What does "thermal expansion" describe?

"Thermal expansion" describes the increase in volume of a substance as its temperature increases. When the temperature of a substance rises, the kinetic energy of its molecules increases, causing them to move more vigorously and take up more space, which leads to an increase in volume. This phenomenon is observed in solids, liquids, and gases, although the degree of expansion can vary depending on the material.

For instance, when metals are heated, they expand, which is why gaps are often left in bridges and railroad tracks to accommodate this expansion. Similarly, liquids in thermometers expand as they are warmed, allowing for accurate temperature readings. Understanding thermal expansion is essential in various fields, including engineering, construction, and thermodynamics, as it affects material behavior under temperature changes.