Hello, From what I know, internal energy of a body = sum of kinetic energies of the particles of the body + potential energy between the particles (intermolecular forces), right? And there's this textbook question which made me question that for a while: Two objects are at the same temperature. Explain why they must have the same internal energy. And the book's answer is: If the objects are at the same temperature, there is no transfer of energy between them, so their internal energy must be the same. But is it true? I always thought the only indicator of temperature of a body is the average kinetic energy of its particles (there's nothing about potential energy). If that's true, and keeping in mind that Internal Energy=KE+PE, then the some two bodies may have the same KE (so the same temperature) but their PE may differ which results with their internal energies being different. What do you think? http://www.hyperphysics.phy-astr.gsu.edu [Broken] seem to confirm my point of view: "Temperature is not directly proportional to internal energy since temperature measures only the kinetic energy part of the internal energy, so two objects with the same temperature do not in general have the same internal energy"