Kenny Early, age 15, of Jamestown, N.Y., for his question:
WHAT MADE ARCHIMEDES GREAT?
Archimedes was a Greek mathematician and inventor who lived from about 287 B.C. until about 212 B.C. Historians call him the father of experimental science. He is considered great because he was the first one to come up with a large number of man's basic scientific discoveries.
Archimedes discovered the laws of the lever and the pulley. These discoveries made it possible for man to build machines that were able to move heavy loads easily.
"Give me a place to stand on, and I will move the earth," Archimedes once said. He was referring to the way a lever can help a man move objects many times his own size and weight.
Archimedes is credited with inventing the Archimedean screw, a device still used to lift water for irrigation. He also invented machines that drove the Roman general Marcellus' army from the walls of Syracuse. One of these machines was the catapult, a weapon that shot large boulders at the enemy. He also came up with an idea of using grappling hooks that could disable ships.
Although he is known for his inventions, Archimedes looked on these as play. He considered mathematics his real work.
Archimedes found a way to determine a more exact value of pi, the ratio of a circle's circumference to its diameter. His discovery made it possible to solve many problems involving the area of circles and the volume of cylinders.
The great scientist also invented a numeration system that was more workable with large numbers than were the Greek and Roman systems. Using his system, Archimedes calculated the number of grains of sand it would take to fill the universe.
He was also the first person to use methods now used in calculus, a form of higher mathematics.
Archimedes also discovered basic laws of hydrostatics, a branch of physics that deals with fluids. One of his laws, called Archimedes' principle, explains buoyancy.
Archimedes was born in Syracuse, which was then a Greek colony. He went to school in Alexandria, Egypt, which was then the center of Greek learning.
Buoyancy is the loss in weight an object seems to undergo when it is placed in a liquid. Archimedes' principle states that an object placed in a liquid seems to lose an amount of weight equal to the weight of the fluid it displaces.
From the same basic idea, the scientist also concluded that a floating object displaces an amount of liquid equal to its own weight.
Some historians report that Archimedes also designed a system of mirrors that could be used to concentrate the sun's rays on an enemy ship and then have those rays set the ship on fire.
Archimedes' screw was used in the Nile Valley for draining and irrigating land.