[Le Repteux]

Quote from: rmolnav on Yesterday at 06:08:45

    1) Sublunar area. When adding two opposite vectors, the biggest prevails: we have a real, "positive" bulge.
    2) Antipodal area. Also two opposite vectors to be added. But now, because moon pull there is smaller, inertial effects (centrifugal forces) prevail: also a "normal" bulge builds !!

You seem to have missed my point, so I will present it differently. 1) means that the vector that prevails is due to gravitation, and 2) means that the vector that prevails is due to rotation, so if we stop the rotation, the prevalence of the inertial vector in 2) should disappear, so the bulge should also disappear, and it is not what we can expect if we apply the gravitation formula to a free falling body.

[rmolnav]

1) means that the vector that prevails is due to gravitation, and 2) means that the vector that prevails is due to rotation, so if we stop the rotation, the prevalence of the inertial vector in 2) should disappear, so the bulge should also disappear, and it is not what we can expect if we apply the gravitation formula to a free falling body.

OK. D.C. and me already discussed that on #211, 212, 213 ...
I had said:
"Let us forget the spaceship, and have just moon and earth.
If, somehow, we "remove" the revolving, both earth and moon will accelerate towards each other … Though only a transient movement, bulges would remain (and increase) until the collision. OK. Therefore, revolving was not causing them (YOUR deduction).
IN A QUITE SIMILAR WAY, we could reason as follows:
If, somehow (a “megaman” grasping the earth at its c.g…?), we “removed” that rectilinear, accelerated movement of earth towards the moon, outer bulge would not only disappear, but even change its sign, because outer earth hemisphere would get additional internal compressive stresses (before they were tensile s.), due to moon´s pull (though smaller than tensile stresses within inner hemisphere, closer to the moon …)
Therefore, if with the differential moon´s gravity maintained, outer positive bulge doesn´t exist, the moon differential gravity cannot be the cause of outer bulge !!
Same way you´ve “reasoned” lot of times … Either both are right, or both are wrong …"
Then he argued that, when he argued we had to let earth free to fall, meaning (I presume) that when saying "remove" the rotation is not to stop earth completely, just its circular movement ...
That I said:
"It´s unbelievable that you consider absolutely necessary to let the earth free to get the rectilinear accelerated movement towards the moon (to have the second bulge), but time and again you say that (as it is in the real case) the curved accelerated movement of the earth (its revolving around the moon-earth barycenter), has nothing to do with the formation of the outer bulge, and that it is not necessary at all !!
They are two different ways inertia manifests itself, but due to same basic Physics laws ...
In the first case, outer hemisphere massive stuff kind of "falls behind", because it is not sufficiently pulled by the moon to get the rectilinear acceleration of the whole earth. The whole earth stretches, and behind bulge also appears.
In the real case, outer bulge equally requires the revolving movement, because outer hemisphere massive stuff is not sufficiently pulled by the moon to get the required centripetal acceleration for the revolving movement. Internal stresses (in both senses, inwards and outwards) appear, earth stretches too, and outer bulge builds too ..."
I did mention neither "centripetal forces", nor "centrifugal forces", to avoid those terms so misunderstood by D.C. ...

[rmolnav]

With gravity, there is no added centrifugal force to consider.

Quote
But I haven´t EVER said that mechanism is the UNIQUE cause of tides ... If we add the (so bravely defended by you) effects of varying moon gravity, we have:
1) Sublunar area. When adding two opposite vectors, the biggest prevails: we have a real, "positive" bulge.
2) Antipodal area. Also two opposite vectors to be added. But now, because moon pull there is smaller, inertial effects (centrifugal forces) prevail: also a "normal" bulge builds !!

The straight-line acceleration under differential gravity does 100% of the job for (1) and (2), so any addition to (2) through your centripetal mechanism will have to be of zero size, rendering the role of that mechanism entirely imaginary.

WITHOUT KNOWING correctly what "centripetal force" is, it is IMPOSSIBLE for you to grasp the Physics of what we are discussing ...
I already told you:
"In relation to a noun such as “force”, one thing is its nature, or its essence, and quite another its let us say function, or its not essential characteristics, what usually is expressed through adjectives.
A force can be big, small, permanent, variable, pulling or pushing contact f., “at a distance f." (not sure the correct English name) … as well as centripetal or centrifugal, a possible additional quality in specific cases, NOTHING TO DO with “classifying gravity as centrifugal force” !!
Different types of forces (or components of forces) can act as centripetal forces, as long as their directions are perpendicular to the affected object trajectory, and in the sense of a “center” (of the circle if circular movement, or the center of curvature if other curved paths).
Gravitational force can act as centripetal force, as long as what above occurs.
E.g.: the parabolic trajectory of a cannon ball is due to the gravitational force action (and the initial speed vector): its tangential component changes the size of the speed, and its component perpendicular to speed vector, acting as a centripetal force, curves the trajectory, not letting the ball to follow its inertial tendency to continue straight" …
... but to no avail, as far as your erroneous mind set is concerned !!
You have serious problems not only in Physics and Logics (as I told you before), but also even in the very use of your own language ...
Donald Trump "essence" is a "man". As he is also an "american citizen", he could be elected as U.S. president, and during his term in office he is having that "function", that job ...
He is both a "man" (essence), and U.S. president (his main function).
Similarly, the essence of "gravitational force" is, as we all (?) know,  that it exists between any two massive objects (or parts of objects), pulling them towards each other, directly proportional to the their masses, and inversely proportional to the square of separating distance.
"Centripetal force" is not the "essence" of anything, it is a "function" any force (or one of its components), and particularly gravitational force, can have as long as it acts on an object, perpendicularly to its linear speed, and therefore making its trajectory to bend ...
Therefore, there is no need of "any addition to (2) through your centripetal mechanism" ... Same real moon gravity pull at each location has to have the function of centripetal force. And if the required centripetal force (mω²r) doesn´t match with gravitational pull at a given location, internal stresses and/or the considered massive piece own weight has to supply the difference, inwards or outwards ... (2nd Newton´s Motion Law has to be satisfied)
And "... with gravity, there is no added centrifugal force to consider" ... Sorry, there is rubbish !!
We can´t choose whether to consider to "add" a centrifugal force or not ... Centrifugal forces are  inertial effects which are ALWAYS present, as long as there is a curved trajectory ...
 

[David Cooper]

The "bulge" nearest the moon is caused by straight-line differential gravity, and so is the "bulge" furthest from the moon. My computer program demonstrates that in action. There is nothing to add to the bulges from the orbital path that isn't already accounted for in full by the straight-line acceleration. That is all there is to it.

What you need to do (if you want to go on disagreeing) is produce your maths to replace mine in the program so that you can show some kind of role for your imagined mechanism that would allow it to add some amount to the far "bulge" that isn't just an addition of zero. Alternatively, you can try to use your mechanism for the far bulge and mine for the near bulge, and then find some magical way to stop my mechanism doubling your far bulge. Good luck with that!

[rmolnav]

The "bulge" nearest the moon is caused by straight-line differential gravity, and so is the "bulge" furthest from the moon. My computer program demonstrates that in action. There is nothing to add to the bulges from the orbital path that isn't already accounted for in full by the straight-line acceleration. That is all there is to it.

1) "... strait-line differential gravity" ... "already accounted for in full by the straight-line acceleration."
Several times you have also said something about not necessary to add anything relative to a movement perpendicular to above mentioned "straight-line" ...
You seem to forget revolving (and rotation) are kind of two-dimension movements: velocity is certainly perpendicular to that straight-line, but both required (to curve the trajectory) centripetal acceleration, and inherent inertial centrifugal force, are parallel to it ... And that gravity pull at a given location is what massive earth stuff can "feel", not any "differential gravity" ... All or part of that moon gravitational pull HAS TO BE "USED" to make each particle revolve, acting as centripetal force and producing a centripetal acceleration, NOT any "straight-line acceleration" whatsoever ... That only would happen with no revolving at all (zero initial speed component perpendicular to gravitational field direction).
Therefore, to disregard completely those facts is erroneous !!
2) "My computer program demonstrates that in action" ...
Computers can´t "demonstrate" anything whatsoever ... It all depends on the inputs and the program, and on our correct (or erroneous) analysis of the output ... 

[Le Repteux]

If, somehow (a “megaman” grasping the earth at its c.g…?), we “removed” that rectilinear, accelerated movement of earth towards the moon, outer bulge would not only disappear, but even change its sign, because outer earth hemisphere would get additional internal compressive stresses (before they were tensile s.), due to moon´s pull (though smaller than tensile stresses within inner hemisphere, closer to the moon …)
Therefore, if with the differential moon´s gravity maintained, outer positive bulge doesn´t exist, the moon differential gravity cannot be the cause of outer bulge !!

Supporting the orbiting earth to avoid that it falls on the moon if we stop its orbiting speed is similar to what would be happening to the earth surface if we would stop its rotation: the earth surface would simply lose its equatorial bulge, and the orbiting earth would lose its gravitational ones. Now if we would reaccelerate the rotation of the two systems progressively, an equatorial bulge would build up progressively on both systems until they reach their orbiting speed, and stopping the speed at that moment would not erase the bulge immediately, it would erase only when they would stop orbiting because they are getting supported again, so it seems that, after all that talk, you may still be right about the two kinds of bulges being similar. The bulges that belong to free falling systems would then only be a free fall particularity. For instance, supporting the earth with a cup shaped support while we would progressively decelerate its orbital speed would progressively erase the tides, and they would automatically reappear as soon as we would remove the support to let the earth free to fall on the moon again. I'll let that idea age a bit in my mind until David comments it. If it is right though, programming such a support in David's simulation and stopping the speed should simply erase the bulges, and removing the support after a while so that the system free falls again should build up new ones progressively.

[rmolnav]

I'll let that idea age a bit in my mind

Thank you. I usually say I have to further "ruminate" (rumiar in Spanish) ... or "chew it over".
Please kindly be careful when saying things such as:
- "... if we stop its orbiting speed is similar to what would be happening to the earth surface if we would stop its rotation"
-" ... orbiting earth would lose its gravitational ones "
 Not quite clear what you are referring to ... because we have two earth "orbits" (around sun and around moon-earth barycenter), their two respective "revolvings", and its daily "rotation" or "spinning" ...

[Le Repteux]

I usually use the words "rotating" and "orbiting" to distinguish the two kinds of rotation, and I was talking of the earth/moon system, so I thought I didn't have to specify it. More importantly, tell me if what I said looks similar to what you mean.

[David Cooper]

You seem to forget revolving (and rotation) are kind of two-dimension movements: velocity is certainly perpendicular to that straight-line, but both required (to curve the trajectory) centripetal acceleration, and inherent inertial centrifugal force, are parallel to it ...

Choose the right frame of reference and it becomes clear that the perpendicular movement is irrelevant. I explained that to you before, but you made no comment.

And that gravity pull at a given location is what massive earth stuff can "feel", not any "differential gravity" ...

Differential gravity simply means that further-away parts of it have less gravity acting on them, so they accelerate less in the direction of that straight-line force. That does the whole job.

All or part of that moon gravitational pull HAS TO BE "USED" to make each particle revolve, acting as centripetal force and producing a centripetal acceleration, NOT any "straight-line acceleration" whatsoever ... That only would happen with no revolving at all (zero initial speed component perpendicular to gravitational field direction).

For every angle you can imagine it moving at, there's a frame of reference that shows that it reduces to straight-line acceleration with differential gravity.

Therefore, to disregard completely those facts is erroneous !!

The "bulges" are fully accounted for by the straight-line acceleration. The perpendicular component is irrelevant.

Computers can´t "demonstrate" anything whatsoever ...

Of course they can - they can show you the consequences of the maths that you program into it, and I programmed it to work on straight-line acceleration with differential gravity.

It all depends on the inputs and the program, and on our correct (or erroneous) analysis of the output ...

You can check the source code and the routine called "run()" where that maths is applied. Your job is to provide your alternative maths for that routine to run on. If you get it right, it should produce the same end result, but with a lot of superfluous number crunching.

[David Cooper]

For instance, supporting the earth with a cup shaped support while we would progressively decelerate its orbital speed would progressively erase the tides, and they would automatically reappear as soon as we would remove the support to let the earth free to fall on the moon again. I'll let that idea age a bit in my mind until David comments it. If it is right though, programming such a support in David's simulation and stopping the speed should simply erase the bulges, and removing the support after a while should build up new ones progressively.

I could add a "hold" button (or modify the "pause" one) to halt the moon and Earth and keep them in place while their gravity continues to act on each other. This would lead to the water on the far side of the Earth being pulled down more strongly than it is at the equator half way between the near and far sides (where the water would be pulled sideways), but it would make no difference to the force on the water on the near side. Hold the Earth like that for a while though and the water will flow to the near side and build up there into an actual bulge. If the planet's spinning though, the water won't have time to build up at the near side, but the application of those forces would doubtless lead to interesting tides: the Earth would fall 38 miles towards the moon in a day if the orbital motion was removed, so the water between the far and near points would perhaps move somewhere close to ten miles eastward in twelve hours and then ten miles west over the next twelve, which adds up to a lot of sloshing about. That would be quite disruptive to the rail network, I suspect.

Edit: that 38 miles a day figure is way out - that's for the moon falling towards the Earth, so the real figure should be closer to half a mile a day.

[rmolnav]

Supporting the orbiting earth to avoid that it falls on the moon if we stop its orbiting speed is similar to what would be happening to the earth surface if we would stop its rotation: the earth surface would simply lose its equatorial bulge, and the orbiting earth would lose its gravitational ones

Last "lost" would not happen if only daily "rotation" stopped: at any location there would be two high tides and two low tides a month ...
But you continue:

Now if we would reaccelerate the rotation of the two systems progressively ...

when before you had said:
" what would be happening to the earth surface if we would stop its rotation" (only one "system" ??).
Sorry, but I find rather difficult to be sure one is "imaging" same case you are actually trying to convey ...

[rmolnav]

Differential gravity simply means that further-away parts of it have less gravity acting on them, so they accelerate less in the direction of that straight-line force

Again, those parts where less gravity don´t accelerate less in that direction than others ... That would require them to increase their velocity in that direction less than others, what obviously doesn´t happen, because the velocity in that direction of all parts keeps being zero !!

[Le Repteux]

I could add a "hold" button (or modify the "pause" one) to halt the moon and Earth and keep them in place while their gravity continues to act on each other. This would lead to the water on the far side of the Earth being pulled down more strongly than it is at the equator half way between the near and far sides (where the water would be pulled sideways), but it would make no difference to the force on the water on the near side. Hold the Earth like that for a while though and the water will flow to the near side and build up there into an actual bulge.

I was suggesting a cup shaped support to avoid the tides to build up on the near side. I knew that we needed a glass shaped one to avoid any displacement from the far side to the near one, but this way, we can't imagine the far side tides as easily. What I'm trying to show is that if the orbiting earth was supported the way the rotating one is supported, which is everywhere except at its surface, stopping the orbiting speed would erase its orbiting bulges the same way stopping the rotating earth would erase its equatorial bulge, and then letting it fall towards the moon (or accelerating it to its orbital speed again) would build up the free fall bulges again, but we could also only give it enough speed to get an equatorial bulge instead of a free fall one, and then increase that speed until it becomes a free fall one. As I said, from this analysis, it looks as if the free fall and equatorial bulges were only particularities of gravitational bulges.

[Le Repteux]

Supporting the orbiting earth to avoid that it falls on the moon if we stop its orbiting speed is similar to what would be happening to the earth surface if we would stop its rotation: the earth surface would simply lose its equatorial bulge, and the orbiting earth would lose its gravitational ones

Last "lost" would not happen if only daily "rotation" stopped: at any location there would be two high tides and two low tides a month ...
But you continue:

Now if we would reaccelerate the rotation of the two systems progressively ...

when before you had said:
" what would be happening to the earth surface if we would stop its rotation" (only one "system" ??).
Sorry, but I find rather difficult to be sure one is "imaging" same case you are actually trying to convey ...

Read my first quote again: I said there that if both orbiting and rotational speeds were stopped, then both the equatorial and gravitational bulges would disappear. I'm comparing two kinds of rotation to see if they are equivalent, so when I say orbital speed, I'm talking of the orbital rotation, and when I say rotational speed, I'm talking of the non orbital one.

[rmolnav]

Read my first quote again: I said there that if both orbiting and rotational speeds were stopped, then both the equatorial and gravitational bulges would disappear. I'm comparing two kinds of rotation to see if they are equivalent, so when I say orbital speed, I'm talking of the orbital rotation, and when I say rotational speed, I'm talking of the non orbital one.

You didn´t actually mention "both", but said one case was similar to other, not both "stops" together ...
In any case, I prefer not to consider earth is orbiting the moon, let alone it is in a "free fall" ... As moon is also moving (and much more than earth), the dynamics of moon-earth dance (always at same distance from each other) should be rather considered as a kind of "spinning" around the barycenter of a unique extended two-parts body (though earth only revolves).
That way the dance effects are really similar to the daily spinning of earth, but with a some 28 days complete cycle ...
According to one of the NASA scientists I referred to some weeks ago:
"As the earth and moon whirl around this common center-of-mass, the centrifugal force produced is always directed away from the center of revolution. All points in or on the surface of the earth acting as a coherent body acquire this component of centrifugal force".
And, as I´ve already said, at closer to moon hemisphere stronger moon´s pull prevails. And at further hemisphere, where moon´s pull is smaller, centrifugal force prevails.
That is why "we have two high moon-related tides a month", and due to the daily earth spinning, we perceive them twice a day (on top of the permanent equatorial bulge, that has nothing to do with moon-earth dynamics).

[David Cooper]

Differential gravity simply means that further-away parts of it have less gravity acting on them, so they accelerate less in the direction of that straight-line force

Again, those parts where less gravity don´t accelerate less in that direction than others ... That would require them to increase their velocity in that direction less than others, what obviously doesn´t happen, because the velocity in that direction of all parts keeps being zero !!

I expect people to be able to correct the wording for themselves and then to recognise the idea that the text is intended to communicate (and which all intelligent readers will automatically take from it). Let me reword it for nitpickers. Differential gravity simply means that further-away parts of it have less gravity acting on them so they lag behind a little under that acceleration, this resulting in a lower pressure there, while the nearer parts have more gravity acting on them, so they do the opposite, reacting more quickly than the planet as a whole and again generating a lower pressure there. The accelerations are simultaneous and equal in practise, but they wouldn't initially be simultaneous if there was no moon and you suddenly introduced the moon into the system - the lags would occur while the lower pressures are established, and then the acceleration is equalised.

[David Cooper]

I was suggesting a cup shaped support to avoid the tides to build up on the near side. I knew that we needed a glass shaped one to avoid any displacement from the far side to the near one, but this way, we can't imagine the far side tides as easily.

The cup would have to be more of an enclosing sphere with a little hole in the top.

What I'm trying to show is that if the orbiting earth was supported the way the rotating one is supported, which is everywhere except at its surface, stopping the orbiting speed would erase its orbiting bulges the same way stopping the rotating earth would erase its equatorial bulge,

There are no orbiting bulges to erase, so it's hard to follow what you're trying to do.

and then letting it fall towards the moon (or accelerating it to its orbital speed again) would build up the free fall bulges again, but we could also only give it enough speed to get an equatorial bulge instead of a free fall one, and then increase that speed until it becomes a free fall one. As I said, from this analysis, it looks as if the free fall and equatorial bulges were only particularities of gravitational bulges.

Well, I can't follow it well enough to work out what that analysis is doing. (The whole issue is already resolved too, so I'd rather work on other things like LaFreniere's work and just leave rmolnav to his delusions.)

[David Cooper]

And, as I´ve already said, at closer to moon hemisphere stronger moon´s pull prevails. And at further hemisphere, where moon´s pull is smaller, centrifugal force prevails.

On the side nearest the moon, stronger moon's pull prevails, and on the side furthest from the moon, weaker moon's pull prevails. One single mechanism acting on both sides.

[rmolnav]

Differential gravity simply means that further-away parts of it have less gravity acting on them so they lag behind a little under that acceleration, this resulting in a lower pressure there, while the nearer parts have more gravity acting on them, so they do the opposite, reacting more quickly than the planet as a whole and again generating a lower pressure there. The accelerations are simultaneous and equal in practise, but they wouldn't initially be simultaneous if there was no moon and you suddenly introduced the moon into the system - the lags would occur while the lower pressures are established, and then the acceleration is equalised.

What you explain would be a pretty good analysis ... only if there were no earth-moon revolving/rotation , and earth were actually accelerating along a rectilinear path towards the moon ...
But nature keeps moon-earth separation fairly constant, thanks precisely to that "dance" ... which also produces other dynamical effects that you loftly keep despising ...
At earth c.g. there is a balance between moon´s gravitational pull, and centrifugal force inherent in the revolving of earth around the barycenter. But that only happens at a section there (all points at same distance as earth c.g. to moon c.g.).
And, I repeat:
 

... at closer to moon hemisphere stronger moon´s pull prevails. And at further hemisphere, where moon´s pull is smaller, centrifugal force prevails.

... and water from each hemisphere "piles up" (though relatively very, very little) respectively at sublunar and antipodal areas !!

[Le Repteux]

For clarity purposes, I need to specify that I changed my mind. At first, I agreed with David's differential pulling on free falling bodies, and now, I agree with Rmolnav about orbital rotation being involved in the tides. Please, reread that post and tell me if you understand it differently.