In this paper, we analyze different presentations in a historical text by Galilei and a textbook for high school of the parabolic motion of a projectile with a lens developed within Mathematics education research on argumentation and proof (cognitive unity; Mariotti et al., 1997; Pedemonte, 2005). The analysis highlights possibilities and problematic issues, with particular attention to the aspects related to continuity and rupture between argumentation and proof in textbooks and the different interdisciplinary relationships between mathematics and physics mirrored by historical sources and textbooks. We discuss how a comparison between them can be exploited to develop a discourse about interdisciplinary that can enlarge the view of the relationship between the two disciplines and didactical implications that can be inferred from this comparison.