Which statement best defines conduction?

• A. Gain or loss of heat through direct contact between two materials at different temperatures
• B. Transfer of heat by movement of fluids
• C. Transfer of heat through vacuum
• D. Heat transfer by insulation

Answer: (A)

Conduction is heat transfer that occurs when two objects touch and have different temperatures, so energy moves from the hotter material to the cooler one through molecular interactions and, in metals, through free-moving electrons. This direct contact enables energy to be passed along without any bulk movement of the substance. In contrast, heat transfer by the movement of fluids describes convection, heat transfer through vacuum describes radiation, and insulation refers to reducing heat transfer rather than describing a transfer mode itself.