  We investigate the dynamics of a dimer bouncing on a vertically oscillated
plate. The dimer, composed of two spheres rigidly connected by a light rod,
exhibits several modes depending on initial and driving conditions. The first
excited mode has a novel horizontal drift in which one end of the dimer stays
on the plate during most of the cycle, while the other end bounces in phase
with the plate. The speed and direction of the drift depend on the aspect ratio
of the dimer. We employ event-driven simulations based on a detailed treatment
of frictional interactions between the dimer and the plate in order to
elucidate the nature of the transport mechanism in the drift mode.
