THE SAILING SHIP

The earth moves ! ! !

How is that we can't feel it?

Why don't we slide off?

Will we fly to the moon?

Why does a stone falling from a tower not fall backward (as when a stone falls from the mast of a moving ship)?

In his book The Dialogue, Galileo discusses the claim of Aristotelian scientists that the earth does not move. These scientists claimed that if the earth moved, we would feel it. Just as one feels the motion of a boat, so should we feel the movement of the earth.

These claims were heard among men of science and men of the church on the streets of Italy, following the publication of Galileo's claim that the earth moves. Up until the time of Galileo, scientific thinking was based on the physics of Aristotle, including the geocentric system.

In order to answer these contentions, Galileo used the example of the sailing ship to represent the moving earth.

In Italy, which is a peninsula, ships were in very common use. They were employed to transport people and goods from one country to another, and from one city to another, along the shore, and along rivers and canals as well. In Galileo's day, the use of ships to demonstrate the motion of bodies was common. Galileo himself frequently used the motion of ships in order to understand, explain and demonstrate the qualities of moving objects.

Galileo's rivals claimed that if the earth moved, a stone thrown off a tower should have fallen backward and not straight down to the base of the tower, just like a stone dropped from the mast of a sailing ship. They took this example as proof that the earth does not move. In his response to their contentions, Galileo likened the sailing ship to the moving earth.

If we drop a stone from the mast of a sailing ship, where would the stone fall?

What are the forces acting on a stone dropped from the mast of a sailing ship?

Galileo showed that the stone would fall to the base of the sailing ship's mast and that on the moving earth too, the stone will fall to the base of the tower, as can be seen from experience. Galileo used this example to show that the movement of the earth is possible. Galileo explained this phenomenon through his discussion of the law of inertia, based on his experiments with the inclined plane.