24
A FLOATING OBJECT
DISPLACES ITS OWN
VOLUME IN LIQUID
ARCHIMEDES (287–212 BCE)
T
he Roman author Vitruvius,
writing in the 1st century
BCE, recounts the possibly
apocryphal story of an incident that
happened two centuries earlier.
Hieron II, the King of Sicily, had
ordered a new gold crown. When
the crown was delivered, Hieron
suspected that the crown makerIN CONTEXT
BRANCH
PhysicsBEFORE
3rd millennium BCE
Metalworkers discover that
melting metals and mixing
them together produces an
alloy that is stronger than
either of the original metals.600 BCE In ancient Greece,
coins are made from an alloy of
gold and silver called electrum.AFTER
1687 In his Principia
Mathematica, Isaac Newton
outlines his theory of gravity,
explaining how there is a force
that pulls everything toward
the center of Earth—and
vice versa.1738 Swiss mathematician
Daniel Bernoulli develops
his kinetic theory of fluids,
explaining how fluids exert
pressure on objects by the
random movement of
molecules in the fluid.had substituted silver for some of
the gold, melting the silver with the
remaining gold so that the color
looked the same as pure gold.
The king asked his chief scientist,
Archimedes, to investigate.
Archimedes puzzled over the
problem. The new crown was
precious, and must not be damagedThe difference in
upthrust between the
two is small, but it can
be detected if you hang
them on a balance in water.The displaced water
causes an upthrust.
The partly silver crown
experiences a greater
upthrust than the gold.Silver is less dense
than gold, so a lump
of silver will have a
greater volume than
a lump of gold of the
same weight.A crown made
partly of silver will have
greater volume and displace
more water than a lump
of pure gold of the same
weight as the crown.Eureka!