A semiclassical model, based on a solution of the Vlasov equation for finite systems with moving-surface, is employed to study the isoscalar dipole modes in nuclei. It is shown that, by taking into account the surface degree of freedom, it is possible to obtain an exact treatment of the centre of mass motion. It is also shown that a method often used to subtract the spurious strength in RPA calculations does not always give the correct result. An alternative analytical formula for the intrinsic strength function is derived in a simple confined-Fermi-gas model. In this model the intrinsic isoscalar dipole strength displays essentially a two-resonance structure, hence there are two relevant modes. The interaction between nucleons couples these two modes and changes the compressibility of the system, that we determine by fitting the monopole resonance energy. The evolution of the dipole strength profile is studied as a function of the compressibility of the nuclear fluid. Comparison with recent dipole data shows some qualitative agreement for a soft equation of state, but our model fails to reconcile the monopole and dipole data.
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