I discuss the interaction and subsequent merging of a target barred galaxy with a spherical satellite.

If the companion has sufficiently high density it reaches the center of the target galaxy, having lost only a small fraction of its mass. There it forms (or contributes to) a bulge population and thus drives an evolution along the Hubble sequence (Sc to Sa). Such events can destroy bars. The high central concentration formed by the extra mass of the companion after the merging prohibits the growth of a new bar. Low density companions get shredded before reaching the center. Their material forms a thick disc.

The disc of the target galaxy gets thickened by an amount depending on the mass of the companion and the angle of its initial orbit with that of the target disc. If the orbit of the companion is initially at an angle with the plane of the disc then the disc tilts, but is not destroyed.

We discuss the effect of softening on the force between particles representing a given mass distribution, compared to the true values of the forces in this distribution. As already shown by Merritt (1996), if the softening is too small the estimates of the forces will be too noisy, while if the softening is too large we get a systematic misrepresentation. In between there is an optimum softening, for which the forces in the configuration approach best the true forces. The value of this optimum softening depends both on the mass distribution and on the number of particles used to represent it. Thus for higher number of particles the optimum softening is smaller. More concentrated mass distributions necessitate smaller softening, but the softened forces are never as good an approximation of the true forces as for not centrally concentrated configurations. Comparing homogeneous Ferrers ellipsoids of different shapes we show that the axial ratios do not influence the value of the optimum softening. Finally we compare two different types of softening and find that the spline softening (Hernquist and Katz 1989) gives somewhat better representation of the forces than the standard Plummer softening.