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Question
If you have a very long and rigid pole
and have an observer on each end, if one of them pushes the pole how soon will the
other one feel it? Can this response time be shorter the time it would take light to
travel the length of the pole?
Asked by: Dmitry Meerson
Answer
The rigidity of any pole depends on the material from which
it is made, but there is no material that is infinitely
rigid. A push on one end of a pole only appears to be
transmitted instantaneously to the other end because of
its relatively short length compared to the speed of
transmission. Each atom must influence its neighbor along
the pole via electromagnetic force, which in turn is carried
by (guess what?) 'light' photons!
So yes, the speed at which a push on one end of the
rod travels to the other end is subject to the same
universal speed limit, the speed of light, as any other
physical phenomenon. Therefore, you could NOT use a
'rigid' pole to transmit signals faster than light to
another observer.
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor
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