Physics in Perspective

, Volume 16, Issue 4, pp 440–460 | Cite as

“Galileo’s Machine”: Late Notes on Free Fall, Projectile Motion, and the Force of Percussion (ca. 1638–1639)

  • Stefano SalviaEmail author


My paper focuses upon the problem of determining the nature, establishing the proportionality, and measuring the intensity of the force of percussion of a projected or falling body, as treated in the Sixth Day of Galileo’s Discorsi e dimostrazioni matematiche intorno a due nuove scienze (1638). This fragment was written around 1638–1639 as part of two additional Days of the Discorsi, which Galileo never finished and remained unpublished until 1718. Galileo’s last works on percussion show a significant step towards a generalization of his own views on uniform and accelerated motion that will later lead to the Newtonian principle of inertia. The experiment with two equal weights hanging on a pulley, performed in Arcetri during the same period, is compared with the Paduan 1604–1608 experience of the “water balance.” Both account for more than three decades of inquiries into what Galileo called forza della percossa, which marked the transition from preclassical to classical mechanics.


Galileo Galilei machine percussion 



Special thanks to Roberto Vergara Caffarelli (Department of Physics, University of Pisa) for his inspiring reconstructions of Galileo’s experiments, as well as for the coinage of the name “Galileo’s machine” itself. I am also very grateful to Massimiliano Badino (Centre d’Història de la Ciència, Universitat Autònoma de Barcelona) for his helpful remarks during the writing of my paper.


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Copyright information

© Springer Basel 2014

Authors and Affiliations

  1. 1.ImperiaItaly

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