The work deals with revealing the quantum nature of the heat absorption phenomenon by a thermal system, describing the phenomenon with a proper energetic interpretation. At first, the existent description of the heat absorption phenomenon by a system has been described. Then the mechanicalthermal analogy was introduced, using it for a better explanation of the determined thermal notions. A set of characteristics of the heat absorption phenomenon was developed by taking advantage of this analogy. The starting point from the source thermal characteristics, being differential dependence of thermal force on temperature, has been regarded. That made it possible to achieve a detail solution, being the reason model of the described natural system, which is the model having a physical sense.