This report is part of a long-term research on the construction of mathematical meanings through the interaction with various technologies. The research involved a set of teaching experiments based on body motion with sensors and calculators at different school levels, from kindergarten to secondary school. Here I refer to the one developed in a junior high school, involving 20 students of 8th grade (age 13). The focus is on the cognitive evolution of the students towards the construction of meaning for the performed motion, from a functional point of view. Particularly, the passage from a uniform to an accelerated motion is analysed. The data are interpreted within a semiotic-cultural approach, as stated by Radford (2003), by looking at the progression in the introduction of signs and the shared use of them. (Contains 11 figures.)