Re: Another Rotating Cylinder Problem - explain from moving frame view

On Mon, 17 Apr 2006 03:16:54 +0000, David wrote:

On Sat, 15 Apr 2006 11:02:17 +0100, "Martin Hogbin"
<goatREMOVETHIS123@xxxxxxxxxx> wrote:


"David" <dseppala@xxxxxxxxxxxxx> wrote in message
news:2781421lvufjvsa14pmj5fnvk52d3mutdd@xxxxxxxxxx
On Fri, 14 Apr 2006 18:29:50 +0100, "Martin Hogbin"
<goatREMOVETHIS123@xxxxxxxxxx> wrote:


"David" <dseppala@xxxxxxxxxxxxx> wrote in message
news:5e5v32hhd167p57ikjfcvnfm82o1thjecu@xxxxxxxxxx
Can anyone explain this rotating disk problem from the point of view
of a moving observer?

Davis Seppala is one of the mysteries of this group. Unlike
Spaceman, for example, he is smart enough to dream up endless SR
puzzles, many of them involving accelerating reference frames,
yet by his own admission he has practically no understanding of
SR.

Is he really an expert on the subject testing posters'
understanding?

Is he a bunch of psychology students performing some kind of
experiment on us all?

Is he just a troll who delights in stirring up discussion and
argument?

Any suggestions?
He is none of the above. David's understanding of Einstein's notions
so far is much like David's comprehension of E. M. Escher's drawings.
He gets to points in problems where there seems to be contradictory
results as in his posting on 4/10/2006 where a moving rigid rod is
always parallel to the x-axis and loops about the x-axis in a circular
pattern at a 10 meter diamter circle yet no forces are applied to the
rod to make it continue in this circular pattern. Or in this posting
where as tension on a straight wire increases the center of the wire
moves away from a straight line. This is opposite to typical
experiences - wires form straight lines when stretched from two points
with nothing in between them to interfere with the straight line. This
does not make sense to David.

Then what David should do, as he has been told many times, is to
make sure he fully understands basic SR _in inertial frames_ with
only _inertial motion_ involved.

If he could demonstrate a sound understanding of Einstein's
postulates,
I cannot demonstrate a clear "understanding" of Einstein's postulates. I
know the two main hypotheses stated in relativity are that all physical
laws are the same in any given inertial reference frame and that the speed
of light is constant and independent of the motion of the emitting source.
The translated text I read actually used the word "velocity" of light
instead of speed. We all know the velocity of light (speed and direction)
must vary with the motion of the light source but the speed can possibly
be constant. Although stated as a definition and not as a hypothesis
Einstein states that "time" at two points cannot be defined at all unless
the "time" required to travel from A to B equals the "time" required to
travel from B to A. I readily admit that this statement of time that
Einstein characterizes as "true by definition" seems to me more like a
hypothesis than something true by definition.
what an inertial frame is,
An inertial frame is one in which no accelerations or higher order changes
in position of objects occur. In in a real sense we do not find inertial
frames except in rare situations since any kind of motion causes the
frame to accelerate slightly. But these are negligible in a practical
sense.
the train experiment,
I'm not certain which train experiment you are referring to. To
demonstrate that one inertial frame is identical to every other frame
there is a real life experiment where the acceleration of a train is so
small that passengers on either of two trains cannot easily tell which
train is moving out of the station or not. This is not much of a physics
experiment since it merely demonstrates lack of needed sensitivity in
measuring devices, so I don't know if this is the experiment you are
referring to or not.
and the pole and barn paradox the others would be much more willing to
help him.
The pole and barn paradox. What am I supposed to do here? Plug in values
in the time and length separation formulas to show in one inertial frame
where the two door closings are simultaneous and the pole just fits gives
values that in another inertial frame the two doors open and close at
different times and this is compensated precisely by the legnth
contraction?

Yes, this would be a great start. Actually do the calculation and post
the result, thus demonstrating that you've gotten to first base.

You frequently request others to post calculations for you. Do one
yourself, and post it.

If you already understand it, it won't be hard to do and won't take
much time. If you _don't_ already understand it, you'll actually
learn something useful from it. So, the exercise will be
either easy or valuable (or both) and it'll impress everybody who's
currently throwing tomatoes at you, and give you a chance to say "See
I told you all along I understood (at least) this much of it!".

So, yeah, do it, Dave!


Maybe you want me to plug in the length contraction, and
then add the product of the time difference & V (distance traveled) to
see if I get the correct number. This only demonstrates an understanding
of algebra.

I should point out that is no good his saying, 'Yes, yes, yes, I
know all that', he must clearly demonstrate that he fully
understands basic SR before anyone will accept that his questions
are serious.
I suspect this posting still won't result in any physics answers to my two
cylinder questions I posted - this one and the one 4/10/2006. But we'll
see.
David

Will he make a concerted effort to understand the basics and show
that he has done so or will he continue as before? We shall see.

Martin Hogbin




--
Nospam becomes physicsinsights to fix the email

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Relevant Pages

  • Re: Another Rotating Cylinder Problem - explain from moving frame view
    ... 4/10/2006 where a moving rigid rod is always parallel to the ... This does not make sense to David. ... An inertial frame is one in which no accelerations or higher order ... I'm not certain which train experiment you are referring to. ...
    (sci.physics.relativity)
  • Re: Another Rotating Cylinder Problem - explain from moving frame view
    ... yet by his own admission he has practically no understanding of ... results as in his posting on 4/10/2006 where a moving rigid rod is ... An inertial frame is one in which no accelerations or higher order changes ... I'm not certain which train experiment you are referring to. ...
    (sci.physics.relativity)
  • Re: Another Rotating Cylinder Problem - explain from moving frame view
    ... yet by his own admission he has practically no understanding of ... results as in his posting on 4/10/2006 where a moving rigid rod is ... An inertial frame is one in which no accelerations or higher order ... I'm not certain which train experiment you are referring to. ...
    (sci.physics.relativity)
  • Re: Another Rotating Cylinder Problem - explain from moving frame view
    ... no understanding of SR. ... results as in his posting on 4/10/2006 where a moving rigid rod is ... An inertial frame is one in which no accelerations or higher order ... I'm not certain which train experiment you are referring to. ...
    (sci.physics.relativity)
  • Re: Two photons... relative distance question
    ... around this stuff for the first time and am always quite prepared to be ... My understanding is that within a specific inertial frame of reference ...
    (sci.physics.relativity)
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