  Aims. We aim to improve the understanding of the physical mechanisms behind
the slower than free-fall motion and the two-stage evolution (an initial phase
of acceleration followed by an almost constant velocity phase) detected in
coronal rain events.
  Methods. Using the Mancha3D code, we solve the 2D ideal MHD equations. We
represent the solar corona as an isothermal vertically stratified atmosphere
with a uniform vertical magnetic field and the plasma condensation as a density
enhancement described by a 2D Gaussian profile. We analyse the temporal
evolution of the descending plasma and study its dependence on parameters such
as density and magnetic field strength.
  Results. We confirm previous findings that the pressure gradient is the main
force that opposes the action of gravity and slows down the blob descent and
that larger densities require larger pressure gradients to reach the constant
speed phase. We find that the shape of a condensation with a horizontal
variation of density is distorted as it falls, due to the denser parts of the
blob falling faster than the lighter ones. This is explained by the fact that
the duration of the initial acceleration phase, and therefore the maximum
falling speed attained by the plasma, increases with the ratio of blob to
coronal density. We also find that the magnetic field plays a fundamental role
in the evolution of the descending condensations. A strong enough magnetic
field (greater than 10 G in our simulations) forces each plasma element to
follow the path given by a particular field line, which allows to describe the
evolution of each vertical slice of the blob in terms of 1D dynamics, without
influence of the adjacent slices. In addition, under the typical conditions of
the coronal rain events, the magnetic field prevents the development of the
Kelvin-Helmholtz instability.
