The Naked Scientists

The Naked Scientists Forum

Author Topic: Are frames of reference even more misunderstood than centripetal force?  (Read 30592 times)

Offline Pmb

  • Neilep Level Member
  • ******
  • Posts: 1838
  • Physicist
    • View Profile
    • New England Science Constortium
Well that's part of my point that this entire argument hinges on which model you choose to use. 
Not from what I've seen. There are two classes of physicists who chime in on this subject:

Class 1) The Newtonian viewpoint: gravitation is merely an artifact of looking at things from the 'wrong' point of view. (See Peacock in link above)

Class 2) From the standpoint of an observer in the accelerating frame, the inertial force is actually present. If one took steps to keep an object "at rest" in S', by tying it down with springs, these springs would be observed to elongate or contract in such a way as to provide a counteracting force to balance the inertial force. To describe such force as "fictitious" is therefore somewhat misleading. (See A.P. French)

Anyway, regarding the fundamental particles, I wasn't trying to prove or disprove anything.  I'm legitimately curious.  I suspect there might actually be "centrifugons."  After all, we suspect that gravity is governed by gravitons, and "centrifugal force" is an inertial force like gravity.  Would inertial forces also be governed by gravitons?  I don't know, but its interesting.
It seems to me that if gravitons existed then they must exist in inertial frames. In fact their existance should be frame dependant, just like inertial forces.

A similar thing should happen in electromagnetic field. See http://home.comcast.net/~peter.m.brown/ref/falling_charge.htm
« Last Edit: 05/05/2012 05:10:46 by Pmb »
 

Offline JP

  • Neilep Level Member
  • ******
  • Posts: 3366
  • Thanked: 2 times
    • View Profile
I find the following comments confusing:
My point still holds that when we Newtonian mechanics in inertial reference frames ... centrifugal force is not a force in that model.
What you've said here, literally, is "In inertial frames of reference, inertial forces don't exist and when they don't exist they are not forces?"

See my confusion? Sorry I didn't cacth myself earlier. :(

That's exactly my point.  In introductory physics we restrict ourselves to models in which inertial forces do not exist and therefore "centrifugal force is not a force" is perfectly valid within that model.  The only reason we have to stress this is that students have already heard the name and confuse it with centripetal force, which does exist in that model.
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
Class 1) The Newtonian viewpoint: gravitation is merely an artifact of looking at things from the 'wrong' point of view. (See Peacock in link above)

Ah yes, but my example was careful to avoid gravity. I'm not entirely confident about this, but I suspect it's virtually impossible to explain the case of the subject on a rotating platform without a centripetal force component. The trick, if there is a trick, is that the platform was initially stationary.
 
Quote
Class 2) From the standpoint of an observer in the accelerating frame, the inertial force is actually present. If one took steps to keep an object "at rest" in S', by tying it down with springs, these springs would be observed to elongate or contract in such a way as to provide a counteracting force to balance the inertial force. To describe such force as "fictitious" is therefore somewhat misleading. (See A.P. French)

If you are in an accelerating frame, and you determine that it is rotating, you have just established that you are rotating within an inertial frame, in which case there is no "centrifugal" anything, and if you are in an accelerating frame without reference to any other frame, there still is no "centrifugal" anything because there is no rotation. 
 
 
 

Offline Pmb

  • Neilep Level Member
  • ******
  • Posts: 1838
  • Physicist
    • View Profile
    • New England Science Constortium
Ah yes, but my example was careful to avoid gravity.
I was talking to JP, wasn't I?

Pete
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
Ah yes, but my example was careful to avoid gravity.
I was talking to JP, wasn't I?

Pete

Will I have to conclude that my superior logic prevails?
« Last Edit: 06/05/2012 05:32:04 by Geezer »
 

Offline Pmb

  • Neilep Level Member
  • ******
  • Posts: 1838
  • Physicist
    • View Profile
    • New England Science Constortium
Will I have to conclude that my superior logic prevails?
Geezer - Can you restate what point you were trying to make? I'm ashamed to say that I losttrack of your argument.
 

Offline Pmb

  • Neilep Level Member
  • ******
  • Posts: 1838
  • Physicist
    • View Profile
    • New England Science Constortium
I think that after one did a survey of the literature tat one would conclude that whether inertial forces are refered to as real or not depends on the author. I've found it difficult to conclude what the census is.
 

Offline Pmb

  • Neilep Level Member
  • ******
  • Posts: 1838
  • Physicist
    • View Profile
    • New England Science Constortium
I'll make this one last comment before I go back to bed. If one uses Netonian physics but insist that inertial forces are not real then one must accept that the gavitational force is not real because in Newtonian dynamics the force is proportial to the mass of body.
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
I'll make this one last comment before I go back to bed. If one uses Netonian physics but insist that inertial forces are not real then one must accept that the gavitational force is not real because in Newtonian dynamics the force is proportial to the mass of body.

That's why I was trying to leave gravity out of it :)


In the example I gave, the subject stepped on to the platform while it was stationary. The platform then started to rotate, and the subject followed a curved path.

Here's a restatement of the question:

How was it possible for the subject to follow a curved path without a component of the force acting on him pointing towards the axis of rotation?
 

Offline Pmb

  • Neilep Level Member
  • ******
  • Posts: 1838
  • Physicist
    • View Profile
    • New England Science Constortium
I'll make this one last comment before I go back to bed. If one uses Netonian physics but insist that inertial forces are not real then one must accept that the gavitational force is not real because in Newtonian dynamics the force is proportial to the mass of body.

That's why I was trying to leave gravity out of it :)


In the example I gave, the subject stepped on to the platform while it was stationary. The platform then started to rotate, and the subject followed a curved path.

Here's a restatement of the question:

How was it possible for the subject to follow a curved path without a component of the force acting on him pointing towards the axis of rotation?
Sorry. It's too late and my brain has turned to mush. lol! I'll get to this tomorrow.

Pete
 

Offline Pmb

  • Neilep Level Member
  • ******
  • Posts: 1838
  • Physicist
    • View Profile
    • New England Science Constortium
How was it possible for the subject to follow a curved path without a component of the force acting on him pointing towards the axis of rotation?
Geezer - Please accept my appologies for not being able to get around to your question in full. I'm spending all of my spare time learning about Dark Matter. After that it will be something else ad. infinitum. Sorry. But I do post here so I'll do my best to get around to what I best can. My thoughts and my allegiencies are all over the place right now.
« Last Edit: 07/05/2012 22:59:28 by Pmb »
 

Offline Geezer

  • Neilep Level Member
  • ******
  • Posts: 8328
  • "Vive la résistance!"
    • View Profile
PMB - No problem!
 

The Naked Scientists Forum


 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums