100 Greatest Science Discoveries of All Time: Levers and Buoyancy

Year of Discovery: 260 B.C.

What Is It? The two fun da men tal prin ci ples un der ly ing all phys ics and
en gi neer ing.
Who Dis cov ered It? Ar chi me des
Why Is This One of the 100 Great est?
The con cepts of buoy ancy (wa ter pushes up on an ob ject with a force equal to the
weight of wa ter that the ob ject dis places) and of le vers (a force push ing down on one side of
a le ver cre ates a lift ing force on the other side that is pro por tional to the lengths of the two
sides of the le ver) lie at the foun da tion of all quan ti ta tive sci ence and en gi neer ing. They rep re
sent

hu man ity’s ear li est break throughs in un der stand ing the re la tion ships in the phys i cal
world around us and in de vis ing math e mat i cal ways to de scribe the phys i cal phe nom ena of
the world. Count less en gi neer ing and sci en tific advances have depended on those two
discoveries.
How Was It Dis cov ered?
In 260 B.C. 26-year-old Ar chi me des stud ied the two known sci ences—as tron omy and
ge om e try—in Syr a cuse, Sic ily. One day Ar chi me des was dis tracted by four boys play ing
on the beach with a drift wood plank. They bal anced the board over a waist-high rock. One
boy strad dled one end while his three friends jumped hard onto the other. The lone boy was
tossed into the air.
The boys slid the board off-cen ter along their bal anc ing rock so that only one-quar ter
of it re mained on the short side. Three of the boys climbed onto the short, top end. The
fourth boy bounded onto the ris ing long end, crash ing it back down to the sand and cat a pult ing
his three
friends
into the
air.
Ar chi me des was fas ci nated. And he de ter mined to un der stand the prin ci ples that so
eas ily al lowed a small weight (one boy) to lift a large weight (three boys).
Ar chi me des used a strip of wood and small wooden blocks to model the boys and their
drift wood. He made a tri an gu lar block to model their rock. By mea sur ing as he bal anced
dif fer ent com bi na tions of weights on each end of the le ver (le ver came from the Latin word
mean ing “to lift”), Ar chi me des re al ized that le vers were an ex am ple of one of Eu clid’s pro por
tions
at
work.
The force
(weight)
push ing
down on each
side
of the
le
ver
had
to be pro por
tional
to the lengths
of board on
each
side
of the bal
ance
point. He
had dis
cov
ered
the
math
e
mat
i
cal
con cept
of le vers,
the most
com
mon
and basic
lifting
system
ever
devised.