All the phenomena of nature are characterized by motion; this is an essential property of matter, having infinity of aspects. For instance, the motion can be mechanical, physical, chemical and biological; there correspond various sciences of nature. Among them, mechanics studies the objective laws of the mechanical motion of material bodies, the simplest form of motion of matter; we will deal with such a study in what follows. The scientific study of matter has put in evidence its existence in the form of physical systems. The simplest physical system is the substance, which is met in nature in the form of material body; we will consider these.
