What does density measure?

Density measures the relationship between the mass of a material and its volume. Specifically, it quantifies how much mass is contained in a given volume of that material. Density is calculated by dividing the mass of a substance by its volume, usually expressed in units like grams per cubic centimeter (g/cm³) or kilograms per cubic meter (kg/m³). Therefore, in terms of the provided options, associating density with weight reflects a certain understanding; however, it's important to recognize that weight is influenced by gravitational pull on the mass, while density provides a more intrinsic property of the material itself.

When considering this context, the other choices do not accurately define what density measures. Volume itself is a separate measurement and does not account for the mass. Thermal resistance pertains to a material's ability to resist heat flow and bears no relevance to density. Elasticity relates to a material's ability to return to its original shape after deformation, which is also distinct from the concept of density. Each of these properties serves different functions in material science, highlighting the unique nature of density as a critical measure of how closely packed the particles in a substance are.