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From: ray@othervax.UUCP (Raymond D. Dunn)
Newsgroups: net.puzzle,net.math
Subject: Expansion of metals
Message-ID: <714@othervax.UUCP>
Date: Mon, 28-Oct-85 12:14:10 EST
Article-I.D.: othervax.714
Posted: Mon Oct 28 12:14:10 1985
Date-Received: Thu, 31-Oct-85 22:51:47 EST
References: <7458@watdaisy.UUCP> <636@hou2b.UUCP>
Reply-To: ray@othervax.UUCP (Raymond D. Dunn)
Organization: Philips Information Systems - St. Laurent  P.Q., Canada
Lines: 18
Xref: linus net.puzzle:1015 net.math:2076
Summary: 

In article <636@hou2b.UUCP> halle@hou2b.UUCP (J.HALLE) writes:
[ re expansion of metal with a hole in it ]
>This looks like a job for a first semester high school physics student.
>As you heat the metal, it expands in all dimensions.  It stays exactly
>congruent (assuming uniform heating).  Thus the hole expands, a spherical
>bubble inside expands, a square hole stays square, etc.

This is not exactly true.  External forces will, obviously, affect the way
expansion takes place, but what is more interesting, is that internal forces
caused by the expansion, force that expansion to take place non-uniformly.
This was not recognised for years, so that railway lines were always made up
from short sections separated by expansion joints.  Modern welded track
however contains no expansion joints in many miles of track.  In this case,
longitudinal expansion *only* takes place at the ends of the welded section.
As I understand it, this is *NOT* due to the external forces of the track
ties etc.

Ray Dunn.   ...philabs!micomvax!othervax!ray