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


"David" <dseppala@xxxxxxxxxxxxx> wrote in message
news:alu54295av6mfu56squas3gfb22g2gl31h@xxxxxxxxxx
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 you may be interested to read a paper by Ives, in which he actually
*derived* the LT's from conservation of energy and momentum - and by which
those "two main hypotheses" follow (I'll have to scan it, but will be happy
to do so).

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.

Just see the dictionary: "velocity" can also be synonym for "speed" - only
in recent years it has increasingly been used as distinguished from speed.
Language is full of such tricks...

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.

He simply adopted the then existing convention as published by Poincare, who
apparently agreed with Lorentz that this convention is generally *untrue* in
reality. There have been endless discussions about this as some people can't
understand that a convention is not required to be "really true", and on top
of that, Einstein's view of "reality" was very peculiar...

Harald


.

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