[syhprum]

I think it wrong to say that the gravitational waves emitted by a large planet such as Jupiter orbiting the Sun are to weak to be detected not by LIGO like devices of course but they certainly influence other planets and pull them into resonance.

[rmolnav]

#21 hamdani yusuf
I´m referring to something rather old, but I remembered that somebody had mentioned the case of passengers in a car, and recently I saw a good physical description of it, which certainly matches with what I´ve said many times ...
You mentioned there:
"In a turning moving car, the road forces the wheels sideway which in turn forces other parts of the car which is then felt by the passengers. The passengers don't receive any force directly from the road".
And I recently saw:
"When the car travels through the curve the passenger's inertia resists acceleration, keeping the passenger moving with constant speed and direction as the car begins to turn. From this point of view, the passenger does not gravitate toward the outside of the car but the car curves to meet the passenger. Once the car contacts the passenger, it then applies a sidewise force to accelerate him or her around the turn with the car. This force is called a centripetal force because its vector changes direction to continue to point toward the center of the car's arc as the car traverses it. Now we know that the car is acting upon the passenger and therefore the passenger must be acting upon the car with an equal and opposite force. We know that this reaction force have to be opposite to the centripetal force, which is directed to the center of the circular motion. Therefore this reaction force is directed away from the center and we call it centrifugal force. It is important to realize that this centrifugal force acts upon the car, not the passenger".
http://schools.wikia.com/wiki/Centrifugal_force
I would add that "Once the car contacts the passenger .." can be applied to the permanent contact between e.g. modern seats adapted to the body and the passenger.
So, it is not only a passenger´s "sensation", as some people say just caused by his tendency to continue on the straight line of his velocity. They are REAL forces which occur as reactions to whatever is forcing them to turn.
The error would be to consider that those forces act on the passenger, as referred to on last quoted phrase.
Anyhow, as i´ve also said several times, reality is more complex: internal centrifugal (and centripetal, of course) forces also act within passenger body, between his different parts ...
But considering the passenger as a single "object", I find the description very good.

[rmolnav]

Yesterday I sent another post (#73) to "Why Do We Have Two High Tides A Day?":
http://www.thenakedscientists.com/forum/index.php?topic=49715.msg504169#lastPostAs
As it is directly related to centrifugal forces, I´ll repeat it here:

Last couple of months I´ve been discussing our "issue", and also the sheer concept of centrifugal force, on "livescience". On some of their last web pages they had shown the idea I´m refuting that centrifugal f. is a kind of taboo, something not real …
Some minutes ago I sent them:
"It´s funny. Just a few minutes ago I saw that Lauren Cox, more than six years ago, on a page ALSO FROM LIVESCIENCE,
http://www.livescience.com/29621-what-causes-the-tides.html
showed a stand very, very similar to mine (linking cause of tides to REAL centrifugal forces):
"The moon's gravitational pull on the earth is strong enough to tug the oceans into bulge. If no other forces were at play, shores would experience one high tide a day as the earth rotated on its axis and coasts ran into the oceans' bulge facing the moon.
… As the moon circles the earth, the earth moves in a very slight circle too, and this movement is enough to cause a centrifugal force on the oceans.
… This inertia, or centrifugal force, causes the oceans to bulge on the opposite side facing the moon ..."
I just wouldn´t say "This inertia, or centrifugal force ...". It is a real, "inertial" force, in the sense that it is due to 3rd Newton´s Principle, based (as the other two) on inertia physical REALITY.
http://www.livescience.com/52488-centrifugal-centripetal-forces.html "

[rmolnav]

I do hope the lack of comments/replies in last ten months is due to most of you agree with what exposed by me ... Something similar used to happen relative to the sites of LiveScience I linked. But, to my surprise, some day this recent summer (or spring?), they changed to show main article, but saing "Nº of comments: 0", and certainly all comments were gone !! I have to say those sites are headed by articles by some science contributor, but afterwards they don´t usually send any further comment ... As far as I can remember, they were at least three directly related cases, relative to Newton´s 3rd Motion Law, Centripetal and Centrifugal forces, and the reason why we weigh less at the Equator. I´ve recently been sending new comments refuting their errors in several ways, similarly to what I did here last year. Anybody interested, please kindly have a look at them:
https://www.livescience.com/46561-newton-third-law.html
https://www.livescience.com/52488-centrifugal-centripetal-forces.html
https://www.livescience.com/32504-would-i-weigh-less-at-the-equator.html

And please reply if any doubt and/or opposite idea. With further, detailed discussion, I am almost 100% sure I would be able to convince you.

[Colin2B]

I do hope the lack of comments/replies in last ten months is due to most of you agree with what exposed by me ...

Vain hope.
There are many reasons why people stop responding to a thread, but unless you get a positive “yes you are right” don’t assume anything. Most likely is that they still disagree.

Haven’t been following this one, might take a look. Can you summarise the main ‘exposure’?

[rmolnav]

Thank you. You are right, I can´t assume anything, I just "hope" ...
Im sure you know there is a lot of confusion regarding centrifugal force out there. Last year I refuted erroneous ideas (not only here), I should say "as far as I can understand". But I must also say I feel pretty sure about my stand.
You can tell English is not my mother tongue. And I type with only a finger of each hand ... Before summarizing the main exposure of this thread, in order to save time, I have been looking at your posts of last year last months, to see if you, perhaps in another thread, could have posted something touching the issue. Just to see if you could also be in the for me "erroneous side" (to my surprise, I have found many, many people "there" ...)
Fortunately I´ve found something which shows perhaps you agree with me, al least that you don´t consider centrifugal force as something NOT existing as a real force, just something "apparent", or "ficticious". I´ve only read your nº 1 reply so far:
https://www.thenakedscientists.com/forum/index.php?topic=68827.msg501090#msg501090
I know a ficticious centrifugal f. is frequently used when in a non inertial frame of reference, just supposing it applied to same considered rotating object, the one actually affected only by the centripetal force ... But that DOES NOT mean real centrifugal forces don´t exist !!
Newton´s 3rd law refers to TWO objects (they also could be two parts of an object ...) ... If object A exerts a centripetal force on B (to make it rotate), B exerts on A an equal but opposite force, quite REAL, which has to be called centrifugal ...
That simple! And one can analyze many, many cases, and find clear explanations for them thanks to real centrifugal forces. But without their existence, many errors turn up ! 

[rmolnav]

I´ve found another comment of yours:
"… perhaps it helps to consider the force you and your passengers feel as your car goes around a bend.
You all agree you feel what you would describe as a force, it feels real and has a genuine effect of pushing you to one side, however, another part of you knows it is only because you are following a curved path"
https://www.thenakedscientists.com/forum/index.php?action=profile;u=39298;area=showposts;start=450
I would change your last phrase ... That force is due to the fact that you are following a curved path, but to say "only" is misleading ...
Imagine three of you, transversely situated in the car, shoulder to shoulder, and outer shoulders pressing car windows. Just to allow to follow only their curved paths.
Outer window exerts a centripetal force on outer passenger, and, due to that, according to Newton´s 3rd law that passenger exerts a real outward force on the window: centrifugal force ...
And that passenger has to exert also a centripetal force on central passenger, to oblige him to follow a curved path ... Again according to Newton, central passenger exerts an outward force on outer passenger ... Real, centrifugal force. And so on ...
Both mentioned passengers not only feel a "sensation" of being pushed outward ... They are ACTUALLY being pushed outward, by quite REAL forces, exerted by their inner contiguous passengers ...
Especially outer one "suffers" those outward pushes, centrifugal forces, as long as they add up ... He could even get his chest broken, if sufficient speed (not easy in a car!), because his outer shoulder is also being pushed inward.
Also outer window could break. Neither people, nor windows break due to only "apparent" forces !!!

[puppypower]

If you look a centrifugal force, this is motion connected to a curved path. What this brings to my mind is a connection to the curvature of space-time.

If we had a large cloud of low mass density, collapsing into a star, a rotation will appear in the cloud, that generates centrifugal force. Gravity causes the mass density to increase, which causes spacetime to contract and increases the  curvature of space-time.  In this case, centrifugal force is a reaction to the action of gravity that also parallels the increasing curvature of spacetime. The centrifugal force vector acts in the same direction one would expect of antigravity. gravity-antigravity action and reaction.

If you look at this closer, centrifugal force, in general and beyond this targeted example, is more connected to a curved path in space, but not in time. It is not exactly moving in terms of the curvature of spacetime but only with respect to space.

If you look at force, which is mass times acceleration, and acceleration is d/t/t, acceleration or d/t/t contains an extra dimension of time, compared to space-time or d-t. 

As such, the centrifugal force follows curvature in space, while generating a force, which has the extra time dimension of acceleration, compared to space-time. Centrifugal force parallels space-time, but it is expressed in a disjointed way as a separated curved path in space, and a separated aspect of time (potential); acceleration.

Say I take a ball in a string and make it move in a curve path. I use force the make the ball move in a curved path in space. I am also generating time potential via the active force. One may then ask does this action cause a reaction in spacetime? The answer may be yes, since the ball has mass and I am generating an antigravity vector wth respect to me. There should be a slight tweak.

[Colin2B]

Fortunately I´ve found something which shows perhaps you agree with me, al least that you don´t consider centrifugal force as something NOT existing as a real force, just something "apparent", or "ficticious".

Yes, I think that the fictitious forces, including Coriolis, are poorly named. I tend to think of them as frame dependent forces, so you view their cause or effect differently depending on which frame you are observing from.
Having skimmed over a few posts in this thread I see part of it is about tides. I agree, there is a frame where earth & moon rotate around a common point resulting in centrifugal force pushing tide bulge on opposite side to moon, this is one of the standard ways of analysing tidal effects.
I know some people get het up about centrifugal force because they have read that it is fictitious, or because of the motivating force coming from centripetal acceleration. Problem is that they happily talk about the force pushing them back into a car seat as it accelerates, but that force is no less fictitious because the body is trying to stay still while it is the car seat supplying the force.

[rmolnav]

Problem is that they happily talk about the force pushing them back into a car seat as it accelerates, but that force is no less fictitious because the body is trying to stay still while it is the car seat supplying the force.

Thank you, but I´m not quite sure whether you completely agree with me ...
Unless we all keep in mind  that "Newton" reaction forces are as REAL as "primary" action forces, confusion will persist !
Inertia concept is something kind of vague, just a "tendency" (?) of objects NOT to accelerate, keeping constant their speed (or stillness). But Newton laws put it into clear and REAL math-physical stuff, relations between two interacting objects, REAL forces, masses and accelerations ...
In your example, the car seat is certainly supplying the "primary" force. Otherwise the passengers could not accelerate (1st and 2nd laws). But it is equally certain that, as a reaction (3rd law), each passenger supplies a REAL force too, exerted backwards on their respective seat back.
If somehow all passengers but the driver suddenly disappeared, without changing manual gas setting, the car acceleration would increase, because before REAL backward forces were being exerted on their seat backs, which were acting as if in the second scenario a parachute fixed at the car back structure had suddenly opened, exerting a fully "external" force.
Perhaps the problem is also in that adjective. If we consider the hole car as an object, those action and reaction forces are internal, not affecting 2nd law ... But if we are considering separately the car and the passengers, forces exerted by the car on the passengers are external to them, as well as forces exerted by passengers on the car are external to the car. But all of them are equally REAL!
 

[rmolnav]

(Continuation of #149)
Sometimes I say "primary force", in the sense of kind of previous, but action and reaction forces actually begin (and finish) acting simultaneously.
In some cases to decide which one should be called "action" is rather tricky ...
In one of previously linked LiveScience sites, the one about centrifugal force, it is said:
" ... This brings us to Newton’s Third Law, which states, “For every action, there is an equal and opposite reaction.” Just as gravity causes you to exert a force on the ground, the ground appears to exert an equal and opposite force on your feet ... ( + something else about centrifugal force). In each of these cases, though, there is only one real force being applied, while the other is only an apparent force".
For me there are more than one error in what quoted. Do you agree?

[rmolnav]

Insisting in the idea that the precise use of Newton´s 3rd Motion Law is key to avoid most of the existing confusion, especially about our topic (centrifugal force), I´m going to repeat here last comment I´ve sent to one of previously mentioned sites of LiveScience. It touches what mentioned by me on #150, where I finished "Do you agree?" ...
Also the importance of precision in the use of terms such as our "weight" is shown. Apparently it is something quite clear, but, e.g., if in Physics it is the gravity pull exerted by our planet on an our body, its Newton´s 3rd Law "couple" should be the equal but opposite pull exerted by our body on our planet, NOT the push exerted on us by what below our feet !!
"Perhaps I should firstly have said that I find our question:
"Would I Weigh Less at the Equator?"
not sufficiently precise, and possibly the origin of the confussion.
On the one hand, we commonly consider our weight what gauged in a spring scale, vertically compressed by underneath floor upward push, and our feet downward push (transmited by the rest of our body).
As I previously said, even if our planet were a perfect sphere, the scale at the equator would show a smaller figure than at higher latitudes, let alone at poles ...
On the other hand, we could also define "weight" differently: the sum of gravity atraction exerted by our planet on all parts of our body ...
In that last sense, it certainly depends only on the distance between centers of gravity.
What actually happens is that part of that atraction is not felt by the scale (neither by our feet and legs), because it is causing the centripetal acceleration vector (perpendicular to axis of rotation) required for our rotation at an angular speed of 2PI radians a day. And that acceleration is proportional to the radius, much bigger at the equator (apart from changes in vectors´relative direction).
So, what we commonly call our "weight", for that second definition would be a kind of "apparent" weight !!
By the way, NOAA not only says "Gravity has less pull at the equator", as quoted at heading picture ... They also say:
"Our planet is pudgier at the equator than at the poles by about 70,000 feet. This is due to the centrifugal force created by the earth’s constant rotation".
https://oceanservice.noaa.gov/facts/earth-round.html
We couldn´t even say that centrifugal force is "kind of apparent" ... Such force wouldn´t be able to cause that "massive" deformation !!

[hamdani yusuf]

(Continuation of #149)
Sometimes I say "primary force", in the sense of kind of previous, but action and reaction forces actually begin (and finish) acting simultaneously.
In some cases to decide which one should be called "action" is rather tricky ...
In one of previously linked LiveScience sites, the one about centrifugal force, it is said:
" ... This brings us to Newton’s Third Law, which states, “For every action, there is an equal and opposite reaction.” Just as gravity causes you to exert a force on the ground, the ground appears to exert an equal and opposite force on your feet ... ( + something else about centrifugal force). In each of these cases, though, there is only one real force being applied, while the other is only an apparent force".
For me there are more than one error in what quoted. Do you agree?

I'd like to know how you interpret Newton's third law. Does it mean that total force of any system is always zero?

[puppypower]

When I look at centrifugal force, the curved path reminds me of the curvature of space-time that is induced by Relativity. For example, in the case of the moon going around the earth, gravity is causing a contraction and curvature of space-time, with the moon following a curve path. The centrifugal force vector is opposite to that of gravity and therefore would have the opposite affect on space-time. 

If you look the hydrogen atom, to make it simple, its election moves at about 1/137, the speed of light. That means there is some electron based Special Relativity affect, due to this significant velocity of the election.  At this velocity the electron is in a slightly different space-time reference than the proton. The electron's clock runs slower.

However, since the election is using a curve orbit in the 1S orbital, there is a centrifugal force, whose force vector is in the opposite direction of the EM force vector, that binds the electron and proton. If the centrifugal force was connected to space-time, the centrifugal force vector is implicit of expanded space-time. Theoretically this would speed up the election clock and move the election closer to the same reference as the proton; less uncertainty due to relative references closer to the same reference.

The centrifugal force in atoms is not always a space-time wash. In the case of the metal, gold, its outer election velocity is high enough, and the centrifugal force low enough, to remain relativistic differences between the nucleus and the election cloud. The yellow color of gold is due to a relativistic time or frequency shift in reflected energy see relativistic quantum chemistry.

[rmolnav]

I'd like to know how you interpret Newton's third law. Does it mean that total force of any system is always zero?

Thank you.
Being very careful as I insist we have to be, I answer that it depends on what you mean with "total force of any system" ...
Newton´s third law is about two interacting objects (let us call them A and B). They exert on each other opposite equal forces. In the first place, adding up those two vectors (certainly resulting zero) has no sense, because they affect two different objects ... And I´m afraid that is the main reason of the existing confusion, especially about centrifugal f.
Other forces could be being exerted on A and/or B by other objects, and A, B, or both could be moving at any pace (with or without acceleration). Whatever their movement, if A exerts a force on B, B will be exerting an equal but opposite force on A.
And that also can be applied to two parts of a single object. I remember I talked about that time ago, more than once ... Please kindly have a look at #37 of this very thread, where I said:
"Imaging just a steel cylindrical bar hanging from one of its ends. If we made a horizontal cut, the lower part would fall down. Why it didn´t fall before? Because of internal tensile stresses: the upper side of the section was pulling the lower one, exactly with a force equal to the weight of lower part of the bar.
If we had made the cut a little lower, we could say the same. In this case the weight of lower part would be a little less: just the weight of the slice between the two cuts.
As the slice is not experiencing any acceleration, the sum of all forces applied to is null. The sum of internal stresses it suffers from contiguous material, plus its own weight, has to be null.
If we produced any upward acceleration to the hanging point, internal stresses would increase in such a way that the sum of weight of the slice plus stresses from contiguous material would give a net force that divided by slice mass would be equal to the acceleration”
You can see how careful one has to be when using 3rd and 2nd Newton´s law. 3rd law is applied here to two different interacting parts of an object (they exert equal but opposite forces on each other), but 2nd to a single slice of the bar (all forces external to the slice will make it move with an acceleration equal to total external forces divided by the slice mass).

 

[rmolnav]

For example, in the case of the moon going around the earth, gravity is causing a contraction and curvature of space-time, with the moon following a curve path. The centrifugal force vector is opposite to that of gravity and therefore would have the opposite affect on space-time. 

I must say I haven´t previously commented on your posts because I do not feel sure enough beyond Newton´s Mechanics ...
Perhaps you are right, but watch out ! The essence of centrifugal force in cases such us moon/earth movement is even more "dangerous", prone to confusion, than when not "teleforces" ...
Starting with Newton´s 3rd Law (reason of centrifugal f. reality), the two opposite forces we have are NOT gravity and a centrifugal vector ... They actually are gravity force exerted by earth on moon, and also gravity force but exerted by moon on earth ...
Nevertheless, I´ve several times shown my ideas about centrifugal forces present inside both earth and moon, as internal stresses ... And their condition of partial cause of tidal effects. But I wouldn´t dare connect that to space-time curvature and/or contraction !
 

[puppypower]

Let me expand upon my hydrogen atom example and the centrifugal force associated with the electrons of atoms. In hydrogen, the fast moving electron, is in a different space-time reference, compared to the proton, which is not moving as fast; based on Special Relativity. The hydrogen atom has two references in space-time within itself, although we tend to model based on the massive proton.

The countering centrifugal force; opposite the EM force, and its impact on space-time, can explain the quantum nature of atomic emissions.

If we assume the electron and proton are in two space-time references, and the centrifugal force has a vector opposite to the EM force,  it is possible the centrifugal force and its connection to space-time allows situations where the references of the electron and proton merge. These are the quantum sweet spots. The rest of the positions in space and time; orbital, retain two references and will create uncertainty and randomness; probability function.

[rmolnav]

Many people consider real centrifugal force doesn´t actually exist, that it is something only apparent or fictitious. This very thread started with a question with that idea.
During last couple of years I´ve been refuting that, theoretically and with many practical examples.
In all cases I´ve seen that real force is associated with either two objects in contact, or two contiguous parts of a single object. And based on Newton´s 3rd Motion Law.
So, before any further comment on what said by puppy power in #156, "the centrifugal force associated with the electrons of atoms" (what justifies to say that?), I´m going to go beyond what I said in #154, in order to show (once more) that real centrifugal forces do exist.
The example in #154 about the vertically hanging steel cylindrical bar tried to put cristal clear how 2nd and 3rd Newton´s Laws (certainly thanks to inertia) make two opposite, vertical tensile forces be exerted on each side of any bar section.
Let us now suppose the bar rotating (at constant angular speed), in a horizontal plain, around its C.G.
If we imagine the bar vertically cut in slices, we can deduce that as each slice has to have a centripetal acceleration, contiguous slices have to exert forces to cause that acceleration.
Slices at their extremes ("A" slices) only have one contiguos slice each (B slices). B has to exert an inward force on A, equal to ω²r times its mass. Then, A exerts same but outward force on B (Newton´s 3rd Law). THAT is a real centrifugal force !
B slice has ω²r acceleration, with a little smaller "r". As it is being pulled outward by A, C slice has to pull inwards B with a force bigger than that in a quantity equal to ω²r (its smaller "r") times its mass. Then, B exerts same but outward force on C: ALSO a real centrifugal force ...
We could continue that way up to the bar C.G.
All slices are being stretched due to those centripetal and centrifugal forces, both equally REAL.
Similarly, if e.g. an athlete in a circus is somehow made rotate hanging from his hands (even not horizontally, just with some inclination), he does feel centrifugal forces, but no just as a "tendency" to move along the tangent due to inertia. He actually feels his body is being stretched due to REAL forces, centripetal and centrifugal.

[PmbPhy]

What is centrifugal force?

I'm a late comer to this rather long thread so some of what I'm going to say might have already been mentioned.

The centrifugal force is an inertial force which means that it can only exists within non-inertial frames of reference. That is to say that the centrifugal is that force which appears due to the observer being in a non-inertial (i.e. accelerating) frame of reference. Another kind of inertial force is the Coriolis force. And the most important type of inertial force in general relativity is the gravitational force. This can be a bit confusing when explained in a short post so a long time ago I created a web page which defines and describes inertial forces. If you'd like to read it then its at

http://www.newenglandphysics.org/physics_world/gr/inertial_force.htm

There is a passage in there which comes from an article that Einstein wrote on general relativity where he explains why we should think of inertial forces as "real" forces. He specifically talks about the centrifugal force. There are three other textbook quotes from texts currently being used which say the same thing. They're "modern" textbooks if we understand "modern" to mean that the topic being discussed is on the theories currently being taught. It doesn't mean that they were written within the last 5 years. Lol!

[rmolnav]

I'm a late comer to this rather long thread so some of what I'm going to say might have already been mentioned.

You have forgotten you sent posts long ago ... I remember your user´s name, and have seen your first post was in 24/8/2016, where you logically (?) said something similar:
"Simply put, centrifugal force is an inertial force. If you're at rest in a rotating frame of reference then objects which are moving with no acceleration in the inertial frame will accelerate in your frame"
I posted tens of examples similar to recent ones, always trying to find clearer cases to refute that restrictive definition of centrifugal force (and other errors)
If, e.g., you have read my last post, you must have seen each imaginary slice exerts an outward force on inner contiguous one, as direct consequence of Newton´s 2nd and 3rd Laws ... Aren´t those forces real "centrifugal" forces (forces in the sense "fleeing" from a center), WHATEVER the reference frame ??
In that post you referred to accelerations ("...objects which are moving with no acceleration in the inertial frame will accelerate in your frame"). That is quite clear... It´s similar to what happens, e.g., when pilots of two sailing ships, each with its own course and speed, look at each other ... We have what is called "relative course" ... What you see is the result of deducing your own vector velocity from the other´s ...
But I consider that to extend that idea of moving reference frames to forces is rather erroneous, or at least it can lead to confusion.   
I´m going to bring up another example, not mentioned before as far as I can remember.
Imagine a fun ground whip, where we all enjoyed when children. Let us put a weight between two springs, already a little stretched, forming a horizontal radial line with one extreme fixed to the closed handle bar, and the other to the seat back.
When the cart (?) at most bent part of its trajectory, inner spring will be clearly stretched much more ... If it were a spring scale it would show the increase of forces acting on its hooks. The weight would be exerting an outward force on outer scale hook, that is a real CENTRIFUGAL force (scales don´t gage only "apparent" or "fictitious" forces)
And that would be a fact, whatever it were observed by somebody standing still outside the installation, or by somebody inside the cart and experiencing same accelerations as the weight ...