Re: Einstein's math and physical objects

From: Tom Roberts (tjroberts_at_lucent.com)
Date: 01/13/05 

Date: Thu, 13 Jan 2005 21:02:22 GMT

dseppala@austin.rr.com wrote:
> If you do some simple experiments rotating disks with two strings
> attached, you will find that if the disks have less than 180 degrees
> of rotation, you can take your finger, for example, and place it
> between the separated wires at one disk and slide it along through the
> wires until you reach the other disk. However if the disks have a
> relative rotation greater than 360 degrees, you cannot do this. A
> knot forms which prevents you from sliding your finger all the way
> between the wires from one disk to the other disk.

This is not a "knot", it is merely a twist of the two wires. Yes the
wires touch, but they do not tie any real knot. If you used an
atom-sized "finger" it could indeed slide along the wire as above, as
long as you rotated it around properly.

Note also that you are looking at this system from its approximate rest
frame (i.e. within a meter/second or so) -- no SR effects are involved
at all.

[aparently here you switch back to the original problem]
> In the original
> rest frame, one can always slide their finger from one disk to the
> other, even if you view the wires/strings as a helix with zero
> diameter - the wires don't entangle each other. In the final rest
> frame, this is impossible because of the knot that forms.

There is no knot at all. Moreover, the wires do not touch or twist or
"entangle". This is a DIFFERENT PHYSICAL SITUATION from your holding the
disks in your hands and twisting them. Go back and re-read my analogy of
a focal-plane camera -- that is a MUCH better model of how it looks in
the final frame.

Tom Roberts tjroberts@lucent.com

Relevant Pages

  • Re: Einsteins math and physical objects
    ... > disk B. Now stretch a wire from the top of disk A to the top of disk ... > wires will cross each other. ... > as measured in this frame. ... It might help to imagine replacing the disks by a long circular cylinder. ...
    (sci.physics.relativity)
  • Re: Einsteins math and physical objects
    ... >> disk B. Now stretch a wire from the top of disk A to the top of disk ... the two wires do not cross each other. ... >> as measured in this frame. ... >> events measured in the original reference frame, ...
    (sci.physics.relativity)
  • Re: Einsteins math and physical objects
    ... > disk B. Now stretch a wire from the top of disk A to the top of disk ... > wires will cross each other. ... > the rotation rates, the two disks remain in phase. ... > as measured in this frame. ...
    (sci.physics.relativity)
  • Re: Einsteins math and physical objects
    ... >> predict the final configuration of the wires in frame A by staying ... Let's say the wires ... disks are 180 degrees out of phase, and the wires cross. ... As viewed in the original reference frame, let the center of each disk ...
    (sci.physics.relativity)
  • Re: A rotating disk PARADOX??
    ... >> wire, generating a magnetic field. ... A metallic disk is in the field, ... >> We connect wires to the middle and edge of the disk, ... >> which must exert torque on the disk. ...
    (sci.physics.relativity)