Galileo and Tennis: Reconciling the New Physics with Commonsense

This paper discusses a passage from the Second Day of Galileo’s Dialogue in which explicit reference is made to the game of tennis and, more specifically, to spinning balls. This often overlooked passage forms part and parcel of the tightly-knit argumentative structure of the work, and provides key arguments against Aristotelian physics. Furthermore, Galileo’s choice of terms shows how careful he was in his use of analogies as effective tools to reconcile the new physics that he was struggling to introduce, with common sense. Finally, and most interestingly, by comparing this passage with a similar one from Galileo’s unpublished writings, this paper shows the extent to which Galileo was interested in the physics of spinning balls and how he planned to include a discussion of it in a work that he began shortly after the publication of the Sidereus Nuncius, but never managed to finish.