Speed(s)
Jean-Marc Lévy-Leblond · American Journal of Physics · 1980
Three simple distinct operational procedures are given for transforming the empirical notion of speed into a formal concept. While in the Galilean theory of space-time, the three quantities coincide with the customary velocity, they differ in the Einsteinian theory. In particular, it is shown that ’’rapidity’’ has a direct and natural physical meaning.