Comment on "On the Origin of Frictional Energy Dissipation"

In their interesting study (Ref. [1]) Hu et al have shown that for a simple "harmonium" solid model the slip-induced motion of surface atoms is close to critically damped. This result is in fact well known from studies of vibrational damping of atoms and molecules at surfaces. However, for real practical cases the situation may be much more complex and the conclusions of Hu et al invalid.