  In recent times there has been considerable interest in scenarios for quantum
gravity in which particle kinematics is affected nonlinearly by the Planck
scale, with encouraging results for the phenomenological prospects, but also
some concerns that the nonlinearities might produce pathological properties for
composite/multiparticle systems. We here focus on kinematics in the
$\kappa$-Minkowski noncommutative spacetime, the quantum spacetime which has
been most studied from this perspective, and compare the implications of the
alternative descriptions of the total momentum of a multiparticle system which
have been so far proposed. We provide evidence suggesting that priority should
be given to defining the total momentum as the standard linear sum of the
momenta of the particles composing the system. We also uncover a previously
unnoticed feature concerning some (minute but conceptually important) effects
on center-of-mass motion due to properties of the motion of the constituents
relative to the center of mass.
