Relative Motions

Abstract

We have already seen that the equations of motion depend on the reference frame. The law of motions, and more generally all the laws of Physics, transform, as we say, from one frame to another. This chapter is dedicated to the study of these transformations. We first consider the transformations between frames at rest with one another, namely the translations and rotations of the axes. We then consider frames in relative motion and learn that, when the relative motion is a translation with constant speed, the laws of physics do not change their form. This is the relativity principle established by Galilei. Finally we shall study the motion in accelerated frames and introduce, in particular, the concept of inertia force or pseudo-force.