  We obtain the explicit expression of the friction on a moving quantized
vortex, following the formulation of Thouless, Ao and Niu. It is shown that the
friction on a moving vortex is sensitive to details but does not change the
transverse force. We provide a general thermodynamic interpretation for the
mutual independence of the transverse force and the friction. The friction is
evaluated for the case of quasiparticle contributions in a clean fermionic
superfluid, showing a new feature of logarithmic divergence.
