Which factor is NOT involved in heat transfer?

Heat transfer occurs primarily through three mechanisms: conduction, convection, and radiation, all of which are influenced by certain key factors. The temperature difference serves as the driving force for heat transfer, as heat flows from areas of higher temperature to areas of lower temperature. Thermal conductivity is a material property that indicates how well a substance conducts heat; materials with high thermal conductivity transfer heat more effectively than those with low conductivity. Surface area impacts the rate of heat transfer because a larger surface area allows for more heat to flow between the hot and cold regions.

Density of material, while relevant in some contexts (like determining buoyancy and the characteristics of materials), does not directly impact the mechanisms or rates of heat transfer in the same way the other factors do. It is not a primary factor influencing how heat is transferred between objects or within a system. Thus, understanding these different factors clarifies why density is not typically associated directly with the process of heat transfer.