Physics@Brock

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Thermal expansion of "long strips of metal"

Rails are essentially long strips of metal, subject to daily and seasonal heating/cooling and thus to tremendous thermal expansion/contraction. Properly laid rails must accommodate for that, traditionally by leaving small gaps between sections of the rail track (which are responsible for the familiar clickety-clack of the train's wheels). If not enough of a gap is left, the rails will expand to fill the gap and then will begin to buckle, with disastrous consequences!

However, modern rail technologies require smoother, straighter rails suitable for much faster travel, and a popular solution is the so-called continuous welding technology, where the rail is made as one continuous strip of metal right at the rail-laying site. Of course, thermal expansion must still be accommodated; one possibility is illustrated on the right.