  For the evolution of density fluctuation in nonlinear cosmological dynamics,
adhesion approximation (AA) is proposed as a phenomenological model, which is
especially useful for describing nonlinear evolution. However, the origin of
the artificial viscosity in AA is not clarified. Recently, Buchert and
Dom\'{\i}nguez report if the velocity dispersion of the dust fluid is regarded
as isotropic, it works on a principle similar to viscosity or effective
pressure, and they consider isotropic velocity dispersion as the origin of the
artificial viscosity in AA. They name their model the Euler-Jeans-Newton (EJN)
model. In this paper, we focus on the velocity distribution in AA and the EJN
model and examine the time evolution in both models. We find the behavior of AA
differs from that of the EJN model, i.e., although the peculiar velocity in the
EJN model oscillates, that in AA is monotonically decelerated due to viscosity
without oscillation. Therefore it is hard to regard viscosity in AA as
effective pressure in the EJN model.
