Talk:Coriolis force/Archive 1

message: "there is no real force acting on the object"... 'k, gotta explain something to me.
Any time a body's world line deviates from a straight line in whatever coordinate system one's using, a force has to be concocted to account for that. If we're fool enough to use polar coordinates, we have to come up with Coriolis forces. If we're fool enough to use a rotating coordinate system, we need to invent centrifugal forces.
But didn't general relativity do the same thing to gravity? Isn't, in fact, any "force" that operates in strict proportion to the mass of the affected body, imaginary - an acceleration term that can be eliminated by an appropriate change of coordinates?
Aren't Coriolis and gravity equally imaginary?
: (William M. Connolley 20:26, 21 Feb 2004 (UTC)

message: Coriolis force is a fictitious force, but there's a catch.
Consider the pair 'centrifugal force' and 'centripetal force': in the setting of a pilot training centrifuge they are very much different. The centripetal force is a mechanical force, transmitted by fysical contact. The percieved centrifugal force is, if it is transmitted, equally strong for all particles of your body. Like having gravity around, as soon as you break fysical contact, you don't feel anything. <BR>
Imagine a rotating disk, very slippery, just a little bit of friction. An object attached to a rope is released, and it is slowly allowed to move away from the center of rotation. Each time the distance to the center of rotation is increased, the object is slipping for a while, until its angular velocity is once again synchronized with the rotating disk. In the inertial frame of reference, the acceleration vector is a function of spatial coordinates and the amount of angular velocity mismatch. In the rotating frame of reference the acceleration vector points in the "opposite direction", and there too it is a function of spatial coordinates and the amount of angular velocity mismatch.<BR>
Both acceleration vectors are referred to as 'the coriolis force'. :-( <BR>
I'd say go for the inertial reference frame. In the inertial reference frame there is at first a mismatch in angular velocity. The friction force, although insufficient to provide immediate grip, causes the object to catch up and become synchronized.<BR>
In the rotating reference frame there is at first a mismatch in angular velocity, that - seen from the rotating frame - looks like a spooky accceleration. Friction force slows that spooky motion down to zero velocity, and then the spooky acceleration is gone too. Cleon Teunissen 13:11, 29 Jan 2005 (UTC)
replies: text: The account above is not quite correct. Seen from the inertial reference frame: as long as there is a velocity component away from the center of the disk, the mismatch in angular velocity increases, because there isn't sufficient friction to do the necessary work immediately. As soon as the velocity away from the center stops, the angular velocity mismatch stops increasing. The friction force may not be enough to synchronize the velocities entirely<BR>This model approximates the problems in weather modeling. In weather modeling, using a stationary Earth together with the fictitious coriolis force is the best calculation strategy, of course. In the weather model the fictitious force is always doing work, the air currents are always deflected, inducing circulating flows. In the inertial reference frame the inertia is doing the work. Cleon Teunissen 14:54, 4 Feb 2005 (UTC)
thread_title: Coriolis force: possible source of confusion

message: (William M. Connolley 22:32, 29 Sep 2004 (UTC)
thread_title:  Taylor-P theorem 

message: (William M. Connolley 22:14, 21 Nov 2004 (UTC)
thread_title:  Mach is inappropriate 

message: Historically, Foucault used the pendulum to prove once and for all that the Earth is rotating.
So, what assumptions under this proof have been challenged by general relativity?
In general relativity space-time is part of the physical world, energy is carried away from pulsars orbiting each other, the energy is carried away in the form of propagating deformations of space-time, usually called gravity waves.
Space-time is sensitive to direction of motion. Once motion is started, zero-curvature space-time is transparent only to a continuation of that motion in a straight line. Direction of motion is conserved, and this is valid for a pendulum too. 
Around a non-rotating mass the distribution of space-time deformation is spherically symmetrical. However, according to general relativity, the gravity around a rotating mass has such an interaction with the universal space-time, that in the neighbourhood of the rotating mass the direction of space-time is affected too. Gravity Probe B has been build to verify that prediction of general relativity. The theoretical physicists expect that the gyroscopes onboard Gravity Probe B will be affected due to moving through space-time with the property that is also called gravitomagnetism. The expected deviation is 42 milliseconds of an arc over the course of a year.
That gives an indication of the error in the pendulum experiment when set up to show the Earth is rotating.
Apart from the gravitomagnetic correction, general relativity confirms that the pendulum experiment provides proof that the earth is rotating.
So, is it possible to create circumstances in which there is a space-time geometry related centrifugal force, and a space-time geometry related coriolis force? I think Einstein's money would have been on the hypothesis that a hollow cylinder, sufficiently massive, and spinning sufficiently fast, would have inside a deformation of the geometry of space-time with properties that are the exact couterpart of the fictitous forces. How fast would be fast enough? Probably the wall of the cylinder would have to approach the velocity of light very, very closely. Cleon Teunissen 10:55, 3 Feb 2005 (UTC)
thread_title:  Foucaults pendulum and fictitious force 

message: Cleon Teunissen 08:37, 4 Feb 2005 (UTC)
replies: text: I just want to add that Coriolis Force is also visible for masses that fall in mine shafts. The falling masses will tend to move to the east side of the pit, as compared to the vertical of the place. The most important effect is at the Equator.
I have moved this remark to the discussion page, because it is a comment; it starts with 'I just wanted to add [...] The comment disturbed the coherency of the existing text. Cleon Teunissen 08:37, 4 Feb 2005 (UTC)
thread_title:  Coriolis effect on masses falling in mine shafts 

message: Cleon Teunissen 11:50, 4 Feb 2005 (UTC)
thread_title:  The coriolis effect, inertia, fictitious force, and doing work. 

message: I have been reading the explanations of the principles of inertial flow metering. 
The tutorial on the website of Micro Motions offers extensive explanation. <BR>
External link:  the Micro Motion tutorial<BR>
The flow operating principle is explained for both the curved tube version and the straight tube version. As far as I can tell, the operation of these flow meters is based on the phenomenon of precession, not on the coriolis effect. Precession has a torque and a angular velocity as input, and it results in a torque. It is calculated with a vector cross product. <BR>
The coriolis effect has as input angular velocity and a component of a velocity away from the hub of rotation. It needs a cosine to be calculated, hence the vector cross product. The output of a coriolis calculation is a force, not a torque. The inertial flow meters designed by Micro Motion use sensors that pick up effect due to torque. Cleon Teunissen 08:38, 6 Feb 2005 (UTC)
replies: text: On second thoughts: it doesn't really matter. The coriolis effect and precession are two manifestation of a single underlying dynamics, I guess. Cleon Teunissen 09:32, 6 Feb 2005 (UTC)
replies: text: Third thoughts: the curved tube mass flow meter operating principle can be understood as precession or as coriolis effect, depending on what aspects are emphasized. The straight tube mass flow meter is just wonderful engineering thinking, and its all coriolis effect. Cleon Teunissen 08:33, 7 Feb 2005 (UTC)
thread_title:  How do inertial flow meters work? 

message: :Image:Corioliseffectanimatie.gif, from de.  Duk 02:02, 7 Feb 2005 (UTC)
replies: text: Hi Duk, I know that animation, I saw it in the dutch wikipedia 'coriolis effect' article. In this animation there is no friction at all, so in this animation it's 100 % coriolis effect. But in the case of a 100 % coriolis effect there is no noticeble manifestaton of inertia. When there is friction between the rotating disk and the object on it, then the object is accelerated, and then inertia manifests itself. So I think an animation that would incorporate fricton would be even better. Cleon Teunissen 08:42, 7 Feb 2005 (UTC)
thread_title:  Animation available 

message: I think any phrasing like: "the coriolis force appears as a result of coordinate transform." should be avoided, that phrasing doesn't represent a physics fact.<BR>
Take the example of the electric car designed to charge its battery system when it decelerates with respect to a larger mass.<BR> 
In the inertial reference frame, the car decelerates from top speed to zero, recharging batteries; the inertia of the car is doing work. <BR>
In the reference frame that is co-moving with the car, the large object that the car is firmly resting on decelerates with respect to the car. The car has been switched to braking, and a force pushing in a forward direction is doing work, charging the cars batteries. <BR>
In both reference frames the same physics is going on; in both frames the manifestation of inertia is acting in the same direction, doing the same amount of work. In both reference frames, the forward acting force only acts when the car is braking, and the amount of forward force is at all times exactly proportional to the level of braking.<BR>
Changing the coordinate system doesn't change the physics, it's only that sometimes, after a coordinate transform, one of the forces involved gets a different name. --Cleon Teunissen 14:47, 8 Feb 2005 (UTC)
thread_title:  In all reference frames the physics is the same 

message: the previous formula was:
:2m\left(\mathbf{v} \times \mathbf{\omega}\right),
I replaced that with the formula I found in the french wikipedia coriolis article
:\vec{F}_C=2m(\vec{v_r} \times \vec{\omega})
where the arrow above the symbol indicates vector quantities, m is mass, \vec{v_r}  is the component of the velocity in the radial direction, and \vec{\omega} is the angular velocity of the coordinate system. 
The calculation of the coriolis force must be designed in such a way that it produces a force that is tangent to the circle. Therefore, the velocity vector that is used as input for the vector cross product must be the radial component of the velocity 
It appears the that   markup doesn't have a boldface version of /omega, therefore I copied the notation with the arrows above the symbols. --Cleon Teunissen 18:31, 9 Feb 2005 (UTC)
thread_title:  The formula for the coriolis force 

message: External link: Alistair B. Fraser's 'bad coriolis' webpage <BR>
In the current article on the coriolis effect the above site is referred to. It is a webpage by Alistair B. Fraser, who has committed himself to debunking bad meteorology, bad physics teaching, bad science in general. 
Alistair B. Fraser writes in answer to a question: "It is true that the Coriolis force does no work." In answer to another question he writes: "[...] the magnitude of the Coriolis force on an object is independent of the direction in which that object is traveling." And to another question: "No, I don't mean the Coriolis effect. [...] I am referring to the Coriolis force." 
Now, I have written that when the coriolis effect is involved the manifestation of inertia is always doing work, and so on. So what's up? I suddenly realized what exactly Alistair B. Fraser is referring to. Roughly, there are three sorts of situations to consider: 
# an object is resting on a rotating disk, and there is so much friction that the object is guaranteed not to slide. Calculation of motion is straightforward then. 
# an object is resting on a rotating disk, and it has some grip, it is somewhat constrained, but it's not enough to prevent the object from "lagging behind" if the object is moved in a direction away from the hub. That's tricky to calculate. 
#an object is in motion close to a rotating disk but there is no actual contact. That is once again straightforward to calculate, just adding vectors.
Everything I write is about the second situation. The second situation is what applies in for example the case of the movement of masses of air in meteorological modeling. 
The things that Alistair B. Fraser write fall into their proper place when it is recognized that he is talking about the third situation. For example, Alistair B. Fraser writes about a turntable on a desk and carefully moving a pencil in a line that is straight with respect to the desk while the turntable is rotating. <BR>
Imagine a hovercraft above a very large rotating disk. The hovercraft makes several passes over the rotating disk, and everytime the hovercraft is just coasting; straight-line inertial motion. On the underside of the hovercraft there is a device that releases a drop of ink every second. Then all the tracks are seen to be curvilinear. So, if there is no interaction between the disk and the object, if they constitute two independent systems, then, according to Alistair B. Fraser, the coriolis force is causing the hovercraft to move in curvilinear motion all the time. Another claim of Alistair B. Fraser about the independent systems situation is that the magnitude of the coriolis force is independent of the direction of the object's motion in the inertial coordinate system. And since there is no contact between the object and the rotating disk, no work is being done, of course. --Cleon Teunissen 16:08, 7 Mar 2005 (UTC)
thread_title:  Alistair B. Fraser 

message: I did a major rewrite and rearrangement of the article. The exposition at the beginning is aimed at paving the way for understanding the role that the coriolis effect plays in atmospheric motions. Probably, most people will look for information on the coriolis effect in the context of atmospheric phenomena. The first sections treat the basics. As the article goes on, the discussions gradually become deeper and more specialized. 
I'm considering to move this talk page to Talk:Coriolis_effect/archive1, because the current length of this talk page approaches or has already exceeded 32K. Now, after this major rewrite, might be just the time for it.
--Cleon Teunissen 10:31, 8 Mar 2005 (UTC)
thread_title:  Major rewrite march 8th 2005