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Stick-Slip motion is the basis for the description of a great variety of phenomena characterized by the presence of sliding friction between bodies with elastic features. In this article a simple experimental equipment for the analysis of this kind of dynamics is described. A wide set of possible experimental observations and measures are presented. This equipment has been tested at the university of Napoli Federico II in courses for undergraduate students and in the teacher training school for secondary education.

Abstract: We study the site-bond percolation problem for clusters of holes and particles with antiferromagnetic order by means of the Bethe cluster approximation. We find that the droplets (i.e.P B =1–e –|K|/2) diverge at the antiferromagnetic critical pointH=0,T=T c; however forHne0 they diverge along a percolation line which is different from the Antiferromagnetic Phase Boundary except atT=0.

We analyze the properties of theq-state ferromagnetic Potts model for realq. The nature of the phase transition at the critical point is first-order forq?2, and second-order forq=2. The random-bond percolation limitq?1, and its second-order-like transition, are not related to the previous behaviour since they arise from non-stable phases of the system. It is suggested that this property characterizes the model on high-dimensional lattices, too.