A REDUCTION PROPERTY FOR A CLASS OF MECHANICAL SYSTEMS WITH FRICTION F. Cantrijn Abstract. A reduction scheme is established for a special class of non-Hamiltonian systems, defined on a cotangent bundle, which are invariant under the Hamiltonian action of a compact Lie group and for which the corresponding momentum map yields a conformal invariant. The reduction is constructed in terms of a suitably normalized momentum map and the reduced spaces are canonical manifolds. The class of systems under consideration in particular encompasses the phase space description of certain types of mechanical systems with friction. Keywords. Symmetry, reduction, canonical manifolds. MS classification. 58F05, 70G99.