A new approach to the vakonomic mechanics
  The aim of this paper is to show that the Lagrange-d'Alembert and its equivalent the Gauss and Appel principle are not the only way to deduce the equations of motion of the nonholonomic systems. Instead of them, here we consider the generalization of the Hamiltonian principle for nonholonomic systems with nonzero transpositional relations.   By applying this variational principle which takes into the account transpositional relations different from the classical ones we deduce the equations of motion for the nonholonomic systems with constraints that in general are nonlinear in the velocity. These equations of motion coincide, except perhaps in a zero Lebesgue measure set, with the classical differential equations deduced with d'Alembert-Lagrange principle.   We provide a new point of view on the transpositional relations for the constrained mechanical systems: the virtual variations can produce zero or non-zero transpositional relations. In particular the independent virtual variations can produce non-zero transpositional relations. For the unconstrained mechanical systems the virtual variations always produce zero transpositional relations.   We conjecture that the existence of the nonlinear constraints in the velocity must be sought outside of the Newtonian model.   All our results are illustrated with precise examples. 
J. Llibre, R. Ram\'irez and N. Sadovskaia
math-ph math.MP