  In this paper, we define Jacobi fields for nonholonomic mechanics using a
similar characterization than in Riemannian geometry. We give explicit
conditions to find Jacobi fields and finally we find the nonholonomic Jacobi
equations in two equivalent ways: the first one, using an appropriate complete
lift of the nonholonomic system and, in the second one, using the curvature and
torsion of the associated nonholonomic connection.
