Talk:Coriolis effect

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Proposed Changes[edit]

Aside from the above discussion, there are still a number of small housekeeping tasks in this article. Keeping to the "carefully and correctly" advice, my plan is to start with changes that should be agreeable to everyone. It's important to start out with a positive working relationship, so when disagreements arise (and they will), we'll have a solid foundation to provide what Wikipedia needs of this article. It cannot be ignored that scholarly literature regularly speaks to how confusing this subject is, even at the highest levels of academia.

These proposals are posted for comment, and if none are given or they are positive, the article itself will be changed after a week. The discussion will remain OPEN, as sometimes seeing the change in the article will expose it's weaknesses, and it's need for further editing.

  • The term "anticlockwise" appears here and there. I propose this be changed to "counter-clockwise" throughout. This change would provide consistent terminology in the article.
Done Watchwolf49z (talk) 16:06, 29 December 2012 (UTC)
  • In the History section, change the sentences `By the early 20th century the effect was known as the "acceleration of Coriolis".[6] By 1919 it was referred to as "Coriolis' force"[7] and by 1920 as "Coriolis force".[8]` to `The effect was known in the early 20th century as the "acceleration of Coriolis"[6], and by 1920 as "Coriolis force".[8]`. We'd be giving up the apostrophe for a cleaner sentence. Watchwolf49z (talk) 16:35, 22 December 2012 (UTC)
Done Watchwolf49z (talk) 16:06, 29 December 2012 (UTC)
  • We have a mixture of formats for units of measure. I propose all be giving as "mks units (Imperial units)" throughout.
Done ... except in the bathtub section and tossed ball section. Changes there go past the intent of this proposal. Watchwolf49z (talk) 16:47, 5 January 2013 (UTC)
One suggestion - rather than manually inserting the conversions to imperial units, perhaps template:convert would be a better alternative. I noticed that it's already being used in some of the same parts of the article where you put in some imperial units. Just a suggestion, though. --FyzixFighter (talk) 05:28, 7 January 2013 (UTC)
Agreed, it's just easier to type the numbers in ... I do see the advantage to using the template, just need to learn the attributes &c. Watchwolf49z (talk) 17:55, 12 January 2013 (UTC)
ReDone using convert template throughout, except the "o'clock" units. Watchwolf49z (talk) 16:07, 26 January 2013 (UTC)
  • The first sentence in the “Causes” section uses the phrase “exists only”. This is only true for the Coriolis force, and the Coriolis effect as used in Physics. However, the Coriolis effect exists in all reference frames as used in weather science. I propose changing “exists only” with “is best viewed” giving The Coriolis effect is best viewed when one uses a rotating reference frame. Watchwolf49z (talk) 15:00, 29 December 2012 (UTC)
Let's not start to obscure the facts again. In a non-rotating frame, there is no acceleration perpendicular to the flow of particles. Not in physics, not in meteorology. −Woodstone (talk) 15:54, 29 December 2012 (UTC)
Withdrawn Watchwolf49z (talk) 16:06, 30 December 2012 (UTC)
The intent of this change is to make the statement more consistent to the definition being used in this article. If you have a reference, then we can change the definition and leave this alone. Please use the preceding section for challenges to the citations and notability of usages involving gravity. Watchwolf49z (talk) 23:46, 29 December 2012 (UTC)
I'm agreeing with Woodstone here. I also don't see how changing that statement is more consistent with the definition being used in the rest of the article. Where are the other statements that you see being not consistent with that first line in "Causes"? Also, do you have a reference that the definition for the Coriolis force/effect in weather sciences is different than it is in the rest of physics? Those references you cited above do not (imo) support such a view. In the absolute frame (eq 11-6 in Haltimer & Martin), there is no Coriolis force/effect - just gravity, pressure, and friction. The Marshall & Plumb reference also repeats several times that the Coriolis force is a result of describing motion in the rotating frame (bottom of page 172 and top of page 173). For example in its GFD lab V it states: "Notice that the puck is 'deflected to the right' by the Coriolis force when viewed in the rotating frame..." and later "Viewed from the laboratory the puck moves backwards and forwards along a straight line...When viewed in the rotating frame, however, the particle is continuously deflected to the right... This is the 'deflecting force' of Coriolis." And again on pg 186: "The deflection 'to the right' by the Coriolis force is indeed a consequence of the rotation of the frame of reference: the trajectory in the inertial frame is a straight line!" That is not to say that cyclones don't spin - but an observer in space that is not rotating with the earth will not see unexplained deflection perpendicular to the direction of motion and can explain the fluid dynamics in weather systems with just gravity, pressure, and friction. It is only when we attempt to describe weather in the relative, rotating frame of the earth that we need to include the Coriolis and centrifugal forces in order to "take into account the effect of observing acceleration in a rotating frame of reference." (pg 160, Haltiner & Martin). --FyzixFighter (talk) 04:45, 30 December 2012 (UTC)
I also disagree strongly with this proposed change, and I can't see how either of the two references Watchwolf49z has cited can be read as supporting either it or his assertion that "the Coriolis effect exists in all reference frames as used in weather science". Haltiner and Martin never use the term "Coriolis effect" at all, and Marshall and Plumb use it only three times, but never define precisely what they mean by it.
Although it's not entirely clear to me from this article's or Marshall and Plumb's exposition precisely what the term is intended to refer to, I have always presumed it referred to that part of a body's displacement relative to some chosen reference frame which is attributable to its Coriolis acceleration in that frame. But both Watchwolf49z's sources—just like all others—tell us that the Coriolis acceleration is uniformly zero in a non-rotating frame, and consequently there can be no displacement attributable to it in such a frame.
I agree that the wording of the first sentence in the Causes section could probably be improved, but I strongly disagree that this can be achieved by replacing "exists only" with "is best viewed". I would prefer it to be replaced with something like "only occurs" or "is only non-zero" . The latter substitution presumes that the term "Coriolis effect" is intended to have some at least vaguely quantitative, rather than a purely qualitative, connotation, but then Marshall and Plumb do imply just this on page 143 where they refer to it as being "weak" near the equator.
I suppose one could take the view that the Coriolis effect does actually exist in a non-rotating reference frame but just always happens to have a constant magnitude of precisely zero, but I know of no reliable source which actually does so, and I don't believe that the article's doing so would improve it.
David Wilson (talk · cont) 07:34, 30 December 2012 (UTC)
I have no problem with vectors of zero magnitude and yet still have direction, like dF/dt. Turns out Coriolis effect mass flow meters use an oscillating frame of reference (, which gives a zero force twice per oscillation. I think it would improve this article if the general statements were stated generally, and let the specific applications state their own frame of reference. For example, physics uses a rotating frame, meteorology uses a Newtonian frame, mass flow meters use an oscillating frame and so on. Watchwolf49z (talk) 16:12, 1 January 2013 (UTC)
How are you defining "Newtonian frame" and how is it different from a rotating frame? Is there a source that says if and how meteorology uses such a frame? --FyzixFighter (talk) 02:15, 2 January 2013 (UTC)
The definition of a Newtonian frame is left to the reader to choose. Any would be fine as long as rain is observed. I can’t source that statement, no one’s ever researched otherwise. Watchwolf49z (talk) 17:38, 3 January 2013 (UTC)
If I were to read "Newtonian frame", although I don't recall encountering it very often, I would assume it meant a frame where Newton's laws of motion apply, or in other words a classical inertial frame. Using a non-inertial frame, eg a rotating frame, Newton's laws of motion do not hold unless we bootstrap them with "fictitious" forces. From the two sources you mentioned above, I would say that meteorology does not work in a "Newtonian frame" how I have chosen to define it, but in a rotating frame. All this is to say, I think the sources we've seen indicate that the Coriolis effect of physics and meteorology are the same with physics using a general rotating frame and meteorology using the specific rotating frame of the planet. If we did meteorology in an inertial frame where we saw the earth spinning, the Coriolis effect/acceleration/force would not be observed or needed. So perhaps let me be a little bit more direct - in your statement above ("...physics uses a rotating frame, meteorology uses a Newtonian frame, mass flow meters use an oscillating frame and so on") what does the "Newtonian" of "Newtonian frame" mean to you? --FyzixFighter (talk) 19:06, 3 January 2013 (UTC)
How about that, we’re in complete and total agreement as to the definition of Newtonian frame ... go figure. The equation I posted in the previous section in stated in an inertial frame of reference, specifically one that is stationary to the stars as an approximation for the purposes of this discussion. The next step in the derivation gives us daVa/dt = b + ( gr + fCoriolis + fCentrifugal ) + F . This also stated in an inertial frame of reference, as there is nothing inherit to vector addition that changes this frame. That’s a notable example of Coriolis force/acceleration/effect existing in a non-rotating frame of reference. I ask again, why is imperative that Coriolis force/acceleration/effect not exist in such a frame? Watchwolf49z (talk) 18:38, 5 January 2013 (UTC)
Which line in the derivation (page number or equation number) is that - I'm having a little bit of a problem finding it? What I do see is after giving the equation of motion in the inertial frame (eq 11-6) where no Coriolis force is needed, it then proceeds to give the equation for dV/dt (the velocity in the rotating frame) (eq 11-7) and it is here that the real forces have to be supplemented with the Coriolis and centrifugal force in order for F/m=dV/dt to be true when V is given with respect to a rotating frame. But in the non-rotating, inertial frame only the real forces (pressure b, gravitation ga, and friction F) appear in the equation of motion. The Coriolis force only appears when we express our force balance in terms of relative, rather than absolute velocities. The Coriolis force is a consequence of the rotation of the frame of reference; when the frame of reference is not rotating, there is no Coriolis force. That's what the sources tell us (see also the opening paragraph of section 1.5 in ref 18). --FyzixFighter (talk) 03:33, 6 January 2013 (UTC)
I’m not clear on the answer to my question. Perhaps you could elaborate some on your talk page. Watchwolf49z (talk) 17:55, 12 January 2013 (UTC)
Perhaps I should clarify, “Aside from” means “at the exclusion of” information concerning the equations of motion for fluids in these proposals. “Agreeable to everyone” means that disagreement, even if politely, courteously and briefly stated, would veto the proposal. Watchwolf49z (talk) 16:06, 30 December 2012 (UTC)
  • This is a continuation of the above, AND inherits the stated disagreements (and veto). I propose changing the sentence to The Coriolis effect is only non-zero in a rotating reference frame. The issue is usage in English, where "when they are viewed" is not the exact same thing as "only exists". Now, if it's absolutely imperative the syntax be changed from from the definition, then so be it. Just remember that any unreferenced material ... in the article ... is subject to future challenge and removal per Wikipedia policy. Watchwolf49z (talk) 16:06, 30 December 2012 (UTC)
I think that I favor saying "The Coriolis effect only occurs in..." as another editor above suggested since it's not clear from any text I've seen how you actually quantify the Coriolis effect (as opposed to quantifying the Coriolis acceleration and force). IMO, that's more in-line with the sources we have. Do we have any sources that contradict this? --FyzixFighter (talk) 02:15, 2 January 2013 (UTC)
The equation for the deflection can be deduced from the equations of the observed and observer. It’s a lot of analytical geometry, but it can be done. The derivative of this equation establishes existence in a non-rotating frame. The proof of this is in any first year calculus book. I think we both know this proposal is going to be withdrawn. I’m sure the reference to the statement in the article explains why the derivative is discontinuous here as well. Watchwolf49z (talk) 17:38, 3 January 2013 (UTC)
Withdrawn - Hallelujah Watchwolf49z (talk) 16:47, 5 January 2013 (UTC)
  • In the Rossby number section, a baseball example would be more accessible to the intended reader. I propose replacing the garden material with (and my arithmetic should be checked): A baseball pitcher may throw the ball at U = 45 m/s (100 mph) for a distance of L = 18 m (60 ft). The Rossby number in this case would be 32,000. Needless to say, one does not worry about which hemisphere one is in when playing baseball.Watchwolf49z (talk) 18:38, 5 January 2013 (UTC)
Done Watchwolf49z (talk) 16:22, 12 January 2013 (UTC)
Done Watchwolf49z (talk) 16:22, 12 January 2013 (UTC)
  • Draining in bathtubs and toilets - It looks like the paragraphs got mixed up. The information in the second paragraph is far more notable than in the first. I find it reads just as well both ways, although reversing the paragraphs doesn’t create a contrast. The information flows into each other quite well. I propose reversing the order of these two paragraphs and deleting the phrase "In contrast to the above". Watchwolf49z (talk) 17:55, 12 January 2013 (UTC)
Done Watchwolf49z (talk) 19:32, 19 January 2013 (UTC)
  • Distant Stars - This is currently unreferenced. I have the feeling it can be found in all the archives, and someone will need to track it down. On the other hand, I’m not seeing how this is notable. Astronomers just point their polar axis toward Polaris, stars then track a straight line across the eyepiece. I propose deleting this section entirely, based on lack of notability. Watchwolf49z (talk) 17:55, 12 January 2013 (UTC)
This section was inserted after an edit war with an editor with a rather confused mixup with orbital equations. It represents the most pure case, where nothing really moves; there is only rotation. Let's keep it. −Woodstone (talk) 19:04, 12 January 2013 (UTC)
Do you remember how long ago? That's where the reference is I'll bet. Throw up the footnote and it'll be good, far and away more notable than fruit flies. Watchwolf49z (talk) 19:57, 12 January 2013 (UTC)
The current version was entered on 2011-09-30. There is no reference on talk, but it is a straightforward application of the general formula, so none is needed. But isn't it insightful to realise that the curved path of Sun during the day is mostly due to the combined Coriolis and Centrifugal forces?−Woodstone (talk) 04:53, 13 January 2013 (UTC)
Yeah, this would be an edit war alright. After reading WP:OR, I'm left with the impression that this section would cause us to be denied "Good article" grade. Perhaps if the insight was more explicitly stated the reader could understand which secondary source this illustrates. I just don't know, as long as one of us thinks it's notable, then it belongs in the article. Watchwolf49z (talk) 15:14, 14 January 2013 (UTC)
Withdrawn. Watchwolf49z (talk) 19:32, 19 January 2013 (UTC)

An Aside[edit]

I'd like to find out what everybody thinks of the idea of moving Tossed ball on a rotating carousel sun-section from Special Cases into it's own section, and then putting this new section just after History section. The reason is to get a simple and more detailed example to the readers' eyes before we go into the formula and causes. I've chosen this particular example because it is fairly common in the literature, and footnoting a reference would be almost a "pick-em" decision. Does anyone have a favorite, or can I just throw one up that substantiates the statements in the article? Watchwolf49z (talk) 16:19, 24 January 2013 (UTC)

  • An IP editor tagged the Bullet sub-section for a citation. This is already given in the Causes section as Littlewood (1953). I propose just adding the footnote and clear the tag. Watchwolf49z (talk) 16:07, 26 January 2013 (UTC)
Done Watchwolf49z (talk) 17:39, 2 February 2013 (UTC)
  • In the Bathtub section, we have the parenthetical phrase once per day at the poles, once every 2 days at 30 degrees of latitude. I was just in Miami, I rotated once per day. I propose just deleting the whole phrase as not relevant to the statement. Watchwolf49z (talk) 16:07, 26 January 2013 (UTC)
This refers to the factor sin φ, which appears in the horizontal component of the rotation at latitude φ. There is no Coriolis force on the equator. But agree to omit in this context. −Woodstone (talk) 22:26, 26 January 2013 (UTC)
Done Watchwolf49z (talk) 17:39, 2 February 2013 (UTC)

I've undid a couple edits, the IP edit is obvious, the other was because it was duplicated in the references. I'm okay with this duplication and agree that the Persson (1998) is a good selection for "Further Reading". Watchwolf49z (talk) 17:39, 2 February 2013 (UTC)

Thank you, Woodstone ... there's a bit of dialog from last week on his talk page. I'm still thinking of bringing in Waleswatcher in on this, GK can't just call anyone he pleases a vandal. Watchwolf49z (talk) 13:37, 3 February 2013 (UTC)
Please check you minds whether an empty link is worthy of explaining the coriolis force. Vandal might not be the best characteristic of an empty mind. Gabriel Kielland (talk) 20:49, 3 February 2013 (UTC)
Two points:
  • Copies of articles once pointed to by dead links can often be found by using the Wayback Machine, as in fact was the case for this particular "empty link".
  • While you're entitled to remove dead links from an external links section, there is no requirement—as far as I know—that this must be done immediately. A preferable alternative, in my opinion, is to tag the link with a Dead link template. This should increase the chances that someone who might be a little more enterprising than you are will be able to track down a live link to a copy of the original resource.
David Wilson (talk · cont) 12:49, 4 February 2013 (UTC)
  • The Littleton (1953) reference has an addition statement. I propose moving it into the article itself in the Bullet section. Watchwolf49z (talk) 17:39, 2 February 2013 (UTC)
  • There wasn't any discussion about moving Tossed ball on a rotating carousel sun-section up in the article. I propose that now, let's see what it looks like. Watchwolf49z (talk) 17:39, 2 February 2013 (UTC)

I undid the IP edit, 1835 is the correct date of publication (see `further reading` section). However, the added `de` might be technically correct, as in Gaspard-Gustave de Coriolis, I don't know enough Italian to know the difference. Watchwolf49z (talk) 20:57, 4 February 2013 (UTC)

I'm sorry that my comment isn't constructive in that it doesn't offer an alternative, but it seems to me that this article is confusing in that it mixes the effects of an object moving over a rotating body when it is NOT BOUND to that rotating body (e.g. throwing an object to someone on a turntable) with the effects of an object moving over a rotating body when it IS BOUND to that body (e.g. weather systems on earth, figure skater spin, office chair spin). THe former of these is simply a frame of reference effect, which is pretty simple; the latter is conservation of angular momentum (and the coriolis effect). What's more the deflection in trajectory is opposite for the two effects. ??

PhilDWhite (talk) 21:34, 6 February 2013 (UTC)

Yes, the article is incomplete. You are certainly welcome to help, there's still quite a bit that can be said in this matter. The physics presented is sound, but the meteorology is somewhat lacking. All I ask is be quick to revert your own edits if someone voices an objection. = Watchwolf49z (talk) 16:22, 8 February 2013 (UTC)
@PhilDWhite - do you have a source that makes this distinction? At least in the case of weather systems, the two sources mentioned previously (Marshall et al. and Haltimer et al.), which talk about this in the meteorology context, seem to derive the Coriolis force/effect based on the transformation from the non-rotating to the rotating frame, which to me would seem to be true for both bound and unbound objects. From my reading, I don't see this distinction made in the literature, but perhaps there's a source out there that does?
I do not believe that there is such a distinction. Martin Hogbin (talk) 13:41, 20 February 2013 (UTC)
If the objects aren't bound to the sphere, wouldn't they fly off into space? Weather occurs in atmospheres which by definition is a fluid bound by gravity. = Watchwolf49z (talk) 15:17, 21 February 2013 (UTC)
Yes, so what? Martin Hogbin (talk) 16:58, 21 February 2013 (UTC)
Well ... it would improve the article if this was made more clear? = Watchwolf49z (talk) 18:03, 21 February 2013 (UTC)
What exactly needs to be made clear? We need to make clear that is one Coriolis force, which is an inertial force found only on rotating frames of reference, but it can appear in a variety of circumstances. Do you agree? Martin Hogbin (talk) 18:22, 21 February 2013 (UTC)
By the way, why do you mark your comments as minor edits they are just normal edits and if you mark them as minor some interested parties may miss them. Martin Hogbin (talk) 18:23, 21 February 2013 (UTC)
Well, that would depend on precisely what assumptions you're making, which aren't spelt out precisely enough to give a definite answer to the question. If you're assuming that the force of gravity on a body at rest on the surface of the Earth were somehow suddenly turned off, a more apt description for its initial motion would be "float off" rather than "fly off". In the rotating frame of the Earth the only appreciable force or pseudoforce initially acting on the body would be the centrifugal, which would produce an acceleration of only about 3.3cm/sec2 at the equator. After 10 seconds a body starting from rest on the equator would have risen only about 1.5 m and be travelling at only about 1.1km/hr, almost vertically upwards relative to the surface of the Earth, and the Coriolis force on it would still be negligible. After 100 seconds it would still have risen only about 16.5 m and be travelling at about 11km/hr. At that speed, air resistance would be enough to start reducing its upward acceleration somewhat. Nevertheless, it would eventually pick up sufficient speed for the Coriolis force to produce a noticeable and gradually increasing drift to the west.
But as long as we're going to make counterfactual hypotheses—i.e. that a body is not subject to gravity—why should we assume that it starts from rest on the surface of the Earth? Suppose instead that it's propelled westward down the centre of a perfectly evacuated toroidal tube encircling the Earth's equator. Suppose that the centre of the tube is at a distance r from the centre of the Earth, and that the body is propelled at speed ω r, where ω is the angular velocity of the Earth's rotation. In the rotating frame of the Earth The body is subject to a vertically upward centrifugal force of ω2 r and a vertically downward Coriolis force of 2 ω2 r. The resultant downward pseudoforce of ω2 r is exactly enough to prevent the body from "flying off" to the upper surface of the tube, and will keep it moving at speed ω r along the tube's centre. With respect to the distinction you are trying to draw between bodies "bound to the sphere" and ones "not bound" to the sphere, would this body count as belonging to the former or the latter category? And, more to the point, why would it belong to either one, rather than the other?
While I don't want to deny categorically that any such distinction can be drawn, I have to say that, like Martin Hogbin, I haven't the foggiest idea what it is that you're trying to make "more clear". Unless you're really able to make it more clear on this talk page, I don't think it would be possible for you to do so in the article itself.
David Wilson (talk · cont) 03:32, 22 February 2013 (UTC)
P.S. To forestall any quibbles that my toroidal tube example wouldn't work because of the Earth's motion around the Sun—or various other practical difficulties—I should acknowledge that yes, I realise that this would be so, and that I have simply ignored them.
David Wilson (talk · cont) 03:53, 22 February 2013 (UTC)

Intuitive explanation of the Coriolis effect[edit]

I made an edit 2/17/2014 by adding a paragraph to the intuitive explanation of the Coriolis effect. It was removed 6 days later by tentinator. I would like to be given a reason for its removal. The explanation I gave is intuitive, accurate, and easy to understand. A Thousand Clowns (talk) 02:30, 24 February 2014 (UTC)

The intuitive explanation is awful! I cannot understand it. There's a lot of jargon in it. The bottom line is that your rotational velocity of the earth declines as you move to the poles and vice versa. Thus, if you start at the equator, (which has the highest rotational velocity), because of conservation of momentum, as you move north (or south) you retain the eastward momentum you had at the equator. Meanwhile, the Earth beneath you is slowing down, so you will move to the east relative to the ground. When proceeding toward the equator, you have a small rotational velocity, thus as you move the Earth's surface under you appears to speed up, and you will move west relative to Earth's surface. If there's no objections, I will attempt to rewrite this section presently. Warren Platts (talk) 15:57, 30 March 2014 (UTC)
Many have gone before you to try for a better intuitive explanation. Note that it should not only explain the effect on North/South movements, but also for East/West, which is equally large (and preferably also for up/down). −Woodstone (talk) 16:52, 31 March 2014 (UTC)

Contradiction regarding vortex circulation in schematic figures[edit]

The photo showing the vortex over iceland says the vortex spins 'counter-clockwise', whereas the figure of the earth below, showing the vortex circulation patterns, shows vortices spinning clockwise on the northern hemisphere. One of the two must be wrong, apparently. — Preceding unsigned comment added by (talk) 14:26, 14 April 2014 (UTC)

Both are correct. They occur in different circumstances. The first shows airflow caused by air pressure differences, the second the trajectory of a floating object in absense of driving forces. −Woodstone (talk) 16:16, 14 April 2014 (UTC)
I recommend making a note about this difference in the caption for the lower figure. Otherwise one has the initial impression that the figure is wrong. — Preceding unsigned comment added by MuTau (talkcontribs) 17:33, 6 October 2014 (UTC)

Coriolis force is not intuitive[edit]

The second sentence in the lead is quite correct. If an object is moving towards the centre, in the case of clockwise rotation, it will be deflected to the left. It's always to the left for clockwise rotation, no matter whether the object is moving towards or away from the centre of rotation. But for the case where it is moving towards the centre, the situation is counter intuitive. If it were simply a case of the observed deflection from a frame of reference that is rotating clockwise, then the deflection for an object moving towards the centre would be to the right. That's why I removed a few words from the first sentence. By all means restore if you think I am wrong, but I would like to hear some comments. (talk) 18:42, 13 November 2014 (UTC)

I guess I'm not seeing the connection between your above argument and the phrase "when they are viewed" in the first sentence. IMO the phrase is important because when a moving object is viewed in a non-rotating frame, there is no Coriolis force. Even for an stationary observer watching a ball roll across a rotating table, if she does the mechanics in her stationary frame there still is no Coriolis force. I've reintroduced the phrase with some tweaking to make clear what is meant by "viewed". This is in line with every reliable source that says that the Coriolis force is an artifact of the rotation of the reference frame being used to describe the objects motion. Do you have a source that says otherwise? Perhaps the confusion is that the velocity that goes into calculating the Coriolis force is the velocity in the rotating frame and not the velocity in stationary frame? --FyzixFighter (talk) 15:10, 15 November 2014 (UTC)
Sorry, second thought here. I think I see your argument now, but I disagree with the statement that the deflection for an object moving towards the center would be to the right if it were simply a case of observed deflection from a frame of reference. For example, if we have an object moving with constant velocity in a straight line from some point on the rim to the center as seen in a stationary reference frame, then in a reference frame with clockwise rotation the initial velocity has a radially inward component as well as a tangential component in the counter-clockwise direction. The object then will be seen in the rotating frame to curve to its left (based on its velocity in the rotating frame) and eventually pass through the center. For me this is easier to seen when taken to an extreme, ie that of a very very small radially inward velocity as seen in the stationary frame. However in a clockwise rotating frame the object is seen to be moving counter-clockwise and slowly spiraling inwards. In the rotating frame the spiraling inwards is explained as the Coriolis effect deflecting the object radially inward, or in other words to the left relative to the objects mainly counter-clockwise velocity (as seen in that frame). --FyzixFighter (talk) 16:13, 15 November 2014 (UTC)

FyzixFighter, I'll use the case of firing a cannon from a rotating platform to illustrate my point. If a cannon is fixed on a rotating platform and then fired, the Coriolis force acts on the cannon ball as a natural consequence of conservation of angular momentum. However, if we are on a rotating platform and observe a cannon that is not on the platform, firing from the stationary ground below the platform, the situation is quite different. In the former case for a clockwise rotation and a cannon firing inwards to the centre, the deflection will be to the left as per the Coriolis force. In the latter case, the deflection will appear from the rotating frame to be to the right. My point was that a Coriolis force acts within a rotating system. Observation alone is not sufficient. We need more than just observation for a Coriolis force to occur. That's why I adopted a bear minimalist approach to the wording, in order to avoid these subtleties. Coriolis force is about everything being in the rotating system. Your amendment uses the idea that the Coriolis force occurs when the motion is described in a rotating frame. It might, but it might not. It depends on other factors as well. Best to leave it as I suggested in order to avoid such issues in the lead. Maybe these issues can be discussed in a special section. (talk) 17:42, 15 November 2014 (UTC)

Sorry but I still disagree. In the latter case, the deflection in your latter case (a stationary cannon firing inwards observed from a clockwise rotating frame), I see the deflection due to the Coriolis effect being to the left relative to the cannonball's velocity in the rotating frame, mainly because in the rotating frame, the cannonball has a counter-clockwise component to its velocity along with the radially inward component. If the deflection where to its right, the cannonball would curve away from the center. Instead, the deflection is to its left and towards the center so that both the rotating observer and the stationary observer agree that cannonball crosses the center. To sum up the points and to see where we may disagree:
  1. The initial velocity of the cannonball in the clockwise rotating frame has both a radially inward component and a counterclockwise tangential component
  2. The cannonball follows a curved path so that it crosses the center
  3. The deflection is to the left relative to the cannonball's velocity (if you were facing the direction the velocity vector points)
In your former case, a stationary observer doesn't see a Coriolis force and will see the cannonball follow a straight line once it leaves the cannon. Only in the rotating frame will an observer have to invent a fictitious force perpendicular to the ball's velocity to explain cannonball's motion in that frame.
Like I said, all the sources I've seen are pretty clear in saying that the Coriolis force/effect is an artifact of describing the motion in a rotating frame. Whether you have rotation of objects or not relative to the stationary frame is irrelevant, it's all about whether or not the coordinate system/reference frame is rotating. Do you have sources that suggest otherwise? --FyzixFighter (talk) 18:21, 15 November 2014 (UTC)
Clockwise rotation. Cannon on the ground under the rotating platform, not participating in the rotation. Cannon fires ball radially inwards to the centre. People on the rotating platform will observed the cannon ball deflecting to its right and spiraling anti-clockwise into the centre point. No Coriolis force. Imagine a clock is painted on the ground directly below the rotating platform. The cannon ball goes from 12 o'clock to the centre, in a straight line. To people on the platform, that line will regress anti-clockwise like a clock hand moving backwards. The cannon ball will be moving away from them to the right.
Now consider a cannon fixed on the platform and firing ball radially at the centre. Coriolis force will deflect the ball to the left, and the ball will miss the target. Let me check out some references to see what I can find out regarding whether or not it's purely a matter of observation. (talk) 18:41, 15 November 2014 (UTC)
Perhaps this is the issue. The Coriolis effect is not about transformation of the velocity vector from the stationary to the rotating frame. In the stationary frame, the cannonball has a constant radially inward velocity, while in the clockwise rotating frame the initial velocity is both radially inward and anti-clockwise - I guess you could call this right relative to the radially inward velocity, but this is not the Coriolis effect found in textbooks. The Coriolis effect is what causes the ball to spiral inward to the center, so that the path of the ball is initially anti-clockwise but curves to the left (relative to the velocity of the cannonball) until it hits the center so the path looks something like a deformed "C" in the rotating reference frame. Note that the left/right definitions we are using here and in the article are with respect to the cannonball's velocity and not with respect to any observer. --FyzixFighter (talk) 19:06, 15 November 2014 (UTC)

First hit on google implies that it's about the rotating system and not about how it's observed. (talk) 18:49, 15 November 2014 (UTC)

So what is the difference between saying it's about the rotating system and not about the rotating reference frame? --FyzixFighter (talk) 19:06, 15 November 2014 (UTC)

OK. Even Gaspard Coriolis himself didn't see it as an observational artifact. He was working on coordinate frames fixed in rotating systems. If it were only an observational artifact, then we wouldn't observe the Coriolis effects in the atmosphere from space. And consider the rim of a spinning gyroscope. If we subject it to forced precession, the rim velocity becomes radial to the forced precession axis, and a Coriolis force causes it to tilt at right angles to the forced precession. That is a real effect, not an observational artifact. My point is that the Coriolis force is more than just an observational effect. The Coriolis force is a product of conservation of angular momentum within a rotating system. That's why it's best to leave the wording in the lead in a bear minimalist form. By using the terms 'observe' or 'describe' you are implying that real effects such as atmospheric effects or gyroscopic effects, magically come about as a result of making observations from a rotating frame of reference. It's just not as simple as that. That's why I reduced the wording in the lead to the simple term "in a rotating frame of reference". Anyway, let's leave it for somebody else to decide. I'm glad that you are thinking about the matter and I hope that others will think about it too, because the sources are not consistent. (talk) 19:57, 15 November 2014 (UTC)

Putting it all very simply, in the case of single particle motion, the Coriolis force is not just about how we observe the motion from a rotating frame of reference. It's about how we observe conservation of angular momentum from a rotating frame of reference. But you can't put that in the lead. That's why it's best to leave 'observe' or 'describe' out of the lead altogether, because it is misleading in the absence of the caveat about conservation of angular momentum. (talk) 20:50, 15 November 2014 (UTC)

Actually, I'll try, but feel free to take out the clause about angular momentum if you are not happy about it. (talk) 20:52, 15 November 2014 (UTC)

Just because the force is an artifact of the rotation of the frame doesn't mean that effect isn't real. Take your example of the cannonball fired from the cannon on the rotating platform. In the rotating frame the cannonball has no angular momentum, so in the rotating frame it looks like the momentum is not being conserved which is why we have to introduce fictitious forces (momentum conservation is just another way of saying F_net=ma=dp/dt) to explain why it misses. However, in the stationary frame the cannonball leaves the cannon with both a r-hat and a theta-hat component to its initial velocity. Once it leaves the cannon, it follows the projectile path expected for that initial velocity - no Coriolis force is needed to describe its motion. Both frames agree that the cannonball misses the target, but they don't agree on why. Conservation of momentum only holds in stationary frames so effects that are attributed to conservation of momentum/inertia in the stationary frame have to be attributed to fictitious forces in non-stationary frames.
To paraphrase John Taylor's "Classical Mechanics" pg. 350, both the Coriolis and centrifugal forces are at root kinematic effects, resulting from our insistence on using a rotating frame of reference. In a few simple cases, it is actually easier to analyze the motion in an inertial frame and then transform the results to the rotating frame. However, the transformation between the two frames is usually so complicated that it is easier to work all the time in the rotating frame and live with the "fictitious" Coriolis and centrifugal forces. --FyzixFighter (talk) 21:41, 15 November 2014 (UTC)
It's an artifact of a real effect as viewed from a rotating frame of reference. That real effect is the conservation of angular momentum relative to the inertial frame. It's the conservation of angular momentum aspect that we were missing out on, in the earlier part of the discussion. Hence, when the cannon on the platform fires, the man on the ground sees no Coriolis force. He only sees conservation of angular momentum with respect to the origin of the rotating frame. On the platform however, they only see a Coriolis force while conservation of angular momentum appears to have broken down. (talk) 22:06, 15 November 2014 (UTC)
Yes, I would agree with those last three sentences. But also remember that momentum conservation is part of Newton's laws of motion. More generally, conservation of momentum (both linear and rotational) appears to be broken in any accelerated frame which is why introduce fictitious forces like the centrifugal and Coriolis forces. This is why the sources say the fictitious forces are artifacts of the rotation frame - they are added only to bootstrap Newton's laws to rotating frames, but in the preferred inertial frame they do not exist. As long as we are describing rotating systems from a stationary reference frame, we don't have to invoke a Coriolis force. --FyzixFighter (talk) 22:24, 15 November 2014 (UTC)

FyzixFighter, See your talk page. There is alot more to this topic than can be discussed here. (talk) 10:22, 16 November 2014 (UTC)

"Analogy to Magnetism"[edit]

The magnetic force is not similar to a Coriolis force, there ist no analogy beyond the cross product. The cited paper is not reviewed, not even published! Meier99 suggested this analogy in the german-wikipedia-article as well [1], but it was reverted and the resut of the discussion between the members of the WikiProject Physics ist clear: No original research - and no reliable source. I have deleted it for the second time. Kein Einstein (talk) 14:04, 25 November 2014 (UTC)

Ther are some similarities. Like a charged particle in a magnetic field a particle movong under the influence of just the CF does no work. Martin Hogbin (talk) 17:10, 10 April 2015 (UTC)

Variation with lattitude[edit]

I have removed a section stating that the force is greatest at the poles because it is misleading. As the article states, the Coriolis force depends only on the velocity of the object and the angular velocity of the reference frame. The Coriolis force is therefore independent of position on the Earth's surface.

For an air mass constrained to move parallel to the Earth's surface the Coriolis force does cause a greater diflection near the poles, which is what the source says, 'The Coriolis deflection decreases as latitude decreases, until it is zero at the equator'.

Because of this complication, I do not think the added text is suitable for the lead. I might be added in an appropriate section of the body ofthe article, where there is room to explain in more detail. Martin Hogbin (talk) 17:07, 10 April 2015 (UTC)

Hello Martin, I think the information is both sourced and relevant. It is about the horizontal component of the coriolis effect been stronger near the poles. in the previous sentence it was making reference about movement along the surface, so I think it is implied that we are talking about the horizontal component and that we are not changing altitude (with respect to earth).
The effect is due to changes in linear speed on the reference frame (Earth's surface) at different latitudes. Caused by the fact that even though the angular velocity of Earth is constant the diameters of circles of latitude is different at different latitudes and so linear speed is maximum at the equator and minimum at the pole.
The maximum change in that linear speed increases as we approach the poles the derivative of the cosine of the latitude is 0 at 0 (equator) and reaches its maximum value at 90 or -90 (the poles) which means that the rate of change in linear speed at the surface when we change circles of latitude (going north or south) approaches 0 as we near the equator 5 degrees travelling north from there make the diameter decrease by 0.4% (1-cos(5)) while five degrees from a pole towards another increase the diameter by 8.72%.
If the surface travel is within a circle of latitude there is no horizontal effect with respect to the frame of reference as linear velocity remains constant along a circle of latitude. Regards.--Crystallizedcarbon (talk) 19:03, 10 April 2015 (UTC)
I agree that the information is sourced and relevant but I do not think it is that clear that you are talking about the horizontal component of the CF. To make it clear, as you have done here, takes more text which makes it a bit long for the lead. It is better to add new text to the body of the article anyway rather than add everything to the lead.
Why not add your bit to an appropriate part of the body ofthe article, wher oit can be explained properly? Martin Hogbin (talk) 19:38, 10 April 2015 (UTC)
Hello Martin, I will follow your advice and I promise to add a more detail description to the body to make sure it is clearly explained, but I hope you don't mind that I have also restored it to the lead (with small changes, It was written force by mistake, when it is just an effect and I also mentioned the horizontal component), as I think it is important and it will help the casual reader understand better the effect. Regards.--Crystallizedcarbon (talk) 22:08, 10 April 2015 (UTC)