ray@othervax.UUCP (Raymond D. Dunn) (10/28/85)
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