Talk:Fictitious force/Archive 1

message: (William M. Connolley 20:10, 3 Nov 2004 (UTC)
replies: text: Well, feel free to edit away :) I simply created this article because the term is used, although finding a definition is actually quite difficult. -- ALoan (Talk) 11:13, 4 Nov 2004 (UTC)
replies: text:  (William M. Connolley 18:24, 4 Nov 2004 (UTC)
replies: text:  I said difficult, not impossible.  Look at some of the external links.  There is no problem in finding people who use the expression, and they must intend it to mean something.  The context often allows you to work out what they seem to mean by it, but I certainly did not "invent" a definition.  -- ALoan (Talk) 18:54, 4 Nov 2004 (UTC)

text:  (William M. Connolley 23:20, 4 Nov 2004 (UTC)
replies: text: No, none of them define the term, but they all use it, and some of them explain what they mean (if only tangentially, in how they use it).  If you click through from mathworld to centrifugal force and Coriolis force, you can see the sense in which they are using the term. -- ALoan (Talk) 10:14, 5 Nov 2004 (UTC)

text:  (William M. Connolley 12:57, 5 Nov 2004 (UTC)
replies: text: Please do - I invited you to do so above - feel free to edit away. -- ALoan (Talk) 13:01, 5 Nov 2004 (UTC)
thread_title:  Disagree 

message: Cleon Teunissen 08:22, 22 Jan 2005 (UTC)
thread_title: Reference frames and translations

message: The introduction should be more clear and simple.
Duk 03:51, 29 Nov 2004 (UTC)
thread_title: Definition

message: Mathematically, newtonian dynamics is a limiting case of relativistic dynamics. At non-relativistic speeds, the higher order terms in the formula's become negligable, and the formulas become identical to the newtonian formulas. To use a computer metaphor: to everyone's surprise (and delight) relativistic mathematics is backwards compatible with newtonian mathematics. For the first time in the history of physics a completely novel mathematical formulation was backwards compatible.
Therefore I was keen to find an interpretation of relativistic dynamics that mirrors that mathematical backwards compatiblity. I think I found that in the concept of geodesic motion. At non-relativistic speeds, and non-relativistic volumes of space, relativistic space is indistinguishable from euclidian space. Newtonian mathematics describes a straight line as the shortest distance between to points: that is the newtonian geodesic. Newtonian dynamics says that a force is required to make an object deviate from moving along the geodesic. Newtonian dynamics categorizes anything that causes deviation from moving along the newtonian geodesic as a force, hence gravity is categorized as a force.
According to general relativity, when you are standing on the surface of a planet there is only one force. The surface of the planet is pushing you, accelerating you in a direction away from the center of gravity.<BR>
(Anything else going on is space-time geometry related.) <BR>
So yeah, gravity is fictitious, but the fact that your distance to the center of the planet remains constant is not fictitious. Cleon Teunissen 10:18, 30 Jan 2005 (UTC)
thread_title: Relativistic dynamics is backwards compatible with newtonian dynamics

message: Within the GR section, it says: constant acceleration of space-time towards the center of the planet. This makes it sound like some real physical thing is moving, which it isn't. William M. Connolley 18:11, 31 Jan 2005 (UTC)
replies: text: I have made sure not to write that the space-time is moving, I only wrote the space-time is accelerating. In physics, if you cannot measure something, nor any consequences of it, it is pointless to make statements about it. Space-time is transparent to motion, so I think the concept of a velocity of space-time is meaningless. The consequences of the acceleration of space-time are measurable: masses gravitate towards each other. I agree that in good old newtonian dynamics and good old euclidian space acceleration implies motion. However, general relativity isn't newtonian, and it isn't euclidian. Cleon Teunissen 09:15, 1 Feb 2005 (UTC)

text: Cleon Teunissen 11:15, 1 Feb 2005 (UTC)
thread_title: General relativity isn't newtonian

message: Within the GR section, it says: constant acceleration of space-time towards the center of the planet. This makes it sound like some real physical thing is moving, which it isn't. William M. Connolley 18:11, 31 Jan 2005 (UTC)
replies: text: According to general relativity, when two masses are orbiting each other they lose angular momentum due to radiation of gravitational waves. So what is carrying away that energy? In general relativity, space-time is categorized as being a part of the realm of real, energy-carrying physical things. Cleon Teunissen 14:41, 1 Feb 2005 (UTC)
thread_title: General relativity isn't newtonian #2

message: According to general relativity, the reference frame that is co-moving with an observer who at some stage in her yourney is being accelerated by a mechanical force, can without ambiguity be distinguished from the reference frame that is co-moving with an observer who at no stage in his yourney is being accelerated by a mechanical force.
When calculations are performed, both the observers, performing the calculation in their own co-moving reference frame only, agree that the observer that at some stage in her yourney was being accelerated by a mechanical force has incurred more time dilation. (More time dilation means: less time has elapsed in the comoving reference frame.)<BR>
External link: The story of non-symmetric journeys, also known als 'the twin paradox' 
<BR>
Cleon Teunissen 10:22, 1 Feb 2005 (UTC)
thread_title:  Symmetry, special relativity and general relativity 

message: I think we should add http://xkcd.com/123/ ;-) --Itub 15:10, 20 September 2007 (UTC)
replies: text: It's been added to centrifugal force several times. Consensus seems to be that it does not add real encyclopedic value to the article. (Being hysterically funny is not an encyclopedic value). –Henning Makholm 18:03, 22 September 2007 (UTC)
replies: text: I know, I was (mostly) joking. However, I think this comic has the best answer to the perpetual questions that pop up here from people who think that fictitious forces "do not exist". Very educational. ;-) --Itub 15:58, 24 September 2007 (UTC)
replies: text: I think the comic would be an excellent illustration, either to this article, or to the section entitled "confusions and misconceptions" at centrifugal force. Unfortunately it is licensed under Creative Commons Non-Commercial, while Wikipedia requires Creative Commons Share-Alike (I think). Anybody feel like writing the artist and asking him to re-license it? --PeR 10:51, 25 September 2007 (UTC)
replies: text:  I understand that the artist makes his living partly from merchandise sales. Any Wikipedia-acceptable license must entail a blanket permission for anyone to print and sell t-shirts (or whatever) with the comic alone (i.e., not necessarily in an encyclopedia context). Though that particular strip is not (as far as I can see) currently being merchandised, it is still one of the more popular Xkcd strips, and it seems rather unlikely that the artist would agree to letting go of it in that way. –Henning Makholm 08:28, 29 September 2007 (UTC)
replies: text:  The obvious motivation for the artist would be that Wikipedia would link to xkcd, thus driving traffic to the site, increasing t-shirt sales. Anyone else making t-shirts with that comic under the CC license would also have to credit the original artist, so it would probably increase, rather than decrease, his sales. --PeR 09:35, 29 September 2007 (UTC)
replies: text: Speculating probably won't help, we would have to ask the author. But first, do we really have a consensus for including the strip in this article (or in centrifugal force? --Itub 17:21, 29 September 2007 (UTC)

text: The article is fun, but unhelpful. Brews ohare (talk) 14:35, 11 May 2008 (UTC)

text: This is a reasonable suggestion. To an unsophisticated reader, the term fictitious may indeed be equated with something which does not exist, and hence requires a clear explanation early in the article. An alternate way of regarding these forces might be as apparent, induced or even frame-referenced forces, because their effects can clearly be observed and measured within the observer's frame of reference. Peter b (talk) 21:27, 25 February 2012 (UTC)
thread_title:  Recommended reading 

message: The problem with Fictitious Forces is that misleading name!  "Fictitious" is pejorative  and implies non-reality to lay-ears (kinda like "imaginary" numbers).  It is of vital importance to discuss and clarify the fact that "fictitious" is only one of the names for what is merely a force that arises when converting between accelerating and non-accelerating frames.  There is nothing unreal about it (as is incorrectly implied by the name) -- that's what the xkcd cartoon was about.  The cartoon illustrates the point well and would serve as a useful illustration of the problem of "fictitious" being misunderstood as "unreal".  Even if the cartoon isn't included, this problem must be addressed.  The cartoon can still be included as a reference (it is reliable) if it can't be pasted in.
108.7.244.101 (talk) 06:17, 27 July 2011 (UTC)
replies: text: This is a reasonable suggestion. To an unsophisticated reader, the term fictitious may indeed be equated with something which does not exist, and hence requires a clear explanation early in the article. An alternate way of regarding these forces might be as apparent, induced or even frame-referenced forces, because their effects can clearly be observed and measured within the observer's frame of reference. Peter b (talk) 21:27, 25 February 2012 (UTC)
thread_title: That awful misleading name ("fictitious")

message: I've deleted the addendum by 97.66.28.156 (Talk) about fictitious force. It appears to contradict the discussion that precedes it, which is entirely accurate. In my view, "fictitious force" is a technical term, as defined in the article, and clearly present in the noninertial frame of the accelerating car. The addendum confuses it with a "feeling" by the car passenger. That is not a correct interpretation. Brews ohare (talk) 15:31, 14 May 2008 (UTC)
thread_title: Removal of addendum

message: Substituted at 20:33, 2 May 2016 (UTC)
thread_title: Assessment comment

message: On 10 July, user:Brews ohare tagged the Rotating reference frame page with an RfD tag and asserted that "This article is a poorly described version of what is done better in the Fictitious force article".  I've converted that to a  tag since this appears to be a request to merge and redirect (or possibly just redirect) content here, not a nomination to delete a redirect.  
I have no opinion yet on the proposal to merge/redirect.  Rossami (talk) 21:17, 10 July 2008 (UTC)
replies: text: I have revised Rotating reference frame to remove its obscurities. It now is an application of Fictitious force to the case of a rotating reference frame. I think that the article has value as a simple example that is more accessible than the general treatment in Fictitious force so I am removing the merger template. Brews ohare (talk) 16:57, 29 September 2008 (UTC)
thread_title:  Merge and redirect from [[Rotating reference frame]] 

message: If it happens that there´s a fast change one can realize that he doesn´t just appercept
but is superposed with imagination. If the change going on is to small this will not 
be realized. Only if the change is going on too fast or no change at all is going on for 
a long time.
91.19.40.170 (talk) 11:28, 1 March 2009 (UTC)
thread_title:  Sounds like the afterimage effect 

message: if a person lets out a tethered force on a rotating platform, he should soon note that the farther out on the platform the greater force in the tether is required. This should give him some indication that he is in a physical system that involves more than just the length of the tether. And if somebody told him that the force in the tether was related to the kinetic energy of motion of the tethered object, he might be able to deduce that he was on a rotating platform. But he wouldn't regard the force in the tether to be fictitious, Because it's a real measurable force and has the same reality as the force of gravity even if he doesn't have an explanation for it.WFPM (talk) 00:57, 28 February 2012 (UTC)
thread_title: Changes in perception of centrifugal force

message: As I understand the point of this math, we are trying to reformulate the laws of motion in another reference frame.  Obviously A is inertial, B is not.  We have an object that can then be modeled in either frame.  Because of this, I have a very hard time with parts like this:
  \frac {d\mathbf{v}_\mathrm{B}}{dt} =\sum_{j=1}^3 \frac{d v_j}{dt} \mathbf{u}_j+ \sum_{j=1}^3 v_j \frac{d \mathbf{u}_j}{dt} =\mathbf{a}_\mathrm{B} + \sum_{j=1}^3 v_j \frac{d \mathbf{u}_j}{dt}.  
This equation implies the following.  As far as I can tell, this is the only definition of this variable in the article.
 \mathbf{a}_\mathrm{B} = \sum_{j=1}^3 \frac{d v_j}{dt} \mathbf{u}_j 
Am I just missing something?  This acceleration is useless for modeling things in the B reference frame because it's converted (by means of the B unit vectors) into the A reference frame orientation.  If you were going to model the motion of something in the B reference frame you would need  a_j = d^2 x_j / dt^2 , and nothing here provides that.  There's not even an easy way to get it.  Alan (talk) 18:22, 13 November 2012 (UTC)
thread_title:  Is anything here actually in the B reference frame? 

message: I think one of the greatest problems in physics, especially today, is for people to mistake the difference between a real force and an apparent force, or a real parameter and a derived parameter. The concept of space-time curvature is fraught with the ability of the human mind to create illusions that contradict reality.
The mistake that is made with so-called fictitious forces seems to be substituting acceleration for force. An acceleration 'seems' to be observed and a force is implied. Basic engineering analyses will quickly reveal the cause of such distortions. With centrifugal forces, it becomes immediately apparent, with a little analysis, that in the case of someone swinging a bucket of water around his head, there is only one force, besides gravity, and that is an inward force along the rope toward the swinger, called centripetal force. There is no centrifugal force traveling outwardly along the rope.
The implication is that acceleration is causing a force rather than the other way around. In Newton's F = ma, the equation can be expressed mathematically as a = F/m, which makes sense mathematically but not in reality. An acceleration requires a force but a force is not dependent on an acceleration. Forces and masses are real but acceleration is a phenomenon observed by the human mind that has little meaning in reality.
We need to be clear about the difference between the reality that is there without humans and the quasi-reality the human mind introduces. Humans introduced the concept of time by observing the rotational period of the Earth and subdividing it into hours, minutes and seconds. That fabricated reality was introduced to F = ma as acceleration, a changing phenomenon that can be observed by the human mind but measured only by introducing the human invention of time. 
When we observe motion using mathematics, we begin to introduce qualities to nature that are not there. For example, time cannot dilate in reality simply because there is no such phenomenon as time. Something is dilating, and if we look closer, without the math, it becomes obvious that the dilation is an illusion produced by the human mind. By transposing equations so that time becomes an independent parameter, the equation can be worked out so that time seems to dilate. In reality, that cannot happen. 
I have no doubt that an explanation exists for what is worked out mathematically as time dilation and I think it needs serious investigation. I have the same lack of doubt that the answer will involve real forces and masses and their properties, not something worked out mathematically that is implausible.
In the same way, fictional forces are fictitious because they are distortions of the human mind. Objects in flight involving the Coriolis effect don't curve due to a force on them, they curve because the human mind is deluded into seeing the curvature and presuming a force is causing the curvature.
Space-time curvature is equally a distortion of the human mind. We have created 3-dimensional coordinate systems to measure space, and time to keep tract of events and moving objects. None of that exists in reality, but when we plot it mathematically, we build a case in our minds for time dilation and space-time curvature.  — Preceding unsigned comment added by Gordoxyz (talk • contribs) 18:21, 12 July 2013 (UTC)
thread_title:  Fictitious forces and illusions 

message: In the end of the "Detection of non-inertial reference frame" section, the article incorrectly says that the focault pendulum proves the rotation of the Earth. Suppose the Earth is not rotating and that the pendulum is going along a really thin elliptical path that is slow slightly elliptical that we can't tell with the naked eye that that it's not passing through the bottom position, then the fact that acceleration varies as the sin of the angle from the bottom rather than linearly combined with the noneuclidian geometry of a sphere making the circumference of any circle on a sphere be less than π times its diameter means the pendulum will still precess anyway if it's swings aren't perfectly linear. An observed rotational period of 24 hours or more is probably so long that that distance away from the bottom position the pendulum must pass in order to have that rate of precession is so slight that we can't tell with the naked eye that it's not passing through the bottom position.Blackbombchu (talk) 18:26, 25 September 2013 (UTC)
thread_title:  Focault pendulum doesn't prove rotation of the Earth 

message: Pseudo force is a much better name for this, and the page should be moved. Bumblebritches57 (talk) 17:51, 25 February 2015 (UTC)
thread_title:  Name 

message: In § Detection of non-inertial reference frame, the article says an observer can tell whether or not they're in an accelerating frame of reference but that's not true. They would be unable to distinguish a rectilinear fictitious force from a gravitational field or a combination thereof. Since the gravitational constant is so small, any gravitational field the same strength as that at the surface of Earth would vary at an ever so slow rate with respect to position, to tiny a difference to distinguish it from a rectilinear fictitious force which would have a uniform force field according to Newtonian physics. Blackbombchu (talk) 15:54, 23 June 2015 (UTC)
thread_title:  Wrong information about fictitous forces 

message: Wouldn't it be better to encourage the use of the term "apparent force", which is well-used in literature, has the same definition, and is more apt?
"Fictitious" implies "doesn't exist" or "made-up".
"Apparent" means "what you detect" without implying it's what's actually there.
"Apparent wind" is commonly used in sailing, and is perfectly apt.  No sailer would ever talk about "pseudo-wind" or "fictitious wind" as he sets his sails to the apparent wind. Shouldn't physicists be at least as clear in use of terms as sailors?  — Preceding unsigned comment added by Learjeff (talk • contribs) 17:46, 17 June 2014 (UTC)
thread_title:  Please change this entry to "apparent force" 

message: The result of the derivation in 'Rotating coordinate systems' currently reads:
:
\mathbf{F}_{\mathrm{fict}}  = - 2 m \boldsymbol\Omega  \times \mathbf{v}_\mathrm{B} - m \boldsymbol\Omega  \times (\boldsymbol\Omega \times \mathbf{x}_\mathrm{B}) - m \frac{d \boldsymbol\Omega}{dt} \times \mathbf{x}_\mathrm{B}.
in which \mathbf{x}_\mathrm{B} is the position vector for the particle/object in the rotating reference frame B (not A!).  It is stated that the first term is the Coriolis force, the second term is the centrifugal force, and the third term is the Euler force.
Contrast the formulæ in this article with those on 'Rotating reference frame':
* the Coriolis force:  
\mathbf{F}_{\mathrm{Coriolis}} = 
-2m \boldsymbol\Omega \times \mathbf{v}_{\mathrm{r}}
* the centrifugal force:  
\mathbf{F}_{\mathrm{centrifugal}} = 
-m\boldsymbol\Omega \times (\boldsymbol\Omega \times \mathbf{r})
* and the Euler force:  
\mathbf{F}_{\mathrm{Euler}} = 
-m\frac{\mathrm{d}\boldsymbol\Omega}{\mathrm{d}t} \times \mathbf{r}
in which \mathbf{r} is the position vector of the particle/object in the inertial reference frame A (not B!).  
Although \mathbf{r} and \mathbf{x}_\mathrm{B} could be equal for some specific choices of the rotating reference frame B, it does not appear that they are generally equal, and I didn't see a clear restriction defined in this article.  
—DIV (120.19.160.192 (talk) 14:23, 6 September 2016 (UTC)
thread_title:  Rotating coordinate systems