  From a consistent expression for the quadriforce describing the interaction
between a coloured particle and gauge fields, we investigate the relativistic
motion of a particle with isospin interacting with a BPS monopole and with a
Julia-Zee dyon. The analysis of such systems reveals the existence of
unidimensional unbounded motion and asymptotic trajectories restricted to
conical surfaces, which resembles the equivalent case of Electromagnetism.
