  Using molecular dynamics (MD) we study the dependency of the contact
mechanics on the sliding speed when an elastic block (cylinder) with a ${\rm
cos} (q_0 x)$ surface height profile is sliding in adhesive contact on a rigid
flat substrate.The atoms on the block interact with the substrate atoms by
Lennard-Jones (LJ) potentials, and we consider both commensurate and(nearly)
incommensurate contacts. For the incommensurate system the friction force
fluctuates between positive and negative values, with an amplitude proportional
to the sliding speed, but with the average close to zero. For the commensurate
system the (time-averaged) friction force is much larger and nearly velocity
independent. For both type of systems the width of the contact region is
velocity independent even when, for the commensurate case, the frictional shear
stress increases from zero (before sliding) to $\approx 0.1 \ {\rm MPa}$ during
sliding. This frictional shear stress, and the elastic modulus used, are
typical for Polydimethylsiloxan (PDMS) rubber sliding on a glass surface, and
we conclude that the reduction in the contact area observed in some experiments
when increasing the tangential force must be due to effects not included in our
model study, such as viscoelasticity or elastic nonlinearity
