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What causes heat to move from a hotter object to a colder object?

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heating In a thermoelectric generating system a heat source—usually fueled by coal, oil, or gas—is used within a boiler to convert water to high-pressure steam. The steam expands and turns the blades of a turbine, which turns the armature of a generator, producing electric power. A condenser converts any remaining steam to water, and a pump returns the water to the boiler.

Heat moves from a hotter object to a colder object due to the principles of thermodynamics, specifically the second law of thermodynamics. This spontaneous flow occurs because it results in a net increase in the entropy of the system.1

In physical terms, this transfer is driven by a temperature gradient—a difference in temperature between two areas. In a solid, this manifests as the movement of energy from an area of high particle agitation to an area of lower agitation through molecular contact. In fluids, this process is further facilitated by the movement of the atoms or molecules themselves.2

This direction of heat flow is fundamental to nature; a process where heat spontaneously moves from a colder body to a hotter one is impossible, as it would violate the second law of thermodynamics. This transfer continues until the objects reach thermal equilibrium, at which point their temperatures are equal and the net flow of heat ceases.312