Thermal expansion

Thermal expansion is the tendency of matter to change in shape, area, and volume in response to a change in temperature. In the general case of a gas, liquid, or solid, the volumetric coefficient of thermal expansion is given by



\alpha_V = \frac{1}{V}\,\left(\frac{\partial V}{\partial T}\right)_p $$

The subscript p indicates that the pressure is held constant during the expansion, and the subscript V stresses that it is the volumetric (not linear) expansion that enters this general definition. In the case of a gas, the fact that the pressure is held constant is important, because the volume of a gas will vary appreciably with pressure as well as temperature. For a gas of low density this can be seen from the ideal gas law.