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J. Perelman
"Entertaining physics". Book 1.
Chapter 6. Thermal phenomena


To the question: “What is the length of Oktyabrskaya railway?” someone replied:

- Six hundred and forty kilometers on average; in summer, three hundred yards longer than in winter.

The surprising answer is not as absurd as it may seem. If the length of the railway to be called the length of the continuous track, he really should be in summer is longer than winter. Let us not forget that from heating the rails are extended on each degree Celsius for more than one 100000-th of its length. In hot summer days the temperature of the rail can be up to 30 - 40° and above; sometimes the rail is heated by the sun so much that it burns your hand. In winter frosts rails are cooled to 25° and below. If you dwell on the difference of 55° between summer and winter temperature, then multiplying the total path length of 640 km 0.00001 and 55, will get about 1/3 km it turns Out that in fact a railway line between Moscow and Leningrad in the summer on the third kilometer, i.e., about three hundred yards longer than in winter.

Changes here, of course, not the length of the road, and only the sum of the lengths of all the rails. It's not the same, because rails does not abut each other closely: their joints left the small gaps of stock for free elongation of the rails when heated [this Gap, if the length of the rails 8 m, should be at 0° size 6 mm To fully close this gap needs to increase the temperature of the rail to 65 °C. When laying tram rails cannot, in technical terms, to leave gaps. Ego usually does not cause curvature of the rails, so as a result of their immersion into the soil temperature fluctuations are not so great, and the way of fastening the rails to prevent lateral distort. However, in a very strong heat tram rails still bent, as shown in the attached figure, filled with pictures.]. Our calculation shows that the sum of the lengths of all of the rails increases the total length of these gaps; the total elongation in the hot summer days can reach up to 300 m compared with its value in the bitter cold. So, the iron part of the October road really summer at 300 m longer than in the winter.

Bending tram rails due to intense heat.

The same happens sometimes with the rails of the railway track. In fact, on the slopes of rolling stock train at movement carries the rails for a (sometimes even with sleepers), eventually to such sections of the route clearances often disappear, and rails are bonded to each other with the ends flush.

Entertaining physics J. Perelman


System Orphus


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