Undergrad Coriolis force, real or just an illusion?

[A.T.]

**** math if I don't understand the point...

I explained the point multiple times: To extend the applicability of Newton's 2nd Law to non-inertial frames we introduce these inertial force terms.

every formula don not come from nowhere,there is some understanding behind that which make this formula..

Sure, you can look up the derivations of those formulas. It boils down to computing the coordinate acceleration difference between inertial and non-inertial reference frame, multiplying that by mass, and calling it "force".

 

[russ_watters]

If it like you say,than you can hower in the air above africa until south america will appear under you,this is nonsense!
Air,aircraft, everything what is in Earth gravity field moves with Earth together,..
But I still don't understand why then projectil must do correction...
so I still do not understand what coriolis force really is ,it is confusing

The previous description was missing a key piece: it comes into play when you move over the surface and the speed it is rotating under you changes.

 

[jbriggs444]

Why did not include in calculation Earth revolution about sun,or maybe milky way rotation etc etc etc?

The rotation rate of the Earth is approximately 365 times as rapid as its orbit around the sun. So even if it were relevant at all, its contribution to Coriolis would be small. But it turns out to be completely irrelevant.

We do not use a rotating reference frame that is tied to the rotation rate of the Earth about the sun. We use a rotating reference frame that is tied to the absolute rotation rate of the Earth -- to its rotation rate with respect to the distant stars. It is that rotation rate, based on the sidereal day that is relevant.

The rotation of the galaxy is irrelevant for similar reasons. It is both small and irrelevant.

 

[Change in pressure]

The rotation of the galaxy is irrelevant for similar reasons. It is both small and irrelevant.

That make sense,so small so irrelevant...
This is how answer must look like...

(Do you maybe have answer why horizontal correction exist even when you shoot est-wet, west-est?)

 

[jbriggs444]

T
(Do you maybe have answer why horizontal correction exist even when you shoot est-wet, west-est?)

Because the Earth is rotating under the projectile as it flies. If you are anywhere in the northern hemisphere then the Earth is like a phonograph platter that is rotating counter-clockwise. If you are shooting east, the platter in front of you is rotating left/northward. If you are shooting west, the platter in front of you is rotating left/southward. If you are shooting south, the platter in front of you is rotating left/eastward. If you are shooting north, the platter in front of you is rotating left/westward.

Near the north pole, the picture is just this simple. As you approach the equator, the platter is tilted so that the rotation is no longer about a vertical axis. The horizontal component of the deflection is weakened accordingly and replaced with a vertical component that varies with direction (tending to produce drop if you shoot east and lift if you shoot west but no effect if you shoot north or south). As you proceed south beyond the equator, the horizontal Coriolis component re-emerges, but reversed. Now the phonograph platter is viewed from below. From this viewpoint it is rotating clockwise.

 

[A.T.]

That make sense,so small so irrelevant...

Not just irrelevant because its small. Irrelevant for the other reasons stated. And also small.

 

[FactChecker]

There are two aspects of the Coriolis effect.
1) An object at the equator is traveling very fast from West to East. An object at the North Pole is not traveling West to East at all; it is just rotating. Suppose an object is shot from the equator toward the north? What happens to all that West to East velocity? It's still there and it causes the object to move Eastward compared to the Earth surface that it is going over. (Here I am assuming that the object is holding constant altitude so that its radius from the axis of rotation is decreasing.) That is one aspect of Coriolis.
2) Suppose an object is shot horizontally toward the East. It wants to go in a straight tangent line, which would make it's altitude increase. (To keep it simple, ignore gravitational force.) Meanwhile, the Earth surface is curving around under it and is getting ahead (in angle). The object is climbing instead of turning to keep it's angle position up with the surface. So the object falls behind and appears to be drifting toward the West (compared to what you would expect from the velocity it was shot toward the East). That is a second aspect of Coriolis.

 

[jbriggs444]

Exactly at the equator, the east-west deflection for a northward shot is precisely zero. Coriolis ignores the component of velocity parallel to the axis of rotation. [Artillery tables may report a slight deflection because an actual artillery shot will have a non-negligible vertical component. You could see a larger correction for indirect/plunging fire and a lower correction for direct/line of sight fire]

However, as the projectile arcs northward and inward toward the axis of rotation, the inward component of the motion results in the eastward deflection that is eventually seen.

 

[A.T.]

Dont understand why horizontal correction exist even if you shoot directly est to west or west to east,because bullet going on same latitude where Earth has same "speed" ,so from my logic it must have only vertical correction?

Note that even if you stopped the Earth's rotation, ballistic projectiles fired east/west from a location not on the equator, would not stay on the same latitude, but deviate towards the equator (regardless if you fire east or west). This is not the Coriolis effect, but simply how orbits work.

 

[russ_watters]

If you are anywhere in the northern hemisphere then the Earth is like a phonograph platter that is rotating counter-clockwise.

Just to be clear, is the orientation of this platter a slice through Earth along the line of latitude, through Earth's center or sitting on the locally flat Earth?

 

[jbriggs444]

Just to be clear, the orientation of this platter is a slice through Earth along the line of latitude, right? Not a plate sitting flat on the locally flat Earth.

In my minds eye, a tilted plate is similar enough to a flat plate to be used for illustration purposes. When you want accuracy, you have to add the $\cos \theta$ terms to express the difference quantitatively.

 

[Change in pressure]

Exactly at the equator, the east-west deflection for a northward shot is precisely zero. Coriolis ignores the component of velocity parallel to the axis of rotation. [Artillery tables may report a slight deflection because an actual artillery shot will have a non-negligible vertical component. You could see a larger correction for indirect/plunging fire and a lower correction for direct/line of sight fire]

However, as the projectile arcs northward and inward toward the axis of rotation, the inward component of the motion results in the eastward deflection that is eventually seen.

You mean on this?

first case,cylinder rotate at 50RPM ,men A throw ball to men B,ball will come to men B because man A and B rotate with same speed or ball velocity vector is parallel to axis or rotation.

second case,men A and B have different speed,so ball will not come to person B..also ball velocity vector is not parallel to axis of rotation

 

[russ_watters]

In my minds eye, a tilted plate is similar enough to a flat plate to be used for illustration purposes. When you want accuracy, you have to add the $\cos \theta$ terms to express the difference quantitatively.

I edited this to add an option and reframe as a question...

I seem to have a missing piece, and it's the orientation of a plate for the 3d case. The ball rolling across a record in 2d is easy to see, but it doesn't help for the 3d case. When I visualize this, a flat plate With its axis corresponding to Earth's axis doesn't have north-south movement, only east-west movement. A plate fixed to Earth's surface need not rotate about its axis (the vertical)at all (only about an external axis). So I'm thinking that for the plate to rotate south ahead of you, it must be a slice through Earth's center, like a great circle route.

 

[A.T.]

first case,cylinder rotate at 50RPM ,men A throw ball to men B,ball will come to men B because man A and B rotate with same speed or ball velocity vector is parallel to axis or rotation.

If A aims at B, the ball will not reach B.

 

[Change in pressure]

If A aims at B, the ball will not reach B.

If air drag is not exist, why would not reach?

 

[A.T.]

If air drag is not exist, why would not reach?

Why would it follow the curvature of the cylinder to meet B at B's new position?

 

[RPinPA]

If it like you say,than you can hower in the air above africa until south america will appear under you,this is nonsense!

You can't. An artillery shell or ballistic missile is not hovering. It's following an elliptical orbit, same as any spacecraft .

Air,aircraft, everything what is in Earth gravity field moves with Earth together,..

If it's in the lower atmosphere, there is certainly the effect of the atmosphere pushing along with the surface of the earth. That's of course important to aircraft, which ride on that atmosphere. But that's not the case with an artillery shell or especially a ballistic missile, which goes nearly into space.

 

[FactChecker]

If it's in the lower atmosphere, there is certainly the effect of the atmosphere pushing along with the surface of the earth. That's of course important to aircraft, which ride on that atmosphere. But that's not the case with an artillery shell ...

I wondered about this. A bullet is effected by winds, but those wind velocities are large compared to the average velocity differences we are concerned with here. So the wind of the rotating atmosphere, compared with an artillery shell, can probably be ignored.

 

[jbriggs444]

You mean on this?

first case,cylinder rotate at 50RPM ,men A throw ball to men B,ball will come to men B because man A and B rotate with same speed or ball velocity vector is parallel to axis or rotation.
[snip drawing of rotating vertical cylinder with man low on cylinder tossing projectile at man standing directly above]

In that case, if we adopt the rotating reference frame there is no immediate Coriolis force because the initial velocity is parallel to the axis. However there is a centrifugal force which gives rise to a radial acceleration. The radial acceleration, in turn gives rise to a radial velocity and an associated Coriolis force. The combination of the two explains the spiral path observed from the rotating frame as the rising projectile flies away from the cylinder.

[And if we work in an inertial frame, we see a straight line trajectory that does not follow the curve of the cylinder to track the circularly moving target]

[snip drawing of rotating vertically oriented cone with man low and far from axis tossing projectile at man standing high and near the axis]

In that case, there is an immediate Coriolis force and corresponding deflection. This is in addition to the centrifugal force that also exists.

 

[Change in pressure]

If you are shooting east, the platter in front of you is rotating left/northward. If you are shooting west, the platter in front of you is rotating left/southward. If you are shooting south, the platter in front of you is rotating left/eastward. If you are shooting north, the platter in front of you is rotating left/westward.

Can explain this left/nortwarth ,left/southward, with some animation or picture?
I don't understud that,I see only vertical correction when shoot est-west ,west-est.

axis of rotation is prependicular to latitude plane,so this platter is not tilted,so ho can horizontal deflection genereted?

 

[jbriggs444]

Can explain this left/nortwarth ,left/southward, with some animation or picture?
I don't understud that,I see only vertical correction when shoot est-west ,west-est.

axis of rotation is prependicular to latitude plane,so this platter is not tilted,so ho can horizontal deflection genereted?

In the temperate latitudes, the axis of rotation does not lie parallel to the surface on which you stand. The rotation vector (pointing out of the pole) has a non-zero component in the direction of the local vertical.

 

[A.T.]

I don't understud that,I see only vertical correction when shoot est-west ,west-est.

I would suggest you learn to apply Newton's Laws of motion in inertial frames. Judging by your cylinder example you have some misconceptions there.

Using rotating frames to analyze ballistic motion in a radial gravitational field, and expressing it in components relative to the curved surface is more complex.

 

[Delta2]

To directly answer the question of this thread:
IMO, Coriolis force cannot be classified as real. Real forces are the ones that belong to one of the following four categories
1). Gravitational
2). Electromagnetic
3) Strong Nuclear
4) Weak Nuclear

I don't think that Coriolis force belong to any of the above categories so it is not real, it is fictitious. The various phenomena and effects we observe and we attribute them to Coriolis force, are in fact due to the rotation (spin) of Earth around its axis. This rotation is real (of course !) but Coriolis force is not real.

 

[jbriggs444]

To directly answer the question of this thread:
IMO, Coriolis force cannot be classified as real. Real forces are the ones that belong to one of the following four categories
1). Gravitational

You might want to rethink that one. It's fictitious as well.

 

[Delta2]

You might want to rethink that one. It's fictitious as well.

Eh what , gravity is fictitious? Maybe according to relativity but not in classical physics

 

[Jeffery Winkler]

Not so impossible. You can still take a hovering helicopter from New York to London but it will take longer to get there.

Try the following experiment. Get out of your chair and stand up. Jump vertically up in the air. Did you land in the same place where you were standing before or off to the side because the Earth moved beneath your feet while you were up in the air? Try the same experiment on a moving train. You will land in the same place in relation to the floor as you were at before. You do not stop moving in relation to the ground outside just because you are not physically touching the train. Do you believe that if you did this experiment on the Concorde that you would be killed when you hit the back of the cabin?

 

[jbriggs444]

Eh what , gravity is fictitious? Maybe according to relativity but not in classical physics

That fact throws a bit of cold water on the question, no?

Does it really matter whether gravity is real or an illusion as long as we agree about the experimental results?

 

[Delta2]

That fact throws a bit of cold water on the question, no?

Does it really matter whether gravity is real or an illusion as long as we agree about the experimental results?

Er sorry I thought we were in the regime of classical physics here, the sub forum of this post is Classical Physics indeed. It is just not the same thing to say gravity is fictitious force (according to GR) as to say Coriolis is fictitious force, different meaning of fictitious I think. But anyway, gravity is considered to be one of the four fundamental forces of the universe in most books and papers for me gravity is a lot more real than Coriolis. Coriolis force is just a mathematical expression disguised as a force, the only thing real about it is the rotation of the system that seems to "generate" it, but a rotating system does not generate Coriolis force in the same way as the curvature of space time generates gravity.

 

[A.T.]

I shoot on est on 40th parallel,I see only vertical correction,shoot will come a little bit higher,because target appear to move down as Earth rotate...But my shoot do not cross other parallels...

Ignoring air resistance the bullet will move on an elliptical orbit in a plane that contains the center of the Earth. So it will obviously not stay above the 40th parallel, because the plane containing the 40th parallel doesn't contain the center of the Earth. Look up on how orbits in an radial gravitational field work

 

[jbriggs444]

It is just not the same thing to say gravity is fictitious force (according to GR) as to say Coriolis is fictitious force

It is the same machinery -- the mathematics of coordinate systems -- that is responsible for coordinate accelerations of free falling objects in arbitrary coordinate systems in general relativity and for the coordinate accelerations in accelerated coordinate systems in classical mechanics.