A linear relationship has been found between the drop energies of impact sensitivity detected by sound and the drop energies of "the first reaction" for 28 polynitro compounds. In the sense of this relationship, the compounds studied fall into three classes. The reason of the said diversification lies in the decomposition reaction rate at the temperature of the beginning of their thermolysis. It is stated that some relationship exists between vibrational excitation by impact, on the one hand, and thermal activation of the molecules of energetic materials, on the other one.