Coefficient of thermal expansion

Solids mostly^[1] expand in response to heating and contract on cooling.^[2] This response to temperature change is expressed as its coefficient of thermal expansion.

The coefficient of thermal expansion is used:

• in linear thermal expansion
• in area thermal expansion
• in volumetric thermal expansion

These characteristics are closely related. The volumetric thermal expansion coefficient can be measured for all substances of condensed matter (liquids and solid state). The linear thermal expansion can only be measured in the solid state and is common in engineering applications.

1. ↑ Some substances have a negative expansion coefficient, and will expand when cooled (e.g. freezing water
2. ↑ The reason is that during heat transfer, the energy that is stored in the intermolecular bonds between atoms changes. When the stored energy increases, so does the length of the molecular bond.