  In relativistic dynamics, force and acceleration are no longer parallel. In
this article, we revisit the relativistic motion of a particle under the action
of a constant force, $\boldsymbol{f}$. \ For a two-dimensional motion, the
final velocity in each axis is $(f_{i}/f)c,$ independently of the initial
velocities, yielding an asymptotic velocity always parallel to the force. The
particular case in which the force is applied in a single axis is analyzed in
detail, with the behavior of velocity and acceleration being exhibited for
several configurations. Some previous results of the literature concerning
velocity and acceleration behavior are improved and better explored.
Differently from which was previously claimed, it is shown that a negative
acceleration component can exist in the direction of the biggest force
component and that acceleration does not decrease monotonically to zero.
