According to the second law of thermodynamics, heat will flow unaided from which type of body?

The second law of thermodynamics states that heat naturally flows from a higher temperature body to a lower temperature body. This principle is fundamental to our understanding of thermal processes and energy transfer. Heat transfer occurs spontaneously in this direction, which is a manifestation of natural processes tending to move towards a state of increased entropy.

When a hot body (higher temperature) and a cold body (lower temperature) are placed in contact, energy in the form of heat will flow from the hot body, resulting in the cooling of the higher temperature body and the warming of the lower temperature body until thermal equilibrium is reached. This concept is crucial in various applications, including refrigeration, where the design relies on removing heat from cooler areas and expelling it to warmer surroundings.

In contrast, heat does not flow from lower temperature bodies to higher temperature bodies without external work being applied. This is why refrigeration systems require energy input to move heat against this natural direction of flow. A situation involving two bodies at equal temperature or in thermal equilibrium would not allow for heat transfer at all, as there is no temperature gradient to drive the flow of heat.