When heating metal objects, what is the physical change observed?

When heating metal objects, the physical change observed is expansion. Metals are made up of atoms that are arranged in a lattice structure. When heat is applied, the atoms gain kinetic energy and begin to vibrate more vigorously. This increase in vibrational energy causes the atoms to move apart from each other, leading to an overall increase in the volume of the metal—hence, it expands.

This property can be observed in many day-to-day scenarios, such as when metal rails on a train track expand during hot weather, which could lead to bends and warps if there isn’t enough space to accommodate that expansion. The concept of thermal expansion is crucial in various applications, including engineering and construction, to ensure structural integrity in response to temperature changes.

The other options involve different processes. Contraction refers to a decrease in size typically caused by cooling, while melting and freezing pertain to changes in state rather than mere dimensional changes. Melting is the transition from solid to liquid, and freezing is the transition from liquid to solid, both occurring at specific temperature thresholds (melting point and freezing point) rather than being a direct result of heating alone.