Heat will always flow between two bodies if they are ___________________.

Heat transfer occurs between two bodies when there is a temperature differential between them. This principle is rooted in the laws of thermodynamics, specifically the second law, which states that heat energy will spontaneously flow from a hotter body to a cooler body until thermal equilibrium is achieved. The greater the temperature difference, the faster the rate of heat transfer will be.

In scenarios where the two bodies are at the same temperature, no heat flow occurs because the driving force for the transfer—temperature gradient—is absent. Other factors, like proximity and the materials’ properties, can influence the rate and efficiency of heat transfer, but the fundamental requirement for heat to flow is that the bodies must be at different temperatures. Thus, the condition that heat will always flow between two bodies if they are at different temperatures correctly captures the essential requirement for heat transfer.