User talk:William M. Connolley/Coriolis effect

In the article the question is raised: what is a real force?

It is common to see the Coriolis force described as "making it look like a force is acting upon the object, but actually there is no real force acting on the object". This prompts the question, "what is a real force"?

By general agreed definition, a force has the property that it can transfer momentum from one object to another. Example: the dynamics of a gravitational slingshot.

Among the interactions of Nature, gravitation is one of a kind. All other forces, like for example electrostatic force, have the characteristic that the acceleration they cause is a locally measurable acceleration, accelerometers on/in the object will show a reading. Gravitation is unique, when objects are being accelerated by gravitation accelerometers on/in the object show zero acceleration.

For a slingshot the presence of a single force is necessary and sufficient. In the case of a sling, that single "sling-force" is provided by the tension in the rope, in the case of a gravitational slingshot that single "sling-force" is provided by gravitation.

If it cannot produce a slingshot when acting as a single force, then it is not a force. --Cleon Teunissen | Talk 6 July 2005 07:25 (UTC)

A spectacular example of momentum-transfer dynamics can be seen in a particular kind of bicycle racing on the banked track of a velodrome. Tens of professional cyclists are teamed up in pairs. It is a relay race, with the addiion that the cyclists transfer their momentum. At all times one member of the pair is going full speed, the other is going less fast, so he can recuperate. Prior to a transfer the rested team member positions himself, reaches behind with one hand, and the fast man, overtaking from behind, grasps the other guys hand, and transfers as much of his momentum to the other guy. (It would be too dangerous for the cyclists to attempt such a transfer while negotiating a curve. The equivalent of a gravitational slingshot would be to transfer momentum in the curve of the track.) --Cleon Teunissen | Talk 6 July 2005 07:25 (UTC)

Taylor columns

In the article it is stated:

See Taylor-Proudman theorem for a startling consequence of the Coriolis effect: in a rotating reference frame, [...] the fluid velocity is identical at all points along any single vertical line (known as a Taylor column).

The Geophysical Fluid Dynamics lab, part of MIT, set up for educational purposes, shows a demonstration of Taylor columns:

Definitions:
(1) When the surface of the fluid is flat, the state of the fluid is called 'non-rotating'.
(2) When the surface of the fluid has assumed a parabolic shape, then the state of the fluid is called 'rotating'.

A videocamera is attached to the turntable, in such a way that it is co-rotating with rotation of the turntable.

When the fluid is rotating, then there are Taylor columns.

Dye is added to the fluid to make the dynamics of the Taylor columns visible.
If the fluid is rotating then effects due to the Taylor columns are seen when looking at the rotating fluid from a non-rotating point of view and they are seen when looking at the images taken by a co-rotating videocamera.
Conversely, when the fluid is non-rotating, then there are no Taylor columns; no Taylor columns as seen from a non-rotating point of view, no Taylor columns when looking at images taken by a rotating videocamera.

One of the experiments that Taylor performed was to release a ping-pong ball from the bottom of a tank with rotating fluid. It takes more time for the ping-pong ball to rise to the surface when the fluid is rotating, when the fluid is rotating then there is more resistance to being displaced by the ping-pong ball then when the fluid is non-rotating

Identifying what does and does not elicit Taylor columns

There are two rotational variables: whether the fluid that is being observed is rotating or not, and whether the point of view of the observer is rotating or not.

We see Taylor columns in the following two situations:
(1) a fluid rotating with respect to an inertial frame of reference,
(2) a fluid stationary with respect to a rotating frame of reference that is rotating with respect to an inertial frame of reference.

What the current article states:

In changing from one coordinate system rotating relative to another [...], a term appears in the equation of motion described by the formula for Coriolis acceleration:

[...]

See Taylor-Proudman theorem for a startling consequence of the Coriolis effect: [...] in a rotating reference frame, the fluid velocity is identical at all points along any single vertical line (known as a Taylor column).

It is not directly clear how the reader is to understand the expression 'a fluid in a rotating reference frame'. However, we can try to retrace the steps. The article does acknowledge that Taylor columns can be elicited. Presumably the reader is to understand that the expression 'a fluid in a rotating reference frame' is to be understood as synonymous with 'a rotating fluid'. That interpretation reconciles the article with the experimental demonstration.

It is not directly clear how the reader is to understand the expression 'changing from one coordinate system relative to another'. Retracing the steps: presumably what is meant is that the expression 'changing from one coordinate system to another' refers to actually setting the fluid itself into rotation. That interpretation of the article reconciles it with the experimental demonstration.
--Cleon Teunissen | Talk 8 July 2005 06:38 (UTC)

THere is no difficulty in understanding the meaning of ch-from-one-coord-sys. It has its standard meaning, which need have nothing to do with physics. 'a fluid in a rotating reference frame' is slightly imprecise: it is implicitly understood to mean "in comparison with the laboratoty frame". But fluid-in-a-ref-frame is, of course, not at all synonymous with a rotating fluid. William M. Connolley 2005-07-08 13:44:13 (UTC).

OK, I wanted any reviewers to be absolutely certain about that.

The article states:

(1) That the term 'coriolis acceleration' refers to coordinate transformation, which does not alter the physics.

(2) That the coriolis effect alters fluid characteristics; it elicits Taylor column behaviour in fluids. MIT demonstration of Taylor column behaviour.
--Cleon Teunissen | Talk 8 July 2005 18:31 (UTC)

The coriolis effect is not physics. It is kinematics. If that helps to clarify my version. William M. Connolley 2005-07-08 20:06:46 (UTC).

the physics of Taylor columns

http://ace.acadiau.ca/math/karsten/Projectwebpages/TimandJeff/fluid.pdf
By Jeff Quilliam and Tim Wotherspoon
from the article by Jeff Quilliam and Tim Wotherspoon:

The Taylor-Proudman Theorem. It was first derived by Proudman in 1916 and was experimentally verified by G.I. Taylor shortly after.

Taylor's experiment consisted of a rotating cylindrical tank of fluid. The tank is rotated at a high frequency. Once the fluid settles into solid-body rotation, a small cylinder (a fraction of the height of the fluid) is dragged along the bottom of the tank. Dye is then injected into the fluid. In a non-rotating tank, the dye is free to move anywhere in the fluid. However, in the rotating tank, the dye would be diverted from passing over the cylinder as if the cylinder's height were extended in a column from the top to the bottom of the fluid

A paper by Seelye Martin and Robert Drucker which appeared in the Journal of Geophysical Research in May of 1997 sought to explain ice flows in the Chukchi Sea by the presence of Taylor columns. The Chukchi Sea is located just north of the Bering Strait between Alaska and Russia (a high latitude where the depth of the ocean is almost parallel to the axis of the Earth's rotation). Examining microwave imagery for the region during the summers from 1992-1994, the pair found that as ice flows melted and receded, ice remained preferentially over Herald Shoal, a region much more shallow than the surrounding waters Martin and Drucker postulated that this was due to a Taylor column trapping the cold water and ice in the region above the shoal.
[end quote from paper by Jeff Quilliam and Tim Wotherspoon]

The dynamics of Taylor column behaviour in fluids is physics.

The version of the article at User:William_M._Connolley/Coriolis_effect contradicts itself. In the opening section the article claims that the coriolis effect is not physics. Everywhere else in the article it keeps describing coriolis effect as a physical causal agent, the article states that the physics of Taylor columns is a consequence of the coriolis effect, that is one of the examples.

In the scientific literature the coriolis effect is described as a physical causal agent, altering physical behaviour.
--Cleon Teunissen | Talk 9 July 2005 07:02 (UTC)

Uneven wear on railroad tracks

In the the version of the article at user:William_M._Connolley/Coriolis_effect it is stated:

the Coriolis effect can have (in addition to its obvious atmospheric effects) a visible effect over large amounts of time and has been observed to cause uneven wear on railroad tracks and cause rivers to dig their beds deeper on one side.

Clearly coordinate transformations do not cause uneven wear of railroad tracks. The article states that 'the Coriolis effect [...] has been observed to cause uneven wear on railroad tracks [...].
--Cleon Teunissen | Talk 9 July 2005 09:57 (UTC)