We present a series of simulations on systems of beads enclosed in two-dimensional (2D) boxes, and compare the results of molecular dynamics (MD) and event-driven algorithms. The beads collide inelastically and are submitted to vibrations. We vary over a wide range the parameters: the amplitude and the frequency of the vibrations, the number of particles, and the inelasticity of the collisions. While the height of the center of mass of the system scales with respect to the restitution coefficient , the number of beads N and the typical velocity of the bottom plate, the functional dependence differs from the findings in 1D systems. We find that the MD results depend strongly on the time tc during which the particles are in contact.