I cannot understand the mechanical systems in the picture. In the picture a) how can f is scattered equally to M, K1, K2, B1 and B2 ? Where do you know this? How can two systems be equivalent of each other? In the picture (b) if f is applied, how can the force on M is Ma, a is acceleration. < Mentor Note -- Improved contrast version of UPLOAD > View attachment 111153 Source: Automatic Control Engineering by Francis H.Raven Thank you.