A steel railway track is 500 m long at 10 C. The coefficient of linear expansion of steel is 12 x 10^-6 per C. (a) How much longer is it on a hot day at 40 C? (b) What gap must engineers leave per kilometre of track? Solution: (a) delta_L = alpha L delta_T = (12 x 10^-6)(500)(40 - 10) = (12 x 10^-6)(500)(30) = 0.18 m = 18 cm. (b) Per kilometre the expansion is (12 x 10^-6)(1000)(30) = 0.36 m = 36 cm, so expansion gaps totalling at least this must be provided or the track will buckle.