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Author Topic: What is centrifugal force?  (Read 7682 times)

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

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.

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?

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 ...

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.

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)

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 »

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.

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.

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.

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)

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.

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.

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.

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.

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.

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.

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" ...

rmolnav

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Re: What is centrifugal force?
« Reply #93 on: 26/10/2016 10:09:13 »

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.

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.

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.

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.

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.

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 ...

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 ...

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Re: What is centrifugal force?
« Reply #99 on: 29/10/2016 07:24:45 »