What exactly is centrifugal force


by hms.tech
Tags: centrifugal, force
stevendaryl
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#73
Jan30-13, 10:48 AM
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Quote Quote by sophiecentaur View Post
Haha
I suppose I have to take your point because my suggestion is not falsifiable. But I think that the inverse, - i.e. that Science definitely can establish 'real truth'- probably is falsifiable.
I tend not to talk about truth, one way or the other. I prefer to discuss the ideas without worrying too much about whether they are truth, or something in our heads, or what.
dextercioby
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#74
Jan30-13, 10:50 AM
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"Inertial forces" as you (stevendaryl in post #78) mention are a step forward from Newton's postulates (which always have the <with respect to an inertial reference frame> text in them) to Einstein's General Relativity, parallel in a way to the step in which you replace Newton's postulates to Einstein's ones in Special Relativity.
sophiecentaur
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#75
Jan30-13, 10:55 AM
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Quote Quote by stevendaryl View Post
I tend not to talk about truth, one way or the other. I prefer to discuss the ideas without worrying too much about whether they are truth, or something in our heads, or what.
Then I guess you are not far from being a Real Scientist.
DaleSpam
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#76
Jan30-13, 01:52 PM
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Quote Quote by stevendaryl View Post
The claim that nothing matters other than quantitative predictions is itself a philosophical claim. It's funny that the people who bring up "that's just philosophy" as an argument are the ones who actually end up making the strongest philosophical claims.
I don't think it is a philosophical claim, I think it is a semantic claim. I.e. "physics" is defined as X, Y is not X, therefore Y is not "physics".
stevendaryl
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#77
Jan30-13, 01:59 PM
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Quote Quote by DaleSpam View Post
I don't think it is a philosophical claim, I think it is a semantic claim. I.e. "physics" is defined as X, Y is not X, therefore Y is not "physics".
Okay, but who gets to define what the word means? It seems to me that the meaning is provided by watching what physicists actually do, rather than how they would answer question "What is physics?"
DaleSpam
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#78
Jan30-13, 02:08 PM
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Quote Quote by rcgldr View Post
A reactive force is a response to acceleration of an object wrt inertial frame.
No, the reactive force is an equal and opposite reaction to the other force in a 3rd law pair. This is Newton's 3rd law, which seems to confuse people in rotating frames for some reason. It has nothing to do with acceleration of a specific object since the acceleration of the interacting objects can be different and the acceleration depends on the net force rather than the individual forces.

Quote Quote by rcgldr View Post
In an inertial frame, once the floor is cut, the astronaut and the floor cease to accelerate, so there is no reactive centrifugal force.
Sorry, I guess I didn't my proposed scenario clearly. I specified that the bolts were "suddenly" cut for a very important reason. As the astronaut is standing on the floor the floor is under stress with centripetal forces from the bolts and a centrifugal reaction force from the astronaut. The centripetal force is greater than the centrifugal reaction force so there is a net acceleration towards the center.

When the bolts are suddenly cut the stress is relieved from the outside of the section of floor, but the inner part of the floor (where the astronaut is standing) is still under stress. This sets up a shear wave where the floor material transitions from stress to stress-free. During the time between when the bolts are suddenly cut and when that shear wave reaches the feet of the astronaut the centrifugal reaction force still exists, the feet and floor are still in contact, and the floor is accelerating in a direction away from the center. It may help to think of the floor as being made of a stretchy rubber material.

The centrifugal force is every bit as "centrifugal" as the centripetal force is "centripetal". The centrifugal force points away from the center, the centripetal points towards the center. If either is unbalanced then it will result in acceleration in the corresponding direction. If there are other forces involved then the actual acceleration depends on the net force, per Newton's 2nd law.

Quote Quote by rcgldr View Post
In a rotating frame
I intended to discuss the reactive centrifugal force only from the perspective of the inertial frame in order to avoid any possible mix-up with the fictitious (inertial) centrifugal force in the rotating frame.
DaleSpam
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#79
Jan30-13, 02:11 PM
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Quote Quote by Andrew Mason View Post
The reactive centrifugal force disappears immediately as soon as the bolts are cut.
Hi Andrew Mason, obviously my description was poor since rcgldr had exactly the same response. Please see my response to him in the post above.
DaleSpam
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#80
Jan30-13, 02:18 PM
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Quote Quote by stevendaryl View Post
Okay, but who gets to define what the word means?
Physicists, in particular, the subset of physicists who write physics textbooks. (Maybe we can include Webster and other dictionary writers too)

Quote Quote by stevendaryl View Post
It seems to me that the meaning is provided by watching what physicists actually do, rather than how they would answer question "What is physics?"
That would be true if physicists did nothing besides physics. However, since physicists do other things besides physics, the definition must come from the answer to the question you posed. That way you can distinguishing between when they are doing physics and when they are doing things that are not physics.
stevendaryl
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#81
Jan30-13, 03:03 PM
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Quote Quote by DaleSpam View Post
That would be true if physicists did nothing besides physics.
Granted. Here's an analogy: sports. Athletes are people who play sports. Of course, an athlete does things besides play sports, but I don't think that an athlete is any better at defining what a "sport" is than anyone else. They can describe what they do when they play sports. I don't think that physicists have any more insight into what "physics" is than an athlete does about what "sports" are.

Anyway, when Einstein, or Newton, or Schrodinger, or just about any other physicist was engaged in doing physics, it certainly wasn't coming up with formulas that make predictions. They were engaged in the struggle to understand the world. That activity is a big part, I would say the center, of what I consider to be physics.
A.T.
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#82
Jan30-13, 03:10 PM
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Quote Quote by stevendaryl View Post
Of course, it doesn't matter what you call them...
So it doesn't matter if you call certain terms "forces" or not. After all it doesn't change the quantitative result of the calculations. That is my point.
stevendaryl
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#83
Jan30-13, 03:13 PM
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Quote Quote by A.T. View Post
So it doesn't matter if you call certain terms "forces" or not. After all it doesn't change the quantitative result of the calculations. That is my point.
My point was that it doesn't make any difference what you call things, but that for reasoning, it gets in the way to lump things together that are different sorts of objects.
A.T.
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#84
Jan30-13, 03:28 PM
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Quote Quote by Andrew Mason View Post
This is exactly why the term "reactive centrifugal force" should not be used. It gets confused with the fictitious centrifugal force.
I don't see how you can confuse the two. One is an interaction force that exists in every frame, the other is an inertial force that exist only in rotating frames. The diferences are listed in the table here:
http://en.wikipedia.org/wiki/Reactiv...trifugal_force

Calling it "centripetal" as you suggest, despite the fact that it points away from the center, that would be confusing.
sophiecentaur
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#85
Jan30-13, 03:39 PM
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Quote Quote by stevendaryl View Post

Anyway, when Einstein, or Newton, or Schrodinger, or just about any other physicist was engaged in doing physics, it certainly wasn't coming up with formulas that make predictions. They were engaged in the struggle to understand the world. That activity is a big part, I would say the center, of what I consider to be physics.
That assumes everyone has your view of things. I very much doubt that they were as naive as to think they were actually near a conclusion. You cannot have any knowledge of their motives but you must know that anyone who breaks ground in any of this (since the concept of God given laws has ceased to be taken for granted, at least) can only hope to improve on existing scientific models. Models are not 'truth'; they are statements that can be shown to predict the outcomes of certain experiments.
Your three example Scientists were as fallible and human as the next man in many respects and may well have believed at times that the truth is there but they would have been only too aware that it was their models that were the test of their achievements
DaleSpam
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#86
Jan30-13, 04:26 PM
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Quote Quote by stevendaryl View Post
I don't think that an athlete is any better at defining what a "sport" is than anyone else
I don't know the athletic literature very well, but whoever would write a mainstream textbook on sport would be the one who gives the authoritative definition of the word "sport". (or Webster et al.)

Quote Quote by stevendaryl View Post
what I consider to be physics.
The problem is that if you define "physics" and I define "physics" and we don't agree to use some common definition that we both consider authoritative then we cannot easily communicate since we are using the same symbol with different meanings. That is why we rely on authoratitive sources for definitions of terms, not just each individual's whim. An individual who refuses to use standard definitions and insists on using their own causes all sorts of communication problems.

In any case, we are straying from my main point, which was that a "that's just philosophy" statement is a semantic statement, not a philosophical statement. I wasn't attesting to the accuracy of A.T.'s statement, and I won't debate the merits of different definitions. Semantic arguments are boring because they are always arguments from authority and someone can always refuse to recognize your chosen authority and substitute their own prefered authority (usually themselves).
A.T.
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#87
Jan30-13, 04:35 PM
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Quote Quote by stevendaryl View Post
for reasoning, it gets in the way
Whatever that means...
stevendaryl
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#88
Jan30-13, 04:44 PM
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Quote Quote by A.T. View Post
Whatever that means...
I gave plenty of examples of what I meant. If you didn't understand what I meant after that, you could ask follow-up questions.
stevendaryl
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#89
Jan30-13, 04:47 PM
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Quote Quote by DaleSpam View Post
The problem is that if you define "physics" and I define "physics" and we don't agree to use some common definition that we both consider authoritative then we cannot easily communicate since we are using the same symbol with different meanings.
I don't think that's true. The fact that you and I might disagree about specific cases whether something is or is not "physics" or a "sport" or "music" does not get in the way of communication if there is substantial overlap.
stevendaryl
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#90
Jan30-13, 04:51 PM
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Quote Quote by sophiecentaur View Post
That assumes everyone has your view of things.
No, it doesn't. If people have different points of view, that's fine--there's room for lots of different kinds of physics. The sort of physics that is done by cosmologists, or loop quantum gravity people, or those working in the foundations of quantum mechanics is very different from the kind of physics that is done in solid state physics or biophysics. There is room for all.


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