  In this paper we revisit the concept of chaotic velocity within the context
of relativistic kinetic theory. Its importance as the key ingredient which
allows to clearly distinguish convective and dissipative effects is discussed
to some detail. Also, by addressing the case of the two component mixture, the
relevance of the barycentric comoving frame is established and thus the
convenience for the introduction of peculiar velocities for each species. The
fact that the decomposition of molecular velocity in systematic and peculiar
components does not alter the covariance of the theory is emphasized. Moreover,
we show that within an equivalent decomposition into space-like and time-like
tensors, based on a generalization of the relative velocity concept, the
Lorentz factor for the chaotic velocity can be expressed explicitly as an
invariant quantity. This idea, based on Ellis' theorem, allows to foresee a
natural generalization to the general relativistic case.
