Principle of Flotation

Galileo believed Archimedes' Principle, that denser objects than water sink in water.
(To be precise, the Principle states that the buoyant supporting force from the water on an immersed object is equal to the weight of the water displaced by the object. That is, it is equal to the weight of a volume of water equal to the volume of the object.  So if the object is denser than water, its weight is greater than the buoyancy force and it sinks.)

It was pointed out to him that a ball made of ebony sinks in water, but a flat chip of ebony floats. We now understand this in terms of surface tension, but that had not been understood in Galileo's time. Nevertheless, Galileo gave an essentially correct answer: he observed that the chip floated somewhat below the previous level of the surface, dragging the water down slightly around its edges, so one should consider the floating body to be the chip plus the thin sheet of air over it, and putting these together gives an average density equal to that of water. Galileo discussed problems of this kind with a Florentine patrician, Filippo Salviati, and a group of his acquaintances.

(Found at http://www.phys.virginia.edu/classes/109N/lectures/gal_life.htm     
Lecture notes of Michael Fowler  (Physics 109: Galileo and Einstein .)
Commonwealth Professor
Department of Physics
University of Virginia
http://www.phys.virginia.edu/classes/109N/lectures/gal_life.htm

How can something as large as a cruise ship or any ship float?  Check this out!!

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