Relativity in Classical Mechanics

Abstract

In order to describe the motion of a system of particles in classical mechanics, it is necessary first to choose a frame of reference—that is, an origin and a set of right-handed Cartesian axes. Sometimes there is a natural choice. In a projectile problem, for example, it is sensible to take the z-axis to point directly upwards and to pick out the origin and the direction of the x-axis from the initial conditions. Such choices become embedded in our physical intuition to the extent that it is difficult to think clearly about a problem in an unconventional frame—with the z-axis pointing downwards, for example, or at an angle to the horizontal.