  In these remarks, we clarify the problematic aspects of gravitational
interaction in a weak-field limit of Kaluza-Klein models. We explain why some
models meet the classical gravitational tests, while others do not. We show
that variation of the total volume of the internal spaces generates the fifth
force. This is the main reason of the problem. It happens for all considered
models (linear with respect to the scalar curvature and nonlinear $f(R)$, with
toroidal and spherical compactifications). We explicitly single out the
contribution of the fifth force to nonrelativistic gravitational potentials. In
the case of models with toroidal compactification, we demonstrate how tension
(with and without effects of nonlinearity) of the gravitating source can fix
the total volume of the internal space, resulting in the vanishing fifth force
and consequently in agreement with the observations. It takes place for latent
solitons, black strings and black branes. We also demonstrate a particular
example where non-vanishing variations of the internal space volume do not
contradict the gravitational experiments. In the case of spherical
compactification, the fifth force is replaced by the Yukawa interaction for
models with the stabilized internal space. For large Yukawa masses, the effect
of this interaction is negligibly small, and considered models satisfy the
gravitational tests at the same level of accuracy as general relativity.
