What was Archimedes' contribution in Physics?
There were many. He is famous for the saying, "If I had a lever
big enough I could move the world." Actually, a more accurate
translation would be: If I had a firm enough place to stand, I
could move the world.
He is also most known for hi invention of the Archimedes screw
for pumping water.
Main article: Archimedes' principle
Archimedes may have used his principle of buoyancy to determine
whether the golden crown was less dense than solid gold.
The most widely known anecdote about Archimedes tells of how he
invented a method for determining the volume of an object with an
irregular shape. According to Vitruvius, a votive crown for a
temple had been made for King Hiero II, who had supplied the pure
gold to be used, and Archimedes was asked to determine whether some
silver had been substituted by the dishonest goldsmith.
Archimedes had to solve the problem without damaging the crown, so
he could not melt it down into a regularly shaped body in order to
calculate its density. While taking a bath, he noticed that the
level of the water in the tub rose as he got in, and realized that
this effect could be used to determine the volume of the crown. For
practical purposes water is incompressible, so the submerged
crown would displace an amount of water equal to its own volume. By
dividing the mass of the crown by the volume of water displaced,
the density of the crown could be obtained. This density would be
lower than that of gold if cheaper and less dense metals had been
added. Archimedes then took to the streets naked, so excited by his
discovery that he had forgotten to dress, crying "Eureka!" (Greek:
"εὕρηκα!," meaning "I have found it!"). The test was conducted
successfully, proving that silver had indeed been mixed in.
The story of the golden crown does not appear in the known works
of Archimedes. Moreover, the practicality of the method it
describes has been called into question, due to the extreme
accuracy with which one would have to measure the water
displacement. Archimedes may have instead sought a solution
that applied the principle known in hydrostatics as Archimedes'
principle, which he describes in his treatise On Floating
Bodies. This principle states that a body immersed in a fluid
experiences a buoyant force equal to the weight of the fluid it
displaces. Using this principle, it would have been possible to
compare the density of the golden crown to that of solid gold by
balancing the crown on a scale with a gold reference sample, then
immersing the apparatus in water. The difference in density between
the two samples would cause the scale to tip accordingly. Galileo
considered it "probable that this method is the same that
Archimedes followed, since, besides being very accurate, it is
based on demonstrations found by Archimedes himself."