"http://en.wikipedia.org/area_thermal_expansion"^^ . "When the temperature of a substance changes, the energy that is stored in the intermolecular bonds between atoms changes. When the stored energy increases, so does the length of the molecular bonds. As a result, solids typically expand in response to heating and contract on cooling; this dimensional response to temperature change is expressed by its coefficient of thermal expansion." . . . . . "Area Thermal Expansion"@en .