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[Phys-L] Back to "moving clocks" [was: Re: student mathematical capability]



At 08:18 -0500 9/15/05, Rick Tarara wrote:

To that end, Special Relativity is introduced in
the form of Einstein's Postulates and the consequences of those postulates
as summarized in 'moving clocks run slow', 'moving masses increase', and
'moving lengths contract'.

I continue to be bothered by phrasings such as the above during this
discussion. Not because I believe that the authors don't understand
that it is not completely accurate to say things this way, but
because it seems to indicate a willingness to let students think
about it in this way. If students come away from an introduction to
relativity thinking that there is a difference between "fixed" and
"moving," or that those two words have some absolute meaning, then
they have missed the whole point of relativity. Neither motion nor
lack of motion has any meaning whatever unless it can be expressed in
terms of "relative to some particular observer," and that is so
important to the students' understanding of relativity that we need
to incorporate the appropriate phrasing into our everyday language
just so we never let the students get very far from that essential
idea. It is far too easy for a student to translate "moving clocks
run slow," when looking at it from the other person's perspective,
into "well, I am now moving, so the other person's clock must be
running faster since it is 'at rest.'" Until students are thoroughly
imbued with the idea that *all* motion is relative, they will not
understand the symmetry inherent in Einstein's relativity, and the
ensuing requirement that absolute simultaneity must be abandoned.
This is one of the most important results of relativity and one of
the most difficult for students to understand. As long as they
haven't completely internalized the idea that all motion is relative,
they will never understand the issues around simultaneity.

Hugh
--

Hugh Haskell
<mailto:haskell@ncssm.edu>
<mailto:hhaskell@mindspring.com>

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