Final answer:
Thermal expansion is the increase in size of a material as its temperature increases, which happens because the increased kinetic energy of the particles causes them to move apart.
Step-by-step explanation:
The phenomenon you're referring to is known as thermal expansion. Most materials expand upon heating because the increase in temperature causes their molecules to move more and thus occupy more space. When a solid heats up, it retains its proportions but increases in size; this expansion occurs in all dimensions, meaning in terms of length, area, and volume. For instance, when a metal plate with a hole is heated, the material around the hole expands the same way it would if the material filling the hole were still there, which means the hole expands as well.
Understanding thermal expansion is important for many practical applications, such as designing buildings, bridges, and railways, to accommodate temperature changes without causing damage. The increase in the kinetic energy of particles upon heating causes them to vibrate more vigorously and to push each other apart, leading to an expansion of the material.
This concept also underpins the operation of thermometers, which measure temperature changes based on the expansion and contraction of liquids like mercury or alcohol.