What physical property changes when a material is heated and expands?

When a material is heated, its molecules gain kinetic energy, leading to an increase in their movement. This increased movement causes the material to expand, resulting in a change in its volume. As the temperature rises, the spaces between the molecules become larger, allowing the overall size of the material to increase. This phenomenon is typically observed in solids, liquids, and gases, making volume a key physical property that changes with temperature.

Density, which is the mass per unit volume, is not directly affected by heating in a straightforward manner since heating can decrease density as volume increases. Temperature itself is a measure of the kinetic energy of the molecules but does not change when a material expands; it is the cause behind the expansion. Mass remains constant regardless of the heating process unless material is added or removed, which does not occur simply through heating. Therefore, volume is the correct answer, as it is the property that directly changes when a material expands due to heating.