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From: DSeppala on 9 Oct 2009 10:05
Let there be a arbitrarily large circular ring of steel in a frame
I'll call the rest frame. Let that ring rotate at some high angular
velocity. The motion of the ring causes a length contraction of this
ring circumference and a shortening of the diameter of this ring as
viewed in this rest frame.
Now look at this same rotating ring from an inertial reference
frame that has the same instantaneous velocity as the top of the
ring. In that moving frame, the top of the ring has zero relative
velocity to this moving frame so there is virtually no length
contraction of the ring at the top of the ring. However, the bottom
of the rotating ring is moving in the opposite direction to this
moving frame, so in that same moving frame the bottom of the ring is
seen to have a substantial length contraction. The question is if the
length contraction at the top of the ring is different from the length
contraction seen at the bottom of the ring, why do observers in the
moving frame see the shape of the rotating ring as the same shape as a
non-rotating ring of the same diameter in the rest frame? If there
was a ring that wasn't rotating but was the same diameter and
circumference as the rotating ring and they shared the same center
point, all observers must view them as the same shape, otherwise there
would be space-time points where the rest frame observers see points
from both rings present whereas the moving observer would only see a
point from one of the two objects present, which cannot be.
How is this explained using Einstein's concepts of time and
distance?
Thanks,
David Seppala
Bastrop TX
From: Dono. on 9 Oct 2009 10:32
On Oct 9, 7:05 am, DSeppala <dsepp...(a)austin.rr.com> wrote:
> Let there be a arbitrarily large circular ring of steel in a frame
> I'll call the rest frame. Let that ring rotate at some high angular
> velocity. The motion of the ring causes a length contraction of this
> ring circumference and a shortening of the diameter of this ring as
> viewed in this rest frame.
> Now look at this same rotating ring from an inertial reference
> frame that has the same instantaneous velocity as the top of the
> ring. In that moving frame, the top of the ring has zero relative
> velocity to this moving frame so there is virtually no length
> contraction of the ring at the top of the ring. However, the bottom
> of the rotating ring is moving in the opposite direction to this
> moving frame, so in that same moving frame the bottom of the ring is
> seen to have a substantial length contraction. The question is if the
> length contraction at the top of the ring is different from the length
> contraction seen at the bottom of the ring, why do observers in the
> moving frame see the shape of the rotating ring as the same shape as a
> non-rotating ring of the same diameter in the rest frame? If there
> was a ring that wasn't rotating but was the same diameter and
> circumference as the rotating ring and they shared the same center
> point, all observers must view them as the same shape, otherwise there
> would be space-time points where the rest frame observers see points
> from both rings present whereas the moving observer would only see a
> point from one of the two objects present, which cannot be.
> How is this explained using Einstein's concepts of time and
> distance?
> Thanks,
> David Seppala
> Bastrop TX



Good questions, Seppala.
Here is the answer to all of them:

http://www.tempolimit-lichtgeschwindigkeit.de/rad/rad.html
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