Résumé
Coulomb friction commonly generates problems with multiple solutions. After examining an elementary example, one proposes to include the values of contact forces in the description of each state of the investigated system. This turns out to be what popular time-stepping numerical techniques implicitely do. Specifically, the Contact Dynamics computational policy , whose principle is recalled, offers this as an option with the additional advantage of improving computation speed. Thanks to this option, the evolution of the considered systems is predicted with negligible ambiguity. Alternatively, Contact Dynamics techniques may be used to explore the plurality of the solutions to problems stated in the traditional way. In this line, two examples of the assessement of contact forces in granular assemblies are presented, with the set of solutions graphically displayed.