  Feedback from star formation is thought to play a key role in the formation
and evolution of galaxies, but its implementation in cosmological simulations
is currently hampered by a lack of numerical resolution. We present and test a
sub-grid recipe to model feedback from massive stars in cosmological smoothed
particle hydrodynamics simulations. The energy is distributed in kinetic form
among the gas particles surrounding recently formed stars. The impact of the
feedback is studied using a suite of high-resolution simulations of isolated
disc galaxies embedded in dark halos with total mass 10^{10} and 10^{12}
Msol/h. We focus in particular on the effect of pressure forces on wind
particles within the disc, which we turn off temporarily in some of our runs to
mimic a recipe that has been widely used in the literature. We find that this
popular recipe gives dramatically different results because (ram) pressure
forces on expanding superbubbles determine both the structure of the disc and
the development of large-scale outflows. Pressure forces exerted by expanding
superbubbles puff up the disc, giving the dwarf galaxy an irregular morphology
and creating a galactic fountain in the massive galaxy. Hydrodynamic drag
within the disc results in a strong increase of the effective mass loading of
the wind for the dwarf galaxy, but quenches much of the outflow in the case of
the high-mass galaxy.
