  We solve numerically the equations of motion for the collapse of a shell of
baryonic matter falling into the central regions of a cluster of galaxies,
taking into account of the presence of the substructure inducing dynamical
friction. The evolution of the expansion parameter a(t) of the perturbation is
calculated in spherical systems. The effect of dynamical friction is to reduce
the binding radius and the total mass accreted by the central regions. Using a
peak density profile given by Bardeen et al. (1986) we show how the binding
radius of the perturbation is modified by dinamical friction. We show how
dynamical friction modifies the collapse parameter of the perturbation slowing
down the collapse.
