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Galileo’s Theories of Free Fall and Projectile Motion as Interpreted by Pierre Gassendi

  • Carla Rita Palmerino
Part of the Boston Studies in the Philosophy of Science book series (BSPS, volume 239)

Abstract

In October 1640, Pierre Gassendi left the port of Marseilles on a trireme with the intention of carrying out on the open sea an experiment that Galileo had described in the Dialogo sopra i due massimi sistemi (1632), but of which he had claimed that he had never performed it.1 In the presence of Louis de Valois, Governor of the Provence, Gassendi confirmed Galileo’s prediction that a ball dropped from the head of a mast of a moving ship landed exactly at the foot of the mast irrespective of whether the ship was at rest or was instead moving at high speed.2 This observation was fraught with important implications, for it falsified one of the principal arguments against the diurnal motion of the Earth. Partisans of the Ptolemaic and the Tychonian theories had argued that just as a ball dropped from the masthead of a moving ship struck the deck at some distance behind the foot of the mast, so on a rotating Earth an object dropped from a high tower would not touch the ground next to the tower. Having verified that a falling body behaved exactly in the same way on a ship in motion and on a ship at rest, Gassendi felt entitled to conclude, following Galileo, that the behavior of objects on the surface of the Earth did not allow for any conclusion as to whether the Earth rotated or not.

Keywords

Horizontal Motion Downward Motion Causal Explanation Free Fall Circular Motion 
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References

  1. 1.
    Galilei, Dialogue [Drake], p. 145. However, in his Lettera a Francesco Ingoli in risposta alla “Disputatio de situ et quiete Terrae” (1624), Galileo claimed to have personally carried out this experiment (see Galilei, Le Opere [Favaro], vI, p. 545). For a discussion of this claim, see i. a. Ariotti, “From the Top to the Foot;” esp. pp. 201–202; Conti, “La dimensione sperimentale., According to Conti, the “experimental baptism” of Galileo’s relativity principle took place on the Lake of Piediluco in April 1624, during Galileo’s stay at Prince Cesi’s residence at Acquasparta.Google Scholar
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  • Carla Rita Palmerino

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