Talk:Centrifugal force/Archive 2

message: Cleon Teunissen 16:23, 12 Jan 2005 (UTC)
replies: text: (William M. Connolley 19:43, 12 Jan 2005 (UTC)
replies: text: Cleon Teunissen 22:08, 12 Jan 2005 (UTC)
thread_title:  Newton's third law of motion 

message: I have rewritten the article.
The first section is written for people with no phyisics background at all. The first section aims to stay as close to everyday experience of motion as possible.<BR>
As the article goes on, the level increases.<BR>
The final sections assume that the reader has a lot of physics knowledge. Cleon Teunissen 07:04, 30 Jan 2005 (UTC)
thread_title:  Rewrite of the article, 30 jan 

message: 202.156.2.82 wrote:
:The centrifugal force may be understood as arising from the tendency of the stone to move in a straight line, or a path tangential to its position on the circle.
I have removed this remark because it leads to an inconsistency. If there would be a centrifugal force then the centripetal force would be prevented from maintaining the circular motion. The circular motion is maintained, so there is only one force at play: centripetal force. 
Because of inertia a force is required to make an object deviate from moving in a straight line. Manifestation of inertia opposes the centripetal force, but it does not prevent the centripetal acceleration.
Without inertia, objects would be instantly accelerated to lightspeed. Because of inertia acceleration is proportional to the exerted force. The bottom line: inertia is not a force. Inertia involves opposition to change,  but inertia never prevents the change. --Cleon Teunissen | Talk 14:49, 22 Apr 2005 (UTC)
thread_title:  How circular motion is to be understood 

message: I'm dismayed to see the amount of damage that has been done to physics literacy by the "Fictitious Force" falacy.
Centrifugal force is just as "real" a force as the one a wall exerts on you if you bang your head against it.  And that's what should be done to the so-called educational "experts" who, at some point, decided that there were such things as fictitious, fake, or phantom forces.
How all this started, as best I can determine, is this: an effort was made in middle school curriculum development to "correct" the understanding of the forces that give rise to circular motion.  "They" (you know, Them) decided it was misleading to describe that pail on a rope as pulling on the rope, when in fact it was the rope that was pulling on the pail.  And that's fine as far as it goes.  It is a change in point of view.  It describes circular motion as caused by the acceleration of an object, changing its direction of motion from linear to circular, due to the application of a centripetal force.  It's true, it's a good way to describe it, and it probably does help in gaining an understanding of circular motion; or would have, except for what happened next.
Somehow, while the new concept was making its way into the hands of middle-school educators, somebody overreacted.  Rather than switching the emphasis from the centrifugal to the centripetal force, the thought pendulum swung too far, and people began teaching that there was no centrifugal force.  That's rubbish.
Newton's Third Law tells us that unmatched forces do not exist in the universe.  In any force interaction between two objects, the forces exist in pairs.  Each force of each pair is the same magnitude as, and opposite in direction to, its partner.  Furthermore, it does not matter whether any motion occurs as a result of the interaction, or not.  The 3rd law holds perfectly whether you are pushing on a brick wall or whether you are pushing on a shopping cart (accelerating it).  The force back on your hand by the object is the same as the force of your hand on the object.  The cart accelerates not because there is something wrong with the 3rd law, but because the sum of all the forces acting on it (your hand is but one) is non-zero.
If centrifugal force did not exist, it would be the only known example of 3rd law failure.  Thankfully, that's not the case.  Centrifugal force and Centripetal force are a 3rd-law force pair, just like any other.  It's certainly true that centripetal force is the force that maintains circular motion.  And it's a wise way to approach teaching the matter.  But it's a simple physical fact that when the rope pulls on the pail, the pail does pull back.  It has no choice.  Forces exist in pairs.  
And that's the way centrifugal force should be taught.  It is the Newton's 3rd law reaction force to the centripetal force.  That doesn't make it false, fake, fictitious, or phantasmic.  It's real.  All reaction forces are real.  If they weren't, rockets would not take off, and you wouldn't hurt your head if you banged it on the wall.  
It does not help anyone's understanding of physics to imply that there are phantom or magic forces around us.  And the damage done by teaching that centrifugal force does not "really" exist when it can obviously be directly experienced by anyone, fosters a distrust of empirical evidence. 
Beyond that, it's just wrong.
The wiki article needs to be fixed, but I hesitate to take a crack at it myself, because it's not a simple edit.
Anyone have suggestions?
--68.239.184.113 17:08, 31 July 2005 (UTC)
thread_title:  Centrifugal Force *is* a force 

message: Jeepien Wrote:
:It is easy to tell whether someone is a victim of this confusion.  Propose the following to them: "Since by the 3rd law, all forces occur in strictly balanced pairs, all acceleration is impossible."   If they are tripped up by that, or begin to deny that the 3rd law applies universally, they are victims.  If they can easily point out the fallacy, they have their concepts straight. --Jeepien 02:31:43, 2005-08-01 (UTC)
Hi Jeepien,
I think you and I do not really disagree. I may use rather different metaphores but I doubt there is a real difference.
It seems to me that Newton's third law is the key element here. Newtons third law is intimately connected to the principle of relativity of inertial motion. In the Principia the third law's formulation is very reminiscent of statics, but in its application in mechanics it is about interactons between pairs of objects.
The law of equilibrium of forces in the context of statics is of course quite unrelated to newtons third law of motion. If an object is glued to a table then the glue transmits (if stressed) the counterforce of the table. The table can be bolted to the floor, etc etc
When an observer and an object are both free-floating in space and the observer pushes an object, then according to newtonian mechanics you will both accelerate,(away from each other) but the common center of mass of the two of you will remain in inertial motion. Strictly speaking none of these assertions of Newtonian mechanics is provable, but it all works so well it would be absurd to demand more corroborating evidence. Does the object push back? Srictly speaking we don't know, what we see is that Newtons third law holds good.
Any violation of Newtons third law is at the same time a violation of 
the principle of relativity of inertial motion. The principle of relativity of inertial motion makes asserting Newtons third law inevitable. 
Newtons's third law does not trip me up. In fact, I use Newton's third law to provide a distinction between force and non-force. Force is what happens in physical interactions between pairs of objects. Inertia involves an interaction, but there is only a single object, so important as it is, inertia is not to be categorized as a force
I will have another good look at what you wrote, to see if I should stop using particular metaphores. --Cleon Teunissen | Talk 10:22, 8 August 2005 (UTC)
thread_title:  The siginificance of Newton's Third Law 

message: clearly, the expressions 'ínertia' and 'mass' are interchangable. The amount of mass is measured by measuring the ratio of amount of force and the resulting acceleration (m=F/a).<BR>
Is there anything we can say about the origin of inertia? Not all particles have mass. Photons have no mass, and they are instantly accelerated to lightspeed. Particles with inertia on the other hand, have an interesting property: the acceleration is proportional to the applied force. 
That is somewhere between the extremes: if an object would have infinite inertia, then every finite amount of force would not move it. If an object has zero inertia, then it instantly jumps to lightspeed. But inertia is somewhere in between that: acceleration is proportional to the applied force.
There is an interesting analogy with the phenomenon of inductance. A current circuit with a coil with self-induction in it will not particularly resist current strength; it will conduct a wide range of current strengths. If the current circuit is super-conducting it will conduct current without the necessity to keep applying a voltage. Suppose some voltage is applied, a voltage that tends to increase the current strength. The very first change in current strength leads to a change of the magnetic field of the coil. The change of the magnetic field induces an electric field, and this induced electric field opposes the applied voltage. Inductance opposes change of current strength, but does not prevent change of current strenght, for the mechanism can only come into action when there is some change of current strength. In operation it is a self-tuning mechanism.
When there is a coil with self-induction in a current circuit, then the current strength is by good approximation proportional to the applied voltage. By contrast, without the coil with self-induction, applying a voltage on a superconducting conductor causes an immediate jump in current strenght. 
It is not clear how far the analogy between inertia and inductance extends, but I find it an interesting analogy. --Cleon Teunissen | Talk 10:59, 8 August 2005 (UTC)
thread_title:  Inertia and Mass 

message: In the context of a rotating coordinate system the equation of motion contains a term for a centrifugal force (and a term for a coriolis force).
In the context of the rotating coordinate system these fictitious forces perform the job that in the context of a non-rotating coordinate system is performed by F=ma.
Sometimes it is formulated as follows: "Centrifugal force is present only in a rotating coordinate system." That sounds very odd to me. 
The confusion here is that a habit has grown to use the same label 'centrifugal force' for two quite different situations. Some people blindly assume that since in both situations the same name is used, it must actually be the same.
I try to spot that kind of confusion, and avoid it. When thinking about rotational dynamics, for example the dynamics of a gravitational slingshot I do all the thinking from/in the perspective of the non-rotating frame of reference. --Cleon Teunissen | Talk 17:28, 10 August 2005 (UTC)
thread_title:  The origin of the expression fictitious force 

message: There are two completely different definitions of centrifugal force, that were mixed and matched in the entry. The author sounded confused. I kept some of their examples, and emphasised the distinction between the two definitions, and which one is more commonly used. I also removed some confusing extraneous material from the latter half of the entry. The entry could use some maths, perhaps deriving the centrifugal force from the chain rule and a time dependent coordinate change.
:Can I define the terms "fictitious centrifugal force" and "reactive centrifugal force" and use them in this article, or would that count as original research? --Ihope127 17:49, 25 September 2005 (UTC)
replies: text: Those terms seem very uncommon, if there is a better way to refer to a definition, try to find it.  I'd suggest breaking the article into sections, one being titled "Fictitious force" and one being titled "Reaction force", or something like that.  —siroχo 23:47, 26 September 2005 (UTC)
thread_title:  Two Definitions 

message: Can somebody help a Wikipedia-editor-wannabe (me) who barely got through high school physics?  while checking up on some WikiLinks in other articles, I linked the article on Plate spinning to Centrifugal force.  After reading through these comments, now I'm not so sure that was a good idea.  Can one of you "physics" eggheads look at that article, figure out what's right, and either let me know or fix it yourself?  Thanks.  Joe 02:23, 3 October 2005 (UTC)
replies: text: That's a great answer.  But I'm not sure if it answered my question.  Simply put, is the link to Centrifugal force appropriately used in the article on Plate spinning?  Yes?  No?  If not, can somebody fix it or tell me what is more appropriate?  Joe 13:53, 12 October 2005 (UTC)
replies: text: I changed it to "Plate spinning relies on the gyroscopic effect, like it also applies for a spinning top. This makes balancing easier." I think that is more relevant than centrifugal force.--Patrick 16:06, 12 October 2005 (UTC)
thread_title:  What does "plate spinning" use? 

message: Usually, when the pivot-ball example is  utilized, the rope is not perpendicular to the pivot but oblique. Therefore the tension in the rope can be splitted into two component forces, one that is vertical and opposed to mg, and one that is horizontal, this last one being the centripetal force. 
In a rotational reference frame, the horizontal component is in opposition with the centrifugal force. </br>
In an inertial reference frame, it is not, simply because there is no centrifugal force in that frame. </br>--24.202.163.194 05:26, 5 January 2006 (UTC)
thread_title: Pivot-ball example

message: In the inertial reference frame, as well as in the rotational reference frame, we must split the tension in the rope into two component forces to explain the behavior of the ball. 
One component is horizontal and directed toward the pivot where the center of the plane of rotation is situated, and which component constitute the centripetal force acting on the ball.
The second component is vertical and directed upward, which component constitute the opposite force to the gravitational force (mg). 
These two vertical forces explain why the ball doesn't move upward or downward i.e. stay at the same height.
Remark: As the two component forces replace the tension in the rope in the new scheme of forces acting on the ball, so we can say that these two forces are not real, at least as real as the rope, or the pivot and the ball, and thus are fictitious! The centripetal force, being the horizontal component, can therefore be called a fictitious force. --Aïki 05:27, 17 January 2006 (UTC)
thread_title: Component forces

message: To split the tension in the rope into two component forces, is like to replace this force, the tension in the rope, by two other different forces. </br>
To replace, means that the tension in the rope is no more there, and that in its place we have two forces. If the tension in the rope would still be there, we would have then three forces, which would not be a replacement but an addition. 
As these two forces are not materialised by any body, on the contrary of the tension which is materialised by the rope, so we could attribute to these two forces the name 'fictitious'. The same thing can be said of a resultant force replacing two forces seen as components.
In using a system of forces, with its net force, and resultant, component, and equilibrant forces, to analyse and explain the behavior of an object, it is not necessary that each of these forces must represent a material thing. 
To use a system of forces in the way exposed above, is simply to adopt a certain view of the mind on the situation under study. </br>--Aïki 00:59, 21 January 2006 (UTC)
thread_title: View of the mind 

message: In physics, only things that can be measured are considered to be things with physical meaning. For example, we can measure the physical effects of electromagnetism, therefore physicist deem it justified to postulate the existence of an electromagnetic field. Conversely, if some postulated field has no observable effects, then a physicist should not bother to postulate it, much like physicists do not bother anymore to postulate a luminiferous ether.
Clearly, there is no such thing as measuring whether you are 'in an inertial frame of reference' or 'in a rotating frame of reference'. There are no observable differences, any difference between the two is merely psychological, not physics 
Let a tethered ball be circling a stationary pivot. The measurable quantities are the centripetal force, exerted by the pivot on the ball, and the reaction force, exerted by the ball on the pivot. The centripetal force and the reaction force are present both 'in the inertial frame' and 'in the rotating frame'. Any postulated centrifugal force that is supposed to be present only "in the rotating frame" is inherently unmeasurable.
Of course, the equation of motion for a rotating coordinate system is a good tool in the physicist's mathematical toolbox. But it should be recognized that their is no ground for ascribing physical meaning to the concept of 'being in a rotating frame of reference'. 
Excellent time-saving calculational tools without physical meaning are not unusual in physics. For example, calculating the current in electronic oscillator components. To obtain a solution, second order differential equations must be solved, and a powerful mathematical tool to do that is to extend the problem to the number space of complex numbers. The complex number solutions show the way to real number solutions. That is an example of a powerful mathematical tool, without a physical counterpart to the actual mathematical operations. --Cleonis | Talk 15:25, 3 January 2006 (UTC)
thread_title:  The concept of 'being in a rotating frame' 

message: :Clearly there are multiple meanings of the expression 'centrifugal force' in circulation. Wikipedia neutral point of view policy calls for paying due attention to each of the meanings that is 'out there' in wide circulation. --Cleonis | Talk 20:22, 3 January 2006 (UTC)
replies: text:  Sure. I also left both meanings in the intro, just as it was before. Any idea where the alternative meaning originated? Harald88 21:03, 3 January 2006 (UTC)
thread_title: multiple meanings

message: It is not beyond the bounds of possibility that the meaning of the term among scientists has become clarified or even modified in the last 300 years. I agree that both of the meanings described in the article are reasonable, but it is a fact that even the most obvious search shows that current scientific usage of the term is overwhelmingly limited to rotational reference frames. For the article to describe this usage as "occasional" is completely misleading. – Smyth\talk 13:36, 7 January 2006 (UTC)
replies: text: I agree, and there is no reason for such a word at all. Correct immediately. Harald88 15:22, 7 January 2006 (UTC)

text: Do you mean that the section 'Rotating frame of reference' of the article should be enlarged, or that the article suggest that it is use occasionally, or say it is so, or is it another meaning? If you could clarified a little bit more what you mean exactly, it would help. Thank you. </br>    --Aïki 15:37, 7 January 2006 (UTC)

text: Thanks for putting our attention on the inaccurcy of that latest addition, I will correct that (but according to me, that whole part is superflous). But note that the version that you refer to was full of errors and started with a derived (and rather obscure) meaning of the term. In physics, we do not commonly regard rotating frames as valid physical reference frames. Harald88 17:54, 7 January 2006 (UTC)

text: Well, I have to disappoint you: I am a physical engineer, and I always used it in the Newtonian way. Jeepien above is a high school physics teacher and he obviously teaches the same. Thus your claims are outrageous. Harald88 03:33, 8 January 2006 (UTC)
thread_title: Usage as "occasional"? 

message: ::I agree that the centrifugal force is mostly used in rotating reference frames.</br>
But I think there is a distinction to be made between the «meaning» and the «using» of a word or expression. In problems to be solved using a rotating frame, the meaning of  the centrifugal force is not usually express explicity by scientists, because for them, the meaning is evident. It is like the word «inertia», they don't give a definition of it each time they use it! The context is sufficient for them to know in what sense the word must be used. But here, we are in an encyclopedia open to every one. Therefore, we have to explain a little more, at least, what means the terms we use.
Regarding equal status or not, the official politics of wikipedia (NPOV) is to give a fair share to each one i.e. more space for the more important, and lesser space to the lesser important.  --Aïki 18:51, 7 January 2006 (UTC)
replies: text: You show which opinion is apparently most talkative on internet. But the version of a few days ago made many categorical general claims that are factually erroneous in classical physics, and rotating frames are little used. In any case, there is a long paragraph about the derived meaning of centrifugal force in a rotating frame, so where is your problem? Harald88 03:33, 8 January 2006 (UTC)
replies: text:  I show which opinion is overwhelmingly expressed on .edu sites on the Internet. What "categorical general claims" do you mean? – Smyth\talk 11:10, 8 January 2006 (UTC)
thread_title: The «meaning» and the «using»

message: :Aiki, are you saying that the meaning of "centrifugal force" is "any force directed away from the center of rotation"? In that case, I think you are confusing meaning with derivation. Adrenaline is so called because it is produced by the adrenal glands. But this does not mean that every substance produced by the adrenal glands can properly be referred to as "adrenaline", even if scientists in the past may have done so. The defining characteristic of adrenaline is its molecular structure, not its place of origin, just as the defining characteristic of centrifugal force is its relationship to accelerating reference frames, not merely its orientation. At least, that is what the above search shows.
:So let us reorganize the article again, distinguishing the two outward-directed forces as the "fictitious" and the "reactive" centrifugal forces. We will make no statement about which meaning is more "popular" or "important"; we will simply state the facts of usage. Do you agree? – Smyth\talk 11:10, 8 January 2006 (UTC)
replies: text: I agree, except for the logical sequence: it is evident which is the original meaning that is still in use, and which the secondary meaning, from improvising Newtonian physics for rotational frames. Putting that on its head is illogical and therefore confusing. Harald88 11:48, 8 January 2006 (UTC)
thread_title: Proposition of agreement

message: A piece of rock coming from outer the solar system is now entering in it and is attracted by the sun. Depending on its initial direction, it will crash on the sun (or in!), or will turn around it and go away in the outer space. In the second case, his path will be a curved one called hyperbola.
In his coming approach, the object will go nearer and nearer of the sun, till a certain point where it will begin to go further and further away of the sun. At the approaching stage, the force acting on it is directed toward the sun; at the go away stage, the force acting on it is no more directed toward the sun but outward. Taking the sun as the center of the curve, we can then called the force toward the sun the centripetal force, because it is directed toward a center, and the force outward the sun the centrifugal force, because it is directed outward the center.
In this example, there is no need of a rotating frame to have a centrifugal force. The only thing that it is needed, it's to know the direction of the force. That's all!
What is the reason to call a force, any force, by the adjective centrifugal, it is not because that it is viewed from a rotational reference frame, or an inertial frame, or else, but because it is directed outward the center. Nothing else count! Note too, that in a rotating reference frame, the centripetal force is also in the same frame and it is not called centrifugal just because it is in that frame! --Aïki 19:41, 8 January 2006 (UTC)
replies: text: You are obviously confused. In Newtonian physics, the force acting on the object is the gravitational force of the sun, and it's all the time directed towards the sun. And yes, it's a centripetal force. Harald88 20:59, 8 January 2006 (UTC)
thread_title: Centrifugal force without a rotating frame

message: 1- First, thanks to our collaborator Harald88  for having bring to our attention this remarquable demonstration made by Newton.
2- In the two examples that are present in this text, the first one at the beginning, and the second, the Newton-Huygens one, in the SCHOLIUM of  PROPOSITION IV. THEOREM IV., the body never goes along a circular path. It always goes in a straight line, and at a constant speed along this line i.e. in an uniform rectilinear motion, except at the points of deviation, of course. More than that, in the first one, there is not even a circle!
3- In the first one, the body receive impulses at equal amount of times, thus at same lenght of straight line and same areas of triangle. Each triangle have their summit at the same point S, the focal point. Each impulse comes from the outside of the triangles and is directed inward in the direction of the focal point S. This impulse is called here: the centripetal force, and is apply on the body.
4- In the Newton-Huygens one, it is the circle which, at first, receive an impulse when the body hurts this circle, coming from a straight line i.e. any side of the polygone. The force generated by this impulse is directed outward the circle and polygone, and it is called here: the centrifugal force, and it is not at all fictitious or fallacious or imaginary or other seemingly expression.
It's differ from the centripetal force of the first example,  by its direction and its point of application: in the first example, the force is directed inward and applied on the body; in the Newton-Huygens one, the force is outward and applied on the circle. The name centripetal or centrifugal, depends only on the direction: if outward, it is centrifugal; if inward, it is centripetal. It does not depend at all on which body (we can see the circle as a wall i.e. a body) a force, whatever its nature could be, is applied. In both examples, each force is as real as the other one.
( to be continued) --24.202.163.194 20:20, 6 January 2006 (UTC)
thread_title: Newton's BOOK I. OF THE MOTION OF BODIES. SECTION II. Of the invention of Centripetal Forces.

message: Smyth writes here above: "the defining characteristic of centrifugal force is its relationship to accelerating reference frames". What is the source, and who started this alternative definition? &ndash Harald88 11:59, 8 January 2006 (UTC)
replies: text: I have given a very large number of sources that show this to be a current definition, though I can't answer your historical question. – Smyth\talk 17:46, 11 January 2006 (UTC)
replies: text:  Currently the article has no reference list. Perhaps you'd like to contribute by putting your selection WP:CITE of good sources there. Harald88 19:10, 11 January 2006 (UTC)

text: What do you mean by an "active force"? – Smyth\talk 17:46, 11 January 2006 (UTC)

text: A force that deviates an object from inertial motion. Harald88 19:10, 11 January 2006 (UTC)
thread_title:  New terminology -- according to whom? 

message: ---
I moved this Discussion item to here: no point should be discussed between editors in the article space. IMO such points should be discussed here until the discussion is over and consensus is reached about the opinions according to the two different meanings. Below is the current state of discussion, I number the points for ease.
---
Some commonly encountered misconceptions about centrifugal force include:
1 No matter how objects move, there is never any centrifugal force in an intertial frame of reference.
No, that's overstating the case. Although an object's inertia should not be mistaken for a force acting upon itself, that doesn't stop it from acting upon other objects. If there is any force acting inward upon an object, then it exerts an equal and opposite force that may be acting outward at the point of contact -- upon a separate object. 
2 Centrifugal forces always occur when objects are viewed in a rotating frame of reference, irrespective of whether the object follows the frame's rotation.
No -- Inertia may be mistaken for a centrifugal force in a rotating frame, but that is not the only application of the term "centrifugal". In an inertial reference frame, an object forced inward will push back.
3 It is always wrong to speak about centrifugal force.
No,  This misconception is a very common over-reaction against the misunderstanding of inertia. The key here is not to eliminate "centrifugal" from our vocabulary but to detach it from what it is not and use it for what it fits. Since centrifugal force describes any force whose vector rotates with an object of interest to act continuously outwardly, it accurately describes forces like the passenger acting upon a car door during a turn.
4 Centrifugal force is not fictitious but real.
That depends on what apparent force one labels "centrifugal". Used loosely to describe inertia within an rotating reference frame, the "force" is artificial (a product of an accelerating coordinate system). On the other hand (literally), if one spins around with a brick held at arm's length, while no real force pulls the brick outward, the brick does exert a very real centrifugal force upon one's hand.
5 Centrifugal force is just another word for inertia.
In one application, but not all. Aside from the misunderstanding of inertia, there is also opposition to centripetal force -- but acting upon another object. Centrifugal is merely a descriptor indicating direction (like the "normal" force  exerted by an inclined plane). "Centrifugal force" becomes a useful term when used to describe the force with which an object pushes back when forced into circular motion.
6 An outward reaction force against an object exerting centripetal force is a real centrifugal force.
Correct.
Upto here was the discussion (without my comments). Harald88 08:08, 11 January 2006 (UTC)
thread_title: Some common misconceptions