  We present an experimental investigation of the non stationary frictional
properties of multicontact interfaces between rough elastomers and rough hard
glass at low velocities (<= 200 mu m s^{-1}). These systems, for which the
deformation contribution to friction is negligible, are shown to exhibit a
phenomenology which is similar to what is observed for non elastomeric
materials in the same multi-contact configuration, and which are quantitatively
described by the state- and rate-dependent friction laws. This permits to
identify clearly the two contributions to adhesive friction which are mixed in
steady sliding: the interfacial shear stress which appears as thermally
activated formation and breaking of molecular bonds, and the real area of
contact which evolves through viscoelastic creep of the load bearing
asperities.
