Rhonda Greer, age 13, of San Francisco, Calif., for her question:
WHO WAS ARCHIMEDES?
Archimedes has been called the father of experimental science. He was a Greek mathematician and inventor who made some of man's basic scientific discoveries. He lived from 287 B.C. until 212 B.C.
The laws of the lever and the pulley were discovered by Archimedes.
These discoveries led to construction of machines capable of moving heavy loads easily.
"Give me a place to stand on, and I will move the earth," Archimedes once boasted. He was referring to the way a lever can help a man move objects many times his own size.
Archimedes lived in Syracuse, Siciliy, and did much of his work for Hiero, the king of Syracuse.
According to legend, Hiero became suspicious about a new gold crown. He suspected that the goldsmith had not made it of pure gold, but had mixed in some less costly silver. The king asked Archimedes to find out if the goldsmith had cheated.
Archimedes knew that an ounce of gold would have less volume than an ounce of silver, because gold is heavier than silver. Therefore, a crown of pure gold would have less volume than a crown weighing the same, but made of gold and silver.
How could he measure the volume of the gold crown? The idea hit him when he stepped into a tub full of water, and some of the water spilled over the side. He reasoned that if he caught this spilled water in a container and measured it, its volume would equal the volume of his own body.
"Eureka!" he yelled as he ran from the bath into the street without dressing. He was happy that he found a way to solve the riddle of the crown.
He put the crown in water. It displaced more water than an equal weight of pure gold. The goldsmith had cheated.
Archimedes made discoveries in mathematics as well as in physics. He found a way to determine a more exact value of pi, or 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.
A numeration system was invented by Archimedes 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.
Archimedes is credited with inventing the Archimedean screw, a device still used to lift water for irrigation. He also invented machines that drove Roman general Marcellus' army from the walls of Syracuse. One of these machines was a catapult, a weapon that shot rocks at the enemy.
Archimedes also invented grappling hooks that could seize ships and disable them. He also is said to have designed a system of mirrors that concentrated the suns rays to set enemy ships on fire.