This introductory chapter tries to explain what we are going to do, what do
notions such as fluid and a model of a physical phenomenon mean, what for, such
models are developed, and what features of a phenomenon a model should be
necessarily able to describe and so on.
Keywords: Body, Body configuration, Coordinate basis, Event, Fluid, Force,
Frame of reference, Mass, Model, Motion, Place, Space-time continuum, System
of coordinates, Trajectory, World-line.
