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Archimedes' Bathtub - Part 2
by Jeanette Cain
If you were to be weighed while floating in water you would be much lighter than you are when standing on land. The body is lifted because it is
buoyed up by the water. If you can't remember Part 1, you can re-read the article before moving to this section.
We left off with your idea of what a good example would be for explaining Archimedes' principle of buoyancy. Did you think of a submarine? That's okay, I bet you thought of plenty of others.
When a submarine is built, it will weigh less than the same volume of sea water would. How does a captain make a floating submarine submerge? First, he gives the order for the crewmen to pump
water into the ballast tanks. When the submarine's weight becomes as great as the water it has to push out of the way, the submarine will submerge below the water's surface. If the captain wants
to bring the submarine to the surface again, he will give the order for the crewmen to force the water out of the tanks. This causes the submarine to become lighter than the water that it had
displaced and causes it to be pushed to the surface again.
As with the submarine, any object will float, if it weighs less than the water it displaces. If it weighs more, it will sink! Did you know that sometimes ships which have been sunk may be raised
by applying Archimedes' principle? Large tanks will be filled with enough water to sink them: when they reach the ocean's bottom, the tanks will be chained to the sunken ship. The water that is
in the tanks will be pushed out by air that is pumped into them. If enough tanks have been used for this purpose, the total buoyant force will cause the ship to be lifted to the surface.
There is a simple experiment that you may use to prove this theory. Please ask an adult for help! You may teach them about Archimedes and his buoyancy principle, so give them a chance! Adults
need help too! You will need a toy boat that floats, a coffee can with a hole about an inch from the top and a large pan to place the coffee can inside.
First, find a toy boat that you know will float, then weigh it. Secondly, punch a hole in a coffee can about one inch from its top rim. Then, fill the can with water up to the hole that
you have made. Put the coffee can in a larger pan to catch the water that overflows. Next, put your toy boat in the can. Depending on how much your boat weighs, some water will overflow from the
hole into the large pan. Take the water that has overflowed from the large pan, weigh it, and you will discover that it is the same weight as your toy boat.
Have you heard of the principles of levers? This is credited to Archimedes too. Have you ever used a sturdy or strong stick or limb to pry things up that are too heavy for you to lift? If you
have used this method before, you have been using a lever.
A lever can make work much easier because the small force at one end can move a heavy load at the other end. Archimedes' said, "Give me a lever long enough and a place to stand, and I could move
the earth itself." He showed others what a lever could accomplish by pulling a heavily loaded ship along the beach with a lever-all by himself!
After these two discoveries, Archimedes became known as a great inventor throughout many parts of the world. Once, when the Romans wanted to invade the city of Syracuse, the king called for the
help of Archimedes. What do you think Archimedes' used? Levers! He built new and powerful levers called catapults. They worked in the same way as a giant slingshot. Do you think they used small
or heavy stones in the catapults? The stones their enemies were faced with weighed about 500 pounds. It has been said that Archimedes constructed a giant burning glass on which to focus the sun's
rays toward enemy ships which set the ships on fire.
Thanks to Archimedes, Syracuse prevented Roman invasions for many years. Eventually there was a great massacre and the city fell to the Roman Empire. A Roman commander had heard of Archimedes and
had given orders that he was not to be harmed. This allowed Archimedes to continue studying mathematics.
One day, as Archimedes was sketching a diagram in the sand, as he was known to do, a Roman soldier came by and ordered him to stand up. Archimedes was so involved in his work that he paid no
attention to the Roman soldier and continued his sketching. The Roman soldier drew his sword and killed the greatest scientist and mathematician of that time.
Further Study:
Archimedes
Biography and personal facts.
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