On Tue, 23 Aug 2005 09:41:49 +0000 (UTC), bz
wrote:

wrote in
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On Mon, 22 Aug 2005 15:48:25 +0000 (UTC), bz
wrote:

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On Sat, 20 Aug 2005 22:55:42 +0000 (UTC), bz
wrote:

wrote in
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On Fri, 19 Aug 2005 15:07:03 +0000 (UTC), bz
wrote:

wrote in news:4305d0b7.540887@news-
server.austin.rr.com:

This problem is a combination of several problems I've posted in
this group. When I combine the problems, the answers given to me
in previous posts don't work. Here's the problem.

I have two frames which I will call the stationary frame and the
moving frame. Their relative velocity is 0.866 c. In the
stationary frame, parallel to the x-axis there is a rod and a
rotating cylinder. The end points of the rod and the rotating
cylinder are at the same x coordinates. The diameter of the
cylinder is 10 meters and the cylinder is rotating at 10
revolutions per second.

As measured in the moving frame, let the length of the rod and the
length of the rotating cylinder be 1 light-second. At time t0 as
measured in the moving frame, each point of the rod is
simultaneously attached to the surface of the rotating cylinder.
(Assume the rod is made of a material that is very malleable).

As viewed in the stationary frame, one end of the rod was attached
to the rotating cylinder 1.73 seconds before the other end.

Ok.

That means
that the rod wrapped around the cylinder about 17 times in a
spiral pattern.

Nope. From the stationary frame, the rod was rotating along with the
line drawn straight along the surface of the cylinder drawn by a
laser level device before the rod was ever joined to the cylinder.
No. The rod develops a rotation because it is attached to the
rotating cylinder. Prior to being attached, the rod is not rotating
and has zero velocity wrt to the longitudinal axis of the cylinder.


You have a slight problem.
you said:
In the stationary
frame, parallel to the x-axis there is a rod and a rotating
cylinder. The end points of the rod and the rotating cylinder are
at the same x coordinates. The diameter of the cylinder is 10
meters and the cylinder is rotating at 10 revolutions per second.

That puts one end of the rod and some [poorly specified] point on the
rotating cylinder at the same point.

If I assume the point is on the circumference of the cylinder rather
than the center of the cylender [that would make for all kinds of
problems] then you have infinite acceleration of the rod at the moment
of attachment.

Only if the rod is already in motion, can it be attached to the
cylinder.
No. The circumference of the rotating cylinder is about 31 meters.
At 10 revolutions per second, the surface of the cylinder is moving at
about 310 meters / second. Let's say the cylinder contains an
extremely powerful electromagnet, and the rod is steel. When the
magnet is turned on, if the force is strong enough, the magnet will
keep the rod attached to the rotating cylinder. There are thousands
of ways to do this attachment. Surely, you agree that if the rotation
speed is very low, say 0.001 revolutions per second, there would be no
problem attaching the rod to the cylinder - you can do this experiment
with short rod segments. I only picked 10 revolutions per second so
that its easier to envision the rod spiraled completely around the
cylinder as opposed to spiraled over a very small angle.
David

delta v / delta t = acceleration.
Okay, I see what you are saying, I think. I think you are saying
because I said the attachment for each point of the rod takes place at
the same time, t0, you think that means delta t = 0. I guess, I
should have been more precise and pedantic. Let's do that and say the
acceleration time for the rod to equal the rotational speed of the
surface of the rotating rod is 0.1 second and the acceleration starts
at each point at time t0 as measured in the moving frame.
David

ok.

So now, we, like the viewer of a reflection in a funhouse mirror, see an
optical illusion as we see the 0.1 second moment move away from us
[presumably we have a very powerful telescope with zoom capability that
has been programmed to focus on that moment, as it appears to move away
from us.

We see the optical equivalent of a thunder roll, as the sound from
different portions of the path reach our ears.

We recognize that sight and sound can be missleading and that no wrapping
actually occurs.
Wrapping actually does occur. In the rest frame of the rod and of the
rotating cylinder, we are attaching one end of the rod to the cylinder
a second before we attach the other end. The cylinder rotates 10
times before the other end is attached. Since the speeds are everyday
values can actually do this experiment over a much shorter length.
The short rod will attach to the short segment of the rotating disk,
and if we attach one end at a different time then we attach the other
end (the stationary frame view), the attached rod will spiral about
the cylinder. In the problem I posted because of the lengths involved
the spiral and wrapping occur over large distances, but it still
occurs.
David

you have a finite change in velocity (delta v) taking place in zero time
(delta t). This gives infinite acceleration.

Only if the rod is already in motion, can it be attached to the
cylinder.


The stationary observer is intellegent enough to realize that light
moves in a straight line[in the rotating FoR] and that the optical
delusion of a 17 times wrap is exactly that.
....

When I look at myself in a funhouse mirror, I know that I really do
NOT get long and thin or short and fat. When I look at something in
another FoR, I know that things look different from that FoR.



--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is
an infinite set.

remove ch100-5 to avoid spam trap







--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

remove ch100-5 to avoid spam trap