What is the main requirement for an effective heat exchange between two objects?

The main requirement for effective heat exchange between two objects is that they must have a significant difference in temperatures. When two objects are at different temperatures, thermal energy naturally flows from the hotter object, where molecules are moving more rapidly, to the cooler object, where molecules are moving more slowly. This movement of heat continues until thermal equilibrium is reached, meaning the temperatures become equal.

If both objects were at thermal equilibrium, there would be no net flow of heat between them. The mass or the materials of the objects can influence the rate and efficiency of heat transfer, but the driving force behind the transfer is primarily the temperature difference. Hence, for effective heat exchange, a significant temperature gradient is essential.