thermal expansion

The increase in size observed in most materials when heated. The expansion results from the increased thermal motion of atoms. The change in the length of a solid rod equals the product of its starting length, the change in temperature, and ?, the coefficient of expansion. For copper, ? = 1·7 × 10^?5/°C.

In physics, thermal expansion is the tendency of matter to increase in volume or pressure when heated. For liquids and solids the amount of expansion will normally vary depending on the material's coefficient of thermal expansion. 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 functions.

For solid materials with a significant length, like rods or cables, an estimate of the amount of thermal expansion can be described by the ratio of strain:

is the initial length before the change of temperature and the final length recorded after the change of temperature.

For most solids, thermal expansion relates directly with temperature:

Thus, the change in either the strain or temperature can be estimated by:

when

where

is the coefficient of thermal expansion in inverse kelvins. 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.

In general, liquids expand more than solids, and gases expand more than liquids.

Heat-induced expansion has to be taken into account for many structures such railways and bridges, without the use of expansion joints the structures may buckle.