The parallel analysis of wave/agents behaviours can also supply insights about the relationships between medium properties and wave propagation speeds. Speed of propagation of a disturbance in solid rods can be easily measured (Fazio, Guastella, Sperandeo-Mineo, & Tarantino, 2006) and a simple ball-and-spring atomic model of a solid (Chabay & Sherwood, 2004) should allow us to explain propagation of such disturbance.