What is centrifugal force?

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Online Nilak

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Re: What is centrifugal force?
« Reply #50 on: 13/10/2016 06:57:50 »
I've made a computer simulation program in which if you select 2 particles with a certain mass and tie them together with a spring, they can rotate around each other without adding the centrifugal force into the motion equations. I only use F=ma; F=kx; dv=a*dt; dx=v*dt; The same happens if you substitute the spring with a gravitational force F=Gm1m2/r^2. So the centrifugal force is the effect of inertia when changing direction. When motion is restricted on a circle, the force of inertia is produced at every little change in the initial direction. This force can be calculated. If your motion is restricted by a different shape (elipse) it will have different formula ( you need to include an angle). Centrifugal force is not a fundamental force, it is only a formula to use for motion restricted on a circle.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #51 on: 13/10/2016 18:37:39 »
#49 hamdani yusuf
That question has already been dealt with by me (mainly on #28, 36 and 37).
In the first place, we should keep in mind that “centrifugal forces” show up in DIFFERENT fashions ...
Those pictures are only mathematical abstractions of the real thing. The central object is supposed to be much more massive than the other, and, for the sake of simplicity, it is supposed to keep stand still. But, unless it mass were infinite, it is imposible for an object to pull another without moving itself at all.
In both cases we have a primary force: the central object pulls the other (centripetal force).
According to 3rd Newton´s principle, outer object also exerts an equal but opposite force on central one: centrifugal force.
In those cases where there is no physical connection (string, rope, chain ...), both forces are gravitational. By the way, we already know that gravity happens in both senses. It couldn´t be otherwise.
And both objects are considered with their masses concentrated on their gravity center. That is also a simplification. Every particle of each object “feels” independently the gravity pull from the other, not necessarily with same “intensity”, as long as distances are actually different. Those different centripetal forces on each particle originate internal stresses between contiguos particles, that (also due to 3rd principle) go in pairs, being half of them centrifugal.
But I have to come back again to that another day, with clarifying examples.
I already did it last year, under the previously mentioned head subject : “Why are there two high tides a day?”.
In cases where there is a physical connection, the centripetal force is also acting on each particle of both objects, and on each section of the “linking” device, from central to outer object. And on all those places the correspondent centrifugal reaction happens too.   


 

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #52 on: 13/10/2016 19:35:03 »
#50 Nilak
You say:
"So the centrifugal force is the effect of inertia when changing direction".
Not bad idea. But, have you realized that, after all, it is a way of expressing (in a particular case) the three Newton´s Principles?
Whatever happens with linear speed of an object, any change of its direction is a velocity vector change, an acceleration. That results in a curve trajectory.
That acceleration requires an acting force (2nd principle), towards the concave side of the curve (by the way, not necessarily a circumference): centripetal acceleration. If that is exerted (whatever the way) by object  A on B, B by INERTIA tries to maintain its own speed (1st principle), and exerts an equal but opposite force on A: (3rd principle).
But, apparently, you mean centrifugal force is "the effect of inertia" on the object that changes direction ... That seems to establish the idea that centrifugal force in a kind of fictitious force, just an "effect" of inertia.
Please kindly read my #50. There you can see I talk about the "infinite" pairs of centripetal/centrifugal forces acting on the particles of any rotating  object (or just with a curve trajectory). That can be considered an "effect" of inertia,  but it is a REAL force, and it doesn´t mean centrifugal force is not  fundamental. 

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Online Nilak

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Re: What is centrifugal force?
« Reply #53 on: 14/10/2016 00:45:56 »
#50 Nilak
You say:
"So the centrifugal force is the effect of inertia when changing direction".
Not bad idea. But, have you realized that, after all, it is a way of expressing (in a particular case) the three Newton´s Principles?
Whatever happens with linear speed of an object, any change of its direction is a velocity vector change, an acceleration. That results in a curve trajectory.
That acceleration requires an acting force (2nd principle), towards the concave side of the curve (by the way, not necessarily a circumference): centripetal acceleration. If that is exerted (whatever the way) by object  A on B, B by INERTIA tries to maintain its own speed (1st principle), and exerts an equal but opposite force on A: (3rd principle).
But, apparently, you mean centrifugal force is "the effect of inertia" on the object that changes direction ... That seems to establish the idea that centrifugal force in a kind of fictitious force, just an "effect" of inertia.
Please kindly read my #50. There you can see I talk about the "infinite" pairs of centripetal/centrifugal forces acting on the particles of any rotating  object (or just with a curve trajectory). That can be considered an "effect" of inertia,  but it is a REAL force, and it doesn´t mean centrifugal force is not  fundamental.
I've just checked the Wikipedia to see what it says about centrifugal force and I understand the same thing I've tried to explain.
Sorry, reply no 50 is mine.

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #54 on: 14/10/2016 02:18:42 »
...
According to 3rd Newton´s principle, outer object also exerts an equal but opposite force on central one: centrifugal force.
...
If both objects have equal mass, e.g. binary stars, where is the centrifugal force?

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Online Nilak

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Re: What is centrifugal force?
« Reply #55 on: 14/10/2016 05:25:38 »
...
According to 3rd Newton´s principle, outer object also exerts an equal but opposite force on central one: centrifugal force.
...
If both objects have equal mass, e.g. binary stars, where is the centrifugal force?
There are two forces here, for each star, pointing away from the centre of rotation. Also two,
gravity forces, equal to each other and to the centrifugal forces, pointing to the centre of rotation. Instead of gravity you can say the spacetime curvature is causing the attraction if you want to be more precise.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #56 on: 14/10/2016 11:40:29 »
#54 hamdani yusuf
As I said on #51, if you are considering those stars as if all their constituent material were concentrated on their center of gravities, you are right. All action and reaction forces would go towards the center of the twin system.
But that simplification is not what actually happens. Star A material closer to star B, as well as the material of B closer to A, will be pulled by the other star with stronger force than if we consider outer material. Those (NOT EQUAL to each other) centripetal forces are supposed to produce the centripetal acceleration that the rotation requires. But all parts of the stars, due to own gravity, are obliged to rotate at SAME angular speed. Force excess and/or deficit can only be compensated by internal stresses, changes in pressure when gases.
Gases "try" to concentrate either at closest parts of the pair (centripetal force bigger than what necessary for required centripetal acceleration), or at outer parts (centripetal force smaller than what required). If you consider a traverse "slice" at those outer parts, pressure at outer side will be smaller than at inner side (comparing with pressures if they were not rotating). The net force acting on the slice would be CENTRIFUGAL (apart from own gravity force or weight)
By the way, that is also a good picture of the two high tides on Earth: one at Moon side, and the other at opposite side. Whatever the actual material, phenomena are very similar

 
 
 

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #57 on: 14/10/2016 18:02:02 »
Yesterday I happened to run into Einstein … and I think he “told" me that, at least on one of my key ideas, I´m right.
Do NOT worry! I am not going to talk about relativity theory. Our discussion about centrifugal force, and gravity, must continue within Newton´s Physics.
You can see on #37 the case of a bar hanging from one of its extremes, and the different stresses on each of its sections.
My plan was to pass from that rectilinear situation to a rotational one: the bar, in the space without gravity, somehow rotating around an imaginary hinge at one of its extremes. I haven´t done it yet because I preferred to comment other posts.
It would be very, very similar to the vertical hanging bar case. Each part of the bar would “feel” the centrifugal force in a way quite similar to the effect of the bar weight when hanging vertically. The centripetal acceleration implies an effect on the bar equivalent to a kind of outward, radial weight.
And, a real coincidence, yesterday afternoon tve2 (Spain) emitted “Inside Einstein´s Mind”.
There I learnt that when he was young, and “ruminating” about gravity (before any relativity idea), he imagined something almost exactly equal to what above exposed.
When announcing the video, they said it was from NOVA. From previous cases I know they have plenty of videos on their web site, and I found it:
http://www.pbs.org/wgbh/nova/physics/inside-einsteins-mind.html
Here in Spain is not possible to watch those videos, unless paying for them ...
Approximately at 1/3 of the video, there is a scene with a huge square box, with open front side, and a man “floating” inside (as without gravity). Then he falls onto the box floor, and a little later the point of observation goes back, and we can see Earth globe supporting the box. And afterwards, again at a no gravity place, they lift the box with “g” acceleration.
They say it was imagined by Einstein, who thought the man would feel “floating” or falling down, but, when standing on its feet, he couldn´t tell apart the situations when attracted by Earth´s gravity and when no gravity but the box was being accelerated upwards with “g”.
Its conclusion was that gravity and acceleration must be the “same" thing … And that helped him continue his ideas of space-time deformation, and rest of stuff.
Subsequently, I say, centripetal force/acceleration acts on the rotating object as Einstein´s box lifting force, and makes the object “feel” a centrifugal force, exactly as the man on the box floor feels either his weight (no acceleration) or the acceleration (no weight). And, in other cases (f.e. a child on a swing), both forces added up. 



 
 
 

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #58 on: 14/10/2016 18:14:19 »
By the way, as far as I can remember the word "inertia" doesn´t appear ... (?)
Another day I have to send a post about that example of the child on the swing. And another to say something more about the revolving bucket with water ...
And sorry for my rather poor English (after sending the post I´ve seen I say "its conclusion" referring to Einstein´s !!)

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #59 on: 15/10/2016 11:10:25 »
The case of a child on a swing can be simplified as a pendulum.
There is a difference, as long as in the pendulum case the weight is supposed to be hanging from a string knot (the string pulls the weight), but the swing seat is actually pushing upwards the child. That changes the actual field of reaction forces within child´s body, compared to if he were hanging from his hands.
Another day we can talk about the real case of the swing. Today I propose the simplified pendulum example:
Oscillating_pendulum.gif
Any comments)

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #60 on: 16/10/2016 12:10:44 »
Pendulum I
It seems simple, but there are small but important details that, if not being careful, one can misinterpret facts, or at least confuse others …
That´s why I am now going to consider only the scenario statically (and step by step), without any movement: fixed hanging point, string and weight (I´ll call it W), all in a straight vertical line.
- a) Primary acting force: Earth pulls downwards W.
- b) W does not move. According to 2nd Newton´s principle, the sum of all forces acting on W has to be null.
- c) The unique object that can exert another force on W is the string: it must somehow pull W, with equal but opposite force (watch out: those two opposite forces are not action/reaction forces (3rd principle); they are acting on a unique object, and 3rd principle is about two objects exerting a force on each other).
- d) If the string pulls upwards W, applying now 3rd principle to that pair of objects, we can deduce that W must be pulling downwards the string lower extreme.
- e) That force seems to be a centrifugal one (and centripetal the one mentioned on - c)), but we should keep in mind that if there is no rotatory movement at all, a proper “center” does not actually exist.
- f) And when with movement, we have also to be careful with the term “centripetal force”, because it usually refers to the the radial component of adding up all forces acting on W,  which divided by the mass would give us the “centripetal acceleration” that makes W not to follow a rectilinear trajectory. And in many cases some of those added forces may be in the sense of the “center”, but compensated by others and not producing any acceleration by themselves.
 

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #61 on: 17/10/2016 04:29:08 »
Pendulum I
It seems simple, but there are small but important details that, if not being careful, one can misinterpret facts, or at least confuse others …
That´s why I am now going to consider only the scenario statically (and step by step), without any movement: fixed hanging point, string and weight (I´ll call it W), all in a straight vertical line.
- a) Primary acting force: Earth pulls downwards W.
- b) W does not move. According to 2nd Newton´s principle, the sum of all forces acting on W has to be null.
- c) The unique object that can exert another force on W is the string: it must somehow pull W, with equal but opposite force (watch out: those two opposite forces are not action/reaction forces (3rd principle); they are acting on a unique object, and 3rd principle is about two objects exerting a force on each other).
- d) If the string pulls upwards W, applying now 3rd principle to that pair of objects, we can deduce that W must be pulling downwards the string lower extreme.
- e) That force seems to be a centrifugal one (and centripetal the one mentioned on - c)), but we should keep in mind that if there is no rotatory movement at all, a proper “center” does not actually exist.
- f) And when with movement, we have also to be careful with the term “centripetal force”, because it usually refers to the the radial component of adding up all forces acting on W,  which divided by the mass would give us the “centripetal acceleration” that makes W not to follow a rectilinear trajectory. And in many cases some of those added forces may be in the sense of the “center”, but compensated by others and not producing any acceleration by themselves.
I think your examples above don't clear things up, but rather confusing.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #62 on: 17/10/2016 11:45:46 »
#61 hamdani yusuf
"I think your examples above don't clear things up, but rather confusing".
There are not "examples", it is only a rather simple case, analyzed step by step.
Could you please specify which concrete step and/or point you find confusing?
My aim there was that, reading later posts of mine including pendulum oscillation, nobody would erroneously think again (f.e.) similarly to what reflected on your own #38:
"Because if we include the centrifugal force to the equation of the system, total force would be zero which mean no acceleration, contrary to the observation”,
what was later dealt with by me on #39 and 40. I expected it was already clear to you ...
I consider what said on #60, if each paragraph is (one by one) read carefully, should be understood with no difficulty.
I understand they could seem rather far fetched details.
But I´m convinced that, not to have them clearly understood by many people, is the main reason why there is such a big confusion about the subject out there.

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #63 on: 17/10/2016 12:08:46 »
#61 hamdani yusuf
"I think your examples above don't clear things up, but rather confusing".
There are not "examples", it is only a rather simple case, analyzed step by step.
Could you please specify which concrete step and/or point you find confusing?
My aim there was that, reading later posts of mine including pendulum oscillation, nobody would erroneously think again (f.e.) similarly to what reflected on your own #38:
"Because if we include the centrifugal force to the equation of the system, total force would be zero which mean no acceleration, contrary to the observation”,
what was later dealt with by me on #39 and 40. I expected it was already clear to you ...
I consider what said on #60, if each paragraph is (one by one) read carefully, should be understood with no difficulty.
I understand they could seem rather far fetched details.
But I´m convinced that, not to have them clearly understood by many people, is the main reason why there is such a big confusion about the subject out there.
When trying to explain centripetal and centrifugal forces, we should focus more on the generation of force due to circular movement of an object. Don't complicate things with additional forces whose direction is not radial.
In the case of astronauts in ISS, do they experience centrifugal force? Does it have the same magnitude as the centripetal force by earth gravity which keeps them in orbit?

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #64 on: 17/10/2016 19:29:17 »
#63 hamdani yusuf
« on: Today at 04:29:08 » Quote (selected):
"Don't complicate things with additional forces whose direction is not radial".
Certainly, we should not complicate things with any unnecessary stuff ... But please note that a pendulum oscilates because of the action of the very existence of a tangential component of its weight, which produces a tangential acceleration.
My concrete aim was nobody would mix them later when analyzing the oscillation, that is a kind of partial rotation, but with variable speed.
And you also ask:
"In the case of astronauts in ISS, do they experience centrifugal force? Does it have the same magnitude as the centripetal force by earth gravity which keeps them in orbit?"
In that scenario there are also subtleties one has to take into account carefully.
Considering the mass of an astronaut as a hole, 3rd Newton´s principle tell us that, if earth gravity pulls him down, he also pulls earth upwards.
But that pull is negligible to earth.
As a unit, the astronaut only experiences centripetal force, which makes him rotate.
But his body parts and members, if he were much, much taller, would differently experience earth gravity, especially when in  "vertical"  (radial) position.
Why? Because the distance from his head to earth would be greater than that distance from his feet ...
Besides that, the trajectories of those two body parts would be slightly different circumferences ... For a unique angular speed of rotation, that would mean his feet would require a smaller centripetal force than what corresponds to experienced gravity, and the opposite at his head.
Internal stresses/forces would happen to compensate those differences. And internal stress/forces go in pairs, due to 3rd Newton´s principle.
Half of them would be centripetal, and half centrifugal.
That seems bizarre, because distance differences are relatively negligible. But if ISS were much, much bigger in radial sense, other analogous effects would happen there, and be sure they should be taken into consideration. 
 
 

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #65 on: 18/10/2016 02:25:34 »
...
"In the case of astronauts in ISS, do they experience centrifugal force? Does it have the same magnitude as the centripetal force by earth gravity which keeps them in orbit?"
In that scenario there are also subtleties one has to take into account carefully.
Considering the mass of an astronaut as a hole, 3rd Newton´s principle tell us that, if earth gravity pulls him down, he also pulls earth upwards.
...
The pulling of the earth is also centripetal, toward the barycenter of the system. Hence there is no apparent centrifugal force here.

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Offline puppypower

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Re: What is centrifugal force?
« Reply #66 on: 18/10/2016 12:19:54 »
The centrifugal force appears when linear momentum, meets angular momentum, and two merge into angular momentum, while remaining separate and distinct. If we break the merger, the distinction will reappear.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #67 on: 18/10/2016 12:37:49 »
#65 hamdani yusuf
Please note the expression “centrifugal force” does NOT appear in what quoted by you. Not even the term “reaction force” …
3rd principle affects to any object exerting a force on another, and viceversa. But not always is easy to say which is action and which reaction. I have seen it is better not to introduce that issue in my expositions.
Let me transform a little the astronaut case.
Let us imagine he goes out of ISS, to a position keeping the orbit but many meters after the station.
There would be what we can call a dynamic equilibrium: earth pulls the man, but he does not move downwards because there gravity acceleration is exactly equal to the square of his tangential speed divided by the radius of his orbit. Velocity vector only changes direction, and that lets him rotate, as when inside the station.
Surely he would have gone out of ISS with a safety “rope”, let us suppose with a knot around one of his wrists. If another astronaut inside the station tights the rope and strongly pulls him, the dynamic equilibrium ends: that pull increases his tangential velocity. And if we divide gravity attraction by his mass, we get an acceleration smaller than what required to keep him in that orbit (the square of the actual speed divided by the radius) …
The astronaut would move not only tangentially, but also radially, upwards. Then the rope pull would have a downward component. That “centripetal” component of the rope pull, according to 3rd principle would mean our man would also pull the rope, upwards: a CENTRIFUGAL force.
Besides, within the astronaut body, there would be stresses (wrist and forearm would be pulling rest of the body … 3rd principle would also apply there ...
Somebody could say: rather confusing example … Or: well, that is a particular case, with more than two objects (earth, ISS, rope and astronaut).
But in ALL real cases there are many, many more “objects” to be considered, because their different parts (whatever their size) experience gravity attraction from other massive objects independently …
Nature is much more complex than most mathematical simplifications ...

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #68 on: 18/10/2016 18:22:14 »
#65 hamdani yusuf
Please note the expression “centrifugal force” does NOT appear in what quoted by you. Not even the term “reaction force” …
3rd principle affects to any object exerting a force on another, and viceversa. But not always is easy to say which is action and which reaction. I have seen it is better not to introduce that issue in my expositions.
Let me transform a little the astronaut case.
Let us imagine he goes out of ISS, to a position keeping the orbit but many meters after the station.
There would be what we can call a dynamic equilibrium: earth pulls the man, but he does not move downwards because there gravity acceleration is exactly equal to the square of his tangential speed divided by the radius of his orbit. Velocity vector only changes direction, and that lets him rotate, as when inside the station.
Surely he would have gone out of ISS with a safety “rope”, let us suppose with a knot around one of his wrists. If another astronaut inside the station tights the rope and strongly pulls him, the dynamic equilibrium ends: that pull increases his tangential velocity. And if we divide gravity attraction by his mass, we get an acceleration smaller than what required to keep him in that orbit (the square of the actual speed divided by the radius) …
The astronaut would move not only tangentially, but also radially, upwards. Then the rope pull would have a downward component. That “centripetal” component of the rope pull, according to 3rd principle would mean our man would also pull the rope, upwards: a CENTRIFUGAL force.
Besides, within the astronaut body, there would be stresses (wrist and forearm would be pulling rest of the body … 3rd principle would also apply there ...
Somebody could say: rather confusing example … Or: well, that is a particular case, with more than two objects (earth, ISS, rope and astronaut).
But in ALL real cases there are many, many more “objects” to be considered, because their different parts (whatever their size) experience gravity attraction from other massive objects independently …
Nature is much more complex than most mathematical simplifications ...
Why in ISS centrifugal force doesn't seem to be equal to centripetal force?

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #69 on: 18/10/2016 19:48:35 »
#68 hamdani yusuf
I think I´ve already answered similar questions.
If ISS were considered a single object, with all its mass concentrated in its center of gravity, NO centrifugal force would occur there: it only would be interacting with earth, pulling it back with a force equal to the centripetal force required for ISS´s actual speed of rotation at that distance.
But, as ISS has a size, particulary its radial hight, some of its parts are further from earth than others ... Gravity is not EXACTILY the same all through its hight. But all of them rotate at same speed. That produces an actual centripetal force "surplus" at its lower parts, and a "deficit" at upper parts.
That has to be compensated by mean of a field of internal stresses/forces, in pairs to satisfy 3rd Newton´s principle.
Half of them go downwards, and the other half upwards, which can be called CENTRIFUGAL.
Those forces would make ISS stretch in radial sense, the same that happens with ALL cosmic objects rotating around their barycenter.
Certainly, those effects at ISS must be almost negligible, but not completely. Haven´t you realized how  vertically small ISS is? Surely it is so to further minimize those effects.

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #70 on: 19/10/2016 02:40:56 »
Quote
In Newtonian mechanics, the centrifugal force is an inertial force (also called a 'fictitious' or 'pseudo' force) directed away from the axis of rotation that appears to act on all objects when viewed in a rotating reference frame.

The term has historically sometimes also been used to refer to the reaction force to a centripetal force.

The centrifugal force is an outward force apparent in a rotating reference frame; it does not exist when measurements are made in an inertial frame of reference.
That's what wikipedia said.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #71 on: 19/10/2016 12:17:19 »
#70
Wikipedia is not always completely right. Even it has errors.
Last year I already said:
“I know centrifugal force can be considered as an inertial, actually kind of ficticious force … But not only that way”.
(#28 of  http://www.thenakedscientists.com/forum/index.php?topic=49715.25 ).
Besides, what quoted by you is self-contradictory, because they also say:
"The term has historically sometimes also been used to refer to the reaction force to a centripetal force",
and all my examples are based on that fact. They say just "sometimes", but in all my examples that term has been used because pairs of centripetal forces and their reactions were present ... How do you think we should call a force opposite to a centripetal one?

 

 

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #72 on: 19/10/2016 19:13:34 »
#70 (continuation)
Rather than being self-contradictory, Wikipedia article author seems to consider that centrifugal f. actually is the ficticious f. he refers to, that to use the expression for the reaction to the centripetal f. is a kind of exceptional use …
I do consider it would rather be the opposite. His field must be Theoretical Physics or Maths, and he refers to a “trick” for when an inertial frame of reference: the use of a fictitious force, equal but opposite to centripetal f., but both forces applied on SAME unique object.
But the other case refers to a REAL force, which has been acting in the Universe since several billion years ago, since first pair of rotating stars appeared. Since then, hose forces and centripetal ones, together with own gravity of considered cosmic objects, have been deforming, and even broking apart, many of those objects:
"The limiting distance to which a satellite can approach without breaking up depends on the rigidity of the satellite. At one extreme, a completely rigid satellite will maintain its shape until tidal forces break it apart. At the other extreme, a highly fluid satellite gradually deforms leading to increased tidal forces, causing the satellite to elongate, further compounding the tidal forces and causing it to break apart more readily ..."
https://en.wikipedia.org/wiki/Roche_limit

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #73 on: 19/10/2016 23:15:53 »
... How do you think we should call a force opposite to a centripetal one?
It could also be centripetal force. See binary stars.

Centrifugal force is considered pseudo/fictitious because it does not exist when measurements are made in an inertial frame of reference.
« Last Edit: 19/10/2016 23:18:43 by hamdani yusuf »

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #74 on: 20/10/2016 11:12:34 »
#73
Please kindly see #56, were your #54, with two identical binary stars case, was already dealt with.
AT BOTH OUTER PARTS of the pair, gas pressure decreases, and bulges appear, for same reason as our equator diameter is bigger than pole to pole distance: CENTRIFUGAL forces experienced by ANY molecule whose distance to the other star C.G is bigger than the distance between the two C.G.
You seem unable to distinguish the simplified case when considering all star masses concentrated on their respective C.G. (a rather theoretical trick), from REAL cases, in which each molecule actually "feels" gravity (from rest of massive objects) independently.
And 3rd Newton´s principle also applies to ALL those "infinite" tiny forces, and to internal stresses that happen throughout all objects. 

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #75 on: 20/10/2016 11:19:56 »
#72 (continuation)
"Jupiter – the most massive planet in the Solar System – causes the Sun to move at roughly 35km/h”
(both actually rotate around the barycenter axis of the pair, very near to Sun´s C. G.  - apart from other much smaller wobblings due to rest of planets)
"… When the star moves towards or away from you, the wavelength of its light shortens or lengthens, respectively".
http://www.bbc.com/earth/story/20161019-the-first-planet-around-another-star

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #76 on: 20/10/2016 13:28:38 »
#73
Please kindly see #56, were your #54, with two identical binary stars case, was already dealt with.
AT BOTH OUTER PARTS of the pair, gas pressure decreases, and bulges appear, for same reason as our equator diameter is bigger than pole to pole distance: CENTRIFUGAL forces experienced by ANY molecule whose distance to the other star C.G is bigger than the distance between the two C.G.
You seem unable to distinguish the simplified case when considering all star masses concentrated on their respective C.G. (a rather theoretical trick), from REAL cases, in which each molecule actually "feels" gravity (from rest of massive objects) independently.
And 3rd Newton´s principle also applies to ALL those "infinite" tiny forces, and to internal stresses that happen throughout all objects.
There is alternative name for the cause of those bulges : inhomogeneity of centripetal forces among the molecules making up the stars.

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #77 on: 20/10/2016 13:31:39 »
May I know your objection to wikipedia's statement that
Centrifugal force is considered pseudo/fictitious because it does not exist when measurements are made in an inertial frame of reference?

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #78 on: 20/10/2016 18:46:03 »
#77 hamdani yusuf
I have no objection to that statement whatsoever, if THAT is the case: "when measurements are made in an inertial frame of reference".
But in most real cases the frame of reference has NOT to be necessarily an inertial one.
Besides, forces do exist in nature, centrifugal ones included, long, long before anybody could make measurements ... 

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #79 on: 22/10/2016 11:35:33 »
REVOLVING WATER BUCKET
On #44 I brought up this case and asked for possible reasons of water surface change.
There was only an answer, from Alancalverd, “centrifugal force”.
I consider it could be very clarifying to analyze what happens in detail (aiming even laymen could understand) , especially because it is an example of in how different ways matter actually can respond to acting forces: gravitational, centripetal, centrifugal (or whatever we could call them,  “outward inertial forces”? ). As I´ve already said, they produce internal stresses and/or deformations, in different fashions depending on each case.
What causes the water rotate is inner bucket surface rotation, thanks to friction …  Outer water molecule inertia tries to keep constant (tangential) speed vectors. The bucket makes it impossible, kind of PUSH (not "pull" as in other cases we´ve previously seen) inwards the water (centripetal force), and water rotates.
That (forces and movement) is transmitted inwards up to the axis of rotation.
All those transmitted centripetal forces have their “mirror” forces (3rd Newton´s principle), centrifugal ones.
One could ask himself: ok, but if all rotations are on horizontal plans, and centripetal and centrifugal (and friction) forces are also horizontal, why outer water rises (the bigger the radius, the higher the water level)?
If instead of water there were solid stuff (f.e., concrete), only internal (mainly compression) forces would occur. But liquids respond with an increase of what is usually called hydraulic pressure, which acts in ALL directions.
In any point pressure must also be equal to the weight of a 1 cm2 section column of water, from the point up to water surface.
That makes water surface acquire its concave shape. It is a kind of dynamic equilibrium, result of ALL acting forces.







 
 
 

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #80 on: 22/10/2016 12:02:31 »
#79 (continuation)
When mentioning concrete instead of water, as I was thinking of bucket inward pushing the water, I said  there would be mainly compression internal forces (within concrete)
It would be correct if the change were only concrete instead of water, maintaining the bucket.
If there were no bucket, tensile internal stresses would occur instead (by the way, also a clear prove of centrifugal force reality)

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Online jeffreyH

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Re: What is centrifugal force?
« Reply #81 on: 22/10/2016 12:14:37 »
The main problem with the idea of centrifugal force is that the vector tangent to the rotation is producing the outward 'force'. So that if a bucket on the end of a rope stops being confined, the rope is released, it does not move away in the radial direction. If the bucket were on a bungee rope then the experiment would be more interesting. As the speed of rotation increases how does the rope react?
« Last Edit: 22/10/2016 12:21:07 by jeffreyH »

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #82 on: 22/10/2016 13:00:48 »
#81 jeffreyH
If you talk about a bucket following my later posts, please note the case I previously brought up was a bucket on top of a REVOLVING chair ...
(by the way, as a continuation to #80: the bucket with concrete should be a metallic one; if plastic it could barely withstand concrete outward forces ...)
Your case is different. You say :
"The main problem with the idea of centrifugal force is that the vector tangent to the rotation is producing the outward 'force'"
SORRY, but I find that utterly erroneous. You are mixing a "vector tangent to the rotation", which is a VELOCITY vector, and a FORCE (outward, centrifugal, whatever we may call it).
To put it as simple as possible:
1) To CHANGE de direction of that velocity, a centripetal force is required (1st Newton´s principle).
2) In your case, that force is the one caused by the rope, that pulls the bucket (inwards)
3) According to 3rd Newton´s principle, the bucket also pulls the rope (outward, or centrifugal force).
If it were with a bungee rope, the tension would make it elongate, until reaching an equilibrium. The same that happened to the spring of a dynamometer between rope and bucket, case we already dealt with in previous posts ... I suppose you didn´t read them.
 

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #83 on: 23/10/2016 10:56:27 »
In inertial reference frame, water in rotating bucket is experiencing centripetal force done by the bucket's wall. Outer part of water molecules which are directly in contact with the wall then push inner part. Water molecules located in the rotation axis don't experient this force.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #84 on: 23/10/2016 12:01:25 »
#83 hamdani yusuf

Certainly … But I would say that happens whatever the reference frame.
And an inward push (similar to that by bucket inner surface >> contiguous water molecules) is also exerted by each cylindrical layer of water on contiguous inner layer, decreasing in intensity up to the axis of rotation, where water speed keeps null, and no centripetal acceleration is needed to change a constant velocity vector.
And, according to 3rd Newton´s principle, EVERY cylindrical layer of water pushed by outer one, pushes back this contiguous outer layer (outwards) … A real field of CENTRIFUGAL forces …
That´s why water pressure increases from axis to bucket inner surface (at same hight), what changes water surface shape.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #85 on: 24/10/2016 11:34:53 »
#84 (continuation)
Logically, there is a similitud between the revolving water bucket and our planet surface deformation due to its daily revolution.
At the equator, and decreasingly at higher latitudes, ocean water also "feels" centrifugal forces as in the revolving bucket, but their field of vectors is different due to not having a solid barrier as bucket inner surface.
On our planet what makes water not to follow tangential straight lines is the very earth gravity. More precisely, components of local weight vectors perpendicular to North-South axis of rotation.
The further from equator, the smaller tangential velocities. Centripetal force vectors and  local gravity vectors (weights) ad up, and water surface reaches an equilibrium shape, with water "level" increasing from poles to equator.
Within the bucket a similar deformation is not possible, and what increases (from axis to bucket inner surface) is water hight (and decreases closer to revolving axis, because water cannot expand)

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #86 on: 24/10/2016 12:19:34 »
#85 (continuation)
After sending recent post, I´ve seen that now is me who writes something rather erroneous:
" Centripetal force vectors and  local gravity vectors (weights) ad up".
Centripetal accelerations required for the rotation of water are actually due to more forces, weight included.
In each latitud plan, centripetal forces have their mirror outward forces (as exposed in the bucket case), which are centrifugal.
The result of ALL forces exerted on each water particle (own weight, and pressure forces from contiguous particles - inward and outward forces included), divided by the particle mass, must be the required centripetal acceleration necessary for the particle circular movement.
And the equilibrium is reached, as we know, with a shape surface not completely spherical, with equator diameter bigger than N-S poles distance.
 

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #87 on: 24/10/2016 18:02:20 »
in rotating water bucket, the shape of water surface is paraboloid. Similar technique has been used to form mirrors for telescope.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #88 on: 24/10/2016 19:06:58 »
#87 hamdani yusuf

Right. But ...
I already commented that nature is far more complex than most simplifications we make, which aim to get results accurate enough for our needs.
In the case we are discussing, the paraboloid is not perfect, and we only get it after some time of stabilization.
As friction is what makes water rotate, that is inwards transmitted from inner bucket surface up to the axis of revolution. And friction is not 100% effective at "pulling tangentially" inner cylindrical layers of water, as there is always some loss of energy. Especially if instead of water we had a more viscous liquid.
Not considering that, angular speed would be the same across the bucket diameter, and tangential speed would increase from axis to bucket, proportionally to the square of the radius. THAT would cause the paraboloid surface.
But angular speed decreases very slightly from bucket surface to axis of rotation. Much more at initial transient phase, if we started from standing still.
The result is that water hight increases outwards slightly more than in the paraboloid, because centripetal and centrifugal forces do the same, as well as resulting water pressure.

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Offline hamdani yusuf

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Re: What is centrifugal force?
« Reply #89 on: 25/10/2016 02:57:22 »
According to Oliver Darrigol's book that I recently read, Poincare classified source of force as external and inertial forces.
In inertial reference frame, only external force can produce acceleration, such as electromagnetic and gravity, or reduce acceleration like friction.
In Newton's third law, the distinction is ignored. Hence total external force is equal to total inertial force (opposite direction), while the acceleration measured in inertial reference frame only depends on total external force.
Centrifugal force is an inertial type force, analogous with inertial mass in linear acceleration.
For example, a system has two external forces +5 N and -3 N. The mass of the system is 2 kg.
Total external force is 5-3=2 N. Inertial force is equal and opposite to the external force, hence -2N.
The acceleration only depends on the external force, which is 2 N / 2 kg = 1 m/s2.

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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #90 on: 25/10/2016 15:24:55 »
The centrifugal force 
  The centrifugal force is difficult to understand fully unless we break down the Einsteinian mass into frontal and rearward components. The frontal mass is larger than the rearward mass and the geometric mean is the Einsteinian inertial mass. This means that there is a pull on the Earth from the sun at the center of gravity of the Earth. In addition there is a twist on the Earth because the pull of gravity is stronger on the front of motion than the rear.  The Earth wants to move in a straight line but it is twisted to curve. A space time force counteracts this and this is the centrifugal force.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #91 on: 25/10/2016 19:38:54 »
#89 hamdani yusuf
I do agree with most of what you say ...
In most of my examples it was clear that, being equal but opposite to each other (3rd N. principle) the forces (if any) exerted between two objects, their total force is always null. And they would not produce any acceleration to the pair, considered as a hole (a system).
But acceleration IS NOT the unique possible effect of a force. So, null acceleration doesn´t necessarily mean lack of forces.
When two o more objects (included the case of different parts of a single object) are somehow "obliged" to move at same speed, if external forces (for any reason) are not distributed proportionally to masses of each object (o part of an object), they originate internal forces which deform the objects, whatever the sum of all external forces.
And if the system is rotating, as I´ve already exposed in many examples, internal forces are basically perpendicular to axis of rotation, and mainly centripetal and centrifugal forces, 50% of each type. And the can make the objects stretch or shrink, and not equally at different parts of the bodies.
By the way, haven´t you realized that usual expressions are centripetal force, centrifugal force, centripetal acceleration ... but NEVER "centrifugal acceleration"?
That is consistent with facts: centrifugal force is something REAL, but can not produce any acceleration ... Precisely because its origine is that "something" is obliging an object to change the direction of its speed (a centripetal force causing a centripetal acceleration), and the reaction of the object (3rd N. principle) is an equal but opposite force, exerted by the object on that "something" ...
Another example: somebody making a sling with a stone rotate ... The centrifugal force only keeps tight the sling (a centripetal force alone wouldn´t be able to do it) ...
Somebody would say: but when the stone is thrown, it goes tangentially, not radially ... Of course !!!. The centrifugal force was not being exerted ON the stone (if considered as whole), it was being exerted BY the stone, but ON the extreme of the swing. As soon as centripetal force ceases, two main things happen:
1) The stone continues with its velocity vector in that moment (acc. to 1st N. principle).
2) The swing is not tight any more, and bends down, also following some rotational movement, due to its own inertia. Only for a short time, as air friction reduces its angular speed.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #92 on: 25/10/2016 19:54:45 »
#91 (continuation)
Sorry: a couple of times I said "swing", but I meant "sling" ...

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #93 on: 26/10/2016 10:09:13 »
More about the sling case.

As you know, that device is a two part string, with a kind of loop, broader piece joining the two parts at their outer extremes, that supports the stone to be thrown.
In other cases centripetal forces are pulls, but when rotating the sling, mentioned loop piece, as it rounds the stone, actually pushes the stone inwards. And, due to 3rd N. principle, the stone pushes back that loop piece, outwards … Whatever name could be given to that force, it IS centrifugal (“tending" to move away from a centre).

Two pieces of evidence:

Had we put a chewing gum between the stone and the loop piece, it would flatten, due to the fact of being compressed by those opposite forces, on its inner and outer sides.
Were we going to throw a clod instead of a stone, it wouldn´t be possible (unless very softly …), because it would break down, due to internal compression stresses caused by acting centripetal and centrifugal forces.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #94 on: 27/10/2016 19:25:32 »
#90 jerrygg38
Einstein´s gravity theory is difficult to grasp to me (as to most people, I am afraid). So, on this subject I don´t feel sure enough to discuss. That´s why I have not commented your post last days, preferring to deal with others.
But now it seems we are having a kind of rest, and I´ve decided to say a couple of things.
On the one hand, what you say may be right, but I think last words should be: "and this is a centrifugal force”. I´ve already  shown many cases where we also have centrifugal forces, quite different to your case.
And on the other hand, the deep roots of the forces on my examples (gravity, inertial forces, centrifugal forces) may be, according to Einstein´s theory, "bending" of space-time, or related mass changes ...  But I consider that, at least at speeds so much smaller than light speed, ALL cases where centrifugal force may appear can be explained within Newton´s Physics.

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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #95 on: 28/10/2016 13:45:41 »
The main problem with the idea of centrifugal force is that the vector tangent to the rotation is producing the outward 'force'. So that if a bucket on the end of a rope stops being confined, the rope is released, it does not move away in the radial direction. If the bucket were on a bungee rope then the experiment would be more interesting. As the speed of rotation increases how does the rope react?
   The vector tangent to the rotation defines the moving gravitational field of the object. The rope pulls the object away from the field. The centrifugal force is caused by the pressure of the object and future gravitational field verses the present gravitational field.
   If you keep increasing the speed the rope will either break or wind up. If it breaks  the object will continue to move in a straight line tangent to the rotation as it follows its present gravitational field.

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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #96 on: 28/10/2016 13:55:46 »
#90 jerrygg38
Einstein´s gravity theory is difficult to grasp to me (as to most people, I am afraid). So, on this subject I don´t feel sure enough to discuss. That´s why I have not commented your post last days, preferring to deal with others.
But now it seems we are having a kind of rest, and I´ve decided to say a couple of things.
On the one hand, what you say may be right, but I think last words should be: "and this is a centrifugal force”. I´ve already  shown many cases where we also have centrifugal forces, quite different to your case.
And on the other hand, the deep roots of the forces on my examples (gravity, inertial forces, centrifugal forces) may be, according to Einstein´s theory, "bending" of space-time, or related mass changes ...  But I consider that, at least at speeds so much smaller than light speed, ALL cases where centrifugal force may appear can be explained within Newton´s Physics.
  Yes. Newton's physics works quite well to explain most things. I just posed another explanation of the centrifugal force. No curved space time is really necessary. All we have is a moving gravitational force of an object and a force pulling the object toward it. Then we have a present gravitational force vector and a future gravitational force vector. Thus the actual centrifugal force is a small differential vector. No Einsteinian space time is required to understand that.
  To me Einsteinian space time is merely a description of how the gravitational fields work. Space does not curve. Space does not bend. These are strange and false concepts. It is the gravitational fields within space that curves and bends. Einstein is correct in his math but space itself has no properties. It is what exists within space that has the properties.

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Offline jerrygg38

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Re: What is centrifugal force?
« Reply #97 on: 28/10/2016 14:33:23 »
Rmolnav discussion with hundani yusuf with comments from  Jerrygg 10-28-16
Rmolnaw said : By the way, haven´t you realized that usual expressions are centripetal force, centrifugal force, centripetal acceleration ... but NEVER "centrifugal acceleration"?
That is consistent with facts: centrifugal force is something REAL, but can not produce any acceleration
Jerrygg38: The problem is that every atom has its own gravitational field which moves with the object. When a force such as a strong gravitational field such as the Earth acts upon an object it produces an acceleration. When an object is accelerated by the Earth such as a falling apple there is a counter force of the present field of the apple and  the future field of the apple. Thus an actual force is generated. When an object is spinning on a rope the rope acts like the Earth and the counter forces is caused by the motion of the present field of the object and the future field. I have just been working on the centrifugal force for a month or so as my main concern is the fundamental components of the universe. However why hasn’t anyone considered that everything has its own self gravitational field?
    Rmolnav said: Another example: somebody making a sling with a stone rotate ... The centrifugal force only keeps tight the sling (a centripetal force alone wouldn´t be able to do it) ...
Somebody would say: but when the stone is thrown, it goes tangentially, not radially ... Of course !!!. The centrifugal force was not being exerted ON the stone (if considered as whole), it was being exerted BY the stone, but ON the extreme of the swing. As soon as centripetal force ceases, two main things happen:
1) The stone continues with its velocity vector in that moment (acc. to 1st N. principle).
2) The swing is not tight any more, and bends down, also following some rotational movement, due to its own inertia. Only for a short time, as air friction reduces its angular speed.
Jerrygg38 responded: Yes. The centrifugal force produces a differential pressure from the present moving gravitational field of the stone and the future gravitational field of the stone.
  It is important to understand that every piece of matter has its own little gravitational field. The rock has billions of billions of little gravitational fields. They combine to look like a single gravitational field at the center of gravity of the rock. If you move the rock with velocity V, the present gravitational field will resist the motion. However once the rocks speed is stabilized you have a moving rock with velocity V and a moving gravitational field with velocity V and the force is then zero. Just pure classical physics. Einstein’s physics shows up as the speed increases greatly but it also shows up as the binding energy of the hydrogen atom as the Einsteinian mass increase in the first orbit at C/137 is identical with the binding energy. The same is true of the neutrino which is an Einsteinian mass increase as an electron is crushed into the proton at 0.9186C. Therefore Einstein’s work shows up everywhere.

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #98 on: 28/10/2016 19:47:04 »
#97
"Jerrygg38 responded: Yes. The centrifugal force produces a differential pressure from the present moving gravitational field of the stone and the future gravitational field of the stone”
Perhaps you are right, but I have to say I don´t fully understand what you mean, especially with the concept of “pressure”, and subsequently the idea of a “differential pressure” produced by centrifugal force …
As I said on my last post, I think it would be better we keep our discussion within Newton´s Mechanics. It should be sufficient for us to understand the subject.
If the root “metaphysical” cause of gravity and inertial forces is the curving of space-time due to massive objects … OK. But the EFFECTS of those forces can be explained whatever the deep nature of gravity.
Keep in mind many people seem to have difficulties when trying to understand basic Newton´s Mechanics … let alone Einstein´s theories.
You yourself said several absurd things, on your initial #0, #2, #5, #10, #12, #23 … All those only before I sent my first one (#28), which I saw then, but didn´t deal with separately (precisely this morning I read more carefully #0 to 27 …) , preferring to say "SOME of you base your arguments on the idea that …”
So, let me suggest you to try and grasp before the subject within Newton´s boundaries. After that, if you want to go deeper into actual (at least so considered by modern “theories”) nature of gravity, give it a go, and be lucky ...

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Offline rmolnav

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Re: What is centrifugal force?
« Reply #99 on: 29/10/2016 07:24:45 »
#98 (Continuation)
I must say that, previous to my first post #28, yesterday I also saw that others said things which may show some confusion: puppypower (#11), jeffreyH (#15 and 19), PhysBang (#6 and same ? paragraph than hamdani yusuf on #16 and #38 resp.).
And many later posts have also signs of not completely clear ideas, as I said within Newton´s theory simpler realm.
On the other hand, Alancalverd and PmbPhy seem to have it clear. But they have intervened few times. Perhaps they got “tired” ...
I insist: let us firstly try and grasp the meaning of the issue, and the effects of those forces (gravity, inertial f. …) without Einstein´s Mechanics … Understanding of nature of deeper nature of gravity and inertial forces is not necessary to deal with their effects that we can see, feel, calculate, and measure. Einstein theories are much more difficult to grasp for most of us ...