  Two different solutions of the linearized Vlasov equation for finite systems,
characterized by fixed and moving-surface boundary conditions, are discussed in
a unified perspective. A condition determining the eigenfrequencies of
collective nuclear oscillations, that can be obtained from the moving-surface
solution, is studied for isoscalar vibrations of lowest multipolarity. Analytic
expressions for the friction and mass parameters related to the low-enegy
surface excitations are derived and their value is compared to values given by
other models. Both similarities and differences are found with respect to the
other approaches, however the close agreement obtained in many cases with one
of the other models suggests that, in spite of some important differences, the
two approaches are substantially equivalent. The formalism based on the Vlasov
equation is more transparent since it leads to analytical expressions that can
be a basis for further improvement of the model.
