The analytical generalization of the classical dynamical friction
formula (derived under the assumption that all the field particles
have the same mass) to the case in which the masses of the field
particles are distributed with a mass spectrum is presented. It is
found that the dynamical friction deceleration can be significantly
stronger than in the equivalent classical case, with the largest
differences arising for test particle velocities comparable to the
mass-averaged velocity dispersion of the field particles. The present
results are relevant to our understanding of the dynamical evolution
of globular clusters, in particular in the modelization of mass
segregation and sedimentation of Blue Straggler stars and Neutron
stars, and for the study of binary black holes in galactic nuclei.