ABSTRACT
Before seeing how the grouping of co-displacements is generalized in the case of movements in succession, and in order to end this part of the present work devoted to the qualitative operations fundamental to the conception of speed, we thought it would be useful, in relation to Chapter Five (relative movements) to analyse a problem of relative speeds, i.e. of the co-ordination of two speeds into one single apparent speed. Whereas the operational conception of speed is acquired from the level of concrete operations (stage III) in correlation with the conception of time itself, the composition of two speeds, on the contrary, implies formal thinking, and it is in this way that its study completes those of the previous chapters.
