Thermal expansion and contraction definition
Thermal expansion and contraction refers to the property that an object expands when heated and shrinks when it is cold. Since the movement of particles (atoms) in an object changes with temperature, when the temperature rises, the vibration amplitude of the particles increases, causing the object to expand; but when the temperature drops, the vibration amplitude of the particles decreases, causing the object to shrink.
Thermal expansion and contraction are the characteristics of general objects, but water (below 4 ° C), bismuth, antimony, gallium and bronze, etc., shrink when heated under certain temperature ranges, and expand when exposed to cold, just like general object characteristics. in contrast. Therefore, when the water freezes, the ice first appears on the surface of the water. Because the rails have the characteristics of thermal expansion and contraction, the rails must be connected with a certain gap (to prevent the rails from being pushed and deformed by the expansion of the heat when the temperature rises), and then the rails are crossed by the fishtail and the screw. Linked up.