What form of heat transfer is employed by hot packs?

Hot packs primarily employ conduction as their method of heat transfer. Conduction involves the direct transfer of thermal energy through physical contact between materials. When a hot pack, which is usually filled with a substance that retains heat, is applied to the skin, the heat is transferred from the hot pack directly to the skin's surface.

This contact allows the warmer particles in the hot pack to transfer thermal energy to the cooler particles in the skin, effectively increasing the temperature of the tissues beneath. This process helps with pain relief and increases blood flow to the affected area, facilitating healing.

In contrast, convection involves the transfer of heat through the movement of fluids or gases, which is not applicable to the stationary nature of hot packs. Conversion would refer to the transformation of energy from one form to another, such as mechanical energy into heat, but hot packs do not work through this mechanism. Finally, evaporation involves heat transfer through the process of changing a liquid into a vapor, primarily observed during processes such as sweating and is not relevant to hot packs either. Therefore, conduction is the correct and most descriptive form of heat transfer for hot packs.