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

wrote in
:

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


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.

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