This lecture covers mechanical processes related to particle size, including concepts such as sphericity, particle shape, equivalent diameter, and distribution laws. It also discusses properties like density, cohesion, and hardness of particles, as well as phenomena like segregation and arching in divided solids flow. Various types of transport systems for bulk solids are presented, along with grinding theories, types of shredders, and wet grinding techniques. The lecture concludes with a focus on cryogenic grinding and the choice of shredders for different applications.