The impossibility of experimental detection of uniform and absolute motion, also known as the principle of relativity, has not been well discussed in Physics Secondary School classes. In this paper, we present part of a didactical sequence in which topics of Special Relativity are presented to first year students. The discussion of Galilean relativity allowed us to emphasize conceptual aspects of physics and introduce topics of special relativity. The analysis of teaching episodes, extracted from recordings made in class, and the students´s answers to a post - test presented at the end of the teaching sequence, allowed us to infer that we had achieved our goals. The results were excellent, since, but for one student, all the others answered correctly, mentioning as expected the relativity principle so confirming the efficiency of our methodology.