[Colin2B]

Again you are mixing and confusing frames.

I don't think I am. I knew what the observer at the center of rotation was seeing, but I also knew which one was moving faster  ...... When we are rotating, we know we are, and if an observer at rest says that, from his viewpoint, we are not, then we can change places with him so that he can feel the force, which would then be a good reason to change reference frames in this case.

Yes, you are confusing frames and I can see why.
As I said before, it doesn’t matter if we know we are rotating, it makes no difference; in fact it is essential we know so we can calculate the centrifugal force. Even before Sagnac it was possible to detect rotation, Newton used examples of rotating bucket and linked spheres, and Foucault used a pendulum. 
The issue is that vectors can be handled from any frame and at times it is convenient to use a frame at rest with the roundabout - a co-rotating frame. This doesn’t mean that the person on the roundabout thinks they are stationary, just that that is the frame we are analysing from.
Simple example. You are standing on a platform as a train goes past, @rmolnav  is on the train tossing a ball up and down. In his co-moving frame the ball is going up and down, in your rest frame it describes a sine wave. In a similar way we can analyse a rotating roundabout from a co-rotating frame, we just need to obey the rules of dynamics for how that analysis is performed.
So, let’s roll back.
@rmolnav  has put forward a model based on a co-rotating frame. If you want to say that model is wrong you have 2 alternatives:
- You can say that he is not following the rules eg has incorrectly accounted for a force.
- You could also say his model is incomplete.
What you can’t say is that he should consider the motion to be tangential, because that is not part of the rules for this type of analysis, and can only be used from a frame which is not co-rotating.

You can put forward your own analysis based on tangential motion and gravitational attraction to show what ‘really’ happens. However, this will not disprove rmolnav model as you are only offering an alternative analysis from a different frame, and rmolnav might also be forgiven for asking why you didn’t go the whole hog and do your analysis from geodesics and motion relative to them avoiding gravitational force.

I think any further discussion of rotating frame analysis should be done in a separate thread as it is disjointing the discussion between @rmolnav  and @David Cooper

[David Cooper]

We have a 100% guarantee that the Earth is often accelerating away from the moon at times when you claim the "bulge" on the far side of the Earth from the moon is caused by centrifugal force

you could mean earth´s centripetal acceleration must always be "inwards" (towards the interior of the ellipse). Therefore inherent inertial force (centrifugal force), if any, ought to be towards the exterior of the ellipse, and on days close to full moon it couldn´t occur that "the "bulge" on the far side of the Earth from the moon is caused by centrifugal force" ... (as YOU SAY I claim)
Is that what you actually mean ...?

There are at least two ellipses involved - one with the Earth going round the sun and the other with it trying to go round the moon (and moving round the barycentre). The path it's following round the sun is the more significant of the two, the result being that the moon is on the outside of the curved path that the Earth is following when the Earth is in this position between the sun and moon - the moon's pull merely makes the Earth's curved path a little bit straighter at such times than it would be otherwise, having insufficient strength to curve it enough to put the moon on the inside of the curve. This means that, if we ignore other gravitational sources, the acceleration is towards the sun rather than the moon and any centrifugal bulge would have to be on the side of the Earth that faces the moon.

Because now you have added yet another confusing statement:

... we only have to wait six months for that to reverse and you'll certainly have the Earth accelerating towards the sun rather than the moon.

when scenarios sun-earth-moon and sun-moon-earth actually alternate every couple of weeks ...

If you wait two weeks, you then have the moon and sun on the same side of the Earth rather than opposite sides, so that doesn't illustrate the point I'm making. My point is that there could be a greater acceleration from some other source, such as the centre of mass of the galaxy. (That may not be the case - I haven't crunched the numbers to see if it's stronger than the sun's pull on us, but let's just assume for now that it might be.) If the centre of mass of the galaxy and the moon are on the same side of the Earth as each other while the sun is on the opposite side, it could be that the acceleration is towards the moon rather than towards the sun. However, if we wait for a full moon about half a year later, we would then have the centre of mass of the galaxy and the sun on the same side of the Earth with the moon on the opposite side, thereby guaranteeing that the acceleration is towards the sun rather than towards the moon, thereby ensuring that a "bulge" in the sea on the far side from the moon cannot be driven by centrifugal force.

The same argument applies to any other stronger source of gravity from further afield in the universe - there are guaranteed situations when the acceleration is away from the moon rather than towards it.

By the way, it´s clear to me you haven´t even read my post #398, because I didn´t claim mentioned bulge is caused ONLY by centrifugal force ...

The point is that none of this "bulge" can be caused by centrifugal force because in many situations the Earth is accelerating in a direction that makes that completely impossible, and yet the "bulge" is there regardless, revealing that the real cause is not the one you claim for it.

I said:

If we analyze them separately, when with FULL MOON we have:
1) On the one hand sun´s pull is maximum AT LOCAL NOON SIDE. Sun-related centrifugal force at that area, as "outwards" at that time is towards earth´s CM, would actually make sea water level decrease, but less than opposite sun´s pull effect: THAT WOUD GIVE US ONE OF THE SUN-RELATED BULGES.
And on the other hand, at mentioned area moon-related bulge also builds, because moon´s pull there is smaller than moon-related centrifugal force: ONE OF THE MOON-RELATED BULGES.
Both bulges ADD UP, and we have spring high tide at that area, some time after noon due to the gap caused by fast earth daily spinning ...

It's really difficult to make sense of that because of the confusing wording, which is why it's easier for me just to set out what's happening at such times so that you can agree or disagree with each named point:-

The sun is on the inside of the curved path the Earth is following and the moon is on the outside of that curve (and the Earth is accelerating towards the sun, away from the moon, while the moon is also being accelerated towards the sun and is therefore not being left behind). So,

(A) The sun's contribution to the "bulge" nearest the sun cannot be caused by centrifugal force - it is lifted by the sun's differential gravity.

(B) The moon's contribution to the "bulge" nearest the sun cannot be caused by centrifugal force either - it is too is lifted by the sun's gravity, but this is enabled by the moon's differential gravity holding it back progressively less over distance.

(C) The "bulge" nearest the moon could be mistaken for centrifugal force, but it's the sun that would have to be driving that, and we know that this bulge is too big for the sun to generate all of it in that way because if we wait a week, we see the major part of this "bulge" move round in line with the moon. The greater part of this "bulge" is therefore clearly driven by the moon's differential gravity.

(D) The sun's contribution to the "bulge" nearest the moon could arguably be caused by centrifugal force, but none of the moon's contributions to either "bulge" can be attributed to that mechanism.

(E) If the acceleration towards the centre of the galaxy (or something more distant) is stronger, then we could have many situations where no part of any of the "bulges" can be attributed to the moon or sun generating them through centrifugal force - the acceleration may be at 90 degrees to them, and such a force would be so even across the Earth that it would create no "bulge" itself, leaving differential gravity as the sole cause of the "bulges".

The reality is that centrifugal force is never a real part of the mechanism - it is always differential gravity that enables material to be lifted.

[rmolnav]

SORRY, but once more I have to say: RUBBISH !

There are at least two ellipses involved - one with the Earth going round the sun and the other with it trying to go round the moon (and moving round the barycentre). The path it's following round the sun is the more significant of the two, the result being that the moon is on the outside of the curved path that the Earth is following when the Earth is in this position between the sun and moon  - the moon's pull merely makes the Earth's curved path a little bit straighter at such times than it would be otherwise... This means that, if we ignore other gravitational sources, the acceleration is towards the sun rather than the moon and any centrifugal bulge would have to be on the side of the Earth that faces the moon.

WRONG! ...
A) "The path it's following round the sun is the more significant of the two..."
With "the more significant", do you mean the one with bigger tidal effects?
If so, you can tell not even in your own "field" are you right ...
"Differential gravity" (by the way, just an "artificial" force actually existing only inside our minds), is inversely proportional to the cube of the distance, not to its square as the real gravitational forces are (by the way, the only gravity-related forces which can actually be "felt" by material stuff ...)
That´s the reason moon´s gravity gradient is "more significant" than sun´s ... 
B) The barycenter´s orbit around the sun has a really small curvature. When full moon, our planet is at its farthest location inside mentioned orbit, and in only a week time it has to pass to the outside of that very little curved orbit ... How "on the world" could that happen if "the moon's pull merely makes the Earth's curved path a little bit straighter at such times than it would be otherwise" ?
It is absolutely necessary that "Earth´s curved path", during a week before and after full moon, has an opposite curvature, that is, towards the outer side of barycenter´s orbit ...
Therefore, things are actually the opposite to what you say: "...any centrifugal bulge would have to be on the side of the Earth that faces the moon".
Whose mechanism did you say had shattered ??

The sun is on the inside of the curved path the Earth is following and the moon is on the outside of that curve (and the Earth is accelerating towards the sun, away from the moon, while the moon is also being accelerated towards the sun and is therefore not being left behind). So,
(A) The sun's contribution to the "bulge" nearest the sun cannot be caused by centrifugal force - it is lifted by the sun's differential gravity.

Well, I was going to continue to refute all your statements I find erroneous, but after putting quite clear what above, that one of the main "roots" of your stand is completely "rotten", I find it unnecessary.
Surely I could have explained better the details of all those bulge cases ... But I´m afraid the main problem is not in how I explained it, but that you read it not with an open mind, and without any interest to find something "reasonable" ... And, obviously, the very complexity of the scenario:
Each bulge is the result of four nature physical "effects": two of them gravity-related (caused by moon and sun), and two inertia-related (centrifugal forces inherent in earth´s "dances" with moon and earth) ... And they can have equal or opposite sense, what makes rather tricky to grasp them all, let alone to explain each case to people (especially to people with rather low education in dynamics)
Your "arguments" either are physically flawed (as shown above), or are just something like:
 

The reality is that centrifugal force is never a real part of the mechanism - it is always differential gravity that enables material to be lifted.

By the way, when I use bold or capital letters is to help possible readers see quickly what I consider most meaningful sentences (or just words) ... That way they could decide whether to read the rest or not ...

[David Cooper]

SORRY, but once more I have to say: RUBBISH !

Most of what you say is indeed rubbish, so no one expects anything else.

WRONG! ...

No. You merely disagree because you're defending a position that's wrong.

A) "The path it's following round the sun is the more significant of the two..."
With "the more significant", do you mean the one with bigger tidal effects?

Given that the point being addressed there is the shape of the path that the Earth is following, it should be obvious that what's being referred to is the amount of gravitational pull on the Earth from the sun and moon - they are pulling in opposite directions, and the sun's pull on the Earth is inordinately greater.

"Differential gravity" (by the way, just an "artificial" force actually existing only inside our minds), is inversely proportional to the cube of the distance, not to its square as the real gravitational forces are (by the way, the only gravity-related forces which can actually be "felt" by material stuff ...)

Differential gravity is gravity. The word "differential" isn't turning it into something else, but merely draws attention to the fact that it diminishes in strength over distance (inversely proportional to the square of the distance) and that it is this variation in strength that causes tides. An even force doesn't cause tides and cannot generate "bulges" at all.

That´s the reason moon´s gravity gradient is "more significant" than sun´s ...

The reason the moon's gravity gradient is more significant here than the sun's is that the moon is much closer to us, so the force is less even across the Earth as it's spreading out more.

B) The barycenter´s orbit around the sun has a really small curvature. When full moon, our planet is at its farthest location inside mentioned orbit, and in only a week time it has to pass to the outside of that very little curved orbit ... How "on the world" could that happen if "the moon's pull merely makes the Earth's curved path a little bit straighter at such times than it would be otherwise" ?

Imagine a car driving anticlockwise round a circular track with a radius of 93m (93000mm). Underneath the car we have a device that sends a jet of paint down at the ground underneath. This device is attached to the edge of a rotating disc which spins twelve times for every lap of the car. The disc is less than 8mm across. What shape will the resulting line of paint on the tarmac be? Will there be any places on it where it curves to the right? Let's turn the disc to put the paint jet nearest to the inside of the track so that it's like having the Earth between the sun and moon. The equivalent of one day passing is equivalent to the car moving round apx. 1/360 of the track, which is one degree. During that time, the disc under the car will rotate apx. 1/30 of one complete revolution. We can use the cosine function of a calculator to find out how far this moves the jet to the left due to the car's movement and to the right due to the disc's rotation, so let's crunch the numbers. (Incidentally, I did this weeks ago for the Earth, sun and moon - I assumed you had the wit and ability to do the same for yourself, but it's clear that you didn't bother.) We're going to use the hypotenuse and the angle to calculate the amount of movement towards the centre. For the track, we're using the angle of 1 degree and the radius 93000. To get the movement to the left, we need r - cos(1)*r [r=93000mm], and that comes to 14.16mm. To get the movement to the right, we need r - cos(30)*r [r=4mm], and that comes to 0.5359mm.

Given these numbers, there is no possibility of the line of paint curving to the right, but that should be no surprise to anyone with so much as half a grasp of the basics of physics - the sun's pull on us is a lot stronger than the moon's, so we have to be accelerating towards the sun in such a situation rather than towards the moon (unless there's something pulling the solar system even more strongly in the opposite direction, such as a galaxy).

It is absolutely necessary that "Earth´s curved path", during a week before and after full moon, has an opposite curvature, that is, towards the outer side of barycenter´s orbit ...
Therefore, things are actually the opposite to what you say

You failed your maths test. Have another go.

Whose mechanism did you say had shattered ??

The one whose mechanism shattered. Do the maths properly. You keep making out that you're the one who understands the physics here, but in reality you're not only mauling it, but you appear unable even to crunch basic numbers to test your case.

Well, I was going to continue to refute all your statements I find erroneous, but after putting quite clear what above, that one of the main "roots" of your stand is completely "rotten", I find it unnecessary.

You have never refuted any of my statements. All you've done is call them wrong on the basis that they aren't compatible with your errors. (The only exceptions are in cases where you've latched onto irrelevant faults in thought experiments that I've created to illustrate points where I didn't debug them enough to prevent malicious twisting - the core points being made in each case were correct.)

Surely I could have explained better the details of all those bulge cases ... But I´m afraid the main problem is not in how I explained it, but that you read it not with an open mind, and without any interest to find something "reasonable" ...

Oh sure - I obviously don't have an open mind on this because when I first posted in this thread, I was supporting something equivalent to your mechanism rather than attacking it. I switched side early on when I realised that I was wrong, and I did that because unlike you I systematically test my beliefs to try to destroy them in order to minimise the risk of being wrong. I like to work through the maths to check things, but you don't bother to do that because you're too lazy even to lift a calculator and press a few buttons.

Each bulge is the result of four nature physical "effects": two of them gravity-related (caused by moon and sun), and two inertia-related (centrifugal forces inherent in earth´s "dances" with moon and earth) ... And they can have equal or opposite sense, what makes rather tricky to grasp them all, let alone to explain each case to people (especially to people with rather low education in dynamics)

Each bulge is the result of differential gravity. There is no centrifugal force involved. The reason you think it's complex is that you're making an artificial distinction between gravity as gravity and gravity as centripetal force, and all the imagined complexity that you then get mired in comes out of that flawed thinking. The reality is ridiculously simple - it's the total gravitational pull on each particle that tries to move it in a particular direction, and that determines how they push against the other particles around them. If the forces are applied evenly, all the material accelerates in the same direction with zero tidal force. If the forces vary over distance, you have tidal forces. And as for your comment about low education in dynamics, you need to take a good long look in the mirror. A little knowledge is a dangerous thing, and in your case, your effective understanding has likely been reduced far below the level you would have started out with as a child.

Your "arguments" either are physically flawed (as shown above), or are just something like:
 

The reality is that centrifugal force is never a real part of the mechanism - it is always differential gravity that enables material to be lifted.

That last bit isn't an argument darling - it's a conclusion at the end which was derived from the argument that came above it, and the argument above it was correct.

By the way, when I use bold or capital letters is to help possible readers see quickly what I consider most meaningful sentences (or just words) ... That way they could decide whether to read the rest or not ...

You overuse them, but please don't stop - it gives your posts a useful signature which tells people at a glance what quality of post they're dealing with.

[Le Repteux]

Therefore, as centripetal force (previously acting on the passenger) instantaneously disappears when the door opens, it cannot have any effect on the "tangential" movement whatsoever, and the passenger carries on with the linear speed he had got at that very instant (Newton´s 1st Motion Law) ...     

That's similar to what I said, so you are probably raising it because you think I don't think like you about that, and you are also probably saying that I don't know the basics for the same reason. I sometimes do that too. That kind of mistake is due to our intrinsic resistance to change. We can't change ideas instantly, its a law of nature, and during that time, we look for things that may be wrong with others' ideas. No need to take it as a mistake though, because it's inevitable. Resistance to change is precisely what produces the centripetal force, so it applies to anything that exists. Which makes me think that our ideas all have a speed and a direction, thus that they are all about motion. It is logical since animal life is about moving to survive. Forward/backward, right/left, up/down: there is only three directions and two ways for each, so if I'm right, we should be able to reduce all our ideas to those six only possibilities, plus to the importance they have with regard to one another, which is similar to the speed bodies have in their own direction. That speed is relative, in the sense that we can't know which one of us is moving if we are isolated in space, so no wonder why our ideas are relative, in the sense that we can't determine who is right. If an idea has more importance, for instance if a whole group of scientists say it is right, then it is their direction and speed that is taken as a reference, but it doesn't mean that they are right, it only means that, being a larger body, they are easier to detect. One day or another, ideas change, and they can change drastically, which is why it is better to account for that when we discuss them.

[rmolnav]

Quote
It is absolutely necessary that "Earth´s curved path", during a week before and after full moon, has an opposite curvature, that is, towards the outer side of barycenter´s orbit ...
Therefore, things are actually the opposite to what you say
You failed your maths test. Have another go.

Well ... I recently had a go, actually the first, as far as that question is concerned.
And I have to admit I was wrong, even more than what shows your numbers, not completely correct.
I overestimated the fact that the barycenter´s orbit has a very low curvature, not keeping in mind that with such huge radius even small angles can cause relatively big differences in what discussed. As I´ve said several times, after all earth´s revolving around the barycenter is just something like the movement of the waist of a child when playing the hulla-hoop ...
Said that, I also have to say that fact doesn´t "invalidate" what you call "my model" ... I just chose then the wrong argument !
I never said centrifugal force is the unique cause of any bulge (as you and L.R. sometimes say I claim), let alone I used terms such as "the centrifugal bulge", as one of you recently did ...
Last time I referred to that:
 

Each bulge is the result of four nature physical "features": two of them gravity-related (caused by moon and sun), and two inertia-related (centrifugal forces inherent in earth´s "dance" with moon and its revolving around the sun) (edited)

... if applied to the "sunwards" bulge with the scenario sun > earth´s CM > barycenter > moon (full or almost),
1) Sun exerts its stronger pull there.
2) The revolving of earth-moon couple around the sun makes inertia manifest itself as a centrifugal  force, logically in the sense sun > earth´s closest side, what actually opposes to sun´s pull, but with a weaker  strength ...
3) In its "turn", earth´s revolving around the barycenter similarly makes inertia manifest itself as a centrifugal force, this time in the sense moon > barycenter > earth´s CM > sun, that is, contributing to the formation of the bulge on mentioned area.
4) Moon also exerts its pull there, in the sense opposite to effect 3), but smaller.
THE ADDITION OF ALL THOSE FORCES is the total force exerted on the water there (apart from own weight).
As both sun and moon related net effects are in the sense away from earth CM, and they directly add up, we have one of the spring tide bulges.

There is no centrifugal force involved. The reason you think it's complex is that you're making an artificial distinction between gravity as gravity and gravity as centripetal force,

Again: due to the fact that with earth´s revolving water is "forced" to change its linear speed (through a centripetal force), inertia manifests itself as, if you prefer, an "outward" force equal but opposite to the centripetal force, which makes water kind of slightly lighter ... At the place above mentioned, even if there were no gravity gradients, earth revolving around the barycenter would give us a high tide, whatever may be causing the revolving.  And if the revolving pace were  e.g. two fold faster, centripetal force ought to be four times bigger: mω²r (if same radius) ...
Remember: the so called equatorial bulge, due to centrifugal forces, is "unbelievable" huge (tens of km high), basically because earth daily spinning is some 28 times faster than earth-moon revolving ... And in that case no "differential gravity" is involved.

The reason you think it's complex is that you're making an artificial distinction between gravity as gravity and gravity as centripetal force

Again: instead of "gravity as gravity" I would say something like: "the very essence of gravity" ...
And I´m not the one who makes "an artificial distinction" between that, gravity´s ESSENCE, and "gravity as centripetal force" ... Gravity, apart from its "essence", as many other different forces, has the FUNCTION of centripetal force (the "job" if you wish), when that gravitational force makes an object rotate (together with a not null initial speed, perpendicular to the gravitational force, or at least to one of its components).
That is beyond basic Dynamics ... It is basic Logics, or Philosophy if you wish ...

[David Cooper]

Well ... I recently had a go, actually the first, as far as that question is concerned.
And I have to admit I was wrong, even more than what shows your numbers, not completely correct.

I was hoping you'd find that - it was an unintended mistake which I thought of editing a few hours after posting it, but I decided to leave it there to see if you'd mention it. And yes, when the 30's corrected to 12, it pushes things further away from what you wanted, so I know  from what you've said that you have done it correctly now and passed the maths test. (The correct amount of movement to the right is 0.0874mm rather than the 0.5359mm which I previously stated.)

Said that, I also have to say that fact doesn´t "invalidate" what you call "my model" ... I just chose then the wrong argument !

Well, I suppose the trick now is to redefine what your argument was until it becomes the straight-line differential gravity explanation under a disguised name.

... if applied to the "sunwards" bulge with the scenario sun > earth´s CM > barycenter > moon (full or almost),
1) Sun exerts its stronger pull there.
2) The revolving of earth-moon couple around the sun makes inertia manifest itself as a centrifugal  force, logically in the sense sun > earth´s closest side, what actually opposes to sun´s pull, but with a weaker  strength ...
3) In its "turn", earth´s revolving around the barycenter similarly makes inertia manifest itself as a centrifugal force, this time in the sense moon > barycenter > earth´s CM > sun, that is, contributing to the formation of the bulge on mentioned area.
4) Moon also exerts its pull there, in the sense opposite to effect 3), but smaller.

You complain about parts like this not being read, but they are read - they are simply extremely hard to make sense of because of all the referential failures and confusing wordings, and no one has the time to analyse them for hours to try to work out what they might be attempting to say. It takes effort even just to interpret "sun > earth's CM > ..." because you're not using ">" in a mathematical way, but it seems that you're simply setting out their arrangement in space. It would be clearer just to say that you're discussing a situation where the Earth is between the sun and moon. It would also make sense to name the opposite sides of the Earth as NS (nearest sun) and NM (nearest moon) so that they can be referred to without confusion. You could then say (1) sun's pull is stronger at NS.

Next follows the task of making sense of: "(2)The revolving of earth-moon couple around the sun makes inertia manifest itself as a centrifugal  force, logically in the sense sun > earth´s closest side, what actually opposes to sun´s pull, but with a weaker  strength ..."

I don't know what that means. The "revolving around the sun part" suggests that you're thinking about the Earth's path round the sun, so the imagined centrifugal force from that would be towards NM rather than NS, and the bit about it opposing the sun's pull suggests that you're imagining this centrifugal force acting at NS towards the Earth's centre. I have no idea whether that's what you mean by this, but that's the best I can do with it.

Nest we have: "3) In its "turn", earth´s revolving around the barycenter similarly makes inertia manifest itself as a centrifugal force, this time in the sense moon > barycenter > earth´s CM > sun, that is, contributing to the formation of the bulge on mentioned area."

Here we have the same stuff with ">" signs in it, but the order is the same, merely reversed. Why bother with that? You say that the Earth's orbiting of the barycentre creates centrifugal force contributing to the "bulge on mentioned area". Do you mean at NS? Yes - I think you must mean that. However, we now seem to have centrifugal force from (2) acting in one direction and centrifugal force from (3) acting in the opposite direction, and it should be obvious that this isn't acceptable at all. Whichever one loses the strength contest should not be described as centrifugal force.

4) Moon also exerts its pull there, in the sense opposite to effect 3), but smaller.

Just taking (3) and (4), what you have is differential gravity, the reduction in the force over distance leading to less gravitational pull towards the moon for the material furthest from it (at NS), except that when you realise that the Earth's actually accelerating away from the moon, it becomes necessary to change the description a little, so you then have differential gravity with the reduction in the force over distance leading to less gravitational pull toward the sun for the material furthest from the moon (at NS). There is no need to class any of that gravitational pull as centripetal force, and no need to class any of the reduction in force as centrifugal.

THE ADDITION OF ALL THOSE FORCES is the total force exerted on the water there (apart from own weight).
As both sun and moon related net effects are in the sense away from earth CM, and they directly add up, we have one of the spring tide bulges.

The addition of forces is much simpler if you skip the artificial distinction where part of gravity is split off to be classed as centripetal force. So far as nature is concerned, it's all just gravity. Most importantly though, the part that you're calling centrifugal force in (3) cannot be centrifugal if the Earth's accelerating towards the sun, so it is an error to label it as such. In this situation, none of the moon's inputs to the tides can legitimately be described as centrifugal.

At the place above mentioned, even if there were no gravity gradients, earth revolving around the barycenter would give us a high tide, whatever may be causing the revolving.

Not so. If you have no gravity gradients, you have no tidal force. In reality though, you won't get an orbit without a gravity gradient, but you can get very close to it. The sun's pull on the Earth is much greater than the moon's, but the tidal forces from it are smaller because the gravitational pull from the sun reduces much less across the Earth from the near to the far side than the moon's pull does. The galaxy's pull on the Earth may be even stronger (I still don't know because I haven't calculated it), but the gravitational strength from that hardly reduces at all across the Earth, so it doesn't create noticeable tidal forces here. That is equivalent to the evenly applied tractor beam idea discussed many pages ago where the Earth could be swung round and round in tight circles at high speed without any water being flung up at all. This illustrates why it is differential gravity that causes material to lift and not centrifugal force.

Remember: the so called equatorial bulge, due to centrifugal forces, is "unbelievable" huge (tens of km high), basically because earth daily spinning is some 28 times faster than earth-moon revolving ... And in that case no "differential gravity" is involved.

There you actually do have something you can legitimately call centrifugal force, but it's a very different case.

Gravity, apart from its "essence", as many other different forces, has the FUNCTION of centripetal force (the "job" if you wish), when that gravitational force makes an object rotate (together with a not null initial speed, perpendicular to the gravitational force, or at least to one of its components).
That is beyond basic Dynamics ... It is basic Logics, or Philosophy if you wish ...

It's an artificial distinction. If gravity's making one object fall straight down towards the source of that gravity while the same gravity's acting on an object that's orbiting the source of that gravity and passing through a point that the falling object passed through a short time before, what sense does it make to call some of it centripetal force and some of the same force not centripetal? It's just people misnaming things. All we have there is gravity applying a force at that point and applying it in the same direction at the same strength. You've bought into a contrived abstraction which adds unnecessary complexity and which actively misnames things as centrifugal even in situations where the acceleration is in the wrong direction for it to be centrifugal. In the scenario we've been discussing here, there is no centrifugal force involved in generating the tidal forces on the Earth that are caused by the moon. None. Even if we rearrange things by waiting a week till the moon is out the side instead of at a full moon position, we still have an overwhelming acceleration towards the sun which rules out the centrifugal mechanism for the "bulges". It's simply a bad way of analysing what's going on. If the galaxy's centre of mass pulls most strongly, then we could have situations where you also lose all justification for labelling either of the sun-driven "bulges" as centrifugal force because the actual acceleration could be applying at right angles to the straight line passing through the sun, Earth and moon.

A valid mechanism needs to apply in all situations, but there are many situations in which the centrifugal force explanation fails completely to account for the moon-driven "bulges", and in every real situation, some of the components of force that you're calling centrifugal are disqualified from that description when you consider the actual direction in which the Earth is accelerating at the time. In reality though, there's no need to worry about which way the Earth's being accelerated and no need to think of gravity as centripetal force - whatever the Earth's doing, it simply goes where it's pulled and the tides will always apply in accordance with differential gravity because this mechanism works perfectly in all situations, either holding back material most strongly on the near side to the source of the pull (if the Earth's moving away) or pulling it most strongly (if the Earth's moving towards the source), and holding back material least strongly on the far side from the source of the pull (if the Earth's moving away) or pulling it in least strongly (if the Earth's moving towards the source). It really is that simple. With multiple sources, just apply the vectors and work out the combined forces. Nature doesn't distinguish between centripetal gravity force and non-centripetal gravity force, and we shouldn't either. There is no physical difference between the two.

[rmolnav]

Quote
Gravity, apart from its "essence", as many other different forces, has the FUNCTION of centripetal force (the "job" if you wish), when that gravitational force makes an object rotate (together with a not null initial speed, perpendicular to the gravitational force, or at least to one of its components).
That is beyond basic Dynamics ... It is basic Logics, or Philosophy if you wish ...
It's an artificial distinction.

UTTERLY WRONG:
1) Answer Key/What is happening?
" ... When you spin the tray in a circle, the tray is held in its orbit by the string. You must constantly pull on the string to keep the tray from flying off in a straight line. The force you apply to the tray through the string is the centripetal force.
Similarly, for a satellite that is in orbit around the Earth, it is the Earth’s gravity that exerts a centripetal force on the satellite that prevents it from flying off into space. The Earth’s gravity pulls on the satellite like you pull on the string to keep the tray traveling in circular motion.
The Moon is a satellite orbiting the Earth, and the Earth is a satellite circling the Sun. The Earth’s gravity also keeps the Moon in orbit, and the Sun’s gravity keeps the planets orbiting around it".
( Lunar Landing: Swinging Tray - nasa.gov )

2) "... On the opposite side of the Earth, or the “far side,” the gravitational attraction of the moon is less because it is farther away. Here, inertia exceeds the gravitational force, and the water tries to keep going in a straight line, moving away from the Earth, also forming a bulge" (Ross, D.A., 1995).
( Tides and Water Levels - National Ocean Service )

3) "The tension force in the string of a swinging tethered ball and the gravitational force keeping a satellite in orbit are both examples of centripetal forces. Multiple individual forces can even be involved as long as they add up (by vector addition) to give a net force towards the center of the circular path."
( What is a centripetal force? (article) | Khan Academyhttps://www.khanacademy.org/.../centripetal-force.../centripetal-forces/.../what-is-centr… )

4) "One of the uses of centripetal force is calculating the Earth orbit of a satellite. This has been used by scientists for decades in the space program. The idea of an Earth orbit is to keep the object moving at a fixed tangential velocity so that the force of gravity, at that distance from the Earth, is exactly equal to the centripetal force needed to keep it in orbit".
( Centripetal Force: Definition, Formula & Examples - Video & Lesson ...https://study.com/academy/lesson/centripetal-force-definition-formula-examples.html )

5) A centripetal force (Fc) is the force that makes a moving object change direction
is not a particular force, but the name given to whatever force or combination of forces is responsible for a centripetal acceleration
( Centripetal Force - Summary – The Physics Hypertextbookhttps://physics.info/centripetal/summary.shtml )

6) Space satellites are kept in circular or elliptical orbits due to the force of gravity, which acts as a centripetal force.
(Centripetal Force by Ron Kurtus - Physics Lessons: School for ...https://www.school-for-champions.com/science/force_centripetal.htm )

7) The net force acting towards the centre of a circle, keeping the object moving in circular motion, is known as the centripetal force,
e.g.   Gravitational force keeps the Earth in orbit around the Sun.
( Centripetal Force - Physics 298 - Department of Physics and Astronomywww.physics.louisville.edu/cldavis/phys298/notes/centripetal.html )

...

 

 

[rmolnav]

Each bulge is the result of differential gravity. There is no centrifugal force involved ... The reality is ridiculously simple - it's the total gravitational pull on each particle that tries to move it in a particular direction, and that determines how they push against the other particles around them.

As I´ve said many times, THAT "differential gravity" is what actually is quite "artificial" ...
You say "it's the total gravitational pull on each particle that tries to move it in a particular direction, and that determines how they push against the other particles around them” …
First part, OK., but they rather "pull" than "push" ...
And in relation to that fact, I´ve said many times that "transmission" of forces works basically as follows.
Total force exerted on any given particle (because of moon-earth rotation/revolving), has to be equal to the centripetal force required for its revolving, to accomplish Newton´s 2nd Motion Law). The main force “supplier” is moon´s pull AT EACH LOCATION. The other possible forces only can be exerted on each particle by surrounding ones (internal stresses), or by the very gravitational pull from the rest of our planet.
Closer to moon particles "feel" stronger pull than required centripetal force.
THAT excess (and not any "differential gravity") has to be passed onto the rest of earth through their neighbors.
On their turn, those neighbors exert opposite forces back onto considered particle (3rd Newton´s Motion Law).
At farther hemisphere interactions are a kind of mirror image of what at closer hemisphere, because the farther the particle, the bigger the deficit of moon´s pull (compared to required centripetal force).
That constitutes a complex "chain of transmission", where total force acting on each particle (leaving aside own weight) has to satisfy 2nd Newton´s Motion Law (F=mω²r) ...
THAT FIELD OF FORCES, exerted DIRECTLY ON EACH PARTICLE, and the INERTIAL EFFECTS (centrifugal forces included) caused by the fact that all particles are being "forced" to revolve together, ARE ACTUALLY THE DIRECT CAUSE OF TIDES !!
Basically solid earth is stretched, and water moves towards where the two bulges build up.
None of those forces is "artificial", and all are directly felt by considered particle, what implies "natural" additions of forces, without any artificial intervention of our minds. That would be necessary to deduct moon´s gravitational pulls at locations very distant from each other (the so called “differential gravity”), what obviously material stuff can´t do !! 
 

[David Cooper]

It's an artificial distinction.

UTTERLY WRONG:
1) Answer Key/What is happening?
" ... When you spin the tray in a circle, the tray is held in its orbit by the string. You must constantly pull on the string to keep the tray from flying off in a straight line. The force you apply to the tray through the string is the centripetal force.

And as I told you months ago, in a case with a string there's a centripetal force generated by the movement of the tray, a force which ceases to exist if you stop the tray moving. Gravity doesn't behave like that force in the string because it continues to act in full if you stop the moon. It's a radically different case and you should not confuse the two. With a string, the force is generated by the inertia of the tray. With the moon, the Earth's gravitational force isn't generated by the moon's inertia. Don't allow yourself to mix up the two cases on the basis of the word "centripetal" being used for both - you are being misled by language.

2) "... On the opposite side of the Earth, or the “far side,” the gravitational attraction of the moon is less because it is farther away. Here, inertia exceeds the gravitational force, and the water tries to keep going in a straight line, moving away from the Earth, also forming a bulge" (Ross, D.A., 1995).
( Tides and Water Levels - National Ocean Service )

Quoting things from people who've got it wrong doesn't make it right. They simply haven't thought it through properly. You shouldn't be falling into the same trap as you've been shown that the proposed mechanism is bogus.

3) "The tension force in the string of a swinging tethered ball and the gravitational force keeping a satellite in orbit are both examples of centripetal forces. Multiple individual forces can even be involved as long as they add up (by vector addition) to give a net force towards the center of the circular path."
( What is a centripetal force? (article) | Khan Academyhttps://www.khanacademy.org/.../centripetal-force.../centripetal-forces/.../what-is-centr… )

They've failed to state the fundamental difference between the two cases.

You can quote as many examples of gravity being called centripetal force as you like - it doesn't alter the fact that you are making an artificial distinction between parts of that gravitational force that you're counting as centripetal and parts of that gravitational force that you're excluding from that label. It is nothing more than a label and the part that you're applying that label to has no separate causal role on events. You're not seeing the physics because you're tripping over words and labels.

[David Cooper]

Each bulge is the result of differential gravity. There is no centrifugal force involved ... The reality is ridiculously simple - it's the total gravitational pull on each particle that tries to move it in a particular direction, and that determines how they push against the other particles around them.

As I´ve said many times, THAT "differential gravity" is what actually is quite "artificial" ...

It's the actual physics - how can that be artificial? Physics doesn't make any distinction for a molecule of water in the sea nearest the moon to separate out which part of the gravity force on it is centripetal and which is an excess that's non-centripetal gravity. It's all the same force.

You say "it's the total gravitational pull on each particle that tries to move it in a particular direction, and that determines how they push against the other particles around them” …
First part, OK., but they rather "pull" than "push" ...

The Earth (and sea)'s particles are all pulled together by gravity, and they push back against each other. When the moon's differential gravity is applied to the Earth, this cancels some of the stronger pull that holds the particles together in a clump and allows the push to move material upwards. It is equally valid to say "that determines how they push" or "... how they pull" in such a situation.

And in relation to that fact, I´ve said many times that "transmission" of forces works basically as follows.
Total force exerted on any given particle (because of moon-earth rotation/revolving), has to be equal to the centripetal force required for its revolving...

Cracked record. (That means, you're just repeating the same old stuff over and over again.)

I've shown you that there are many cases where your description fails to fit the facts because the Earth is not following the curve you think it is. You are misapplying the word "centripetal" in such cases because the Earth is actually accelerating away from the imagined centre. You are still allowing language and labels to blind you to the actual physics.

That constitutes a complex "chain of transmission", where total force acting on each particle (leaving aside own weight) has to satisfy 2nd Newton´s Motion Law (F=mω²r) ...
THAT FIELD OF FORCES, exerted DIRECTLY ON EACH PARTICLE, and the INERTIAL EFFECTS (centrifugal forces included) caused by the fact that all particles are being "forced" to revolve together, ARE ACTUALLY THE DIRECT CAUSE OF TIDES !!

No - it's an artificial concoction based on flawed understanding of physics. It appears to work if there are only two bodies involved (though even that's an illusion, as shown by cases where the two bodies are moving directly towards or away from each other), but as soon as you introduce a third body, your mechanism is revealed to be horribly broken because the actual accelerations are not of the strength or in the direction that the two-body analysis asserts for them. You are pushing a totally bogus explanation which has been more than adequately disproved in a multitude of different ways. Why do you persist in pushing it?

Basically solid earth is stretched, and water moves towards where the two bulges build up.
None of those forces is "artificial", and all are directly felt by considered particle, what implies "natural" additions of forces, without any artificial intervention of our minds. That would be necessary to deduct moon´s gravitational pulls at locations very distant from each other (the so called “differential gravity”), what obviously material stuff can´t do !!

If I hold a magnet over a piece of iron and it lifts it off the table, I can split the force into two components, one called Jimmy and the other called Gertrude, and then I can add the two forces together and say, "Look! When I add Jimmy and Gertrude together, I get exactly the right amount of force to explain the way the piece of iron lifts, so Jimmy and Gertrude must be key parts of the actual physics involved and it would be wrong to ignore them and just claim there's a single magnetic force responsible for what happens."

"Nonsense!" I hear you say. "There's no justification for making such a division in your example!!"

"Oh, but there is!" says I. "Jimmy is the part of the force that makes the iron weightless, and Gertrude is the part that then makes it lift off the table. There you go - I've just proved that Jimmy and Gertrude are vital parts of the physics and not just an artificial division of a single force. How ridiculous it would be to suggest that it's just one force (magnetic) trying to pull the piece of iron up while working against another force (gravity) which is trying to pull it down! No - it's more complex than that because you have to take into account the amount of magnetic force that makes it weightless and then see how much is left to make it rise off the table. If you don't understand this vital extra complexity, I'll keep throwing it at you over and over again in bold print with multiple exclamation marks."

That is no less ridiculous than what you're doing with your artificial division of gravity. These aren't arbitrary divides because we can come up with good excuses for making them where we do, but they are artificial nonetheless and we should not be misled by them into thinking that things are more complicated than they actually are.

That would be necessary to deduct moon´s gravitational pulls at locations very distant from each other (the so called “differential gravity”), what obviously material stuff can´t do !!

A particle at NM feels more force from the moon than a particle at the Earth's centre, and the particle at the Earth's centre feels more force from the moon than a particle at FM. What kind of calculation are you suggesting material would need to do to work out how to respond to those different strengths of pull?

[Le Repteux]

Remember: the so called equatorial bulge, due to centrifugal forces, is "unbelievably" huge (tens of km high), basically because earth daily spinning is some 28 times faster than earth-moon revolving ... And in that case no "differential gravity" is involved.

There you actually do have something you can legitimately call centrifugal force, but it's a very different case.

I disagree with that, and I think my answer is clear, so I will answer even if Colin2B asked me not to confuse the issue of your discussion.

It is the earth's gravity that produces the centripetal acceleration of its equatorial bulge, so it is also a differential gravity bulge even if it doesn't work like the tidal ones. In fact, the closer we get to the center of the earth, the weaker is the force, and it is at the surface that we get the strongest one, which is the inverse of what we get for the tides. If we stop the rotation, the bulge collapses, but it is only because it is supported by the rest of the earth that it stops collapsing. While it collapses, it suffers differential gravity, and its different parts do not collapse at the same rate, exactly like what would be happening to the different parts of the earth if we stopped it from orbiting the moon. So, if we consider that there is no centrifugal force in the case of the tides, then I think we should also consider that the equatorial bulge doesn't suffers such a force either.

[rmolnav]

It is the earth's gravity that produces the centripetal acceleration of its equatorial bulge, so it is also a differential gravity bulge even if it doesn't work like the tidal ones. In fact, the closer we get to the center of the earth, the weaker is the force, and it is at the surface that we get the strongest one, which is the inverse of what we get for the tides.

I´m afraid you have got it wrong, in two essential details.
On the one hand, average depth of oceans is an almost insignificant fraction of earth´s radius. Therefore, own earth´s pull gradient there is almost negligible.
On the other hand, what counts is not the distance to earth´s CM, but distance to the axis of rotation, which increases from both poles to the equator from null to the earth´s radius ... That positive gradient makes centrifugal force, perpendicular to the axis of rotation, increase from null to mω²r.
At an intermediate latitude, e.g. 45º, the distance to the axis of rotation is cosin 45º times r, app. 0,7r. And at 60º latitude 0,5r ...
That makes plenty of water move towards lower latitudes. In its "turn", that also increases distances to the axis of rotation, what is a kind of positive "double" feedback, because both centrifugal forces increase even more, and own earth´s CM "normal" pull decreases ...
Those details explain how huge the equatorial bulge is.
In earth´s revolving around the barycenter, ω is app. 28 times smaller, and the radius app. 2/3 of r. That makes centrifugal force (always in the sense opposite to the moon) much, much smaller, what vectorially added to moon´s pull at considered ocean´s area, gives us moon-related tides, biggest fraction of total tides.
 

[Le Repteux]

On the one hand, average depth of oceans is an almost insignificant fraction of earth´s radius. Therefore, own earth´s pull gradient there is almost negligible.

The acceleration at the earth's surface is the same whether it is water or ground, so the force is the same too.

On the other hand, what counts is not the distance to earth´s CM, but distance to the axis of rotation, which increases from both poles to the equator from null to the earth´s radius ... That positive gradient makes centrifugal force, perpendicular to the axis of rotation, increase from null to mω²r.

That is true whether we consider a centrifugal or a centripetal force.

Your two details mean that you don't seem to have understood what I meant, but you probably wouldn't have agreed even if you had understood, so let`s see if David understands. That's an important point, because if he agrees with me, he might find a better way to convince you.

[David Cooper]

So, if we consider that there is no centrifugal force in the case of the tides, then I think we should also consider that the equatorial bulge suffers no such force.

Well, officially there's no such force as centrifugal force - it's a pseudo force (unless it's reactive centrifugal force operating the opposite way to centripetal force in cases like the one with a ball on a string), so it's technically wrong already. We already have two radically different cases though, so let's see if we now have a third one:-

(1) A ball on a string when moving round in circles generates the centripetal force in the string. The force acting the opposite way in the string is called reactive centrifugal force, and that's a real force. Stop the ball and the centripetal force and reactive centrifugal force both disappear. Let's also use a transparent ball half full of water though so that we can think about what happens to the water - we would see it being flung into the outer half of the ball opposite the string by an apparent centrifugal force, but the apparent force flinging it there is really just the water trying to go in a straight line.

(2) A moon going round a planet doesn't generate centripetal force, but it goes round the planet because of gravity, and while that gravity can be described as centripetal force, it is really just gravity. Stop the moon and the force which had been described as centripetal continues to act in full, completely untransformed by losing the centripetal label. Note that there is also no reactive centrifugal force involved - that is a clue to the reality that we're dealing with a radically different category of "centrifugal" when dealing with gravity. Now replace the moon with the little transparent ball half full of water and the water will gather all round the sides to leave an air-filled globe in the middle - it doesn't get flung out to the side furthest from the Earth because the Earth's gravity is pulling on it with the same strength as it's pulling on the ball, so there isn't any apparent centrifugal force.

(3) The material on the surface of a planet going round the planet due to the planet's rotation doesn't generate centripetal force either, so it's similar to (2). That material is sitting there because it's moving too slowly to take of into an orbit, so it's like a special case of (2) in which there happens to be contact due to insufficient speed to take off. So is it centrifugal force that makes it rise as part of an equatorial bulge? Obviously it can't be as the only real centrifugal force is reactive centrifugal force, and we don't have any of that acting here.

But let's look at a case without any gravity pulling to the centre. Place balls on the edge of a roundabout (not a road junction, but the rotating disc thing that children play on in playgrounds) and spin it - the balls will roll off. That's like case (3), but without gravity preventing them from leaving the disc. If that's centrifugal force, then it's centrifugal force in case (3) too. Again there's no centripetal force generated here though, so there can be no reactive centrifugal force. The balls just fall off the edge. They are flung away from the centre of rotation, but not directly away from it - the paths they're moving along lead back to the edge of the disc at a tangent rather than a line passing through the centre, and the acceleration force that was applied to them only ever acted at 90 degrees to a line passing through the centre of the disc, so that force isn't centrifugal. Where is the centrifugal force? It only exists from the warped perspective of rotating frames with the balls appearing to accelerate away from the centre, but the balls are not accelerating at all as they leave the disc. In explaining what's happening there, centrifugal force is a false mechanism, but we can still describe this as centrifugal force as a convenient shorthand for what's happening with things moving out away from the centre - we just need to understand that that's a misleading description and translate from that word back to the real mechanism. Crucially, the only kind of centrifugal force that's ever part of a real mechanism is reactive centrifugal force.

If a child's actively hanging onto the edge of the roundabout, then there's centripetal and reactive centrifugal force acting there. With (3) we have the illusion of that same situation created by gravity holding the material on the planet, but there is no reactive centrifugal force, and the material lifts more than it would if there was no rotation, but rather than the material feeling as if it's being flung outwards, it merely feels that it's being pulled down less, and that's a different thing. Should we call it centrifugal? It's a convenient term to use, but it is a different category of centrifugal from the other cases. The complexities here are all in the labels and not in the physics, so the proper cure is simply to avoid using the awkward labels. Centrifugal force only looks fully appropriate in case (1) where centripetal force is generated by something following a curved path and reactive centrifugal force is generated in the opposite direction to match. Centripetal force is also only fully appropriate in case (1). In the other cases, the use of both words becomes more of a metaphor.

[The words are a mess though even in case (1) because they don't include the straight-line cases like when you slam the brakes on in a car, or when a chained dog is jerked to a halt while running at the postman, even though the fundamental mechanism is the same. (If the dog runs at an angle, starting some way to the side of the attachment point of the chain, it may be flung sideways when the chain tightens, that's centripetal force, but the straight-line case is just a special case of this more general case, so rotation or curving should not be a requirement of the definition.) They are both bad labels, and we can see from this thread that they can disrupt people's understanding of the physics involved in some cases.]

Think about a moon in an elliptical orbit. When its speed is too high for it to stay the same distance from the planet that it's going round, we could argue that centrifugal force makes it move further out. (I don't know what it would be called when the moon's moving closer in - there seems to be a vocabulary vacuum there.) That conflicts with rmolnav's usage where he only calls it centrifugal for parts of the moon further out than the centre of mass and he ignores the issue of whether the moon's increasing or decreasing its distance away from the Earth. In the first case we're using a rotating frame in which we measure an acceleration outwards by the moon relative to the Earth, so when we see the moon moving further away, we can put that down to centrifugal force, although we understand that this is not a real mechanism - this would be consistent with our use of the word centrifugal when describing the equatorial bulge forming, and with the balls rolling off the edge of the rotating roundabout. In the other case (rmolnav's), he's using different rules in which he ignores the outward or inward acceleration by the moon and focuses instead on the part further out than the centre of gravity of the moon, calling it centrifugal force on the basis that that material at FE (the point on the moon furthest from the Earth) would follow a different orbit if the rest of the moon wasn't there due to the speed of that material being too high to maintain the same size of orbit as the moon as a whole. This is a very different usage of the word centrifugal - the rules aren't consistent for the different cases. This illustrates again that the complexities are in the words and not in the actual physics - the physics itself is really simple, but we use misleading labels which are riddled with ambiguities, running different rules for them in different cases.

[rmolnav]

D.C.´s posts #415, 416 and 420 are "the last straw ...", but in a positive sense!
I have finally realized he knows better than many scientists from institutions such as:
-NOAA (visit "Tides and Water Levels" - National Ocean Service).
-NASA (visit https://tidesandcurrents.noaa.gov/restles3.html,  and https://tidesandcurrents.noaa.gov/publications/Tidal_Analysis_and_Predictions.pdf
- Univ. of Maine ( "What if the Moon Didn't Exist? — Neil F. Comins", youtube video), who even has publications on "Sources of Misconceptions in Astronomy"...
- Univ. of Ohio ( "phisics.ohio-state.edu”, "Dynamics of Uniform Circular Motion" (Chapter 5, 5.3 Centripetal Force).
- Univ. of Louisville (Centripetal Force - Physics 298 - Department of Physics and Astronomy, www.physics.louisville.edu/cldavis/phys298/notes/centripetal.html 
- Several Physics academies, mentioned on my post # 413.
- Merriam Webster dictionary (“movement”, “to move”, “force”…)
- Oxford dictionary (“centripetal force”) 
- http://www.newenglandphysics.org/other/French_Tides.pdf,
among others.
D.C. has discovered they consider (and even much worse, they teach) quite erroneous things, such as:
- Centrifugal forces (or “outward” forces) intervene on tides (on a revolving celestial body such as our planet)
- Gravity is what generates the centripetal force required for the elliptical orbits of celestial objects.
- Other strange things about “centripetal force” in general (such as it “Is the force that makes a moving object change direction. It is not a particular force, but the name given to whatever force or combination of forces is responsible for a centripetal acceleration”.
- A fraction of moon´s gravitational pull on some earth´s material stuff can be "responsible for its centripetal acceleration”, and the rest for other effects such as deformation and tides.
If you read carefully what above, you can clearly see there are a lot of grave errors … Ah! I forgot most important:
D.C. discovered (#184, and he also refers to this on his last post) that:
"If a force is generated by rotation, that is clearly centripetal force - a force that comes into play because of the rotation ...”.
Not even the great Isaac Newton was able to discover that. According to him (2nd of his universal Motion Laws) things are the other way around: forces generate movements, or change their speed vectors (at a pace given by the acceleration caused by the force, a=F/m). Unbelievable!
And, even more remarkable , according to D.C. (#184):
"I am always more interested in actual science than error-ridden authorities. I haven't seen anyone in science support my position (primarily because I haven't looked for that) - what I'm saying is based 100% on what I see when I look directly at the physics involved in this”.
Definitely, all our group should be proud of having such a genius as a "Naked Science Forum King!”...
I´m going to suggest somebody in charge of The Naked Scientists forum to apply for an Amateur Nobel Prize on Physics for D.C.  Perhaps Global Moderator Colin2B ?

[David Cooper]

D.C.´s posts #415, 416 and 420 are "the last straw ...", but in a positive sense!
I have finally realized he knows better than many scientists from institutions such as:...

It's good to know that you've finally understood that scientists can often be wrong. You've cherry-picked quotes from scientists who back your position, but the mainstream backs my position on this issue.

D.C. has discovered they consider (and even much worse, they teach) quite erroneous things, such as:
- Centrifugal forces (or “outward” forces) intervene on tides (on a revolving celestial body such as our planet)

Pseudo force.

- Gravity is what generates the centripetal force required for the elliptical orbits of celestial objects.

Gravity is simply gravity - it isn't generating a centripetal force, but is merely having the "centripetal" label attached to it, with the result that some people are misled into thinking that this makes some kind of mechanistic difference distinct from it simply being gravity.

- Other strange things about “centripetal force” in general (such as it “Is the force that makes a moving object change direction. It is not a particular force, but the name given to whatever force or combination of forces is responsible for a centripetal acceleration”.

Lovely, but you're failing to understand that it has no magic properties when it's associated with gravity. Gravity is simply gravity and the division that you're making which leads to all the complexity that you have such difficulty working with is artificial and unnecessary - your contrived mechanism is fake.

- A fraction of moon´s gravitational pull on some earth´s material stuff can be "responsible for its centripetal acceleration”, and the rest for other effects such as deformation and tides.

An upside-down understanding. It's just total gravitational pull on each particle (taking into account directions of pull) and you have everything you need.

If you read carefully what above, you can clearly see there are a lot of grave errors … Ah! I forgot most important:
D.C. discovered (#184, and he also refers to this on his last post) that:
"If a force is generated by rotation, that is clearly centripetal force - a force that comes into play because of the rotation ...”.

It's hardly a discovery - it's simply another attempt to get you to understand that there are different cases with different physics involved. Some centripetal force disappears when the movement stops because it's generated by that movement, but not when it's gravity labelled as centripetal force. You still have a magical view of gravity being divided into two components, centripetal and non-centripetal, with them carrying out different mechanistic roles, and that's why you're stuck where you are getting things wrong again and again and again.

Not even the great Isaac Newton was able to discover that. According to him (2nd of his universal Motion Laws) things are the other way around: forces generate movements, or change their speed vectors (at a pace given by the acceleration caused by the force, a=F/m). Unbelievable![/b]

You're misapplying his laws. Set up a heavy object connected by a string to a ball in space (something like a barbell with the string attached to a loop that goes round the handle) and just watch the centripetal force set the ball moving round and round! You believe in magic, but I don't - I say you have to start the ball moving first, and then the centripetal force is generated as a consequence of that movement. Every mainstream scientist will tell you the same thing, and Newton not have disagreed with that either.

And, even more remarkable , according to D.C. (#184):
"I am always more interested in actual science than error-ridden authorities. I haven't seen anyone in science support my position (primarily because I haven't looked for that) - what I'm saying is based 100% on what I see when I look directly at the physics involved in this”.

Apart from definitions of "centripetal", I only looked one thing up, and that was yesterday when I wanted to know what the force in the opposite direction in a string was (reactive centrifugal force). That's how I work - I avoid research as much as possible because research leads you into taking on other people's errors without thinking them through properly for yourself. I prefer to work out how things work first without any outside help, and then look to see what other people think afterwards.

Definitely, all our group should be proud of having such a genius as a "Naked Science Forum King!”...
I´m going to suggest somebody in charge of The Naked Scientists forum to apply for an Amateur Nobel Prize on Physics for D.C.  Perhaps Global Moderator Colin2B ?

Awards of that kind are part of the problem, setting up imperfect authorities and leading people to be lazy and fail to question the science properly. You've already illustrated how easy it is to fall into a wrong position and fix yourself there - you spend your time selectively gathering claims from authorities to back it up and you appear to imagine that that's how points are proved. But it isn't. Science should be about ideas doing battle with each other without any bias from any authority tied to either side. Reason should dictate the winner. The trouble with that though is that most people can't reason correctly, so until we have AGI acting as a perfect impartial judge, we're stuck with troops of monkeys making collective guesses and making some major mistakes. On this issue though, they haven't made a mistake - it's only a minority of scientists who are carelessly putting out incorrect information because they haven't thought things through properly, and you're allowing yourself to be misled by them.

[rmolnav]

Quote
Not even the great Isaac Newton was able to discover that. According to him (2nd of his universal Motion Laws) things are the other way around: forces generate movements, or change their speed vectors (at a pace given by the acceleration caused by the force, a=F/m). Unbelievable!
[/b]
You're misapplying his laws. Set up a heavy object connected by a string to a ball in space (something like a barbell with the string attached to a loop that goes round the handle) and just watch the centripetal force set the ball moving round and round! You believe in magic, but I don't - I say you have to start the ball moving first, and then the centripetal force is generated as a consequence of that movement. Every mainstream scientist will tell you the same thing, and Newton not have disagreed with that either.

What follows is for other possible readers rather than for D.C., incapable of "seeing" correctly physical phenomena.
Newton´s Motion Laws are universal: it is a force what ALWAYS causes movement (or changes its already existing speed)
And I don´t "believe in magic" whatsoever ...
To properly grasp physical phenomena our "vision" is not sufficient. We would need a magnifying lens, both for space and somehow "for time" (a modern camera capable of taking thousands of pictures would do). Or, at least, a reasonable degree of imagination.
An initial linear speed is logically necessary. But it can´t produce directly any force ... At the very first instant a string or wire hanging from a pole is connected to a hook on an object with a linear speed (e.g,. by "superman"), the string or cable has an initial tension (given by superman).
It is absolutely necessary (2nd Newton´s Motion Law) that, during an infinitesimal lapse of time, that tension initiates the change of the speed of the object, what causes the inertial reaction of the object pulling outwards the cable end (3rd Newton´s Motion Law).
Since that very instant we have a centripetal force (that initial cable tension), and the outwards reaction, centrifugal force. And the rotating movement starts.
It is THAT centrifugal force what, in its "turn", actually makes the wire tension increase (the centripetal force), and during following infinitesimal lapses of time, a chain of equal phenomena happens, with progressive velocity vector curving, with corresponding increases of centripetal and centrifugal force (for a period more or less long depending on the momentum mv of the object) ...
Eventually, if no energy added (either directly to the object, or from the inner end of the cable), the object will fall (that fall actually starts at the very first instant, because the tension of the wire always has a vertical downwards component). 
Therefore, it is not the speed (the movement as D.C. says) what causes the centripetal force. Without an initial FORCE, the mentioned initial tension, and those successive and increasing inertial FORCES (centrifugal), we couldn´t have any centripetal force, that is, NO CURVED MOVEMENT could be generated.
So, initial speed don´t generate the rotational movement ... Those mentioned forces change the direction of the initial speed, transforming a rectilinear movement into a curved one.
 So, I don´t need to ...
 

  ... understand that there are different cases with different physics involved.

and it is not "magical" my ...

... view of gravity being divided into two components, centripetal and non-centripetal, with them carrying out different mechanistic roles,

If I push very strongly on somebody´s breast, part of the force will move him backwards, but due to his inertia (tendency to remain still) some of his ribs may break ("different mechanism roles) ...
Who is ...

... getting things wrong again and again and again ??

[David Cooper]

What follows is for other possible readers rather than for D.C., incapable of "seeing" correctly physical phenomena.
Newton´s Motion Laws are universal: it is a force what ALWAYS causes movement (or changes its already existing speed)

When a tennis ball hits the net, does the force of the collision cause movement of the ball that leads to the collision? No. Even you, I hope, are sufficiently intelligent to realise that it was a different force that set the ball moving. Why can't you see that with the case of a ball on the end of a string where its movement energy generates the centripetal force rather than the other way round?

And I don´t "believe in magic" whatsoever ...

Good. Stop using magical in your mechanisms then. Put the causation in the correct order instead of having some of it working backwards.

An initial linear speed is logically necessary. But it can´t produce directly any force ... At the very first instant a string or wire hanging from a pole is connected to a hook on an object with a linear speed (e.g,. by "superman"), the string or cable has an initial tension (given by superman).
It is absolutely necessary (2nd Newton´s Motion Law) that, during an infinitesimal lapse of time, that tension initiates the change of the speed of the object, what causes the inertial reaction of the object pulling outwards the cable end (3rd Newton´s Motion Law).
Since that very instant we have a centripetal force (that initial cable tension), and the outwards reaction, centrifugal force. And the rotating movement starts.

The rotation doesn't add any movement energy to the ball - it just changes its direction of travel. What you keep failing to understand is that forces don't just appear without being caused by something else. A force can cause a movement, and that movement can later cause another force - it works in both directions. While the tennis ball is heading for the net, there is no force. When it hits the net, a force is generated, and it isn't generated by magic.

It is THAT centrifugal force what, in its "turn", actually makes the wire tension increase (the centripetal force)...

No - it's the movement of the ball and the ball's mass (the movement energy) that pushes the tension up.

Eventually, if no energy added (either directly to the object, or from the inner end of the cable), the object will fall (that fall actually starts at the very first instant, because the tension of the wire always has a vertical downwards component).

Don't confuse yourself with gravity - put the experiment in deep space to eliminate extraneous input forces. If the ball is stationary, no centripetal force is generated and the ball remains motionless. We apply a force to the ball to set it moving (not centripetal force), and the ball's movement then generates the centripetal force in the string. As I said weeks ago, we can separate out these events by starting with a ball that isn't attached to the string, so the force applied to get it going is separated in time from the generation of centripetal force - the ball can hook onto the end of the string when it reaches it, and then it's continued movement initiates the centripetal force which modifies the ball's direction of travel.

Therefore, it is not the speed (the movement as D.C. says) what causes the centripetal force.

Of course it is - no movement of the ball means no generation of the centripetal force. The movement of the ball (the energy of it moving) causes the centripetal force - not the other way round. You've learned some laws, but only half understand them and don't know how to apply them. That is one of the hazards of bad education where people are given rules to memorise without being tested on their understanding and correct application and where they are allowed to pass exams with scores of less than 100%.

So, initial speed don´t generate the rotational movement ...

The movement energy (initial speed) generates the centripetal force that causes the change in direction of the movement. This is really basic physics, but you don't understand it because you've been taught to misapply rules and "understand" things on the basis of conformity to misapplied rules. If there are any physics teachers reading this, be careful not to program your students to make the same mistakes because some of them will be stuck with them for life.

Those mentioned forces change the direction of the initial speed, transforming a rectilinear movement into a curved one.[/b]

Maybe it's gradually getting through to you though. That bit's right.

If I push very strongly on somebody´s breast, part of the force will move him backwards, but due to his inertia (tendency to remain still) some of his ribs may break ("different mechanism roles)

Forget the breakage part. If you push him and part of that input of energy would lead to him moving at the same speed as someone who's walking past while the rest of the input makes him go faster than that, that would be an artificial division of the force. That is the kind of artificial division that you're making when you call part of a gravitational pull "centripetal force" and the rest as non-centripetal gravity. I said earlier that you aren't making an arbitrary division and that it's merely an artificial one, but one of my recent posts reveals that your division point is actually arbitrary. I can argue that the centripetal component is the part that would make the planet follow a circle rather than an ellipse, whereas you argue that it's the part that makes it follow the ellipse that it's following. These are two sensible division points, but they are different. Which one of these division points does the actual mechanism tell us is the correct one? The answer is, neither of them - the division is artificial and has no mechanistic role.

[rmolnav]

Sorry, but RUBBISH, AND MORE RUBBISH ...
I´m not going to waste too much time refuting all your errors again and again! Just a couple of things ...
Did you read point 5 of my four days ago post?:

A centripetal force (Fc) is the force that makes a moving object change direction.
It is not a particular force, but the name given to whatever force or combination of forces is responsible for a centripetal acceleration
( Centripetal Force - Summary – The Physics Hypertextbookhttps://physics.info/centripetal/summary.shtml )

Similar definitions can be find "all over the world".
I would add, as I previously did, that "name (is) given" because, for the period that centripetal acceleration does exist, the "JOB" of the that force (whatever its ESSENCE") is to cause it. And that "combination of forces" can include not "complete" forces (only one of their components).
And you say:
 

... one of my recent posts reveals that your division point is actually arbitrary. I can argue that the centripetal component is the part that would make the planet follow a circle rather than an ellipse, whereas you argue that it's the part that makes it follow the ellipse that it's following.

NONE  of your posts reveals any "arbitrary" division point of me !
Please kindly tell us where do I "argue" what quoted. And don´t reply you have no time to look for it ...
It´s you who don´t understand, or don´r read carefully!
I´ve always had quite clear that an initial speed of the orbiting object, and gravity attraction from other nearby celestial object, are needed for the rotation ...
But, at any point of the orbit, gravitational pull vector can be perpendicular to the object´s speed vector, or not (apart from the case of circular orbit). And that pull vector can be divided into two components: one perpendicular, and the other tangential.
The "JOB" of the perpendicular component is to change the direction of the speed vector, towards the "center" of the orbit (more exactly towards the center of curvature of the orbit at that point) ... what ALL physicists (and most laymen) call CENTRIPETAL FORCE (obviously, without loosing its "gravitational" ESSENCE !!).
And the tangential component makes tangential speed size increase or decrease.
That is something an average teenager knows ... Is it too complicated for you to understand ??
I said what follows months ago. I´m afraid your so frequent errors are due not only to rather poor knowledge on physics Science, but also on Philosophy and Logics, or simply on the use of your own language: in your "arguments", you have been mixing the concepts of "essence" and "function" for months (at least) ! 
 
Apart from that ...

When a tennis ball hits the net, does the force of the collision cause movement of the ball that leads to the collision?

Please kindly, when discussing physics (as a Science), use clearly identifiable terms. Otherwise confusion is almost unavoidable ... What do you exactly mean with "the force of the collision" ?? 
Because several "scientifically" called "forces" are present in that scenario !