What does 'thermal expansion' refer to in materials?

'Thermal expansion' refers to the phenomenon where materials increase in size or volume as temperature rises. This physical property is significant in engineering and construction because materials expand when heated and contract when cooled. This process occurs because the kinetic energy of the molecules within a substance increases with temperature, leading to greater movement and spacing between those molecules, which results in a larger overall size of the material.

Understanding thermal expansion is crucial when designing structures and components that will undergo temperature changes, as it can affect tolerances and fit between parts. While the decrease in size due to cold and changes in color or density are related to thermal effects, they do not define the specific behavior of materials expanding as they heat up. Therefore, the concept of thermal expansion is clearly best represented by the increase in size due to temperature rise.