The direct transfer of heat from one substance to another substance that it is touching.

The direct transfer of heat from one substance to another substance that it is touching.

• A. Convection
• B. Conduction
• C. Radiation
• D. Absorption

Answer: (B)

Direct transfer of heat through contact between substances is conduction. It happens when a hotter object touches a cooler one and energy moves from the particles in the hotter object to the cooler one through collisions and interactions between molecules and, in metals, free electrons that shuttle energy quickly. This requires direct contact, so heat moves at the interface rather than by moving the whole fluid or emitting waves. Convection, by contrast, involves the movement of fluids carrying heat with them, like warm air rising or water circulating. Radiation transfers heat through electromagnetic waves and can occur without any touch at all. Absorption is more about a material taking in energy from its surroundings rather than describing a mode of heat transfer itself.

Direct transfer of heat through contact between substances is conduction. It happens when a hotter object touches a cooler one and energy moves from the particles in the hotter object to the cooler one through collisions and interactions between molecules and, in metals, free electrons that shuttle energy quickly. This requires direct contact, so heat moves at the interface rather than by moving the whole fluid or emitting waves.

Convection, by contrast, involves the movement of fluids carrying heat with them, like warm air rising or water circulating. Radiation transfers heat through electromagnetic waves and can occur without any touch at all. Absorption is more about a material taking in energy from its surroundings rather than describing a mode of heat transfer itself.