1

Geology, Palaeontology & Archaeology / Re: Is Mt Everest the tallest mountain on Earth?

« on: 04/09/2019 07:10:47 »

Of course, there is also Mount Chimborazo in Ecuador, which takes advantage of being closer to Earth's equatorial bulge than Everest, putting it further from the center of the Earth than Everest...

Quite right! ... Same FACT I already referred to on #2, almost two years ago !

2

The Environment / Re: Which scientists say we've just 18 months to "save planet from climate change"?

« on: 30/08/2019 12:23:22 »

Do you not agree that the wild fluctuations of temperature over 15 years are weather?

The curve of mean anual global temperature is the result of weather and other oscillating factors (mainly sun radiation and ocean current yearly distribution), and the underlying continuously increase of greenhouse effect, due to CO2 and methane emissions (and positive feedbacks, such as increase in atmosphere absolute humidity, albedo, etc).
Years ago oscillating factors, in years with annual annual cooling due to them, this could prevail over underlying greenhouse effect warming. But recently most years the opposite happens, due to the relatively enormous atmospheric accumulated CO2 concentration ... Even independently from the increase in CO2 emissions in a particular year !!

3

The Environment / Re: Which scientists say we've just 18 months to "save planet from climate change"?

« on: 26/08/2019 20:30:21 »

In the hotter parts of the world, peak power consumption occurs in the hotter months, to drive air-conditioning.

per capita in the richer areas, yes, but over the entire population, the majority of whom live between the tropics where there is very little seasonal variation in temperature, no. And north of the tropic of cancer the maximum temperature occurs in July, not May.[/quote]
Is utter NONSENSE to discuss about any possible short-term correlation temperatures/CO2 emissions, because emissions during short periods CAN´T affect temperatures significantly ...
Global warming is an increase of global/annual average temperatures as a result of "billions" of relatively little CO2 emissions over long periods of time. Over just a few months, meteorological temperature changes are the only changes that can be perceived !!

4

General Science / Re: What is centrifugal force?

« on: 26/03/2019 07:30:07 »

I haven´t replied last D.C. post so far to give other possible readers time to read it quietly.
I hope some have already done , and seen at least some of its persistent errors …
Now I´m going to refer to some of them, all at the very root of D.C.´s “grey” flawed stand.

A) You only refer to Newton when saying:

... a rule that future parts of the action do not cause parts in their past, but that the causation operates from past to future. Perhaps this was so obvious that Newton didn't think it worth mentioning, but you can be sure that he fully understood it to be the case

But I´ve never said Newton didn´t mention that ... ("causation operates from past to future") ... What Newton never said, as far as I know, is that movements, by themselves, can cause forces. He delivered his Motion Rules, stating forces cause accelerations. Therefore, they are absolutely necessary, both to initiate a movement, or to change its velocity vector …
“Your” artificial pole-string-object case and similar cases are far-fetched and uncommon, but natural collisions aren´t rare at all … How could Newton “forget" to analyze what (according to you) happens in those cases, that motion cause forces, and somehow include the results in his Motion Laws ?? Impossible to me.     
As I´ve already said, neither momentum nor kinetic energy are a kind of commodity, directly transferable when a collision or similar cases (such as when the string gets tight). An "exchage currency" is necessary, and it is called impulse. To start that “transference”, in an infinitesimal amount of time the momentum of the moving object HAS TO BE REDUCED by an external force, according to:
∂I = F∂t = ma∂t = m∂v.
That force, depending on each particular case, might be an initial latent force, a string own weight component, static friction, initial material resistance to deformations, etc.
The fact that it is not clearly visible to our eyes doesn´t mean it doesn´t exist … Otherwise the moving object would keep constant its velocity vector (Newton´s 1st Motion Law), and no transference of any momentum could occur !! 
 As a REACTION to that force (Newton´s 3rd Motion Law), the moving object starts exerting an equal but opposite force on the “obstacle” (string or initially still object). And a “chain” of mutual actions and reactions, in milliseconds, massively raise those opposite forces exerted on each other, what  changes velocities …

B) Many other ther errors are basically same error repeated many times !!:
B1)

The only forces acting on it are gravity, pulling it towards the massive object, and the tension force from the ball nearer to the massive object. There is no force pulling the further out ball outwards. The only force pulling outwards is the tension force acting on the inner ball, and that is resisting the stretch.

I´m afraid you haven´t fully grasped what a stretching actually is ... The "pairs" of opposite internal forces which "resist" the stretch logically are inwards (relative to the object, or the two stuck balls in our case). But that´s a clear evidence that some other forces are pulling outwards on both balls, and causing the stretch !!
In the two-ball case, one of the forces is gravitational pull on "forward" ball. The other is not so clearly visible when with only two "objects". But if we imagin "behind" ball cut into transverse slices, every slice is being pulled back by its neighbor, and each one is being stretched by its two next-door neighbors, what works in the sense of forming the further bulge …
Logically what you say also happens: through each section between two contiguous slices, they are pulling each other in the sense of “resisting” the stretch … But that is a kind of “the other side of the coin” !!
B2)

Quote
Those two opposite forces, directly exerted on the balls (by the way, not the case of anything like the so called “differential gravity”), stretch the two-part "object", a clear “tidal” effect, using the adjective in its broad sense.
The actual forces in the object are trying to arrest that stretch; not drive it.

Same comment on B1) applies.
B3)

Quote
But if mentioned balls are stuck together, they aren´t free to move: they are somehow “forced” to accelerate the same, despite the different gravitational pulls exerted on them …
...which means that the different pulls on each will generate tension forces which resist the stretching.

... which means that the different pulls on each (two pulls, each one applied on different locations - not a "differential pull" applied we don´t know where), together with the fact that those pulls don´t match with actual accelerations (what brings up inertial forces),  will stretch the whole.
Regarding material reactions, comment on B1) also applies.
B4)

The stretch is caused solely by the nearer ball being pulled more strongly towards the massive object than the other ball. That is what is applying the stretch. The other forces that are generated in the object are both opposing that stretch

Same comment on B1) applies.
There are some more paragraphs we could comment on similarly ...
C5)

The perpendicular movement makes no difference to the forces in play

.
A movement, even if not "perpendicular", certainly doesn´t directly affect forces … The opposite happens (Newton´s Motion Laws).
But that curved movement has both a velocity ("perpendicular") to forces in play, and also an acceleration, in line with forces in play ...
And you stubbornly (and blindly) keep saying things such as:

In the gravity case though, there is a deeper, more fundamental name for it, and that is gravity, and removing the orbital movement also shows that the correct name for the force is gravity because it remains in play when the word centripetal disappears from it without any loss of the force. That tells you what the force really is.

As far as I can remember, trying to make you see your Logics (and Physics) error, I´ve brought up two analogies so far:
- Donald Trump is "more deeply and fundamentally" a man, a human being ... Do you think we shouldn´t say he is also the President of USA, as if his FUNCTION didn´t exist ??
- The same with an airplane pilot, which also is "more deeply and fundamentally” a human being (ESSENCE), but when flying FUNCTIONS as a pilot.
But to no avail ...
If a moving object follows a curved path (whatever the causes), in an infinitesimal period of time ∂t its velocity vector v changes to v + ∂v ... That infinitesimal increase of velocity vector ∂v divided by the time ∂t is, BY DEFINITION, the acceleration vector of the movement at that point and instant ...
That acceleration HAS TO BE CAUSED by a force (Newton´s 1st Motion Law), exactly F = ma (Newton´s 2nd Motion Law).
For the sake of simplicity, let us suppose the size of the velocity vector keeps constant. In that case acceleration and causing force are perpendicular to the curved trajectory, and, also BY DEFINITION, they get the adjective CENTRIPETAL.
And the force exerting that FUNCTION of "bending" the trajectory, among several other ESSENCIALY different forces, can perfectly be gravity ...
If you don´t change some of your "chips", in particular if you stubbornly keep not accepting that centripetal character (FUNCTION) and its gravitational ESSENCE are quite compatible, you will keep drawing erroneous conclusions (by the way, the same will happen if you keep thinking Newton forgot to deliver "motion --> force" laws)  !!
We could even call that force, during the period mentioned function exists, "gravi-centripetal force" …
And, keeping “centripetal force” in your “grey area” that way, logically makes impossible for you even to just "imagine" the possibility that a CENTRIFUGAL force, (an inertial force requiring the existence of centripetal acceleration and forces), could exist in those cases !!

5

General Science / Re: What is centrifugal force?

« on: 19/03/2019 08:04:36 »

A lot of "literature" on last post, but no scientific explanation of how on earth movement of an object can "cause" and a force on another ...
If there is a symmetry as D.C. says, it should be possible to have "motion --> force" laws, kind of symmetric to "force --> motion" Newton´s Laws.I haven´t seen them anywhere, I asked D.C. for them, but business as usual ...
Leaving aside the tricky case pole-string-object, I´ll go back to a gravitational scenario, to have yet another go.
Remembering the “famous” case of the three balls, let us make it simpler and consider just two, in straight line with a much more massive object exerting gravitational pull on them (for the sake of simplicity, let us consider negligible the gravitational pull between the two balls).
On each ball  ONLY the gravitational pull at its location is exerted, and they, completely free to move, are being accelerated, back one less because the pull is smaller there. That makes them separate more and more.
Inertial “resistance” to accelerate (tendency to keep their velocity constant), proportional to mass and actually given acceleration, is just “overcome” by gravity pull, and they accelerate “without any problem” …
We could “refer" the movement of one of them relatively to the other (non-inertial reference system), and say back one accelerates “backwards”, though only relatively to the other … I would understand even the use of the term “differential acceleration” …
But the term “differential gravity” would be absurd, because the “difference” between the two real pulls is not a force actually exerted anywhere, it is something only exists in our minds, as I´ve said many times. When, e.g., at the beginning of a competition, a bike accelerates more than another, we can say there is a  “differential acceleration”, that can be directly observed and even measured. But the terms “differential thrust” of the engines, and the thrust of one "relatively" to the other, would have no sense at all ...
But if mentioned balls are stuck together, they aren´t free to move: they are somehow “forced” to accelerate the same, despite the different gravitational pulls exerted on them …
Forward ball is being accelerated less than what gravity there would cause if it were “independent” to move … Inertial resistance to accelerate is smaller than actual gravitational pull … A “spare” forward force remains acting on it.
The opposite happens to backward ball: it is being accelerated more than what gravity there would cause if the ball were completely free to move … Inertial resistance to accelerate is bigger than actual gravitational pull … A “spare” backward inertial force acts on it.
Those two opposite forces, directly exerted on the balls (by the way, not the case of anything like the so called “differential gravity”), stretch the two-part "object", a clear “tidal” effect, using the adjective in its broad sense.
It would be utterly absurd to think mentioned backward force could be called “centrifugal force”, because in that one-dimension scenario there isn´t a proper “center”. The same could be said about the term “centripetal force”.
But if the two balls also had an initial velocity perpendicular to the straight line going from them to the object causing the gravity, resulting movement would be a curved one, and mentioned stretch would also happen, exactly for the same reasons ...
In that case of circular (or at least curved) movement, both centripetal and centrifugal force terms are the correct ones used in Physics, though “centrifugal” one certainly not by everybody ...
And please kindly note that closer ball is forcing (pulling) further one to experience an acceleration additional to the one directly caused by gravity, in that case by “contact”, same way as in the string case the hook pulls inwards (centripetally) the rotating, “hooked” object.
And, again, when gravitational pull exerts the FUNCTION of centripetal force, logically it doesn´t change the ESSENCE of it ...
And, also logically, if tangential velocity is somehow reduced to null, that FUNCTION disappears, because we are in a different scenario, the one-dimension exposed above ("centripetal" adjective should be substituted by "forward", and "centrifugal" by "backward").
And the fact that gravity remains even if the "perpendicular" movement is somehow removed doesn´t mean that to call its previously existing FUNCTION as centripetal is erroneous, as D.C. has as kind of "life motive" ... (no wonder D.C. says "centripetal force" concept is a "grey area").
If with initial "perpendicular" movement, the gravity would be somehow switched off, the balls would continue its straight path ... That means gravitational pull (or at least a part of it), when existing, is what causes the curved movement, though initial "tangential" speed, logically again, is a necessary condition.

6

General Science / Re: What is centrifugal force?

« on: 17/03/2019 11:41:43 »

You can chop a dog into as many components as you like, but you will never be able to prove it's a cat. It remains a dog.

Right !

I'm not going to waste my time dissecting a dog to prove it's a dog to someone who's adamant that it's a cat.

WRONG ... because what I "dissected" was TIME, a second into milliseconds, and never said those milliseconds are not TIME any more ...
And however good vision you might have, you would´t notice physical, real things that happen in milliseconds !!
You initially see and object moving, afterwards you see forces that didn´t exist before ... and you conclude thinking something as if you were a child (or a non-educated adult): the movement is what "generates" the forces ...
And you dare say Logics is your speciality !!
Sorry, but as I´ve said many times, it´s useless to discuss with you ... If I have done it for so long, it has been for the sake of any other reader who could be interested.
 

You want to do the experiment in a lab with a ball orbiting an asteroid?

What an absurd way of misunderstanding my words !! I said:
"If you did SOME real experiment in a lab ... "[/quote]
and, logically, I referred to the pole-string-ball case, or something similar.
With suitably placed gauging devices, ultra high-speed camera, and appropriate software, we could see forces building up ("reacting" to other previous "action" force interchanged between the two objects in contact), but ALWAYS starting with an initial force exerted by the string ...
If that initial force didn´t exist at all, nothing could start braking the moving object, what is absolutely necessary for any transference of momentum !!
Remember:

the hook and string end ONLY can be put in motion with an external force, because the ball cannot directly “deliver” any type of energy or momentum as if it were a kind of commodity …
In an initial instant ∂t, if we consider m the average of moved mass of hook and string end, f=ma (1st Newton´s Motion Law).
That force ONLY can be exerted by the ball, and it “comes” from its energy. But for that transformation to happen, part of the ball´s energy has to be transferred to the hook, what happens via impulse I, according to the relation:
I = f ∂t = m ∂v,
Over same instant dif.t, the momentum of the ball decreases also in that amount (the speed inversely to ball´s mass).
From that it can be deduced that same force f, but opposite, is being exerted by the hook on the ball (3rd Newton´s Motion Law). But, though apparently the “primary” force is exerted by the ball on the hook (by the "movement" as you say), that´s not so. Without an initial reduction of the ball´s velocity, part of its momentum couldn´t have been transferred to the hook. And that ball´s momentum reduction requires the force exerted by the hook on the ball initiate the transference of momentum. 

That fully agrees with Newton´s Motion Laws ...
You consider movement can also directly "cause" forces, and once you even said there is a "symmetry" ... Could you please give us Motion Laws "symmetric" to Newton´s, which could allow us explain the case (with affected physical variables, functions and formulas, not just "literature" ? 

7

Physics, Astronomy & Cosmology / Re: Why do we have two high tides a day?

« on: 15/03/2019 17:48:29 »

I didn´t replied last post because the discussion continued on the thread "What is centrifugal force?", and most of what posted was about centrifugal force in general, not to its relation with tides. If interested, you can follow it there.
But on a recent post D.C. referred to tides too, and I replied to that respect:
"Many, you included, say only differential gravity can cause tidal bulges …
Let us imagine moon´s gravity were constant across the earth, maintaining moon´s total pull, and therefore actual distances and moon-earth “dancing” …
The “tendency” of earth revolving particles (both solid and water) not to change their velocity vectors (INERTIA) would cause two “tidal” bulges, but BOTH in the sense opposite to the moon (opposite to the centripetal force, that is, always parallel to line earth C.M. - barycenter - moon C.M.).
That implies that the sublunar “bulge” would actually be the opposite: earth radius decreases at that hemisphere …
That would be similar to what happens if, with our hands, we make a cap of tea on a table follow uniformly a circular path …
As I´ve said on "Why do we have two high tides a day?" thread many times, those centrifugal inertial "effects", added to what caused directly by the varying gravitational moon´s pull (inversely proportional to the square of the distance), is what causes the real tidal bulges !!
Remember what Einstein thought:
"Einstein warmed to the idea that the gravitational field of the rest of the Universe might explain centrifugal and other inertial forces resulting from acceleration".
Do you know better than Einstein ?? Or do you think that gravitational pull, acting as centripetal force (by the way, your "grey" area ...) doesn´t cause centripetal acceleration, and subsequently neither centrifugal forces nor other inertial "effects" are present ??
If so, please kindly give all of us your "reasons", instead of just saying "your imagined centrifugal effects don't exist in the gravity case"

8

General Science / Re: What is centrifugal force?

« on: 15/03/2019 12:25:26 »

Since long ago, time and time again, I´ve seen it is useless to discuss with you, at least on dynamics, because you kind of feel 100 % sure of something ONLY if it is what you think you see in nature, forgetting that in milliseconds many things can happen, impossible for our eyes to see ...
When I once asked you for references supporting some of your ideas, you yourself said (thread "Why do we have two high tides a day", #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 !!!”.
No wonder now, after me saying what quoted below, instead of giving us any alternative scientific explanation (with formulas "converting" physical variables and functions into others, as far as "movement" and forces are concerned):

the hook and string end ONLY can be put in motion with an external force, because the ball cannot directly “deliver” any type of energy or momentum as if it were a kind of commodity …
In an initial instant ∂t, if we consider m the average of moved mass of hook and string end, f=ma (1st Newton´s Motion Law).
That force ONLY can be exerted by the ball, and it “comes” from its energy. But for that transformation to happen, part of the ball´s energy has to be transferred to the hook, what happens via impulse I, according to the relation:
I = f ∂t = m ∂v,
Over same instant dif.t, the momentum of the ball decreases also in that amount (the speed inversely to ball´s mass).
From that it can be deduced that same force f, but opposite, is being exerted by the hook on the ball (3rd Newton´s Motion Law). But, though apparently the “primary” force is exerted by the ball on the hook (by the "movement" as you say), that´s not so. Without an initial reduction of the ball´s velocity, part of its momentum couldn´t have been transferred to the hook. And that ball´s momentum reduction requires the force exerted by the hook on the ball initiate the transference of momentum. 

you now just say:

Newtons laws are on my side

and try to explain us the experiment imagined by you, apparently supporting your stand, in a quite "layman" way ...
Newton stated that the direct cause of movement (acceleration that initiates a movement, or modifies its velocity vector), is ALWAYS a force (external to the object). He also considered a force can directly be caused by another force (as inertial reaction), but he never said what you say, e.g. that a movement can "generate" (?) a force, let alone what you said on mentioned #184:
"If a force is generated by rotation, that is clearly centripetal force - a force that comes into play because of the rotation ...” !!!
You seem to want to change Physics science, at least Dynamics, because I also gave you references such as:
"- 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”) 
among others",
but you keep stuck to your ideas ...
Either you explain them "scientifically", not just telling us what you "see" in nature, or in experiments imagined by you in five seconds (!!):

Why do you find it so hard to think up a practical experiment of this kind to illustrate what you somehow imagine to be an impossibility? It took me about five seconds of thinking time to construct those two examples

or, sorry, your ideas can´t be taken seriously ...
If you did some real experiment in a lab, with modern hardware (at least a camera able to take thousands of pictures in a second), and appropriate software, the results would shed light on the issue, and you could see who is right and who is wrong ...
 

9

General Science / Re: What is centrifugal force?

« on: 13/03/2019 08:28:40 »

Quote
1) An independent initial tension is also a necessary condition ...
No it isn't. The line can be slack. Once you add the perpendicular movement, the tension is produced. When the perpendicular movement is removed, the tension disappears from the line and it goes slack again. That shows very clearly the the order of causation.

WRONG! You talk about " add the perpendicular movement", and "When the perpendicular movement is removed" ... How do you "imagine" those actions could actually be realized ?? Because you don´t even mention Newton´s Motion Laws I referred to, that ALWAYS must be accomplished, as far as movement is concerned ...
When the line is “slack” as you say, its end is supposedly still. And at a certain moment there is a physical transference of momentum (or kinetic energy, if you prefer) between the two “objects” in contact: the ball and the string hook.
As I´ve said several times, the hook and string end ONLY can be put in motion with an external force, because the ball cannot directly “deliver” any type of energy or momentum as if it were a kind of commodity …
In an initial instant ∂t, if we consider m the average of moved mass of hook and string end, f=ma (1st Newton´s Motion Law).
That force ONLY can be exerted by the ball, and it “comes” from its energy. But for that transformation to happen, part of the ball´s energy has to be transferred to the hook, what happens via impulse I, according to the relation:
I = f ∂t = m ∂v,
Over same instant dif.t, the momentum of the ball decreases also in that amount (the speed inversely to ball´s mass).
From that it can be deduced that same force f, but opposite, is being exerted by the hook on the ball (3rd Newton´s Motion Law). But, though apparently the “primary” force is exerted by the ball on the hook (by the "movement" as you say), that´s not so. Without an initial reduction of the ball´s velocity, part of its momentum couldn´t have been transferred to the hook. And that ball´s momentum reduction requires the force exerted by the hook on the ball initiate the transference of momentum. 
So far, all mentioned vectors, in bold letters (velocity, acceleration, force, momentum and impulse) are in the same direction of initial ball velocity. Without any other initial force with not null component perpendicular to those vectors, both ball and hook would continue moving straight in that direction …
ONLY with an initial tension of the string, the rectilinear movement can change and get curved. Now also 1st Newton´s Motion applies, but with force and acceleration vectors in the direction of the string (perpendicular to above mentioned vectors).
And, after that, all steps I listed on a couple of days ago post occur:
"2) That initial tension has to pull perpendicularly the object (initial centripetal force), what initiates the curving of the object´s path ... Otherwise the object would continue moving straight.
3) That "triggers" a chain of action and reaction forces ...
4) First reaction of the object is to pull outwards (centrifugally) the string´s outer end (3rd Newton´s Motion Law) ...
5) That increases the tension of the string, what also increases centripetal force and subsequently the centrifugal inertial reaction exerted by the object on the string´s end ...
6) And so on ..."
Do you know better than Newton, or do you interprete his Motion Laws differently ?? If so, please kindly don´t just say my interpretation is wrong, and give all of us some explanation with formulas (not just things such as "if you add the movement ..." !!).

The whole point is that your imagined centrifugal effects don't exist in the gravity case. The perpendicular movement has zero role in flinging up a tidal bulge.

Also WRONG.
Many, you included, say only differential gravity can cause tidal bulges …
Let us imagine moon´s gravity were constant across the earth, maintaining moon´s total pull, and therefore actual distances and moon-earth “dancing” …
The “tendency” of earth revolving particles (both solid and water) not to change their velocity vectors (INERTIA) would cause two “tidal” bulges, but BOTH in the sense opposite to the moon (opposite to the centripetal force, that is, always parallel to line earth C.M. - barycenter - moon C.M.).
That implies that the sublunar “bulge” would actually be the opposite: earth radius decreases at that hemisphere …
That would be similar to what happens if, with our hands, we make a cap of tea on a table follow uniformly a circular path …
As I´ve said on "Why do we have two high tides a day?" thread many times, those centrifugal inertial "effects", added to what caused directly by the varying gravitational moon´s pull (inversely proportional to the square of the distance), is what causes the real tidal bulges !!
Remember what Einstein thought:
"Einstein warmed to the idea that the gravitational field of the rest of the Universe might explain centrifugal and other inertial forces resulting from acceleration".
Do you know better than Einstein ?? Or do you think that gravitational pull, acting as centripetal force (by the way, your "grey" area ...) doesn´t cause centripetal acceleration, and subsequently neither centrifugal forces nor other inertial "effects" are present ??
If so, please kindly give all of us your "reasons", instead of just saying "your imagined centrifugal effects don't exist in the gravity case"

10

General Science / Re: What is centrifugal force?

« on: 11/03/2019 11:06:53 »

Quote from: rmolnav on Yesterday at 12:29:07
I never said the tension makes the object "start moving round in circles" ...
Of course you didn't, but that is the necessary conclusion if you put the causation the wrong way round by denying that the perpendicular movement causes the tension rather than the reverse. The perpendicular movement of the object is a crucial cause of the centripetal force the string

I repeat: WRONG.
The "perpendicular movement" is obviously a necessary initial condition for the rotation to start, but:
1) An independent initial tension is also a necessary condition ...
2) That initial tension has to pull perpendicularly the object (initial centripetal force), what initiates the curving of the object´s path ... Otherwise the object would continue moving straight.
3) That "triggers" a chain of action and reaction forces ...
4) First reaction of the object is to pull outwards (centrifugally) the string´s outer end (3rd Newton´s Motion Law) ...
5) That increases the tension of the string, what also increases centripetal force and subsequently the centrifugal inertial reaction exerted by the object on the string´s end ...
6) And so on ...
The movement cannot "magically" cause any force by itself ... It is inertia, the "resistance" of the object to change its velocity vector, what can show up as a reactive force ... But for that to happen, as said above, an initial and independent centripetal "action" force is absolutely necessary. Otherwise the object would continue moving straight (1st Newton´s Motion Law)
In any case, that bizarre case imagined by you is a short-life one … To make the object go on turning it´d be necessary that initial independent centripetal force to last longer, e.g. with the inner string end being pulled by a hammer thrower, a case not that different from earth revolving around earth-moon barycenter, always in opposition to moon´s location … The athlete has also to lean back to “compensate” inertial centrifugal reaction of the weight, that is being “forced” to follow a curved path, rather than moving straight.
There are certainly differences, but I´m not going to refer to them now, because I did it recently (#233, 235, 237 and 239).
You don´t agree? ... Well, I have to accept it. But don´t expect to convince me that, just because gravity exists even without any object´s movement, there are no inertial centrifugal "effects" when the object is continuously  changing its velocity vector´s direction ...(due to gravitational pull, ACTING as centripetal force).
As said on mentioned posts, those effects vary depending on the degree and "type" of freedom every affected particle actually has. But they do exist.

11

General Science / Re: What is centrifugal force?

« on: 09/03/2019 12:29:07 »

I repeat: it would be useless to repeat here our past year discussion on the other thread ... But:
 

The tension in the string never causes the object on the end of it to start moving round in circles, and cutting the string to remove that tension does not make the ball stop.

I never said the tension makes the object "start moving round in circles" ... But if an object initially in rectilinear movement start being pulled perpendicularly to its velocity vector, the movement CHANGES into a curved one, whatever the way it is pulled (string, gravity, road/tyre friction, etc).
That force is always what is "accelerating" the object inwards, and CAUSES the movement to be circular (or just curved), instead of rectilinear.
And it is called CENTRIPETAL FORCE by any physicist you may find, whatever your "problems" with the term, certainly a "great area" for you as you said long ago ...

12

General Science / Re: What is centrifugal force?

« on: 08/03/2019 12:15:43 »

It would be utterly absurd (and useless) we to continue here our so long last summer and fall discussion on thread "Why do we have two high tides a day?" ...
But, for the sake of the possible interest of other readers, I´m going to put here something directly related to what you are saying now, root of your erroneous stand, as far as I can understand:

In any case where the force is still acting when the orbital movement is removed, the use of the word "centripetal" was misleading, no matter how firmly established that usage of the word is in science. It is when we stop the object and see that the forces continue to operate in full that we realise that they are not genuinely centripetal because they are still fully in play while the label is no longer valid in any way. That is how you get to a better scientific understanding - you look for the places where your labels break and then you realise that you are dealing with something more fundamental.

I´ve said here time and time again that "centripetal force" is neither an "essentially" new force, nor just a  label we can give any force "at will" !! It is just a FUNCTION, which many essentially different types of forces can EXERT, if they are causing the bending of the trajectory of a moving object ...
A pilot, after landing the airplane and going home, is not EXERTING as pilot whatsoever ... Do you consider we should not "label" him or her as a "pilot" because we "are dealing with something more fundamental" (a human being) ??

With something going round on a string, the centripetal and reactive centrifugal labels don't break when you remove the orbital movement because the forces disappear - they genuinely are generated by the rotational movement.

Many times I´ve told you that is erroneous ... Movement doesn´t actually "generate" forces, the opposite occurs !!
You say "With something going round on a string" ... ?? What follows comes from our last year discussion of that case, if the initial movement were caused hitting the ball with a bat.
Hitting a ball produces a transference of momentum, through forces as always. At the very initial instant some deformations (of the ball and the bat) occur, what produces opposite pushes on each other, which then change both speed vectors … The ball gets a speed, and its inertia tries to make it go straight … If a string attached to a pole prevent that to happen, an initial string tension has to exist for that to occur (otherwise the ball would continue straight). That initial string tension is already an initial centripetal force. What the ball´s inertia does (though only over a very short time) is to further tighten the string, and that means the centripetal force increases (exerted by the string on the ball), and subsequently centrifugal “reactive" force (exerted by the ball on the string) also increases …
The initially rectilinear movement is logically necessary to get it converted into a circular one, but it isn´t actually the cause of of that “conversion” and occurring forces … An independent initial tension of the string is required, that could be called “initial centripetal force” as soon as the rectilinear path changes into curved one (not exactly circular at the beginning, because the elasticity of the string, and the fact that initially could´t be fully tight …). And its further increase, and also increasing centrifugal forces, are not directly caused by the initial rectilinear movement, but a consequence of ball´s inertia, manifesting itself that way after the ball being “forced” to bend its path by initial string tension, initial centripetal force ...
 

13

General Science / Re: What is centrifugal force?

« on: 07/03/2019 12:29:08 »

the gravity pulls on the object, and it does so more strongly on the near side of that object than the far side, so a tension force appears within it (which might pull it apart in the process known as spaghettification). That tension force is not any kind of centrifugal force. That force will be opposed by an opposite force which is likewise not any kind of centrifugal force.

After many months of "dynamical" discussion, you keep not considering the real phenomenon of INERTIA, as if it didn´t exist, and therefore ignoring its "effects" ...
If it didn´t exist, the different pulls (because of the different distances) you talk about wouldn´t be able to generate any "opposite force" and cause spagettification. In that kind of impossible case, the object would get an "average" acceleration (though that is also directly connected to the phenomenon of inertia) ...
What actually causes the "opposite force" is the fact that the smaller pull on far side of the object is insufficient to "balance" inertial "resistance" to accelerate there that much. If a particle there were really "free", it would accelerate less. But the inertial resistance of the particle to accelerate is proportional to the acceleration actually given to it.
That difference between external pull on a particle, and inertial "resistance" to accelerate more than f/ma, is actually the appearing "opposite force". 
As I´ve said many times, far side particles have no way to "know" how much near particles are pulled, let alone how to "calculate" any difference between pulls on distant particles, to react accordingly !!
But all particles "feel" external gravitational pull at their location, and kind of internal inertial "resistance" to beeing accelerated, what, if not in balance, causes a real "opposite force" (exerted by the particle on adjacent particles, as the hammer on the wire) ...
And, as I´ve also said many times, that inertial effect is due to exactly the same reason as in cases were the movement is not along a straight line, but along a curved path ...
The only difference is that on curved ones, gravitational pull and relevant accelerations have not the same direction as the object velocity ... Due to that, the gravitational pull (or at least its component perpendicular to actual velocity vector), ACTING as centripetal force, causes the velocity vector change direction ...
And, similarly to the straight line case, the object offers an inertial "resistance" to being centripetally accelerated, what if not in balance with actual gravitational pull on the particle (e.g., ma>f), equally causes an "opposite force". And a force opposite to a centripetal force is, logically, a centrifugal force !!
But in the straight line case forces and accelerations have not any kind of relation with curved movements, necessary for the existence of the concept of centripetal forces, centripetal accelerations, and centrifugal forces, and where a "center" of curvature does exist ...   

14

Physics, Astronomy & Cosmology / Re: Why do we have two high tides a day?

« on: 06/03/2019 15:02:05 »

WHAT FOLLOWS is a post I sent minutes ago to the thread "What is centrifugal force".
I´ve decided to put it here too, because the issue in directly connected to tides.
On another post I´ll add some "singularities" to be kept in mind in the case of earth´s revolving around earth-moon barycenter ... Centrifugal inertial effects are not quite the same as what exposed about the moon, especially in the case of sea water, not existing on the moon ...:

"Since my last post I´ve frequently found myself ruminating on our issue, trying to find better ways to convey my stand.
On this thread and on “Why do we have two high tides a day”, many times I´ve referred to the different ways inertia manifests itself, depending on the type and degree of “freedom” to move considered material stuff actually has …
The more I ruminate on the issue, the clearer I find that the root of the confusion is that the term “centrifugal force” is used too broadly, even in cases where certainly a “centrifugal effect” does exist, but not as a real newtonian force … But in other cases that centrifugal effect appears, totally or partially, as a real force.
A general term to cover all scenarios could be “centrifugal inertial effect” (CIE?), that always is present if the trajectory of any massive stuff is curved, whatever the cause of that curved path … I´ll try and elaborate as follows.
We all know Newton´s Motion Laws. But I´m afraid not all keep in mind those laws are just the consequence of the basic Physics phenomenon of INERTIA: massive objects (and any part of them) always have a TENDENCY to maintain constant its current velocity vector, and they show a RESISTANCE to any agent trying to accelerate considered massive stuff. Those laws put it in terms of forces: f=ma (2nd law), being 1st law when f=0, and 3rd one the necessary consequence when considering two directly interacting objects.
We can analyze any possible case starting directly from INERTIA phenomenon, instead of using the “tool” of Newton´s Laws, not breeching them though: it´s a kind of other side of the coin …
In some cases, that RESISTANCE shows up as a real FORCE, but certainly not always.

The term CENTRIFUGAL always refers to an outward “tendency” to move, implying the existence of a “center”: the center of a circular path followed by an object, or at least the center of curvature of its CURVED PATH.
It´s convenient to separate cases with direct physical connection between interacting objects (A), from cases when gravity is involved (B).
A) Hammer throwing: the “hammer”, as a whole, is being centripetally accelerated. INERTIA tends to make it go on the tangent, the cable (and the athlete) don´t let it move straight, and the inertial RESISTANCE to being accelerated inwards appears as a real CENTRIFUGAL FORCE exerted by the hammer on the wire´s end … (I´m not considering now internal forces, that would be different if we had a sling instead, and form a “field” of real centrifugal forces, exerted between contiguous particles …).
It´s what David Cooper calls “reactive centrifugal force”. Similar things can be said about other cases such as wheeled wagons on a railway, vehicle rubber tires on road surface (with or without banking), etc., 
B) When gravity is involved, as it changes with distance, it´s paramount to distinguish cases when those changes are practically null (due to the rotating object negligible size, compared with distance to the object causing the gravitational field - e.g.: artificial satellites), from the rest.
B.1) In the first case the objects are in a pure “free fall”. All their particles are accelerated the same. Inertial RESISTANCE to being accelerated (proportional to mass and given acceleration) is precisely what makes necessary the existence of the gravitational pull f=ma: otherwise the object would continue straight.

But now we don´t have even a “reactive” centrifugal force: acting centripetal force, the gravitational pull at that location, is independent from the object´s inertia … If in some moment F were not equal to ma, the object would be free to change orbit (certainly a case quite different from hammer-throwing).
B.2) The simplest case is our moon rotation around earth-moon barycenter.
INERTIA makes every moon´s particle tend to keep moving straight, but all those particles are forced to follow circular paths.
The further the particle, the bigger the radius, and the bigger the acting centripetal force mω˛r.
Inertial RESISTANCE to being accelerated is proportional to ma. If the particles were in a real free fall, they would be free to adjust their orbits to the acting gravitational pull at their location, that varies inversely to the square of the distance.
But that is not possible. If, e.g., we transversely “cut” the moon into too halves, the further one is being centripetally accelerated more than what earth´s pull would cause on that “hemimoon” if it were really free to move. Therefore, ALWAYS existing inertial RESISTANCE to being accelerated is only PARTIALLY compensated by earth´s gravitational pull, the unique force “external” to the moon. That fraction of that inertial RESISTANCE, as on case B.1, doesn´t cause any additional centrifugal effect, let alone force.
But the inertial RESISTANCE not “compensated” that way is still present, and, similarly to what in the hammer throwing case (A), it causes an outward pull on adjacent inner half moon. That is a real CENTRIFUGAL FORCE, quite similar to the one exerted by the hammer on the wire´s end. It “forces” closer half of the moon to keep the common orbit, instead of a smaller one that would match with the stronger earth´s pull on closer “hemimoon”.
On any other transverse section similar things happen, and the moon is stretched in the direction of the straight line earth-moon, what is also called “tidal effect”. By the way, directly connected with the fact that the moon is “tidal locked” to earth (closer and further mentioned halves don´t change, apart from some very tiny “oscillation”).
So, I consider quite opposite stands:
1) In all cases with curved paths real centrifugal forces are present,
2) The fact of having a curved path doesn´t imply the existence of real centrifugal "effects", and real centrifugal forces only appear in cases similar to hammer throwing (never when gravity is involved),
are both erroneous.
And the "invention" of a fictitious centrifugal force for cases when a rotating frame of reference is used doesn´t help diminish confusion ... That just adds something to cause the REAL inertial effects that, logically, disappear when rotation "ceases", as actually happens relatively to mentioned type of frame (precisely called "non inertial" !!)".   

15

General Science / Re: What is centrifugal force?

« on: 06/03/2019 11:41:52 »

Since my last post I´ve frequently found myself ruminating on our issue, trying to find better ways to convey my stand.
On this thread and on “Why do we have two high tides a day”, many times I´ve referred to the different ways inertia manifests itself, depending on the type and degree of “freedom” to move considered material stuff actually has …
The more I ruminate on the issue, the clearer I find that the root of the confusion is that the term “centrifugal force” is used too broadly, even in cases where certainly a “centrifugal effect” does exist, but not as a real newtonian force … But in other cases that centrifugal effect appears, totally or partially, as a real force.
A general term to cover all scenarios could be “centrifugal inertial effect” (CIE?), that always is present if the trajectory of any massive stuff is curved, whatever the cause of that curved path … I´ll try and elaborate as follows.
We all know Newton´s Motion Laws. But I´m afraid not all keep in mind those laws are just the consequence of the basic Physics phenomenon of INERTIA: massive objects (and any part of them) always have a TENDENCY to maintain constant its current velocity vector, and they show a RESISTANCE to any agent trying to accelerate considered massive stuff. Those laws put it in terms of forces: f=ma (2nd law), being 1st law when f=0, and 3rd one the necessary consequence when considering two directly interacting objects.
We can analyze any possible case starting directly from INERTIA phenomenon, instead of using the “tool” of Newton´s Laws, not breeching them though: it´s a kind of other side of the coin …
In some cases, that RESISTANCE shows up as a real FORCE, but certainly not always.
The term CENTRIFUGAL always refers to an outward “tendency” to move, implying the existence of a “center”: the center of a circular path followed by an object, or at least the center of curvature of its CURVED PATH.
It´s convenient to separate cases with direct physical connection between interacting objects (A), from cases when gravity is involved (B).
A) Hammer throwing: the “hammer”, as a whole, is being centripetally accelerated. INERTIA tends to make it go on the tangent, the cable (and the athlete) don´t let it move straight, and the inertial RESISTANCE to being accelerated inwards appears as a real CENTRIFUGAL FORCE exerted by the hammer on the wire´s end … (I´m not considering now internal forces, that would be different if we had a sling instead, and form a “field” of real centrifugal forces, exerted between contiguous particles …).
It´s what David Cooper calls “reactive centrifugal force”. Similar things can be said about other cases such as wheeled wagons on a railway, vehicle rubber tires on road surface (with or without banking), etc., 
B) When gravity is involved, as it changes with distance, it´s paramount to distinguish cases when those changes are practically null (due to the rotating object negligible size, compared with distance to the object causing the gravitational field - e.g.: artificial satellites), from the rest.
B.1) In the first case the objects are in a pure “free fall”. All their particles are accelerated the same. Inertial RESISTANCE to being accelerated (proportional to mass and given acceleration) is precisely what makes necessary the existence of the gravitational pull f=ma: otherwise the object would continue straight.
But now we don´t have even a “reactive” centrifugal force: acting centripetal force, the gravitational pull at that location, is independent from the object´s inertia … If in some moment F were not equal to ma, the object would be free to change orbit (certainly a case quite different from hammer-throwing).
B.2) The simplest case is our moon rotation around earth-moon barycenter.
INERTIA makes every moon´s particle tend to keep moving straight, but all those particles are forced to follow circular paths.
The further the particle, the bigger the radius, and the bigger the acting centripetal force mω˛r.
Inertial RESISTANCE to being accelerated is proportional to ma. If the particles were in a real free fall, they would be free to adjust their orbits to the acting gravitational pull at their location, that varies inversely to the square of the distance.
But that is not possible. If, e.g., we transversely “cut” the moon into too halves, the further one is being centripetally accelerated more than what earth´s pull would cause on that “hemimoon” if it were really free to move. Therefore, ALWAYS existing inertial RESISTANCE to being accelerated is only PARTIALLY compensated by earth´s gravitational pull, the unique force “external” to the moon. That fraction of that inertial RESISTANCE, as on case B.1, doesn´t cause any additional centrifugal effect, let alone force.
But the inertial RESISTANCE not “compensated” that way is still present, and, similarly to what in the hammer throwing case (A), it causes an outward pull on adjacent inner half moon. That is a real CENTRIFUGAL FORCE, quite similar to the one exerted by the hammer on the wire´s end. It “forces” closer half of the moon to keep the common orbit, instead of a smaller one that would match with the stronger earth´s pull on closer “hemimoon”.
On any other transverse section similar things happen, and the moon is stretched in the direction of the straight line earth-moon, what is also called “tidal effect”. By the way, directly connected with the fact that the moon is “tidal locked” to earth (closer and further mentioned halves don´t change, apart from some very tiny “oscillation”).
So, I consider quite opposite stands:
1) In all cases with curved paths real centrifugal forces are present,
2) The fact of having a curved path doesn´t imply the existence of real centrifugal "effects", and real centrifugal forces only appear in cases similar to hammer throwing (never when gravity is involved),
are both erroneous.
And the "invention" of a fictitious centrifugal force for cases when a rotating frame of reference is used doesn´t help diminish confusion ... That just adds something to cause the REAL inertial effects that, logically, disappear when rotation "ceases", as actually happens relatively to mentioned type of frame (precisely called "non inertial" !!).   

16

General Science / Re: What is centrifugal force?

« on: 22/01/2019 14:35:51 »

I have seen it expressed now and again that gravity is an invented power. That mysterious changes in geometry cause gravity. In this way I trust it is vital to nail down a definition.

I was going to  send a reply to quoted "mona2200" post of three days ago, but it has disappeared !! ??
Though gravity as an invented "power" sounds awful, I don´t think the post deserved removal ... After all, Einstein´s theory of curving of time-space, due to the presence of massive objects, as essence of gravity may be considered kind of "mysterious (?) changes in geometry" ...

17

General Science / Re: What is centrifugal force?

« on: 12/01/2019 11:09:28 »

And now that the rock is in orbit, you want to call the entire gravitational force acting on it centripetal force, so it becomes clear that any attempt to call the compressive force centripetal is incompatible with this other kind of centripetal force that's now applying on the rock to hold it in orbit. Also, once the rock is in orbit, there is no centrifugal force in action - the only force there is the gravitational pull which you call centripetal. The imaginary centrifugal force that you want to assert is real here ...

I was referring to what happens at different parts of our planet: the solid core, the liquid magma, and the crust, where real centrifugal forces, "reactive" if you like, do exist.
But you only refer to a loose rock on earth surface, reaching a "weightless" condition thanks to an enormous angular speed increase, something that would´t ever happen because earth crust would break up before, precisely due to above mentioned centrifugal forces, that previously would also have increased more and more the equatorial bulge size.
Nevertheless, in that particular  scenario, what you say "once the rock is in orbit, there is no centrifugal force in action" would be correct, but I´m afraid you don´t fully understand all the dynamic details of what happens, let alone what I say:

What is much more complex is how the object continues to show its inertial "tendency" to follow straight, somehow opposing to the centripetal force which is "forcing" it to bend its path (certainly not always as a “real” centrifugal force). That depends on other details of the scenario, mainly on dynamic details such as grade and type of "freedom" the object has to "reply" acting centripetal force.

.
And when the rock gets "weightless", it is orbiting around earth C.G. (at a fixed point), quite "free" to maintain its linear speed, and experiencing (the rock as a whole) only earth´s gravitational pull, perpendicular to its speed ...
That´s the "essence" of a circular, uniform movement. And the whole earth´s pull is what "forces" the rock to follow a circular path, instead of its natural, inertial tendency to keep constant its velocity vector.
That force is a centripetal force, by definition, not just the way I "want" to call it  ...
The "reply" of the stone to being "forced" that way, in this case is what I also said:

... that object (the rock) wouldn´t affect earth dynamics (though theoretically would also exert an equal but opposite pull on earth, as inertial reaction according Newton´s 3rd Motion Law)

and, on the one hand, if what the rock actually does is to "exert" that force, it couldn´t be considered a centrifugal force (though rock particles keep their "tendency" to "resist" given centripetal acceleration: if the surface were wet, water would move outwards, outdoing water surface tension). And on the other hand, as that force doesn´t affect earth´s dynamic whatsoever (as e.g. happens to the "couple" moon-earth), and the size of the rock is negligible, the case can be considered only as a "free" fall of the rock in a fixed gravitational field ...
Another thing would be if the hight of the rock were not negligible (compared to earth radius). In that case gravitational pull on each rock´s particle would clearly differ from required centripetal force at its location, and they wouldn´t actually be in a "proper" free fall ... Internal stresses (in pairs, centripetal and centrifugal) would appear to compensate those differences, stretching the rock radially.
(I do know you don´t agree with that, long discussed on the thread about tides, but I repeat it here for the sake of other possible readers ...)
As far as I can understand, what you say:

The important point here though is that the imaginary centrifugal force which you're trying to sell is a (fake) force that goes up in strength as the planet rotates faster, and while it does this, the real forces go down - the rock presses down less hard and the ground has less to resist against. The gravitational force goes down a little as the equator bulges a fraction. No real force is going up, but your imaginary centrifugal force is growing stronger as the rotation speed goes up.

is rather confusing.
At current angular speed (or other "intermediate" scenario), only a fraction of gravitational pull FUNCTIONS as centripetal force: just mω˛r ... And that fraction does increase with angular speed ...
As you say, " ... the rock presses down less hard and the ground has less to resist against". Please note that the difference is precisely that value (mω˛r), to satisfy Newton´s 2nd Motion Law. And the rest of gravitational pull keeps earth and rock pressing onto each other (not to be called centripetal or centrifugal forces, because, as said above, they are equal to the fraction of gravitational pull which DOESN´T cause any acceleration ...).
Those action and reaction "compressive" forces, though certainly due to gravity, shouldn´t be confused either with it or with part of it: gravitational pull is exerted between all earth´s and rock´s particles, and mentioned compressions are pushes interchanged by only the particles in contact ...

18

General Science / Re: What is centrifugal force?

« on: 07/01/2019 12:13:50 »

When you start the rotation, you can play games by renaming forces that were already acting before there was any rotation, but they go down in strength while your imagined centrifugal force goes up. Even if you're prepared to accept that these real forces go down instead and you decide to call one of them centrifugal, you would have to call it reactive centrifugal force, which is the only real kind of centrifugal force, acting in response to centripetal force and being equal to it. Then, at the point where the reactive centrifugal force reaches zero and the object becomes weightless, the centripetal force must also have reached zero, revealing that the gravitational force which you also like to call centripetal force in situations with orbiting objects is not the same as the centripetal force that was acting in the opposite direction to the reactive centripetal force that was present up until the object became weightless

With your last post one can tell you haven´t grasped what centripetal force actually is yet!!
As I´ve said many times, any rotation, or any movement of massive particles along a curved path, REQUIRES a net amount of centripetal force exerted on it, that can be provided by different sources … Otherwise, due to inertia the movement would be along a straight line at constant speed, whatever the way it initially got that speed ... That "simple" !!
The only detail not that simple is that FUNCTION as centripetal force can be exerted by either the total amount of a single force, or part of it (in size, or a certain fraction of one of its orthogonal components), or a combination of different forces …
Imaging a sling rotating in a vertical plane. When the string is horizontal, only its tension functions as centripetal force: gravity either increases or decreases linear velocity. But when at upper location gravity, added to string tension, functions as centripetal force, and our hand need not to pull down so much … if we wish to keep a constant angular speed (almost impossible though …). The opposite happens at lower position, because gravity is kind of centrifugal at that point, and string tension (necessarily much higher) minus gravity is what functions as centripetal force …
And at intermediate locations inward radial components of gravity vector, in each case with its sense, added to string tension, are which function as centripetal force.
What is much more complex is how the object continues to show its inertial "tendency" to follow straight, somehow opposing to the centripetal force which is "forcing" it to bend its path (certainly not always as a “real” centrifugal force). That depends on other details of the scenario, mainly on dynamic details such as grade and type of "freedom" the object has to "reply" acting centripetal force. 
You go from the "no rotation" scenario (gravity and internal forces do exist, but no centripetal force required), to an imaginary “perfect” orbiting situation (by the way, quite different scenario from the one I brought up), without considering any intermediate situation (the ONLY ones which could actually happen, as the current spinning at 2π radians/24 h angular speed).
By the way, you say:

... forces that were already acting before there was any rotation, but they go down in strength while your imagined centrifugal force goes up

Previously "acting forces" were gravity and internal compressive forces. Gravity, as a result of the stretching that causes the equatorial bulge, does decrease a little ... But required centripetal force (mω˛r) increases enormously, and bigger and bigger fraction of gravity pull has to function as centripetal force. And any inertial effect, such as centrifugal forces if any, increases more and more ... 
And you also say:
"... you can play games by renaming forces that were already acting before there was any rotation, ..."
It is not a question of "renaming": if earth starts spinning, inertia makes its particles try to follow a straight path (the tangent) ... Required centripetal force at each location only can come from gravity, and from internal interactions that are partially due to gravity ...
Curiously at earth solid core what happens is similar to "your" case of an object hanging from a string and a pole, made rotate with a bat: the material of the core, enormeosuly compressed due to gravity, if somehow made rotate, doesn´t let the particles to follow the tangent, and it gets radially stretched, what can provide the necessary increase of centripetal force: bigger and bigger fractions of gravitational forces (directly or indirectly) exert the FUNCTION of centripetal force.
From there to earth crust, the stuff is liquid, a quite different scenario ... Now it is like a centrifuge. Due to inertia, each particle tries to follow the tangent ... But earth crust doesn´t allow them to do so, and that induces an increase in pressure under earth crust. Initially earth´s crust and gravity provide the required centripetal force (exerted on the magma), and the magma exerts an equal but centrifugal force on the crust (as currently happens).
Own earth crust inertia also causes its deformation (inertial effects on lower latitude parts are much higher, and internal centrifugal forces appear), also tending to an earth equator diameter increase ... 
But at much higher angular speed earth´s crust can´t withstand all internal stresses caused that way, and would break into pieces (long before any "levitation" of outer objects).
By the way, "your" orbiting "weightless" object scenario would be also quite different from the case of a pair of comparable celestial objects rotating around their common center of mass, because that object wouldn´t affect earth dynamics (though theoretically would also exert an equal but opposite pull on earth, as inertial reaction according Newton´s 3rd Motion Law).

19

General Science / Re: What is centrifugal force?

« on: 01/01/2019 11:36:55 »

An object sitting on a non-rotating planet will press down on the surface of the planet and a reactive force will be generated in the opposite direction to oppose it. Neither of those forces can be called centripetal or centrifugal because there is no rotation. If you begin to spin the planet and keep increasing the speed of the rotation, those two forces will both lessen and reach zero when the object becomes weightless. Any analysis which asserts that a centrifugal force is going up as the rotation gets faster is working with an abstraction which does not represent what the real forces are doing. The gravitational force is constant until the object lifts off the ground, and the other real forces are both going down while the imaginary centrifugal force in the abstraction goes up.

1) "Neither of those forces can be called centripetal or centrifugal because there is no rotation. If you begin to spin the planet and keep increasing the speed of the rotation ..." then the "reason" that there is no rotation would not apply, some force would have to function as centripetal force, and "inertial effects" would appear because massive stuff is being accelerated ...
2) "Any analysis which asserts that a centrifugal force is going up as the rotation gets faster is working with an abstraction which does not represent what the real forces are doing":
Wrong, as shown below.
3) "The gravitational force is constant until the object lifts off the ground, and the other real forces are both going down while the imaginary centrifugal force in the abstraction goes up".
Wrong ... Long before any of us could "levitate" on the equator, the equatorial bulge would get much, much bigger, and even, as I said:
 

Earth solid parts are stretched as in the CD case, and also would explode at much higher velocity.

And earth´s crust couldn´t deform so much, let alone break into pieces, without exerting on it strong opposite REAL forces, in our case centripetal forces (the ones which make earth stuff rotate at so high speed), and centrifugal forces (always due to inertia, or "reactive" as you say ...). 

20

General Science / Re: What is centrifugal force?

« on: 31/12/2018 08:45:23 »

By the way, this very morning I saw a clip on Discovery Max tv, where a CD was made rotate at the r.p.m. of a hoover ... The CD suddenly breaks into hundred of small pieces, obviously due to huge tensile internal stresses due to both centripetal and centrifugal forces (the former causing the rotation, and the later the way inertia manifests itself, because all CD particles are being hugely accelerated).
And that, happening in nature, has nothing to do with frames of reference !!
 

Before the year ends ... Happy New Year! ...
...and an additional comment to what above.
In the case of the CD, as in the cases of the centrifuge, the hammer throwing, the sling ..., "solid" stuff is what exerts the centripetal force on the considered rotating "object" (either solid or liquid), and centrifugal forces (inertial as always) are exerted by the rotating "objects" on what exerts the centripetal force (internal stresses included).
Some people think that when gravity is involved (as cause of the curving of the trajectory), without any solid device (such as a string, wire, centrifuge vessel, and own CD material), no centrifugal force exists ...
But quite similar to the CD case is the daily earth spinning ... At its angular speed of 2π radians/24 h. it is causing a relatively huge equatorial bulge (tens of km), affecting both solid and liquid parts of our planet.
Earth solid parts are stretched as in the CD case, and also would explode at much higher velocity.
But what makes water rotate (instead of "following the tangent) is only gravity, exactly a component of water weight vector at each location: the one perpendicular to earth´s axis of rotation ...
At the equator water "lightens" much more than closer to poles, because centrifugal forces are proportional to the radius (mω˛r) ...
If spinning velocity increased, the bulge would get bigger, water would evaporate more ... and eventually something similar to the case of the CD at vacuum cleaner spinning rate would happen !!
Centripetal and real centrifugal forces are necessary for all that to happen, and, again, whatever the movement of any considered observer, and the reference system he or she chose...