Abstract.
The discovery of dynamical friction was Chandrasekhar's best known
contribution
to the theory of stellar dynamics, but his work ranged from the few-body
problem to the limit of large N (in effect, galaxies). Much of this work
was summarised
in the text "Principles of Stellar Dynamics" (Chandrasekhar 1942, 1960),
which ranges
from a precise calculation of the time of relaxation, through a long
analysis of galaxy
models, to the behaviour of star clusters in tidal fields. The later
edition also includes
the work on dynamical friction and related issues. In this review we
focus on progress
in the collisional aspects of these problems, i.e. those where few-body
interactions
play a dominant role, and so we omit further discussion of galaxy
dynamics. But
we try to link Chandrasekhar.s fundamental discoveries in collisional
problems with
the progress that has been made in the 50 years since the publication of
the enlarged
edition.
Keywords : binaries: general - galaxies: kinematics and dynamics
- globular clusters: general - open clusters and associations: general