCF had never been used, nothing would change. Everything could be perfectly well explained.

When you work in a rotating frame, though, the inertial/fictitious force is necessary. It is a completely new force, requiring a special name to distinguish it from all the forces found in an inertial frame. Without it, it would be imposssible to do calculations in a rotating frame without changing the laws of physics.

Do you agree with the above? Martin Hogbin (talk) 10:11, 17 November 2014 (UTC)

Yes, I think I agree with all that. Nevertheless, the traditional meaning of centrifugal force as the force you feel when you twirl a weight on a string, or the force that the sun feels from planets orbiting it, is still commonplace, even though deprecated in how CF is taught in physics books. Both meanings confuse people, I think you'll agree, but that's no reason not to explain and contrast them. Dicklyon (talk) 19:39, 17 November 2014 (UTC)

So what is the force you feel when you try to pull a car along with a rope? Does it have a special name?

The problem comes when you try to explain what causes the reactive centrifugal force. If you explain it carfully as being due to the reaction of the weight on the other end of the string due to the centripetal force being applied to it to maintain its centripetal acceleration you might as well not give it a name as you have described in exactly what it is. The temptation though is to talk about a centrifugal force acting on the weight pulling it outwards, which we all agree is wrong, although there are sources which do say this.

At an elementary level it is very simple to deal with the inertial CF; you do not need it at all. There is no need to mention it even. Most physics is done in an inertial frame and everything can be explained with Newton's laws.

Rotating reference frames are normally only dealt with at undergraduate level or above. At that stage a certain mathematical knowledge and ability is required and, as it is usual to introduce the Coriolis force at the same time, an understanding of the underlying maths and the concept of an inertial forces is needed anyway. The only confusion that arises is with people who have already been given a half-baked meaning of the term, informally or otherwise.

Finally I am not trying to remove all reference to reactive CF, just to downplay it as an alternative or historical meaning of the term. We could also take the opportunity to give a simple explantion here of the inertial force for the non-technical reader and thus remove the 'jargon' tag. Martin Hogbin (talk) 20:13, 17 November 2014 (UTC)

The main problem is calling the reaction force to the centripetal force "centrifugal". In many cases it is centripetal (the two-body gravitational orbit being a good example where the reaction force is NOT centrifugal. Even in cases where it appears to be outward, such as the ball tethered to a post, a case can be made that it is still centripetal (because the post and the earth to which it is attached, prescribes a small rotation about the actual centre of rotation). Dicklyon wants to insist that it can be called centrifugal. That makes it very confusing if not quite wrong.AMSask (talk) 23:09, 18 November 2014 (UTC)

It's not really a problem for us if we understand what "centrifugal" is intended to mean, which is in the direction from the center toward the rotating body in question. The fact that it sometimes applies to a body on the other side of the center, with respect to which it is centripetal, need not complicate that understanding. In any case, nobody is trying to convince you to adopt or use this terminology, so just don't. Dicklyon (talk) 05:02, 19 November 2014 (UTC)

That IS the problem. Centrifugual means "fleeing from the centre". In a two-body gravitational orbit there is NO FORCE tending to cause anything to flee from the centre. If gravity suddenly disappeared, there would be no force at all. The two bodies would each be "fleeing from the centre" but not because of any force. So there is simply no centrifugal force at all. To talk about a "centrifugal reaction force" to the centripetal force of the sun on the earth is simply wrong. If you want to use an Wikipedia article to suggest that it is ok to use the concept of a "centrifugal reaction force" in the case of the earth orbiting the sun you are going to find strong opposition here.

It is more difficult to analyse the tethered ball and post situation because the post is fixed to the earth. But even in the case of a ball tethered to a post, there really is no centrifugal force on the post - the rope is pulling the post toward the centre of mass of the earth - ball system. AMSask (talk) 13:15, 19 November 2014 (UTC)

The real problem is Google. Because of its vast reach you can find reliable sources to say most things. This makes it very hard to give due weight to different views because if one user finds three sources stating a minority view, another user has to find thirty sources to show that it is indeed a minority view. Not everyone can be bothered to do this. A similar problem is that it is hard to find mainstream sources stating that minority views are minority views. For example, there are very few sources on lunar anstronomy saying that the Moon is not made of green cheese. The fact remains, though, that for this millennium at least, there is only one meaning of CF used and taught by mathematicins, physicists, and engineers to any significant degree.

Having looked at the section in the inertial CF it is worse than I remembered it. It gives three! versions of what inertial CF is. That is plain nonsense. The first two are not very good attempts to explain exactly the same thing; the standard understanding of the force, and the third is a specialist and somewhat novel/informal use of the term, mainly relating to robotic systems. Martin Hogbin (talk) 17:58, 19 November 2014 (UTC)

OK, the real problem is Google. That settles it. AMSask doesn't like calling this reaction force centrifugal, and you don't like that people can find reliable sources that do so. Done. Dicklyon (talk) 03:07, 20 November 2014 (UTC)

I like to follow the policy of giving due weight to sources. The policy says [my emphasis]:

Neutrality requires that each article or other page in the mainspace fairly represent all significant viewpoints that have been published by reliable sources, in proportion to the prominence of each viewpoint in the published, reliable sources .

Are you saying that there as many sources that use reacive CF and use inertial CF?

WP:due goes on to say:

Giving due weight and avoiding giving undue weight mean that articles should not give minority views or aspects as much of, or as detailed, a description as more widely held views or widely supported aspects.

That is exactly what I want to do. I have said that I do not want to expunge reactive CF from WP, just give it less prominence, in proportion to is use in sources.

WP:due also says,

Generally, the views of tiny minorities should not be included at all, except perhaps in a "see also" to an article about those specific views. For example, the article on the Earth does not directly mention modern support for the Flat Earth concept, the view of a distinct minority; to do so would give undue weight to it.

This is quite close to the current position on RCF, however, I have no problem with having an article on it and putting it into its proper context but it is no longer part of modern science, mathematics or engineering . Martin Hogbin (talk) 09:21, 20 November 2014 (UTC)