# Thermal Expansion

on . Posted in Thermodynamics

Thermal expansion is a physical occurrence in which the dimensions (size, volume, length, etc.) of a substance change in response to changes in temperature.  When an object is heated, its particles gain kinetic energy and move more vigorously, leading to an increase in the average separation between the particles.  This increase in separation results in the expansion of the material.  The stored energy in the molecular bonds between atoms changes when the heat transfer occurs.  The length of the molecular bond increases as the stored energy increases.

Thermal expansion is a result of the fact that most materials expand when they are heated and contract when they are cooled.  This behavior is due to the fundamental nature of particles in a substance, as they gain energy, they vibrate more and require more space, causing the material to expand.  Different materials have different coefficients of thermal expansion, which quantify how much a material's dimensions change for a given change in temperature.

Thermal expansion has various practical implications and applications, ranging from the design of bridges and buildings to the accurate construction of measuring instruments.  Engineers and designers must take thermal expansion into account to prevent structural issues or measurement inaccuracies that might arise from temperature changes.  Additionally, thermal expansion is crucial in fields such as material science, where understanding how different materials respond to temperature changes is essential for creating durable and functional products.

### Thermal Expansion Types

• Area thermal expansion  -  Area measures length times width and is two dimensional so it is squared.  Expands twice as much as lengths do.
• Linear thermal expansion  -  Linear measures distance or length and is one dimensional.  Can only be measured in the solid state.  The expansion is proportional to temperature change.
• Volumetric thermal expansion  -  Volume measures length times width times height so it is three dimensional so it is cubed.  Can be measured for all substances (liquid or solid) of condensed matter.  Expands three times as much as lengths do.

Some substances such as water can increase or decrease depending on the temperature.