  We present a microscopic calculation of core states contribution to vortex
friction in a type II superconductor at zero temperature. In weak impurity
limit, a perturbative calculation leads to a vortex friction proportional to
the normal state resistivity. With the aid of random matrix theory, vortex
friction due to core states is determined only by the Fermi energy and the
energy gap in dirty limit, similar to the phenomenological results of Bardeen
and Stephen, but disagrees with the results obtained under the relaxation time
approximation. In addition, an explicit demonstration is given on the the
insensitivity of transverse force to impurities.
