abstract: The analysis of percussion (impact) based on the lever law, as set out by Galileo in Le Mecaniche (EN, II, pp. 155-190), soon appeared as unsatisfactory. This is why as early as 1602, Galileo worked mainly on experiments aimed at measuring the moment of percussion. The pieces of information and the testimonies found in the Corrispondenza as well as in the Discorsi (1638) are fairly good illustrations of the difficulties encountered by Galileo. His project of a day fully dedicated to percussion led him to dictate a dialogue to Marco Ambrogetti (around 1638). The dialogue was published in the second edition of the Galileo's Opere (1718), under the title Giornata Sesta… da aggiungersi a i Discorsi … (EN, VIII, pp.321-346). The attempts to establish an equivalence between the effects of percussion and the effects of a dead weight had led him to think that the moment of percussion was indeterminate, or even infinite. In the Sesta Giornata Galilileo intended to justify such an opinion. It seems that Torricelli (1608-1647) did not know that text. However he had received from Galileo some indications on the basis of which he proposed three Lectures (Lezioni Accademiche) held at the Accademia della Crusca on August 27th and September 12th, 1642 and September 24th, 1643; they were published in 1715 by Tommaso Buonaventuri in Florence.
Sur la force de percussion