Levers and Buoyancy
Year of Discovery: 260 B.C.
What Is It? The two fundamental principles underlying all physics and
engineering.
Who Discovered It? Archimedes
Why Is This One of the 100 Greatest?
The concepts of buoyancy (water pushes up on an object with a force equal to the
weight of water that the object displaces) and of levers (a force pushing down on one side of
a lever creates a lifting force on the other side that is proportional to the lengths of the two
sides of the lever) lie at the foundation of all quantitative science and engineering. They represent humanity’s earliest breakthroughs in understanding the relationships in the physical
world around us and in devising mathematical ways to describe the physical phenomena of
the world. Countless engineering and scientific advances have depended on those two
discoveries.
How Was It Discovered?
In 260 B.C. 26-year-old Archimedes studied the two known sciences—astronomy and
geometry—in Syracuse, Sic ily. One day Archimedes was distracted by four boys playing
on the beach with a driftwood plank. They balanced the board over a waist-high rock. One
boy straddled 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-center along their balancing rock so that only one-quarter
of it remained on the short side. Three of the boys climbed onto the short, top end. The
fourth boy bounded onto the rising long end, crashing it back down to the sand and catapulting his three friends into the air.
Archimedes was fascinated. And he determined to understand the principles that so
easily allowed a small weight (one boy) to lift a large weight (three boys).
Archimedes used a strip of wood and small wooden blocks to model the boys and their
driftwood. He made a triangular block to model their rock. By measuring as he balanced
different combinations of weights on each end of the lever (lever came from the Latin word
meaning “to lift”), Archimedes realized that levers were an example of one of Euclid’s proportions at work. The force (weight) pushing down on each side of the lever had to be proportional to the lengths of board on each side of the balance point. He had discovered the
mathematical concept of levers, the most common and basic lifting system ever devised.
3