  A mechanical equivalent system is introduced to mimic the behavior of
multilayer structures with diffusive spin transport. The analogy allows one to
use existing mechanical intuition to predict the influence of various
parameters on spin torques and spin-dependent magnetoresistance. In particular,
it provides an understanding of the sign-changing behavior of spin torque in
asymmetric F/N/F spin valves. It further helps to uncover the physical reason
behind the singular behavior of spin magnetoresistance in devices with
ultra-thin N-layers.
