  For a Chaplygin sleigh moving in the presence of weak friction, we present
and investigate two mechanisms of arising acceleration due to oscillations of
an internal mass. In certain parameter regions, the mechanism induced by small
oscillations determines acceleration which is on average one-directional. The
role of friction is that the velocity reached in the process of the
acceleration is stabilized at a certain level. The second mechanism is due to
the effect of parametric excitation of oscillations, when the internal moving
particle is comparable in mass with the main platform, and, as occurs, a
necessary condition for the acceleration is presence of friction. The
parametric instability and the resulting acceleration of the sleigh turn out to
be bounded if the line of oscillations of the moving mass is displaced from the
center of mass. The steady-state regime of motion is in many cases associated
with a chaotic attractor; accordingly, the motion of the sleigh turns out to be
similar to the process of random walk on a plane.
