In the summer, the rails of the railway become longer than in the winter, so gaps are left between the rails when laying. During the construction of the bridge, one horse of the farm is placed on the rollers. If this is not done, then during expansion in summer and contraction in winter, the truss will loosen the abutments on which the bridge rests.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.