In this talk we are interested in classical vector fields which are not required to be continuous everywhere, that is, defined by piecewise-smooth maps. To perform a qualitative analysis of the phase portraits of a class of discontinuous vector fields, identifying algebraical and topological features for the so called escaping and sliding regions, has been the goal of several researchers, mainly in Control theory, where the discontinuous oscillations phenomena have been modeled by the introduction of discontinuities in semi-linear vector fields, using sign functions. Those systems are called relay systems and they have gain great importance to understand the discontinuous behavior and the interesting phenomena that can be observed. We will analyze a system composed of a block connected to a fixed linear-elastic spring on a moving conveyor belt, subject to Coulomb friction.