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[Phys-L] Re: "moving clock runs slower" (yes)



How to define/choose length and time standards for use in my measurements?
If I want to study events occurring on a moving train, when I am on a
stationary platform, do I use the proper lengths/times of on board rods and
clocks, or do I use the proper length/times of my own rods and clocks? If I
want to express the physics connected with the motion of on board objects
*as viewed from my platform frame*, I will have to use use my own rods and
clocks. These instruments will generate the r and t variables in the
physics as measured from my frame and will properly describe, eg, velocity
dependent forces (qVxB) on particles at rest on the train. My measurements
will be connected by physics equations (eg Maxwell's) using the r, t
readings of my clocks. These are my *real* variables. The proper times and
lengths of the on board instruments are not appropriate for expressing my
physics - they are appropriate for expressing the on board physics.

You may call the proper period of a clock "real", but its only practical use
as a measuring instrument is for an observer at rest in its proper frame.
To moving observers this object is of little practical use as a clock - it
is only another moving object to be studied.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
http://www.winbeam.com/~trebor/
trebor@winbeam.com
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