Equivalent Circuit Analysis

Kirchoff's Loop Rule:

$\parbox{0.8\textwidth}{The sum of voltages (\lq\lq forces'') around any series loop is zero}$

So

$$f_m(t) + f_{R}(t) + f_{R}(t) = 0$$

Laplace transform:

$$F_m(s) + 2F_{R}(s) = 0,$$