  Despite the huge importance of friction in regulating movement in all natural
and technological processes, the mechanisms underlying dissipation at a sliding
contact are still a matter of debate. Attempts to explain the dependence of
measured frictional losses at nanoscale contacts on the electronic degrees of
freedom of the surrounding materials have so far been controversial. Here, it
is proposed that friction can be explained by considering damping of stick-slip
pulses in a sliding contact. Based on friction force microscopy studies of
La$_{(1-x)}$Sr$_x$MnO$_3$ films at the ferromagnetic-metallic to
paramagnetic-polaronic conductor phase transition, it is confirmed that the
sliding contact generates thermally-activated slip pulses in the nanoscale
contact, and argued that these are damped by direct coupling into phonon bath.
Electron-phonon coupling leads to the formation of Jahn-Teller polarons and a
clear increase in friction in the high temperature phase. There is no evidence
for direct electronic drag on the atomic force microscope tip nor any
indication of contributions from electrostatic forces. This intuitive scenario,
that friction is governed by the damping of surface vibrational excitations,
provides a basis for reconciling controversies in literature studies as well as
suggesting possible tactics for controlling friction.
