[Le Repteux]

OK. But it is equivalent to consider each particle of the earth linked by means of a somehow elastic string to moon´s c.g., certainly with tensions (gravity pull) the shorter the string, the stronger.

No need for the strings to be elastic; if they pull more, the particles tied to them will simply accelerate more and the strings will have to shorten to follow the motion of the particles if they are free to move, but if they are not, for instance if the earth follows a circular orbit around the moon and if it is not rotating with regard to the moon, then all the distances that have shortened will stay the same and the strings will not have to shorten anymore.

But you seem to forget that each earth particle is also linked much more strongly to the rest of the earth, to its c.g. if you wish: its own weight.

There is a difference between the action the rotation of a planet and the action the orbital motion of the same planet has on its own particles, and I'm not sure that you figure it out the way I do, so here is a mind experiment about that. If we accelerate the earth's rotation until its surface begins to orbit, the equatorial bulge will get a lot more important than what it is, but once some of the surface will be orbiting, we can slow down the earth and thus reduce the bulge without affecting what is already orbiting. Now, if we then succeed to accelerate at the same time all the orbiting particles again, we won't get a bulge like the equatorial one, but instead, all those particles will follow an elliptic trajectory whose perigee will be located at the place they were accelerated, which means that they will all begin to slow down and move away from the earth for a while until they get at their apogee, and then they will start accelerating again and move closer to the earth until they get at their perigee. Accelerating a circular orbital motion does not produce an equatorial bulge, it produces a pulsation, and it is so because orbiting bodies are free to move from one another radially. It is that liberty that produces the tides in this case, not the rotation.

The water molecules of the seas are free to move radially a bit, and they do so while pulsating a bit as if they were accelerating and decelerating continuously on their orbital trajectory with the moon. David doesn't agree with me on that one but I still think that the tides have something to do with the two faces of the earth not being at the right speed on their orbital trajectory with the moon. If I'm right, it means that there might be no tides if the earth was rotating clockwise instead of counterclockwise, because its two faces could then move at close to their right speed on their orbital trajectory with the moon during their transit, which would incidentally have nothing to do with the centripetal force that produces the equatorial bulges either. That mechanism would not change the way David explains the bulges though, because suddenly stopping the orbital motion of the earth without stopping its clockwise rotation would immediately produce some. That mechanism looks weird because it's new but think of it this way: why would the particles of the earth change their trajectory to produce bulges while they are actually orbiting at the right speed all the time on their orbital trajectory with the moon? After all, it is the difference in the centripetal acceleration at different distances that produces the tides, and it is precisely the same difference that produces the orbital speeds, no?

[rmolnav]

Le Repteux
Thank you.
I have to go more slowly through your post, as well as through David´s.
But just one thing now.
You, and David too, mention earth rotation and equatorial bulge ...
I´ve said many times that (some replying David´s posts), to analyze properly moon-earth dynamics (and the resulting some 28 days tidal complete cycle), we have to disregard completely the daily earth spinning, which has nothing to do with the moon ...
Earth is revolving around moon-earth barycenter, rather than rotating, let alone rotating around the moon !! The dynamics of that movement differs from the case of a proper "orbiting" of a satellite around a planet, or of a planet around the sun ...
The cycle we see (some 24.8 h. complete cycle) is certainly also due to earth daily spinning (the 0.8 h. due to daily moon change of position), but to mix that with the permanent equatorial bulge caused by that spinning is frequent cause of misunderstandings !!

[David Cooper]

I pointed out before that there are multiple versions of the straight-line case which produce the exact same "bulges". If a moon and planet are moving apart, or towards each other, or just on the point where they're stopping moving apart and are about to start moving towards each other, the "bulges" are identical if the distance between the moon and planet are the same in each case. Relativity shows us that this is the case, because the acceleration force is the same in all three cases - if you are co-moving with the planet (or moon) each time, you will expect it to behave the same way in all of these situations, and it will do.

The same applies to a case where there is perpendicular movement involved - we can add it to all three of the previous cases, and what happens? We use a frame of reference where we're co-moving with the planet /moon as before, and we get the exact same "bulges" produced as in the cases where there is no perpendicular movement. Relativity tells us that it must always behave the same way - the only thing producing the "bulges" is the straight-line differential gravity.

What we do have though is a necessary coincidence in that when there is a component of perpendicular movement, we see things behaving as if they're trying to follow paths that match up to the ones that would be predicted for them by analysing things on the basis that centripetal force is involved, and that is what some people trip over when they're looking at this - it matches up so well that they are fooled into thinking that centripetal force must be the cause, but it's a mere illusion. The real explanation is much simpler - the straight line acceleration does the whole job, and that's why you get the exact same "bulges" when the perpendicular movement is completely removed. The perpendicular component of movement is demonstrably a complete irrelevance to the cause.

(This is radically different to the case of a ball on a string where the perpendicular movement is essential to the formation of the bulges because that movement generates the centripetal force that generates the bulges - in that case, the cause can be attributed to centripetal force and by extension to the perpendicular movement of the ball. With orbiting objects, stopping the movement doesn't remove the force that's generating the "bulges" and the persistence of the "bulges" with the same force still acting in full tells you that the cause of the bulges is not centripetal force - it is merely being labelled as centripetal in cases where there is perpendicular movement, and some people then make the mistake of using that label as part of their description of the cause. That's the same kind of mistake as claiming that a boxer whose hand has been cut off would have blood pouring out of the end of his arm because there's no fist on the end of it - the use of the word fist is fundamentally wrong there as it should be referred to as a hand.)

[David Cooper]

I promised a program, and here it is. I might modify it further, but it's got enough done to make it worth sharing now:-

http://www.magicschoolbook.com/science/tides.html

Note how the size of the "bulges" (or more accurately, the strength of the tidal forces) is not dependent on the direction and speed of travel of moon or planet of given masses and sizes, but is determined by one factor alone - distance between the two.

[rmolnav]

As I´ve already said, to discuss with you is useless, among other things because you have so fixed your (wrong) ideas that you are unable to see and/or understand what said to you.
On my post #152 I told you:
"Just one question. You say:
"If you take away the gravitational difference caused by it diminishing over distance, you will have no tides at all. The complexities that you are imagining do not contribute to the tides, even though centripetal bulge does add to to the degree to which the sea bulges away from a spherical shape - the tides are just the distortions added to that already-distorted surface and are not the total distortion away from a sphere".
You seem to refer ("already-distorted surface") to the equatorial bulge caused by daily earth spinning.
That is caused by inertial effects. Water, with a linear speed tangent to equator (if exactly there), tends to follow the tangent. But own earth gravity obliges the water to follow a circular path.
In this case, without any significant gravity differences, we have a relatively huge permanent bulge, because centripetal/centrifugal forces are proportional to the square of angular speed, some 29 times bigger than in the moon-earth "dance"
Somewhere you say tides occur on top of that permanent equatorial bulge. Quite right.
But, why earth daily spinning can cause that permanent equatorial bulge, and (according to you) the some 29 day revolving of the earth around the barycenter (please don´t mix with daily earth rotation !!), besides actual gravity forces on each location, can´t intervene in tides formation ??
In this last earth movement, water (and solid parts too) are also somehow obliged to follow circular paths, instead their inertial tendency to follow the tangents ... Therefore, centripetal and centrifugal forces are also present, and they do intervene on the 29 day cycle of moon-éarth dynamics, and on lunar related tides !!"
And a couple of days ago you said:

If the Earth was rotating once a month, permanent bulges would form on two opposite sides and they would then grow and shrink a little throughout each month as the moon gets closer and further away. The moon's orbit not being circular would also make the bulges move east and west a bit because the Earth's rotation wouldn't track the moon's position in the sky perfectly. The Earth's actual rotation prevents such bulges from forming (because the water can't move fast enough to keep up), so we just have tiny pressure changes acting over a huge area and adding enough energy to generate oscillations that provide the tides that we see.

THERE WE ARE !! ... What in bold is what is actually happening ... !! (though earth "revolves", rather than "rotates", in its dance with the moon)
After so many posts, haven´t you realized even that basic fact ??
How can you have been so sure of your stand, if you continue to mix two quite different movements, and keep considering that when I say earth-moon dance, in particular earth revolving around the barycenter, I´m not referring to that but to earth daily spinning ??
Because, trying yo avoid confusion, I´ve usually been very careful even reserving the term "spinning" for the a day period movement (though "rotation" could also be used), the term "revolving" for the 28/29 d. period movement of earth, and "rotation" for the equal period movement of the moon ... But to no avail, as far as your "blinded" (at least in this case) mind is concerned !!

[Le Repteux]

I promised a program, and here it is. I might modify it further, but it's got enough done to make it worth sharing now:-

http://www.magicschoolbook.com/science/tides.html

Nice simulation as usual David, and since simulations represent real motions, Rmolnav, you should be able to make one that represents what you think. When we halt the inertial motion of the moon on David's one, it falls directly to the earth, but the bulges do not disappear, whereas they should disappear in yours since you think that they need centrifugal motion to appear. I had another idea that may help to illustrate the difference between gravitation and inertia as far as orbital motion is concerned: if we applied a centrifugal motion vector to the moon as a whole when it orbits, its bulges would follow the same motion its CG would follow, and reversing that vector to bring the moon back on its trajectory wouldn't add to them, which means that such a vectorial motion cannot create them.

[rmolnav]

No need for the strings to be elastic;

You are right, but I meant they should not have a quite fixed length, to allow the particles some "freedom" to move ... Analogies aren´t usually perfect!

Molnav, the force applied to a large body made out of particles cannot be treated the same as the force applied to each of its particles taken separately, and you seem to think so. In the case of a body, we need an anchor to hold it, but we can't hold a particle with an anchor. The moon and the earth are not anchored to one another, instead, it is each particle from each of the bodies that is linked to all the particles of the other body by means of the gravitational force, and that force depends on distance, which is not the case with a string. If we would anchor all the particles of the moon to all the particles of the earth by means of strings, there would be no bulge, but since the gravitational force weakens with distance, the closer particles are pulled more strongly than the farther ones and it creates bulges.

Sorry I answered that thinking it had been said by D.C. ...

If we accelerate the earth's rotation until its surface begins to orbit, the equatorial bulge will get a lot more important than what it is, but once some of the surface will be orbiting, we can slow down the earth and thus reduce the bulge without affecting what is already orbiting

Apart from the fact that you are referring to the "spinning" of the earth (clearly out of my stand on moon related tides), you already posted that idea (#188 ), and I replied:
" ...1) The most important: when I´ve mentioned that effect, saying even "permanent" equatorial bulge, and usually adding something like "due to earth daily spinning", I was just saying that due to similar inertial reasons, earth app. monthly revolving around moon-earth barycenter should deform oceans surface, on its own right ... And I even said, at least once, something like "please don´t mix the two movements", because it´s not the first time D. C. seems to think I connect the moon related tides to earth daily spinning !!
Therefore, thank you for your words, but the difference is so obvious, that no additional cases need to be added "to illustrate" it ... The problem is that D.C. and me seem to speak in different languages !!
2) If you ruminated your scenario, let alone if you made some maths, you would find that, before centrifugal forces made some of the earth surface stuff "levitate", earth would kind of explode ...
Logically, equatorial bulge would previously get higher and higher, and also wider. Even with smaller radius at higher latitudes, those forces (proportional to ω²r), would increase dramatically.
And the required angular velocity to orbit at earth surface, I don´t remember any figure, but is really huge !!"
I could make other comments to your post of yesterday (not agreeing necessarily), but surely you have already seen that many of the things you and D.C. are saying  are out of my stand and what I am discussing, because earth spinning has nothing to do with moon-earth dynamics ...
It only changes the perception we have of the real monthly tidal cycle, and produces a small misalignment of the bulges, unable to catch up with sublunar (and antipodal) exact point, due to the high spinning speed (some 28 times higher than moon-earth dance, in terms of angular speed, and being earth radius app. 50% bigger than the radius of earth revolving !!).
All that supposing the barycenter were still, disregarding earth-moon pair revolving around the sun, to make simpler the analysis.

[David Cooper]

As I´ve already said, to discuss with you is useless, among other things because you have so fixed your (wrong) ideas that you are unable to see and/or understand what said to you.

As usual, you accuse others of having your faults.

But, why earth daily spinning can cause that permanent equatorial bulge, and (according to you) the some 29 day revolving of the earth around the barycenter (please don´t mix with daily earth rotation !!), besides actual gravity forces on each location, can´t intervene in tides formation ??

Because if the force being applied was evenly applied rather than diminishing over distance, there would be no tides in a system with two bodies orbiting each other. The whole planet and all the water sitting on it would be pulled equally strongly towards the moon and the whole moon would be pulled towards the planet in the same way with no tidal forces acting at all. With a spinning planet, there is "centrifugal" force "flinging" material out into a bulge round the planet centred on the equator. With two orbiting ones (not spinning) and without differential gravity, there would be no such centrifugal force trying to fling any material in any direction that the planet it's sitting on isn't also moving in (and no equivalent using the preferred equivalent description with the word centripetal). The water would simply sit on the planet and move with it, matching it in acceleration at all times. I told you this long ago, but you never take it in, and that's the root of your entire problem. There is no centripetal/centrifugal factor to add in for tides - it's all done directly by straight-line differential gravity (and you can see this mechanism at work in the computer program).

In this last earth movement, water (and solid parts too) are also somehow obliged to follow circular paths, instead their inertial tendency to follow the tangents ... Therefore, centripetal and centrifugal forces are also present, and they do intervene on the 29 day cycle of moon-éarth dynamics, and on lunar related tides !!"

If you were to apply a force that doesn't diminish over distance and applied it in the same direction to all parts of the planet/moon, and if the planet/moon isn't spinning, there would be no difference in the paths that any parts of the planet/moon follow - they would follow paths through space of exactly the same shape as each other. I've told you this before, but you obviously didn't get it and I don't imagine you'll get it now either. However, all it would take is a little computer program to test it and find that I'm right. Do I need to write one for that too to get simple realities through to you? With gravity, there is no flinging of stuff caused by the orbit of a planet, which is why you shouldn't be misled by anyone attaching the label "centripetal force" to it.

All you have is differential gravity acting on it and a straight-line acceleration which makes the nearest parts try to accelerate more in that direction and the furthest parts try to accelerate least, all happening in such a way that the component of perpendicular movement is a complete irrelevance. However, the result of this straight-line acceleration does lead to the material behaving in a manner that appears to fit with your explanation. The problem with your explanation though is that the mechanism for this still depends on differential gravity to make the material behave in that way, and so your explanation, if stated fully, has to include the real explanation of differential gravity, and the extra bit you're adding about centripetal force being involved is an unnecessary addition to it which is invalidated by straight-line cases. A massive object like Jupiter can tear comets apart through tidal forces even if they are heading directly towards it. Centripetal force is not part of the cause of tides.

And a couple of days ago you said:

If the Earth was rotating once a month, permanent bulges would form on two opposite sides and they would then grow and shrink a little throughout each month as the moon gets closer and further away. The moon's orbit not being circular would also make the bulges move east and west a bit because the Earth's rotation wouldn't track the moon's position in the sky perfectly. The Earth's actual rotation prevents such bulges from forming (because the water can't move fast enough to keep up), so we just have tiny pressure changes acting over a huge area and adding enough energy to generate oscillations that provide the tides that we see.

THERE WE ARE !! ... What in bold is what is actually happening ... !! (though earth "revolves", rather than "rotates", in its dance with the moon)

The word "rotates" means "revolves". I can assure you that the bit in bold is not what is actually happening - the Earth rotates nearly thirty times a month (I forget whether it's 28 or 29 times). You appear to have interpreted what I said in a very wayward manner, perhaps also thinking that I'm referring to the size of the tides varying through the month, but I wasn't referring to that at all. I was talking about an Earth rotating (revolving) once a month such that someone standing on the Earth with the moon overhead would be able to watch the moon there the whole time (when the sun doesn't appear too close to it in the sky). This illustrates the point that English isn't your first language and that you may be misunderstanding all manner of other things that I've said too.

After so many posts, haven´t you realized even that basic fact ??

If you actually understood the text you were reading, you wouldn't be mistaking it for the Earth and moon as they actually are - I was describing a very different scenario.

How can you have been so sure of your stand, if you continue to mix two quite different movements, and keep considering that when I say earth-moon dance, in particular earth revolving around the barycenter, I´m not referring to that but to earth daily spinning ??

I haven't been mixing them at all. Again, your interpretation skills are the root of your problem. The reason you think I'm talking rubbish is that your translation software is rubbish.

Because, trying yo avoid confusion, I´ve usually been very careful even reserving the term "spinning" for the a day period movement (though "rotation" could also be used), the term "revolving" for the 28/29 d. period movement of earth, and "rotation" for the equal period movement of the moon ... But to no avail, as far as your "blinded" (at least in this case) mind is concerned !!

I've been very careful in my wording too, but I can't prevent you from mistranslating everything.

[David Cooper]

...and since simulations represent real motions, Rmolnav, you should be able to make one that represents what you think.

That's exactly what I had in mind when I wrote my program. If he wants to provide his maths, I can replace my maths with his in the function called "run()" - the rest of the program should work fine for both versions (so long as the right values are assigned to the right variables for the force felt at the near and far points of both bodies). If he does this, he will soon find that any calculations he makes involving centripetal force are completely superfluous.

[rmolnav]

The word "rotates" means "revolves".

Not for many scientists:
"revolve / rotate
In ordinary speech these two words are often treated as interchangeable, though it’s “revolving credit account” and “rotating crops.” Scientists make a sharp distinction between the two: the earth revolves (orbits) around the sun but rotates (spins) around its axis".
(Prof. Brians, Washington University)

[David Cooper]

That's interesting - I wasn't aware that any of them restricted the use of words in such an artificial way. RPM, for example, stands for revolutions per minute - not rotations per minute. In this discussion though, you should always be able to work out which meaning is intended by the context - if one interpretation makes sense and the other doesn't, you should go with the one that makes sense instead of choosing the one that doesn't and then launching into an attack based on your incorrect interpretation.

Edit: on looking back, I notice that I did actually use the word "rotate", and you then told me I should have used the word "revolve" and then attacked what I'd said on the basis that you wanted it to mean "revolve" (orbit) rather than "rotate". That's a weird thing to do when it makes full sense the way I said it and is plain bonkers the way you wanted to interpret it.

[rmolnav]

Quote
And a couple of days ago you said:
Quote from: David Cooper on 29/08/2018 22:12:31
If the Earth was rotating once a month, permanent bulges would form on two opposite sides and they would then grow and shrink a little throughout each month as the moon gets closer and further away. The moon's orbit not being circular would also make the bulges move east and west a bit because the Earth's rotation wouldn't track the moon's position in the sky perfectly. The Earth's actual rotation prevents such bulges from forming (because the water can't move fast enough to keep up), so we just have tiny pressure changes acting over a huge area and adding enough energy to generate oscillations that provide the tides that we see.
THERE WE ARE !! ... What in bold is what is actually happening ... !! (though earth "revolves", rather than "rotates", in its dance with the moon)

The word "rotates" means "revolves". I can assure you that the bit in bold is not what is actually happening - the Earth rotates nearly thirty times a month (I forget whether it's 28 or 29 times). You appear to have interpreted what I said in a very wayward manner, perhaps also thinking that I'm referring to the size of the tides varying through the month, but I wasn't referring to that at all. I was talking about an Earth rotating (revolving) once a month such that someone standing on the Earth with the moon overhead would be able to watch the moon there the whole time (when the sun doesn't appear too close to it in the sky). This illustrates the point that English isn't your first language and that you may be misunderstanding all manner of other things that I've said too.

You stubbornly keep ignoring that, IN ALMOST A MONTH, apart from those 28/29 cycles of earth daily spinning, and apart from a little less than a 29/365 of the complete orbit around the sun, our planet does complete a cycle of its revolving around the barycenter ...
Disregarding the daily spinning, which has nothing to do with moon-earth dynamics, we can look at the moon e.g. midnight (when visible), and write down its angular position in its apparent trajectory.
And do the same next day ... We´ll see there has been a change towards the east: THAT is the real movement of the moon. And earth, in its dance with the moon, ALWAYS at the other side of the barycenter, will have followed the same angle in its revolving around the barycenter.
By the way, I posted a link to a google image which shows that "dance" in three different positions, very interesting, but I didn´t see any further comment here ... Did you see it? I said:
(#152 and #153)
"There is an image:
main-qimg-851d9284749b378191c8ae87e4e2e4c2
that can help guys understand better moon-earth dance, especially earth revolving around the barycenter.
By the way: the image has a detail a little bit erroneous ... Any guess?
A Google page appears. Please click on images …"
 

[rmolnav]

I can assure you that the bit in bold is not what is actually happening - the Earth rotates nearly thirty times a month (I forget whether it's 28 or 29 times). You appear to have interpreted what I said in a very wayward manner, perhaps also thinking that I'm referring to the size of the tides varying through the month, but I wasn't referring to that at all.

I could not have thought that, because it is cristal clear, at least to me, that the size of the tides changes over the month as a consequence of adding sun-earth dynamic effects to moon-earth´s, that continuously vary in its relative position (apart from other minor changes).
And, as I´ve said many times, I´m usually discussing only moon-related tides, for the sake of simplicity.

[David Cooper]

You stubbornly keep ignoring that, IN ALMOST A MONTH, apart from those 28/29 cycles of earth daily spinning, and apart from a little less than a 29/365 of the complete orbit around the sun, our planet does complete a cycle of its revolving around the barycenter ...

Ignoring it? Hardly - I've responded to it repeatedly. Do I really have to do it yet again? The Earth goes round in a circle (= revolves round the barycentre), but as I keep telling you, if you apply an even force you can make something follow a circular path without any material being flung off it because all the material follows the same shape of path - I told you long ago why you cannot make a functional centrifuge using an evenly-applied force to cause something to move in a circle. It's only because there is differential gravity that you get some material "wanting" to follow different paths and that's caused by straight-line acceleration force differences rather than it being flung out by centrifugal force, as demonstrated by the case where all perpendicular movement is removed and the same straight-line acceleration force differences lead to the same tidal effect.

By the way, I posted a link to a google image which shows that "dance" in three different positions, very interesting, but I didn´t see any further comment here ... Did you see it? I said:
(#152 and #153)
"There is an image:
main-qimg-851d9284749b378191c8ae87e4e2e4c2

It didn't look like a viable link (and still doesn't), but I also didn't need to see an image of this dance, so I didn't follow it up. If you look at my computer program (assuming you have a machine with a screen big enough for it to work), you'll see the dance played out there, and it's greatly exaggerated because I've started with a moon only 1/8 the mass of the planet that it's going round.

that can help guys understand better moon-earth dance, especially earth revolving around the barycenter.
By the way: the image has a detail a little bit erroneous ... Any guess?
A Google page appears. Please click on images …"

If you can produce an actual link to it, I'll be happy to have a look.

I could not have thought that, because it is cristal clear, at least to me, that the size of the tides changes over the month as a consequence of adding sun-earth dynamic effects to moon-earth´s, that continuously vary in its relative position (apart from other minor changes).

Indeed it does, so you have some excuse for failing to interpret correctly what was said, but I did use the word "rotate" and it meant exactly that - one rotation in a month.

And, as I´ve said many times, I´m usually discussing only moon-related tides, for the sake of simplicity.

I wasn't aware that I was discussing anything other than tides relating to the moon (either caused by it or caused to it), apart from a couple of references to the sun's involvement, but that was many pages back.

[rmolnav]

174 Le Repteux
Looking for something else, yesterday I saw this post of you, which for some reason I had not made any comment on:
"I have a question about the tides that has not been answered yet, so I might as well post it here.
While the earth and the moon execute their common orbital trajectory with the sun, their common barycenter goes at the right speed all the time, but not their respective gravity centers: those are too fast when they transit on the far side, and too slow when they transit on the near side. They should thus behave as if they were at an aphelia on the far side, and at a perihelia on the near one, slowing down on their orbital trajectory with the sun and getting away from it progressively during the first half of their far side transit (and then doing the inverse during the second half), and accelerating and getting closer to the sun during the first half of their close side transit (and doing the inverse also during the second half), what should progressively increase and decrease the distance between them during their transit. I never heard of such an observation, but I can't find a flaw in the logic. Would it be too small to be observable?"
I´m afraid there is a flaw: what you say is valid for a proper orbiting movement of an object, only "feeling" gravitational pull from the other "central" object, and its inertial "tendency" to maintain its initial speed vector (that manifest itself as the controversial "centrifugal force") ...
But earth c.g. speed vectors caused by its revolving around the barycenter have to be added ...
During its far side transit (new moon +/- a week), earth revolving around the barycenter speed vectors have components same sense as orbiting around sun ... Resulting actual speed increases during the first half, and decreases afterwards.
And during the near side (full moon +/- a week), the opposite happens and real speed decreases initially, and increases afterwards.
The size of tides also "oscillates" due to that, being bigger when new and full moons, and smaller when earth changes from closer side to further side or the opposite.
But it´s tough to try and figure out the real dynamics of the combined movement, because apart from what said and the change in distance from sun (and gravity pull from it), also the curvature of the actual path of earth´s c.g. varies: farther parts are less curved than closer parts ...
That implies bigger radius of curvature of further parts of the path, and smaller of closer parts ...
And don´t forget: centrifugal forces are proportional to v²/r (being v the tangential speed, and r the radius of actual curvature of the trajectory in each position).
   

[rmolnav]

The Earth goes round in a circle (= revolves round the barycentre), but as I keep telling you, if you apply an even force you can make something follow a circular path without any material being flung off it because all the material follows the same shape of path

Well, I thought you disregarded earth revolving because you have said (last 29th):
"IF the Earth was rotating once a month ..."
In any case, what quoted is erroneous ... Perhaps material won´t "fly off", but hatever way you could "make something follow a circular path", ALL its massive parts "tend" to follow straight at constant speed ... The basic phenomenon of inertia in Physics !!
And, depending on how the whole body moves, that inertia manifests itself in a way or another, usually as centrifugal force.
But I´m afraid you can´t grasp that, due to the mess you have in your mind even with the much more clear concept of centripetal force ...
Regarding the not working "link":
"main-qimg-851d9284749b378191c8ae87e4e2e4c2"
surely you must know the default solution is to copy and paste it on your search engine, isn´t it?

[rmolnav]

David Cooper #163
Looking for something else, yesterday I saw what follows, included by you as "Note for rmolnav" on a reply to other, that I had not seen before, or at least have not made any comment on ... And it is directly connected to what on my recent posts:
"If your mechanism was correct about the centripetal/centrifugal effect flinging the water out in two bulges at opposite sides as the Earth rotates around the barycentre, wouldn't that generate a single bulge on the side furthest out from the barycentre with the sea lowest on the side nearest to it? That would lead to most places having one tide per day instead of two."
Now you are "almost" completely right ...
In fact, IF ONLY that inertial effect acted on our planet, the sublunar area, on the side nearest to the barycenter, would show even a "negative" bulge ... That would be due to the revolving (instead of rotating) of earth: ALL parts follow identical circles, and are ALWAYS at maximum distance from the moon (within each circular path). Therefore, centrifugal forces are ALWAYS in the same sense of kind of "flying" from the moon ...
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 !!

[Le Repteux]

 

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 !!

In this case, "positive" means due to gravitation, and "normal" means due to inertia, which means that if the rotation would suddenly stop, the inner bulge would increase and the outward one would decrease. But it is not what the law of gravitation means: it means that both ends of free falling bodies are stretched due to a differential acceleration. Your idea seem to be challenging the law of gravitation. Is it?

[David Cooper]

The Earth goes round in a circle (= revolves round the barycentre), but as I keep telling you, if you apply an even force you can make something follow a circular path without any material being flung off it because all the material follows the same shape of path

... In any case, what quoted is erroneous ... Perhaps material won´t "fly off", but hatever way you could "make something follow a circular path", ALL its massive parts "tend" to follow straight at constant speed ... The basic phenomenon of inertia in Physics !!

That's where you keep making the basic error. What I said (the thing you quoted) is fully correct. The whole point is that with an evenly-applied force you can make something follow a circular course with every particle following the exact same shape of curve. Picture a group of rockets in deep space moving along a straight line. They all fire their engines at the same moment, pointing them to the side. All of them follow the same shape of path, maintaining the same configuration with the distances between each rocket and the ones around it not changing at all, but they follow a curved path. Evenly-applied gravity would have the same effect as that, accelerating each rocket at the same time the same amount in the same direction, but no one in the rockets would feel any force from this, unlike in the case where they're using rocket engines to make the turn. With gravity, there is no added centrifugal force to consider. What leads to the tidal "bulges" is that the force isn't evenly applied, but lessens over distance, and that makes a difference to the straight-line acceleration force being applied. There is not extra force needing to be applied to that.

But I´m afraid you can´t grasp that, due to the mess you have in your mind even with the much more clear concept of centripetal force ...

It's you that's repeatedly failing to grasp the point in question. Time and time you reject correct statements that I've made because you don't understand the basic physics.

Regarding the not working "link":
"main-qimg-851d9284749b378191c8ae87e4e2e4c2"
surely you must know the default solution is to copy and paste it on your search engine, isn´t it?

Search uses a lot of energy and is best avoided when there's nothing to be gained from looking at an image that illustrates something you already understand in full.

In fact, IF ONLY that inertial effect acted on our planet, the sublunar area, on the side nearest to the barycenter, would show even a "negative" bulge ... That would be due to the revolving (instead of rotating) of earth: ALL parts follow identical circles, and are ALWAYS at maximum distance from the moon (within each circular path). Therefore, centrifugal forces are ALWAYS in the same sense of kind of "flying" from the moon ...

And the part you still don't understand is that there would be no flinging of material with an evenly-applied force of gravity. What makes the bulge is differential gravity, and that covers the whole thing in one go - different strengths of straight-line acceleration towards the moon.

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.

[rmolnav]

In this case, "positive" means due to gravitation, and "normal" means due to inertia

Sorry if my words could somehow lead you to what you say ...
As I also said, the two bulges are due to the ADDITION of both causes: moon´s gravitation (always towards the moon) and inertial effects (always in the opposite sense) ...
And both resulting bulges are in same sense as defined on a dictionary (distance to earth c.g. increases) ...
In 1) I said "positive" to underline it is the contrary to "negative" (distance to earth c.g. decreases), as I had previously called it for when not counting moon´s pull (not mentioned by D.C.)
In 2) I said "normal" (I could have said "standard"): just a "bulge", what we usually call a bulge ...