Are frames of reference even more misunderstood than centripetal force?

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Offline yor_on

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There really is no ambiguity here.  Can you make your "force" vanish by changing to an inertial (non-accelerating) reference frame? 

Yes:  It's not a force.
No: It's a force.

I liked that one :)
Elegant.

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Offline yor_on

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But reading Graham, Yeah, your point is valid too :)
'Forces' that act on you will be perceived as 'forces' locally. although having been outside your closed black centrifuge you might define it as a centripetal force, but if not knowing of any 'outside'? But then again, to get this effect, doesn't it presume another 'frame of reference' from where it can exist?

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Offline Geezer

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Actually, my question was less about the name given to centripetal reaction and more about frames of reference.
 
I was under the impression that, when a frame is selected, all phenomena within that frame (not just within a subset of space) have to be described relative to that frame, even it that means you have to invent new math. You cannot explain something by selecting data from two different frames simultaneously.
 
This may seem like a major inconvenience, but science is under no obligation to be convenient.
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline graham.d

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Actually, my question was less about the name given to centripetal reaction and more about frames of reference.
 
I was under the impression that, when a frame is selected, all phenomena within that frame (not just within a subset of space) have to be described relative to that frame, even it that means you have to invent new math. You cannot explain something by selecting data from two different frames simultaneously.
 
This may seem like a major inconvenience, but science is under no obligation to be convenient.

I don't think anyone would disagree with that, Geezer. Your "motto" of ... "there ain'ta no centrifugal force either" implies more than that though, hence the lengthy discussion.

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Offline yor_on

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A 'frame of reference' is a tricky subject to me. But yeah, choose one positionally in time and space, and feel free to define it as your 'center', then define everything else from it. But it is also so as with Mach's Principle  How do you define a 'frame of reference' when not having another to prove it against?
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Offline JP

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I don't quite understand your complaint that they aren't named.  They have a variety of names: inertial force, fictitious force, pseudoforce, etc.  All these names include the term "force" but also distinguish them from "real" forces which have different properties.  (I do dislike the terms real and fictitious force, hence the quotes--I would prefer force vs. inertial force.) 

What different properties? Isn't it a point that in a closed system you could not differentiate between an inertial force and any other force? You could only do so by obsevations outside your frame but the properties of the force itself are not different - or so it is contended. Of course you could test for being in a rotating system because of the change in force as you move radially, but the nature of the force is otherwise indistinguishable from that from a gravity field over a small distance.


Sorry for dragging this up now.  I was busy this weekend.

Anyway, I disagree with you on this point.  The only forces which will be indistinguishable from inertial forces are those which are proportional to mass.  If I was in a spaceship with no windows, I wouldn't be able to tell if it was accelerating or sitting still in some external gravitational field because in both cases, the objects would experience motion in my reference frame that was proportional to mass.

If I was in a spaceship under an external electromagnetic field, I would be able to tell if I was accelerating or experiencing a force because acceleration would effect all objects proportionally to their mass, while the electromagnetic field would effect objects proportional to their charge.  There are relatively simple experiments I could conduct in my closed spaceship to determine this.

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Offline Geezer

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If I was in a spaceship with no windows, I wouldn't be able to tell if it was accelerating or sitting still in some external gravitational field because in both cases, the objects would experience motion in my reference frame that was proportional to mass.
 

Ahem! I beg to differ.
 
The motion of objects in a gravitational field would be independent of their mass. Didn't some Italian geezer establish that a wee while ago?
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline JP

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D'oh.  You're absolutely right.  I should say apparent force is proportional to mass. 

(I'm going to blame the benadryl I took for my cold this morning for that one! :p  )

My point still stands, though.  You can only generally eliminate forces that are proportional to mass by choosing an appropriately accelerating reference frame.  For others, you can devise experiments within your closed spaceship that will detect the difference from reference frame effects.

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Offline Geezer

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I'm going to blame the benadryl I took for my cold this morning for that one
 

But it specifically says on the bottle,
 
"Do not operate heavy machinery or alter your frame of reference after taking."
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline graham.d

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JP, I was loose with language in saying "any other force". I should have said gravitational force. Of course one can distinguish EM, Strong, Weak and gravitational forces. I rather took that for granted.

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Offline Geezer

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Graham,
I'm sorry if you find my signature disturbing. I suppose I better keep schtum on the question of the tooth fairy.
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline yor_on

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Yeah, that was how I read you Graham, discussing 'gravity'. And gravity is in my eyes a geometry. But 'frames of reference' is tricky. I still don't know how to define a frame without having another to define it from?

a little like that Chinese thing

Jim and Jam?
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Offline JP

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JP, I was loose with language in saying "any other force". I should have said gravitational force. Of course one can distinguish EM, Strong, Weak and gravitational forces. I rather took that for granted.

So I guess you agree with my point, then?  There is a distinction between inertial forces (which includes gravity if you bring in general relativity) and "real" (insert a better term there) forces. 

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Offline graham.d

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If you class all gravitational forces as inertial forces and all other forces as "real" forces then, by definition, you have made a distinction between these forces. I still don't see a reason not to give some of the inertial forces names though - e.g. Centrifugal, Coriolis - as it is useful to do so.  I guess the point you are making is that you can't have an inertial force without the action of a "real" force. But, as I think you said, "real" is not a good name as the inertial forces are also real (in the more normal use of the word) to anyone experiencing them.

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Offline Airthumbs

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Hi all, I would just like to jump in here at this point..... I have read all the above posts and I really am finding this difficult to grasp so I have a few questions that I would really appreciate some answers to.

When you talk about a frame of reference are you talking about a fixed moment in time? 

Ok then, what is a frame of reference?

Is this just a question of English or is the actual definition of centrifugal force incorrect?

If centrifugal force describes the forces exerted on an object in a spin then why is it incorrect. 

How does a centrifuge work, or is this improperly named?

It was Geezer who introduced me to the concept of centripetal force as opposed to centrifugal and I can categorically state that in my case it is certain that frames of reference are more misunderstood then the other.

I liked the analogy of a roundabout as I can relate to this but it would be very useful if someone could add in a frame of reference to this analogy and explain it a little further if possible.

Thanks all.
Any intelligent fool can make things bigger and more complex... It takes a touch of genius - and a lot of courage to move in the opposite direction. (Einstein)

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Offline graham.d

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A frame of reference is position from which you observe and calculate the motion of any objects. As long as you are totally consistant in doing this, the outcome of your calculation will agree to that of any other observer.

So, in the case of a roundabout or a centrifuge, an external observer sees the mechanical structure of the rotating body and observes that it is rotating. He sees the "centrepetal" force created by the rigidity of the rotating body as a measurable tension in a radial arm and he sees that a person being rotated is being constrained by this force so as to prevent him continuing on in a straight line. This is the simplest way to observe this particular motion and is sometimes called the "rest" frame. From the perspective of the man being swung around, he feels a force pushing him outwards. This is an inertial force and is called a centrifugal force. If he moves in a radial direction he will also experience a side force, which is another inertial force called the Coriolis force. It is possible for him to calculate all these forces and motions from his (accelerated) frame though this is mathematically complex. Such concepts are not encouraged (as JP says) in teaching Newton's laws of motion as these are taught before the student has the capability to work through the maths in a rigorous way. There can be confusion because, in my opinion, children aer aware of "centrifugal" force and usually know the name, before they understand the physics; they then get confused between centripetal and centrifugal force. I understand this issue but feel it could be handled better rather than trying to say the centrifugal force does not exist. Explaining inertial forces is not so difficult, I believe, and, as I think JP agrees, using the word "real" (and implying that inertial forces are not real) is not ideal.

A simpler inertial force is that which you would experience in the proverbial constant acceleration rocket ship. You would not be able to distinguish such a force from gravity (provided you could not look out of the window). In General Relativity it is a tenet that the two are indistinguishable.

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Offline imatfaal

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wish we had a "like" button or rep system for that post Graham - nicely done.
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Offline Geezer

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Yes, but centrifugal force is still not a "real" force. It is the real reaction to the real centripetal force.
 
The reason it's not "a real force" (call it what you will) is because there is no physical phenomenon to explain it, whereas there is a very simple explanation for centripetal force.
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline Geezer

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If we use the argument that children should be taught that centrifugal force is a real force because they can feel it, should we also teach them that the Earth is at the center of the Universe because they can see everything rotating around it?
 
Wouldn't it be much better to take advantage of the situation to teach them that forces have reactions, and what they are feeling is simply the reaction to a force that results from one of the most fundamental scientific principles?
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline graham.d

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You have to then say gravity is not a "real" force too but a consequence of the geometry of space-time. It is all well to define things in these ways but sometimes it is better to use words in the way people already understand them.

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Offline Geezer

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You have to then say gravity is not a "real" force too but a consequence of the geometry of space-time.

I have no objection to that at all, but it doesn't have much bearing on the question I posed:
 
If centrifugal force is "a real force", what physical phenomenon produces it?
 
(BTW - I don't have any objections to "the centrifugal effect" or something similar.)
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline graham.d

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People doing Newtonian mechanics are told gravity is a force. They are not told it is an effect and a consequence of spacetime geometry. There is not any distinction between gravity and an inertial force except for one's frame of reference; they are regarded as equivalent in their nature and behaviour. Centrifugal force is an inertial force, as is the Coriolis force. Note the use of the word "force" here!

I am happy to say how this force comes about as a result of being in an accelerating frame. I am just saying there is nothing wrong with using a common name for it. If you are in a racing car or a centrifuge you would not say I am experiencing a tendency to carry on in a straight line in reaction to being constrained by a centripetal force. You say I am experiencing so much g-force and in a centrifuge it would not be surprising to call that force a centrifugal force.

I feel that this has become an argument over semantics. I think most people in this discussion are not confused by the actual causes and effects so I am happy to bow out and leave the discussion to others. I've had my say.

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Offline Geezer

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Graham,
 
You may think it's about semantics, but I think it's an important issue about how best to teach basic physics.
 
A student is likely to ask the question that I asked, but there is no satisfactory way to answer it without introducing abstract concepts that are only likely to confuse the student (and possibly the teacher) even more.
 
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline Ęthelwulf

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Yes, but centrifugal force is still not a "real" force. It is the real reaction to the real centripetal force.
 
The reason it's not "a real force" (call it what you will) is because there is no physical phenomenon to explain it, whereas there is a very simple explanation for centripetal force.

Just because it is a psuedoforce should not mean to take it as not having a consequence in the mathematics. As I told you before, the black hole and singularity theorems takes the centrifugal force very seriously.

In fact, I am sure I have mentioned this before, but gravity is a psuedoforce of types.

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Offline Pmb

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Quote from: Ęthelwulf link
"...gravity is a psuedoforce of types..."
Why is it so important to keep refering to gravity as a"psuedoforce of types"?

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Offline Ęthelwulf

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Quote from: Ęthelwulf link
"...gravity is a psuedoforce of types..."
Why is it so important to keep refering to gravity as a"psuedoforce of types"?


Because if you study the quality of Geezers arguement, you essentially keep finding the same thing. He keeps making a mention that the centrifugal force is a psuedoforce, that it is not ''real''.

Well, neither is gravity then, but we still take it as being within the framework of field theories. See, originally, Geezer said, ''there is no such force'' --- to ''there is only the centripetal force.'' Now, gravity is well-understood of as the curvature of space, but no one hangs about to say, ''well gravity isn't real because it's a psuedoforce.''

That kind of thinking is never heard of... only from cranks who can't accept that gravity is something we all come to experience in.

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Offline JP

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Not to put words in Geezer's mouth, but I don't think he's saying that a pseudoforce can't have real effects in some reference frame.  I think he's saying (quite reasonably) that you shouldn't group "centrifugal force" together with non-inertial forces by labeling it a force. 

It's certainly quite easy to look back at the idea of pseudoforces once you've had advanced courses in mechanics and say that it's obvious where pseudoforces come from and what they physically mean.  It's incredibly confusing to have your instructor in physics 101 tell you that there are reference frame dependent forces which vanish depending on the reference frame you choose: it's hard enough learning to apply Newton's laws in inertial reference frames.  It makes a lot of pedagogical sense to break "force" into two categories: one which has the properties of "real" forces and one which has the properties of pseudoforce--simply because they behave differently in physics, and the latter category requires a lot more mathematical sophistication to tackle properly.

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Offline Geezer

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Quote from: Ęthelwulf link
"...gravity is a psuedoforce of types..."
Why is it so important to keep refering to gravity as a"psuedoforce of types"?

If we take a case that we are probably all familiar with - the case where we are spinning around on a roundabout, or a carousel, our senses tell us that a force is acting on us in an outward direction radial to the rotation of the device. This is commonly referred to as "centrifugal force".
 
However, if you accept that Newton's laws of motion have not yet been repealed, there is no actual force acting in that direction. There is a force acting in the opposite direction - the centripetal force, and without that force, we would not be rotating at all. The apparent "centrifugal force" is only a reaction to the real centripetal force. That's why it is referred to as a pseudoforce, a fictional force, etc., etc.
 
It's actually impossible to experience any "centrifugal force" in the absence of centripetal force, because, without a centripetal force, there would be no rotation at all.
 
I do know there are other methods, like Hamiltonian Mechanics, that can be used to describe these phenomena, but they go to great lengths to avoid the discussion of any forces, so it's not very likely they will help to resolve the issue.
 
The so-called "centrifugal force" is a consequence of Newton's Laws of Motion. I really don't have any objection to alternative scientific interpretations, but we may not use an aberrant interpretation of Newton's Laws of Motion to disprove Newton's Laws of Motion.
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline Ęthelwulf

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Not to put words in Geezer's mouth, but I don't think he's saying that a pseudoforce can't have real effects in some reference frame.  I think he's saying (quite reasonably) that you shouldn't group "centrifugal force" together with non-inertial forces by labeling it a force. 

The discussion has became so semantic and technical, I've almost lost track of what people are really intending in their discussions.

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Offline Geezer

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The discussion has became so semantic and technical, I've almost lost track of what people are really intending in their discussions.

It's very simple.
 
If you can't explain the physical phenomenon that produces a force, it's not a real force. It's an artifact.
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline Ęthelwulf

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If someone asked me, ''is the centrifugal force real?''

I'd reply with the question ''is the force of gravity just as real as the centrifugal force?''

If the answer is yes, then that is all I need.

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Offline Ęthelwulf

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Let me remind you why you created this thread. It was to denounce what I asked... if an elevator was going straight to the heavens and into space, what would stop it from being ripped apart by the centrifugal forces?

You said, ''that's easy. It won't because the centifugal force does not exist.''

Since that remark, we have made some headway. I have shown that black holes are pivotal to understanding centrifugal forces (taken seriously by physicists) whether it is or not a real force created by physical mediators. We've also established time and time again, that gravity is a psuedoforce, but in light of this we do not go around saying it does not exist.

And what are we stuck on here? Semantics.

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Offline yor_on

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The interesting thing to me is that we presume two frames of reference to proof a force :)
And it doesn't really seem to ah, matter what I call it, or deem it to be.
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Offline JP

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I think we all agree on the physics, but we disagree on what terms should be used to describe different parts of the physics.  The problem with writing this agreement off as semantics is that you're indicating that semantics isn't important in physics.  But the precision of the definitions we give to terms is absolutely critical to science!

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Offline Ęthelwulf

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I think we all agree on the physics, but we disagree on what terms should be used to describe different parts of the physics.  The problem with writing this agreement off as semantics is that you're indicating that semantics isn't important in physics.  But the precision of the definitions we give to terms is absolutely critical to science!

I'm not saying semantics is really not that important, only that it has muddled this conversation to tenebrous levels :P

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Offline Geezer

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Let me try to dispel the muck with a simple experiment:

We have a rotatable circular platform, say, 4 meters in diameter. We step onto the platform, and the platform starts to slowly rotate. We continue standing on the platform as it slowly rotates.

Question: Why do we rotate with the platform?
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline Pmb

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Quote from: Geezer
Let me try to dispel the muck with a simple experiment:

We have a rotatable circular platform, say, 4 meters in diameter. We step onto the platform, and the platform starts to slowly rotate. We continue standing on the platform as it slowly rotates.

Question: Why do we rotate with the platform?

To be extremely general, because as the platform starts to rotate it forces the muck to exert a force between the platform and us. This causes a force on us which causes us to rotate.

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Offline Geezer

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Quote from: Geezer
Let me try to dispel the muck with a simple experiment:

We have a rotatable circular platform, say, 4 meters in diameter. We step onto the platform, and the platform starts to slowly rotate. We continue standing on the platform as it slowly rotates.

Question: Why do we rotate with the platform?

To be extremely general, because as the platform starts to rotate it forces the muck to exert a force between the platform and us. This causes a force on us which causes us to rotate.

Is the force is conveyed by friction between our shoes and the platform?
 
EDIT: Wait a minute. I thought when you apply a force to something it is supposed to go in a straight line. Weren't we just taught that?
 
Why doesn't the force make us go in a straight line until we fall off the platform?
« Last Edit: 27/04/2012 23:05:45 by Geezer »
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline wolfekeeper

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I find this thread to be not very good at all.

Centrifugal force (and coriolis force) are pseudo forces due to a combination of rotation of the reference frame and momentum; and they are needed when you are analysing a situation in a rotating reference frame to get the correct movements; together they explain why the stars spin around the Earth (for example).

You use rotating reference frames when it's more convenient to use them; for example a space elevator would rotate with the Earth, and are thus are particularly easy to analyse in the rotating reference frame.

Another example is the Lagrange points; these are stationary, but only in a rotating reference frame, they are balanced between gravity and the centrifugal (pseudo)force.

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Offline wolfekeeper

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Why doesn't the force make us go in a straight line until we fall off the platform?
Because you're not moving at all in the rotating reference frame that rotates with the platform, at least until the centrifugal force exceeds the friction of your shoes.

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Offline Pmb

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I find this thread to be not very good at all.
The quality of a thread is determined by it's usefulnes to address/answer a person's query/questions. If Geezer gets his question answered to his satisfaction then the thead was a very good thread.

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Offline Pmb

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Quote from: Geezer
Is the force is conveyed by friction between our shoes and the platform?
Yes. So long as you have a good understanding of kinetic coefficient of friction, static coefficient of friction and how to apply them to a rotating platform, shoes and muck.
 
Quote from: Geezer
EDIT: Wait a minute. I thought when you apply a force to something it is supposed to go in a straight line. Weren't we just taught that?
It’s a bit more complicated than that. When an object is sitting on a rotating platform there is a force of friction, which is perpendicular to the direction of motion, which then makes the object move in a circular motion. Eventually, as you increase the rotational motion of the platform the kinetic coefficient of friction increases so as to make the kinetic coefficient of friction becomes greater than the static coefficient of friction and the object then moves in a straight line.

The dynamics are similar to that of a charged particle moving in a magnetic field. See http://home.comcast.net/~peter.m.brown/sr/cyclotron.htm

This is a tricky thing to describe so you may want to rethink it until you get it right since I probably got something wrong in the explanation.  :-'(

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Offline Geezer

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It’s a bit more complicated than that. When an object is sitting on a rotating platform there is a force of friction, which is perpendicular to the direction of motion, which then makes the object move in a circular motion. Eventually, as you increase the rotational motion of the platform the kinetic coefficient of friction increases so as to make the kinetic coefficient of friction becomes greater than the static coefficient of friction and the object then moves in a straight line.


Ah right, but there can only really be one force acting on our hypothetical person via their shoes. Presumably it must act in a direction that continuously changes as the platform rotates?

(It seems Wolfkeeper is unaware of Newton's First Law. The so called "rotating reference frame"* could not exist in the absence of centripetal force.)

*What?! Reference frames do not rotate. Everything else around them might, but they don't. If they did, they would hardly be a reference.
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline wolfekeeper

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Nope, no centripetal force is necessarily involved.

The whole point is to give the same results as a non rotating reference frame. As in, you can take any situation in an inertial reference frame and model the same situation in any rotating reference frame, and the same thing must happen, otherwise you're doing it wrong.

The motion won't usually look the same, but if you do the rotation mapping back to the inertial frame, everything must be the same as if you did it all in the inertial frame.
« Last Edit: 02/05/2012 02:49:48 by wolfekeeper »

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Offline Pmb

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Nope, no centripetal force is necessarily involved.
You're wrong on that point.

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Offline Pmb

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Ah right, but there can only really be one force acting on our hypothetical person via their shoes.
That is not quite true. There is the force due to the centripital force which is due to choice in frame of reference, there is the force of friction and there is the force of friction. The total force is the sum of all the forces acting on the shoes and it is that total force which is responsiple for explanation of the motion of the shoes.
Presumably it must act in a direction that continuously changes as the platform rotates?
I agree with that.
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*What?! Reference frames do not rotate. Everything else around them might, but they don't. If they did, they would hardly be a reference.
In Newtonian Dynamics that would be incorrect. In General Relativity that is incorrect.

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Offline wolfekeeper

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Nope, no centripetal force is necessarily involved.
You're wrong on that point.
Nope.

What you do to derive a rotating reference frame is take the normal inertial frame of reference and calculate a coordinate transformation to transfer everything, all the Newtonian mechanics, to that rotating frame.

When you do that, all the normal physics still works, but two pseudo accelerations/pseudo forces appear, the coriolis and centrifugal, if you apply them both, then (somewhat counterintuitively) Newton's laws still work perfectly, they sort of cancel out the effects of the rotating reference frame.

There is no centripetal that appears at all, although if there was one in the original situation in the inertial frame of reference, then there will be one afterwards, but if there wasn't, then there won't be one afterwards.

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Offline Geezer

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Nope, no centripetal force is necessarily involved.
You're wrong on that point.
Nope.

What you do to derive a rotating reference frame is take the normal inertial frame of reference and calculate a coordinate transformation to transfer everything, all the Newtonian mechanics, to that rotating frame.

When you do that, all the normal physics still works, but two pseudo accelerations/pseudo forces appear, the coriolis and centrifugal, if you apply them both, then (somewhat counterintuitively) Newton's laws still work perfectly, they sort of cancel out the effects of the rotating reference frame.

There is no centripetal that appears at all, although if there was one in the original situation in the inertial frame of reference, then there will be one afterwards, but if there wasn't, then there won't be one afterwards.


But that's my point.

The above is all very well, and mathematically correct, but it only obfuscates this particular problem.

Unless you instantaneously jump into a new frame, there must be a centripetal force, and why would you feel the need to jump into a different frame half-way through a problem?

If we have to instantaneously "change our frame of reference" when we stand on a rotating platform, do we also have to "change our frame of reference" when we step onto a linear moving platform like an escalator, or moving sidewalk, and then describe all the dynamics in terms of pseudo forces? Likewise when we are walking, or rollerblading down the street?

I suppose we could do that, but it seems like an academic exercise.

Of course there are complex situations where these treatments are useful, but from a teaching perspective, if you introduce them too early, you're only going to confuse a lot of students, or other TNS members.
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.

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Offline wolfekeeper

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What you do to derive a rotating reference frame is take the normal inertial frame of reference and calculate a coordinate transformation to transfer everything, all the Newtonian mechanics, to that rotating frame.

When you do that, all the normal physics still works, but two pseudo accelerations/pseudo forces appear, the coriolis and centrifugal, if you apply them both, then (somewhat counterintuitively) Newton's laws still work perfectly, they sort of cancel out the effects of the rotating reference frame.

There is no centripetal that appears at all, although if there was one in the original situation in the inertial frame of reference, then there will be one afterwards, but if there wasn't, then there won't be one afterwards.

But that's my point.

The above is all very well, and mathematically correct, but it only obfuscates this particular problem.

Unless you instantaneously jump into a new frame, there must be a centripetal force,
Nope. It turns out when you do the maths there's a steady 'force' that is proportional to the distance from the axis that points away from the axis, that is proportional to the distance (the centrifugal force), and there's a coriolis force that acts when something moves* (where "moves" means relative to the rotating reference frame), which acts at 90 degrees to the movement and the axis.


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and why would you feel the need to jump into a different frame half-way through a problem?
You don't "jump" in, you just do it all as if it wasn't rotating, and then add on those two fixup force to deal with the fact that you're working in a rotating frame. In many cases either the centrifugal or coriolis cancel out anyway. On the surface of the Earth, the centrifugal mostly cancels for example.
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If we have to instantaneously "change our frame of reference" when we stand on a rotating platform, do we also have to "change our frame of reference" when we step onto a linear moving platform like an escalator, or moving sidewalk, and then describe all the dynamics in terms of pseudo forces? Likewise when we are walking, or rollerblading down the street?
You can, but you wouldn't normally. You only use accelerated reference frames when it's convenient.
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I suppose we could do that, but it seems like an academic exercise.
Using rotating reference frames is what the weather forecast people do. If they didn't the maths gets even more horrible. They pretty much have to use rotating reference frames.

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Offline Geezer

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Nope. It turns out when you do the maths there's a steady 'force' that is proportional to the distance from the axis that points away from the axis, that is proportional to the distance (the centrifugal force), and there's a coriolis force that acts when something moves* (where "moves" means relative to the rotating reference frame), which acts at 90 degrees to the movement and the axis.


You can do the math all you like (and I agree with your math) but it does not serve to provide a good explanation for what actually happened. It's only complicating things unnecessarily.

In this example, our subject experienced a force that continuously changed direction, otherwise he would have traveled in a straight line. "Centrifugal force" does not help to explain the phenomenon. In fact, it's downright misleading.
There ain'ta no sanity clause, and there ain'ta no centrifugal force ęther.