Which is the best example of heat flow by conduction?

The correct answer showcases a fundamental principle of heat transfer, where conduction involves the direct transfer of heat through a material without any movement of the material as a whole. In the case of heat flowing from the inside to the outside of a radiator, the heat is conducted from the hot metal of the radiator to the cooler air outside through direct contact.

This process illustrates conduction effectively: the molecules in the radiator vibrate and transmit their energy to the adjacent molecules in the air without any movement of the air itself at the point of contact.

The other examples represent different methods of heat transfer. The rising of heat from a hot stove to the ceiling is an example of convection, where warmer air moves upward, taking heat with it. Heat absorption by the ground from the sun also does not involve direct contact transfer between solid bodies—this is more related to radiation, where heat is transferred through electromagnetic waves. Lastly, heated air circulating through a room via fans also exemplifies convection, as it involves the movement of air to distribute heat rather than direct molecular interactions indicative of conduction.