| Thermal Expansion |
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To accurately calculate thermal expansion of a substance a more advanced Equation Of State must be used. This equation would be able to calculate thermal expansion among with many other State Function s. Most materials expand when heated and contract when cooled. The amount a material expands or contracts is estimated by the formula: : or : :where is the coefficient of thermal expansion in inverse kelvins, ''L'' is the length in metres, ''T'' is the temperature in kelvins, and is the strain due to thermal expansion. A number of materials have been discovered to contract on heating; we usually speak of Negative Thermal Expansion , rather than thermal contraction, in such cases. In Materials Engineering , the three primary types of materials have well defined rates of expansion. Polymer s expand as much as 10 times more than Metal s, which expand more than Ceramic s. Thermal expansion generally increases with bond energy. See PVT relation. In general, liquids expand more than solids, and gases expand more than liquids. This is due to the relative amount of energy contained in the molecules in each state. When things expand, they take up more space as they are moving around more vigorously, not because the molecules themselves are growing in size. Expansion has to be taken into account for many things, such as when constructing railways. If there are not gaps for the line to expand, the line may buckle. Similar ideas are applied in building bridges, making water pipes and concrete slabs in roads. This phenomenon can be beneficial as well, and is used in techniques like shrink-fitting. |
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