Thermal expansion is the tendency of matter to increase in size-length, area, or volume-as its temperature rises. This occurs because when a substance is heated, its molecules gain kinetic energy, vibrate more vigorously, and tend to move farther apart, causing the material to expand
. There are three main types of thermal expansion based on the dimension affected:
- Linear expansion : increase in length
- Superficial expansion : increase in area
- Volume expansion : increase in volume
The degree of expansion is characterized by the material's coefficient of thermal expansion, which quantifies how much the material expands per degree of temperature increase
. Thermal expansion is generally uniform in isotropic materials but can vary in different crystallographic directions in anisotropic materials. Some materials, like water near 4°C, exhibit negative thermal expansion, meaning they contract when heated within certain temperature ranges
. In summary, thermal expansion describes how materials physically grow larger when heated due to increased molecular motion and spacing
