Every day we experiment motion and shape change of continuum media, assembly of different space dimension structures, fluids, solids which exhibit numerous evolutions either particular or general: large deformations, incompressibility, cavitation, contact, surface tension, defects, dislocations,... Stretch and rotation are a common feature of these motions and phenomenons. We base a continuum mechanics predictive theory on stretch and rotation quantified by matrices. In this Chapter the elements of a predictive theory are defined with a simple example, the motion of a point with respect to a plane: structure, frame, frame tracker, system, shape of the system and shape change velocities, rigid body velocities, system rigidifying motions are defined. We recall the principle of virtual work and the principle of virtual power, and the choice of the virtual velocities. Even in this situation, internal forces may be experimented.