[Le Repteux]

Here is an exert from the page on "Tidal misconceptions" that I found on your last link Rmolnav:

We shall argue that the "tidal bulges", which are the focus of attention in many textbooks, are in fact not due to rotation, but are simply due to the combined gravitational fields of the earth and moon, and the fact that the gravitational field due to the moon has varying direction and strength over the volume of the earth.

[rmolnav]

In reality, for water to want to follow the tangent, it would have to have zero force applied to it by gravity from the other body, and that certainly isn't going to happen

It is more politically correct not to use terms such as rubbish ... O.K.
But how could I call that nonsense? Back to basic again:
1) If water is revolving as a part of the earth, it has a velocity vector.
2) Due to 1st Newton´s Motion Law, its inertial "tendency" is not to change that vector (size or direction), unless a force were applied.
3) If the gravity from the other body were zero, the water would actually "follow" the tangent, rather than just "want to" !!
4) It is precisely the not null force due to gravity, basically from the other body, what is required to overcome mentioned inertia: that vector divided by considered mass will give the acceleration vector necessary to change velocity vector ...
5) Its component perpendicular to initial speed, or part of it if in "excess", will be the centripetal acceleration, absolutely necessary for the water to follow a curved path ...
6) For further details, please have a look at my recent post of a few hours ago ...

[rmolnav]

If there is no force felt, then there is no force by definition. In free fall, no force is felt, and whether we are rotating or not is unimportant since we can't feel any anyway

But our case is not actually a perfect free fall ...
I´m rather tired. Let me just copy what I sent to somebody else a couple of months ago:
"Encyclopaedia Britannica:
"Free-fall, in mechanics, state of a body that moves freely in any manner in the presence of gravity. The planets, for example, are in free-fall in the gravitational field of the Sun ... Gravitational forces are never uniform, and therefore ONLY the centre of mass is in free-fall. ALL OTHER POINTS of a body ARE SUBJECT to tidal FORCES because they move in a slightly different gravitational field. The Earth is in free-fall, but the pull of the Moon is not the same at the Earth’s surface as at its centre; the rise and fall of ocean tides occur because the OCEANS ARE NOT IN PERFECT FREE-FALL"
You may say: OK, but those "tidal forces" are kind of imaginary, just the differences in gravitational field ...
But they are quite REAL, internal stresses within Earth´s material. Otherwise they COULD NOT produce real effects such as tides !!
Gravitational field is something abstract, which exist only in our minds, let alone gravitational field "differences" ... Those concepts are useful for OUR calculations (if well done ...), but material stuff ONLY can react to real forces, either gravitational (always exerted directly on considered stuff), or forces exerted through direct contact by contiguous material elements (pulls, pushes, hydraulic pressure ...)"

[rmolnav]

Here is an exert from the page on "Tidal misconceptions" that I found on your last link Rmolnav:
Quote from: Lockhaven.edu
We shall argue that the "tidal bulges", which are the focus of attention in many textbooks, are in fact not due to rotation, but are simply due to the combined gravitational fields of the earth and moon, and the fact that the gravitational field due to the moon has varying direction and strength over the volume of the earth.

I know that, and I discussed the issue directly with the author, via email.
Initially he kept his stand, but later he said he found my take "interesting" ... But he had a familiar problem (he is 81, and his wife 80), and told me he had at least to take a break in our discussion.
Were you interested, I did put here most of the texts of interchanged pieces of email (#125 to #134).

[David Cooper]

O.K. It´s just a question of terminology. If the force does exist, and produces their effects according to laws of Physics, it does´t matter much the term we use.

Quite right - there's no difficulty in understanding what centrifugal means and in converting to a more correct alternative. Both descriptions map to the same events easily enough. What matters though is that you try to make sure no one develops an incorrect causal understanding of what's going on by thinking there's an outward force being generated by rotation rather than an inward one - whichever wording they use, they must still visualise the force in the right direction. In the same way, when you use the word centripetal in a place where I consider it invalid, you should not turn your sloppy use of the word centripetal into a belief that rotation has a role in generating tidal bulges.

But in my wildest dreams I could have thought I would have to discuss about the term "centripetal force".

Then you need to broaden your mind. Science is a process that leads (generally) towards improved understanding and to repeated corrections in the way things are described and labelled. There are two very different things going on with rotation and force, and a clear distinction should be made between them to prevent people like you from tripping up over them by mistaking one for the other.

Could you please send some link, from a University or similarly reliable source, where one could see that is not another absurd idea of yours ??

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. If a force is generated by rotation, that is clearly centripetal force - a force that comes into play because of the rotation. If a force persists when the rotation is removed, it cannot have been generated by the rotation and has therefore should not, in my opinion, be labelled as centripetal force. It already has a better name as what it actually is: in this particular case gravitational force. If everyone wants to call it centripetal force regardless, that's up to them, but they should not let their sloppy labelling contaminate their understanding of the physics.

The point under discussion in this thread is the cause of the bulges, and the bulges persist when the rotation is removed. You attempt to attribute the bulges to centripetal force, but you're making two errors in the process. (1) The first is that you're playing a game of words - you want centripetal force to be involved because the Earth and moon are following curved paths, and you see cases where authorities have used labels in a particular way which backs your position (where centripetal has either been applied to orbits or appears to include them without specifically stating that it does so), but it is always better to look directly at the physics and use that as a guide to how labels ought to be defined. A force attributed to rotation which (the force) persists when the rotation is removed should not be given a name that implies that it is caused by rotation. (2) Your second error, having brought "centripetal force" into a situation where it doesn't belong causally, is to assert that the rotation drives the bulges on the basis that the rotation necessarily involves centripetal force and centripetal force will necessarily make the water on the outside try to follow the tangent while the Earth tries to follow the curve. In reality, both things will try to follow the same curve if the gravitational force is applied evenly because they are in free fall. What then locks you into your incorrect understanding though is that the gravity isn't evenly applied, so it does allow the water to try to follow a different curved path from the curved path the Earth follows, and a "bulge" appears which fits neatly with that explanation. However, the bulge is exactly the same as the bulge that would be there without the rotation, which shows that it is not caused by the attempt to move along a different path.

There could be some not fully rational usages of the term ... Absurd things are said by many people. But do you really think that term is a "grey area"??

To me it isn't particularly grey, but other people make it so. If they want to attribute it to the rotation purely on the basis that a curved path is involved, even though it is not caused by the rotation, I see that as a clear error.

I sincerely imagine you would find it crystal clear area, if it reinforced your fixed idea that ONLY differential pull from moon (apart from sun´s similar effects) counts for tides !!

Given that the differential pull does account for it in full (and persists with the rotation not present), what is the point of proposing some other cause that cannot add anything to the actual cause?

By the way, the so called "non inertial frame of reference" is something I have in my back log (?), I mean some day I have to try and convey some own ideas about it, surely controversial ...
But I´m sure it won´t be easy at all ... seeing that we can´t agree on even really basic terms !!

We don't need to agree on the use of the term centripetal. The only important task is for us to find agreement on what causes the bulges. If you are determined to call it centripetal force but are prepared to accept that the rotation has no role in generating the bulges, then that will be good enough, but you need to realise that you will be extending the meaning of the word centripetal into an even more controversial area by applying it where there is no rotation at all.

[David Cooper]

But those springs would act as a kind of “information” transmission chain, what in real case is done as internal stresses, transmitting action/reaction forces between contiguous material, a real “mechanism” you´ve rejected several times … You said many times just differential gravity is the mechanism !

Those springs are equivalent to the pressure changes where the "bulges" are. The greater pull on M makes it rise higher above the surface of E, and the mechanism for that is differential gravity.

But if we count with internal stresses, we have to include not only those, but the ones originated by revolving related inertia ...

The rotation doesn't add any such extra stresses because E is in free fall.

The springs would also slightly change their lengths due to the revolving of the earth, even if moon attraction were the same on M and on A …

If you're talking now about the Earth spinning and creating a bulge towards the equator and flattening towards the poles, those are not relevant to tides. If we have a series of balls sitting on springs sitting round the equator of E, all of them will find a height caused by E's spin, then they will gain extra height as they pass through positions M and A and lose all that extra height when half way in between those locations. The extra height above the surface of E that these balls have due to E's spin compared with the height they would be at if E didn't spin is caused by centrifugal force (inertia), but this is not a component of the tidal variation.

M and A, at their maximum distances from the moon (within their own revolving trajectories), with tangential speeds perpendicular to line between moon´s and earth´s centers, would require a centripetal force in both cases towards the moon. Otherwise they could not follow their circular paths.

A is held by E's gravitational force and only rises a little because the moon is pulling on A less strongly than E. This gravitational force is applied independent of the rotation and should not be attributed to the rotation.

Same happens on E, where the centripetal acceleration is provided by moon´s pull there: they exactly match with each other.

Again, this force is independent of the rotation.

Where M moon´s pull is stronger than required centripetal force: part of it does accelerate M towards the moon (the required centripetal acceleration for revolving of M), and the rest is what actually causes the bulge there.

Again you're attributing a force to rotation which is not caused by the rotation. The bulge is caused directly by the greater strength of gravitational pull applied to M.

But where A moon´s pull is smaller, insufficient for the centripetal force necessary to make it follow its circular path. Own earth´s pull has to "supply" the difference. Water kind of become slightly lighter, and a bulge builds also there, same way as previously explained for the formation of the equatorial bulge:

No - it's a different cause. The equatorial bulge is caused by rotation. The tidal bulges are not.

[David Cooper]

In reality, for water to want to follow the tangent, it would have to have zero force applied to it by gravity from the other body, and that certainly isn't going to happen

It is more politically correct not to use terms such as rubbish ... O.K.
But how could I call that nonsense? Back to basic again:

It's your nonsense - you claimed it should try to follow the tangent while the Earth should follow its orbit.

3) If the gravity from the other body were zero, the water would actually "follow" the tangent, rather than just "want to" !!

Indeed. The argument was about an even force being applied to cause a non-rotating Earth to follow a curved path, and with such an even force being applied, the water would follow the exact same curved path and not produce a bulge. This reveals that the bulge cannot be driven by the involvement of a curved path, but by the difference in gravitational strength that actually occurs over distance - the real cause is that it not an evenly applied force.

5) Its component perpendicular to initial speed, or part of it if in "excess", will be the centripetal acceleration, absolutely necessary for the water to follow a curved path ...

You are still trying to attribute the cause to a rotation that is not the cause - the bulge would be there without the rotation's involvement and it is a mistake to try to pin a different cause to it than the actual cause of the bulges. In the first page of this thread, I incorrectly pinned the cause on the same thing as you, but I switched away from that explanation when I realised that the bulges would remain if the rotation was removed - it is not possible for there to be two different causes for the exact same thing. One of the proposed causes is the actual cause, while the other is merely an apparent cause which is easy to mistake for the real one.

[David Cooper]

Let me just copy what I sent to somebody else a couple of months ago:
"Encyclopaedia Britannica:
"...ALL OTHER POINTS of a body ARE SUBJECT to tidal FORCES because they move in a slightly different gravitational field. ...

It doesn't make the mistake there of attributing it to rotation, so what it says is correct.

I've thought of a new static system to use as an example for you which ought to settle the matter. Imagine a stationary Earth with two moons held away from it on opposite sides, each supported by a long, strong rod. These moons would generate tidal bulges. If we rotate the system, an equatorial bulge will also develop in addition to the existing bulges. If we rotate this system at a speed where the Earth's gravity will keep the moons in orbit around it, we can remove the rods and the bulges remain. If we stop the Earth spinning, the equatorial bulge disappears. The tidal bulges remain throughout though, even when we get to this beautiful point where the Earth is both stationary and not rotating. The tidal bulges in this system cannot be caused in any way by the Earth's movement because it has none. Your explanation for the causes of tides is thus shown more clearly than ever to be horribly wrong.

Gravitational field is something abstract, which exist only in our minds, let alone gravitational field "differences" ... Those concepts are useful for OUR calculations (if well done ...), but material stuff ONLY can react to real forces, either gravitational (always exerted directly on considered stuff), or forces exerted through direct contact by contiguous material elements (pulls, pushes, hydraulic pressure ...)"

Nice - so how do you account for the bulges in the system I've just set out for you? Good luck with that one!

[Le Repteux]

Imagine a stationary Earth with two moons held away from it on opposite sides, each supported by a long, strong rod.

To illustrate the difference between the two kinds of effects, we can also imagine accelerating the rotation of the earth until some of the surface starts orbiting, and then completely stop the rotation while part of the surface is still orbiting. What is orbiting got at a certain height and speed because of rotation, but it goes on staying at the same height and speed without it.

[Le Repteux]

I know that, and I discussed the issue directly with the author, via email.
Initially he kept his stand, but later he said he found my take "interesting"

Tell him to join our discussion so that we can defend him from you. You should be ashamed not to respect old people like him! (just kidding :0)

[rmolnav]

To illustrate the difference between the two kinds of effects, we can also imagine accelerating the rotation of the earth until some of the surface starts orbiting, and then completely stop the rotation while part of the surface is still orbiting. What is orbiting got at a certain height and speed because of rotation, but it goes on staying at the same height and speed without it.

I have to prepare with more time my reply to D. C., not only in connection to that ...
Just a couple of things now:
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 !! 
 

[rmolnav]

Instead of refuting the lot of new absurdities I see in your last posts, i´m going to refer only to one, that could be the root of all your "problems" ...
I posted here the basics of "centripetal force", linking the "physics.ohio-state.edu" site I took them from. To no avail as far as your ideas are concerned.
I also explained, step by step and very carefully, the application of that basic concept to our case (see #181, particularly 4 and 5). Also to no avail: your reply shows you have not caught back even a pinch of that stuff ... which perhaps you have forgotten ...
And the day before yesterday, you broke your own "mark":

A force attributed to rotation which (the force) persists when the rotation is removed should not be given a name that implies that it is caused by rotation.

In other paragraphs you also refer to "forces caused (or not) by rotation", or to "forces caused (or not) by certain movement", as if we could say some forces are caused by some movements, and others are not ...
But things are the other way around !! Movements cannot cause any force ... Forces do cause movements (or change them) !!
Your ideas on Physics are flawed even at the very "basics of the basics" level ...
No wonder you say things such as "It doesn't matter how much justification you can find for calling it centripetal force. This is a grey area in which some usages of the word aren't fully rational" ... and so on.
By the way, you could not send us any link where we could see where you took that from, because it´s just what YOU have deduced when reading many things ...
I wonder, couldn´t it rather be a problem of your sight, or of your mind-set ??

[David Cooper]

Instead of refuting the lot of new absurdities I see in your last posts, i´m going to refer only to one, that could be the root of all your "problems" ...
I posted here the basics of "centripetal force", linking the "physics.ohio-state.edu" site I took them from. To no avail as far as your ideas are concerned.

I can't find your link. However, all the definitions I've found of centripetal force make it very clear that rotation is involved, as in movement following a curve. Most definitions also refer specifically to it being a circular path. None of them suggest that centripetal force can apply to a straight line course. When it comes to the tides, they are caused by forces acting in a straight line and the rotation is incidental. That's all there is to it. You are the one posting absurdities by calling things absurdities that are fully valid and can be demonstrated in full through simulations.

I also explained, step by step and very carefully, the application of that basic concept to our case (see #181, particularly 4 and 5). Also to no avail: your reply shows you have not caught back even a pinch of that stuff ... which perhaps you have forgotten ...

"4) It is precisely the not null force due to gravity, basically from the other body, what is required to overcome mentioned inertia: that vector divided by considered mass will give the acceleration vector necessary to change velocity vector ..."

If you wrote that in Spanish it might be easier to understand.

"5) Its component perpendicular to initial speed, or part of it if in "excess", will be the centripetal acceleration, absolutely necessary for the water to follow a curved path ..."

But in both cases you're just building upon the same old error - the bulges are fully accounted for by differential gravity without any rotation being required.

And the day before yesterday, you broke your own "mark":

A force attributed to rotation which (the force) persists when the rotation is removed should not be given a name that implies that it is caused by rotation.

In other paragraphs you also refer to "forces caused (or not) by rotation", or to "forces caused (or not) by certain movement", as if we could say some forces are caused by some movements, and others are not ...
But things are the other way around !! Movements cannot cause any force ... Forces do cause movements (or change them) !!

If a ball is sitting on the end of a rope and is not moving relative to the other end of the rope, there is no force acting through the rope. If you send the ball round in circles though, that movement generates force in the rope. The movement is the cause. The movement of the ball generates the force in the rope - the force from the rope does not set the ball moving. If you're looking for a primary cause for the centripetal force, it's not just the movement of the ball though as the ball could already be moving in a straight line before hooking onto the end of the rope. Once it's hooked onto the rope, the ball's movement then generates a force in the rope, and then the force in the rope changes to course the ball is travelling in. The cause of the force being generated in the rope is thus a combination of the movement of the ball AND the ball being locked to the end of the rope. The force being generated in the rope follows that. Causation has a strict order and you are violating it.

Your ideas on Physics are flawed even at the very "basics of the basics" level ...

Not at all - you are the one who's mauling physics here because you've learned a stack of incorrect rules which you are applying as if they come from a deity. The physics itself should be your guide and not the mistakes of your teachers.

No wonder you say things such as "It doesn't matter how much justification you can find for calling it centripetal force. This is a grey area in which some usages of the word aren't fully rational" ... and so on.

I say it because when something is already explained in a straight line case, that explanation holds in a rotating case and the rotation is irrelevant. The ball on the end of the string only generates a force in the rope when it's going round on the end of the rope. Take the orbit out of it and the force in the string disappears. In the gravity case though, the force continues to act in full when the orbit is removed, and that tells you that it is a radically different case.

By the way, you could not send us any link where we could see where you took that from, because it´s just what YOU have deduced when reading many things ...
I wonder, couldn´t it rather be a problem of your sight, or of your mind-set ??

Everything you need is here - there is no need to follow links to fake authorities. I draw directly upon physics and reason, and I only state what I know is backed up by physics (and when I also know it could be simulated on a computer to show the mechanisms in action and demonstrate that they do exactly what I claim).

[rmolnav]

If a ball is sitting on the end of a rope and is not moving relative to the other end of the rope, there is no force acting through the rope. If you send the ball round in circles though, that movement generates force in the rope. The movement is the cause. The movement of the ball generates the force in the rope - the force from the rope does not set the ball moving. If you're looking for a primary cause for the centripetal force, it's not just the movement of the ball though as the ball could already be moving in a straight line before hooking onto the end of the rope. Once it's hooked onto the rope, the ball's movement then generates a force in the rope, and then the force in the rope changes to course the ball is travelling in. The cause of the force being generated in the rope is thus a combination of the movement of the ball AND the ball being locked to the end of the rope. The force being generated in the rope follows that. Causation has a strict order and you are violating it.

Again and again, utterly twisting actual, basic Physics. I´ll leave it there without any further comment !!
Please, could somebody else post what he or she thinks of that ??

[David Cooper]

Again and again, utterly twisting actual, basic Physics.

What I said conforms 100% to physics, whether basic or otherwise. You are the one twisting physics if you imagine that the force in the rope is the primary cause. The primary cause is the ball's movement in a direction which will then lead to the force being generated in the rope due to the rope being tied to the ball. That comes first. The force generated in the rope then applies to the ball and changes its course.

And don't lose track of the real point under discussion here either. A ball on the end of a string where nothing is moving does not produce a force in the string. A ball that's swinging round in a circle on the end of a string does produce a force in the string. When you stop the ball, the force in the string is lost.

Now do the same thing with an object orbiting a planet with the planet's gravity holding it in that orbit. The movement of the object does not generate the force that holds it in orbit. If you stop the object, the force does not disappear, but continues to act in full and will drag the object down onto the planet.

I don't know which part of that you're incapable of understanding, or how you can have got your thinking into such a tangled state that you can't acknowledge that this is correct and instead repeatedly refer to it (like every other rational, correct statement I supply you with) as rubbish, nonsense, an absurdity, etc. Please switch your brain on properly and stop wasting my time.

[rmolnav]

What follows is mainly intended not for D. C., but for others. Because he doesn´t accept the authority of eminent physicts (if against what he supposes to "see" just observing physical facts), and most likely he won´t accept even definitions from "eminent" dictionaries, such as Merriam Webster:
1) movement: the act or process of moving;  especially  : change of place or position or posture.
2) to move: to change the place or position of / to cause to go or pass from one place to another with a continuous motion.
3) force : an agency or influence that if applied to a free body results chiefly in an acceleration of the body and sometimes in elastic deformation and other effects.
From which part of those definitions could we deduce that "movements can cause forces" ??
As I previously said, couldn´t rather be that either D. C. sight, when observing physical facts, or the way his mind processes information from his eyes, have some type of problem ??

[David Cooper]

From which part of those definitions could we deduce that "movements can cause forces" ??

Think about the ball on the end of a string going round and round and the force generated in that string. What happens when you stop the ball? The force in the string disappears - a force stops the ball, and the change of movement of the ball then changes the force in the string (eliminating it in this case). What happens if you start the ball moving again? The force in the string reappears as a result of the ball moving. You clearly can't start the ball moving creating the force in the string - the movement of the ball comes first. Clearly another force will have to start the ball moving, but that's a different issue - we're only concerned with the cause of the force in the string, and the force that starts the ball moving can also be detached from the system by having the ball move in a straight line for a long time with no force being applied to it after the initial shove. The ball then hooks onto the string and bingo: the force in the string is now generated. The cause of that force is the movement of the ball and it being locked to the end of the string. What's so hard about understanding that?

Another example of movement causing a force is where something collides with something else - the force does not cause that movement, but the movement and collision with something else then causes the force to be generated (before the force modifies the movement).

As I previously said, couldn´t rather be that either D. C. sight, when observing physical facts, or the way his mind processes information from his eyes, have some type of problem ??

No - all that's happened here is that you've revealed a fundamental error in your understanding of physics (and causation). If you were to program simulations and tried to reverse the causality of things, your programs would fail to function correctly. If you simulate a force in the string to try to make the ball move at 90 degrees to the application of that force, it will fail to do what you want - the ball will be pulled directly towards the centre instead. You have to start by applying a force to move the ball in the right direction, and then you have the ball's movement generate the force in the string as a result.

[rmolnav]

That stubbornness of yours doesn´t deserve further explanations, but I´ll continue for the sake of the interest of others ...
Your investigations, if any, are quite the opposite to Sherlock Holmes´s … He would never say the first found suspect was the murderer, without a thorough analysis of all available details !
Despising loftily Newton´s Laws, and what said today by eminent physicists, and definitions given on recognized dictionaries, you just observe what happens (or just seems to happen), and conclude:

If you send the ball round in circles though, that movement generates force in the rope. The movement is the cause. The movement of the ball generates the force in the rope - the force from the rope does not set the ball moving

Think about the ball on the end of a string going round and round and the force generated in that string. What happens when you stop the ball? The force in the string disappears - a force stops the ball, and the change of movement of the ball then changes the force in the string (eliminating it in this case).

That is utterly erroneous both as:
1) physical reality: the centripetal force doesn´t actually disappear ,
2) as logic (?) conclusion: one thing is “correlation” and quite another “causation” (also “ basics of basics” in its realm) 

[Le Repteux]

1) physical reality: the centripetal force doesn´t actually disappear

Are you talking of the force you need to develop to hold to your idea while it is being swung around? (just kidding :0)

[rmolnav]

Quote from: rmolnav on Today at 13:40:36
1) physical reality: the centripetal force doesn´t actually disappear
Are you talking of the force you need to develop to hold to your idea while it is being swung around? (just kidding :0)

I´m not sure of your intentions with that, but if the hammer an athlete is going to throw were suddenly stopped by a physical obstacle, since that very moment centripetal force (previously changing the direction of the hammer movement), would change to accelerate linearly the weight and the wire "inwards", and even the athlete would move back and fall down ... Clear prove that the centripetal force was being exerted by the athlete on inner extreme of the wire, transmitted section by section through the wire, and finally to the weight through outer extreme of the wire !!