  A trimer is an object composed of three centimetrical stainless steel beads
equally distant and is predestined to show richer behaviours than the bouncing
ball or the bouncing dimer. The rigid trimer has been placed on a plate of a
electromagnetic shaker and has been vertically vibrated according to a
sinusoidal signal. The horizontal translational and rotational motions of the
trimer have been recorded for a range of frequencies between 25 and 100 Hz
while the amplitude of the forcing vibration was tuned for obtaining maximal
acceleration of the plate up to 10 times the gravity. Several modes have been
detected like e.g. rotational and pure translational motions. These modes are
found at determined accelerations of the plate and do not depend on the
frequency. By recording the time delays between two successive contacts when
the frequency and the amplitude are fixed, a mapping of the bouncing regime has
been constructed and compared to that of the dimer and the bouncing ball.
Period-2 and period-3 orbits have been experimentally observed. In these modes,
according to observations, the contact between the trimer and the plate is
persistent between two successive jumps. This persistence erases the memory of
the jump preceding the contact. A model is proposed and allows to explain the
values of the particular accelerations for which period-2 and period-3 modes
are observed. Finally, numerical simulations allow to reproduce the
experimental results. That allows to conclude that the friction between the
beads and the plate is the major dissipative process.
