What distinguishes conduction from convection as a form of heat transfer?

Conduction is characterized by heat transfer through direct contact between materials. When two objects at different temperatures touch, thermal energy moves from the hotter object to the cooler one, effectively transferring energy through the interactions of their particles. This process does not require the movement of a fluid; instead, it relies on the collisions of adjacent particles.

In contrast, convection involves the transfer of heat through the movement of a fluid (which can be a liquid or a gas). In convection, warmer parts of the fluid move to cooler areas, carrying heat with them, which does not occur in conduction.

Additionally, conduction cannot take place across a vacuum since, in this case, there is no medium for the heat to be transferred through direct contact. The material composition might affect the efficiency of conduction due to differences in thermal conductivity, but conduction itself does not exist independently of these properties. Therefore, the definition that heat transfer in conduction occurs through physical contact between materials identifies its unique nature compared to convection.