In this work we suggest a sufficiently simple for understanding without knowing the details of the quantum gravity and quite correct deduction of the Unruh temperature (but not whole Unruh radiation process!). Firstly, we shall directly apply usual consequences of the Unruh radiation and temperature at surface gravity of a large spherical physical system and we shall show that corresponding thermal energy can be formally quite correctly presented as the potential energy absolute value of the classical gravitational interaction between this large and a small quantum system with well defined characteristics. Secondly, we shall inversely postulate small quantum system with necessary well defined characteristics and then, after supposition on the equivalence between potential energy absolute value of its gravitational interaction with large system with thermal energy, we shall obtain exact value of the Unruh temperature. Moreover, by very simple and correct application of suggested formalism (with small quantum system) at thermodynamic laws, we shall successfully study other thermodynamic characteristics, especially entropy, characteristic for Unruh and Hawking radiation