Galileo's ship

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Galileo's ship refers to two physics experiments, a thought experiment and an actual experiment, by Galileo Galilei, the 16th- and 17th-century physicist and astronomer. The experiments were created to argue for the idea of a rotating Earth, as opposed to a stationary Earth around which the Sun, planets, and stars rotate.

An argument that was used at the time was that, if the Earth were rotating, there would be detectable effects on the trajectories of projectiles or falling bodies.

Ship's mast experiment

In 1616, after Galileo had already become concerned that he was a target of suspicion by the

Clavius[4] and Giordano Bruno.[5]

Galileo told Ingoli (translated by Stillman Drake): [6]

I have been twice as good a philosopher as those others because they, in saying what is the opposite of the effect, have also added the lie of their having seen this by experiment; and I have made the experiment—before which, physical reasoning had persuaded me that the effect must turn out as it indeed does.

Galileo also discussed the experiment in his Dialogue Concerning the Two Chief World Systems (day 2), [7] but without any assertion that it was actually carried out. A similar experiment discussed by Galileo and other authors such as Oresme, Clavius and Bruno involves a projectile being launched straight up from the surface of the earth. A common Aristotelian-Scholastic argument was that if the earth's surface were moving to the east, then in this experiment the projectile would land to the west of the launching point, contrary to observation.

1632 thought experiment

Galileo's 1632 book

special theory of relativity
, a restatement of Galileo's argument with the then-known laws of gravitation and electromagnetism taken into account.

The proposal

Salviati's experiment goes as follows:[8]

Shut yourself up with some friend in the main cabin below decks on some large ship, and have with you there some flies, butterflies, and other small flying animals. Have a large bowl of water with some fish in it; hang up a bottle that empties drop by drop into a wide vessel beneath it. With the ship standing still, observe carefully how the little animals fly with equal speed to all sides of the cabin. The fish swim indifferently in all directions; the drops fall into the vessel beneath; and, in throwing something to your friend, you need to throw it no more strongly in one direction than another, the distances being equal; jumping with your feet together, you pass equal spaces in every direction. When you have observed all these things carefully (though doubtless when the ship is standing still everything must happen in this way), have the ship proceed with any speed you like, so long as the motion is uniform and not fluctuating this way and that. You will discover not the least change in all the effects named, nor could you tell from any of them whether the ship was moving or standing still. In jumping, you will pass on the floor the same spaces as before, nor will you make larger jumps toward the

bow
or the stern, with yourself situated opposite. The droplets will fall as before into the vessel beneath without dropping toward the stern, although while the drops are in the air the ship runs many spans. The fish in their water will swim toward the front of their bowl with no more effort than toward the back, and will go with equal ease to bait placed anywhere around the edges of the bowl. Finally the butterflies and flies will continue their flights indifferently toward every side, nor will it ever happen that they are concentrated toward the stern, as if tired out from keeping up with the course of the ship, from which they will have been separated during long intervals by keeping themselves in the air. And if smoke is made by burning some incense, it will be seen going up in the form of a little cloud, remaining still and moving no more toward one side than the other. The cause of all these correspondences of effects is the fact that the ship's motion is common to all the things contained in it, and to the air also. That is why I said you should be below decks; for if this took place above in the open air, which would not follow the course of the ship, more or less noticeable differences would be seen in some of the effects noted.

Dialogue Concerning the Two Chief World Systems, translated by Stillman Drake, University of California Press, 1953, pp. 186 - 187 (Second Day).

References

  1. ^ Questions on Aristotle’s On the Heavens. Cambridge (Mass.), Medieval Academy of America (English translation by E.A. Moody of the c. 1340 Latin original)
  2. ^ Le livre du Ciel et du Monde. Book II, Chapter 25 (manuscript). Paris, National Library.
  3. ^ On Learned Ignorance. Minneapolis, The Arthur J. Banning Press (English translation by J. Hopkins of the 1440 Latin original).
  4. ^ In sphaeram ioannis de sacro bosco commentarius, p. 196, "Neque enim valet responsio quorundam..."
  5. ^ La Cena delle Ceneri, III, 5.
  6. ISBN 9780486495422
    .
  7. ^ Galileo Galilei."Dialogue subject ship".
  8. ^ Galileo Galilei. "Dialogo day two boat story (in italian, search at page for 'Riserratevi' yourself to find it)".

Sources

This article incorporates an excerpt from Dialogue Concerning the Two Chief World Systems; the excerpt has been released under the GNU Free Documentation License (GFDL) by the estate of Stillman Drake.
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