What are Archimedes' stories in history? How to distinguish the crown from the real one?

Let's talk about the story of Archimedes first, and then talk about how Archimedes distinguished a crown from a real crown.

In 2 12 BC, the city of Syracuse, located on the beautiful Sicily, was a mess. After a three-year siege of Syracuse, the powerful Roman army cooperated with the traitors in the city and finally broke through this troublesome city.

However, there is an old man in the city who doesn't seem to hear the approaching cry and killing, staring down at the geometric figures drawn on the ground and thinking hard.

At this time, a bloody leather boot stepped on the figure. The old man looked up and found that it was a fierce Roman soldier, so he shouted angrily, "Go away, don't damage my pictures!" " Before he could say the second sentence, the Roman soldier killed the old man, the greatest mathematician in ancient Greece, and was called Archimedes, the god of mathematics.

Archimedes was born in 287 BC, and his hometown Syracuse is located in beautiful Sicily. It is a Greek colonial city with prosperous economy and culture. Archimedes' family is a noble in Syracuse, and is related to Henon, the ancient king of Syracuse. The family is very rich. When Archimedes was eleven years old, with the help of his relationship with the royal family, he had the opportunity to travel across the sea to Alexandria, the cultural center of ancient Greece, where he studied under Euclid's students erato Sese and Cannon.

However, neither a wealthy family nor a lucky opportunity is the fundamental reason why Archimedes became a talented mathematician. His success stems from diligent exploration and unremitting efforts.

According to legend, Archimedes paid close attention to problems and often forgot everything around him. Once, everyone was very concerned about Archimedes' health. They rubbed him with ointment for the Greek bath and pushed him to the bathhouse to take a bath. However, after a long time, he didn't come out. Everyone thought something had happened to him and rushed into the bathhouse to see him. But Archimedes in the bathhouse has forgotten to take a bath and is drawing geometric figures on the body coated with ointment by hand.

Archimedes is not a mathematician who only likes abstract thinking and despises practical application. According to legend, he once made a celestial instrument. With this instrument, you can understand the movement of celestial bodies and calculate the time to start birthdays and eclipses. Some history books also record that he once made a huge parabolic mirror, which could gather sunlight and project it on enemy warships to light the sails.

Mathematician Archimedes was also a great patriot. In 2 15 BC, Roman troops invaded Syracuse by land and sea. At this time, Archimedes was an old man over 70 years old, but for the sake of national security, he did not hesitate to step forward.

Don't underestimate the strength of this old man. It was with his wisdom that the weak city of Syracuse was able to stand in front of the powerful Roman legion for three years, and he made the proud Romans pay a heavy price. In the past three years, it has been difficult not to say that it is a siege, but even to go to the city near Syracuse.

Whenever the Roman army approached the city wall, many stones, large and small, roared out of the city wall and smashed their heads. This is the trebuchet designed by Archimedes.

Whenever Roman naval warships approached the city wall, a machine like a bird's beak would protrude from the back of the city wall and throw huge stones, causing their warships to sink or capsize. These inventions of Archimedes frightened the Romans. Even if a wooden stick appears on the wall, they will exclaim "Archimedes is coming again"! And run away.

However, Syracuse, who fought alone, was no match for Rome, and finally fell. The Roman soldiers who were frightened by Archimedes finally found the chance of revenge. Archimedes passed away, leaving behind the mathematics he loved all his life. According to Archimedes' last wish, his tombstone is engraved with the figure of the ball engraved on the cylinder to commemorate the important theorem he discovered. Archimedes will accompany his beloved mathematics to his death.

So how did Archimedes distinguish a crown from a real crown?

Once, the Greek king gave Archimedes a crown. The king suspected that the goldsmith had mixed silver in Wang Guanzhong and kept the saved gold for himself, so he asked Archimedes to check the composition of the crown.

One day Archimedes jumped into a bathtub full of hot water to take a bath, and some water overflowed. Suddenly, he thought of how to measure the volume of gold.

Archimedes jumped out of the bathtub excitedly, forgot to wear clothes, ran through the streets of the whole city and shouted "Eureka! Eureka! " (Greek is "I found it!") He found that the volume of water overflowing the bathtub was equal to the volume of crown gold put into the bathtub. If the weight of silver and gold are equal, the volume of silver will be larger and more water will be discharged.

Archimedes thus proved that Wang Guanzhong was indeed doped with silver. This is also the origin of Archimedes principle. This is the law of buoyancy.

Give me a lever and I can move the earth. Use solar energy to concentrate light, generate heat and repel the enemy with fire. Distinguishing the authenticity of a crown depends on the principle of density and buoyancy of an object.

In 245 BC, in order to celebrate the grand Moon Festival, King Henon gave the goldsmith a piece of gold as a pure gold crown. Although the finished crown was as heavy as the previous gold, the king still suspected that the goldsmith had adulterated it. He ordered Archimedes to identify whether the crown was pure gold, but he was not allowed to destroy it. This seems an impossible thing.

In the public bathroom, Archimedes noticed that his arm was above the water. Vague thoughts flashed through his mind. He put his arm completely in the water, relaxed, and then his arm surfaced again. He stood up from the bathtub, and the water level around the bathtub dropped; When I sat down again, the water level in the bathtub rose again. He was lying in the bathtub, the water level became higher and he felt lighter. After he stood up, the water level dropped and he felt heavier and heavier. It must be the buoyancy of the water that makes him feel lighter.

This discovery made Archimedes very happy, and he decided to take this opportunity to do experiments on this new discovery. He put stones and stones of almost the same size into the bathtub at the same time and immersed them in the water. The stone sank into the water, but he felt it lighter. He had to press down the block of wood and soak it in water. This shows that buoyancy is related to the displacement (volume) of the object, but not to the weight of the object. How heavy an object feels in water is bound to be related to the density of water (the mass of water per unit volume). Archimedes found a solution to the king's problem here, and the key to the problem lies in density. If the crown contains other metals, its density will be different and the volume of the crown will be different under the same weight.

Putting the crown and the same weight of gold into water, it was found that the crown discharged more water than gold, indicating that the crown was adulterated. More importantly, Archimedes discovered the principle of buoyancy, that is, the buoyancy of liquid to an object is equal to the gravity of the object displacing liquid.

Archimedes, born in a scholarly family, likes to think since childhood and has a strong thirst for knowledge. In 275 BC, Archimedes, aged 1 1, was attracted by the young and promising Syracuse emperor Shiloh and sent him to Alexandria, the cultural center of the Mediterranean basin at that time, to study scientific knowledge. Archimedes, immersed in the sea of books, couldn't sleep all night, drawing all kinds of nutrition from books.

Unlike many ancient Greeks at that time who paid attention to the formation and elaboration of scientific theory, Archimedes paid more attention to scientific theory and its application in practical work and life. After returning to Syracuse, Archimedes invented the earliest water fetching tool in ancient Greece, namely orange peel, using the "lever principle" he discovered, which greatly promoted the development of productive forces. King Shiloh also admired him and jokingly asked him, can your lever make the earth move? At this time, Archimedes said a famous saying that shocked the world. Give me a fulcrum and lever long enough, and I can move the whole earth.

In fact, Archimedes knew clearly that it was impossible for human beings to find a fulcrum and a lever long enough on the earth. The reason why he said this is to show that the "lever principle" is applicable to any object on earth, and the other is to show his confidence in scientific research.

At that time, King Luo Hai asked craftsmen to build a pure gold crown. After the crown was built, the king liked it very much, but the king was worried about adulteration, and the ministers could not distinguish between true and false, so he thought of Archimedes. This time, Archimedes was puzzled by the identification of the crown. Archimedes was lost in thought. He kept writing, drawing and calculating, and put forward many hypotheses. When this was overthrown, he reconsidered from another angle. He was so absorbed that he didn't take a bath for days. The servants couldn't stand it any longer, so they pulled Archimedes to the edge of the bathtub. When he stepped into the bathtub filled with water, the water flowed out until his whole body was immersed in the water. Archimedes had a sudden inspiration and he found a solution.

He ran quickly to the real palace and kept shouting "Eureka, Eureka". Chinese means, I found it. "He asked people to find two tin cans filled with water, with pipes at the mouth, and the water flowing out was discharged into a graduated sink, and then the crown and the same weight of gold were put into the two tin cans respectively. At this time, it was found that the water overflowed from the two tin cans was different. Obviously, the craftsman tampered with the crown material. The volume of key substances is different, so the amount of water spilled is different. As a result, the king was furious and decided to severely punish the craftsman. The king fully believed Archimedes' verification method. He told his subjects not to doubt whatever Archimedes said in the future.

I happened to be reading an Archimedes book recently, and I just answered a wave.

Archimedes was born in 287 BC in a noble family in a small village near Syracuse, Sicily, Greece. He was very rich. His father is an astronomer and mathematician, knowledgeable and humble. Influenced by his family, Archimedes became interested in mathematics, astronomy, especially ancient Greek geometry. Here are some interesting stories to share with you.

1, defending the motherland and inventing the sling crane.

In 2 18 BC, the second Punic War broke out between the Roman Empire and the Carthaginian Empire in North Africa. Maceiras, the supreme commander of the Roman army, led the Roman army to surround the city where Archimedes lived and occupied the seaport. Although Archimedes disapproved of war, he had to do his duty to defend his motherland. Archimedes saw the national crisis, and the sense of responsibility to defend his country prompted him to stand up against the enemy, so he racked his brains and invented slings and cranes to defend against the enemy day and night.

He used the lever principle to make a stone slingshot, which can throw big stones at the warships of the Roman army, or fire spears and stones at Roman soldiers with a transmitter. No enemy near the city wall can escape his flying stone or javelin ... Archimedes also invented various weapons to stop the Roman army from advancing. According to some later records, at that time, he built a huge crane, which could lift the enemy warships into the air and then fall heavily on the water and smash them.

2. Mirror spotlights burn the enemy fleet

One day, the ancient city of Sila was attacked by the Roman army. Young adults and soldiers of the ancient city of Sila went to the front, leaving only the old people, women and children in the city, which was in a very critical moment. At this moment, Archimedes once again stood up for the motherland.

Archimedes asked the women and children to take out their mirrors and come to the coast together, so that the mirror could reflect the strong sunlight to the main sail of the enemy ship. The reflections of thousands of mirrors gathered at one point of the sail, and the sail suddenly burst into flames. The fire burned with the wind, and the Romans didn't know the details, thinking that Archimedes had invented a new weapon. I ran away in a panic.

As for the identification of crown, it is mainly to use the distance of density. He put the crown and pure gold with the same weight in two jars filled with water, and compared the water overflowing from the two jars, and found that the jar with the crown overflowed more water than the other jar. This shows that the crown is larger in volume and different in density than pure gold with the same weight, so it proves that other metals are mixed in the crown.

The significance of this experiment is far greater than finding out that the goldsmith cheated the king. Archimedes discovered the law of buoyancy (Archimedes principle): the buoyancy obtained by an object in a liquid is equal to the weight of the liquid it discharges. [Yi tooth] [Yi tooth] [Yi tooth]

Wang Guanjin's false identification is based on Archimedes principle: an object will be subjected to upward buoyancy in liquid, and buoyancy is equal to the weight of the liquid displaced by the object. Buoyancy = liquid density × liquid volume discharged by the object

King Ashero of Syracuse gave the goldsmith a piece of gold as a crown. After the crown was made, the king felt a little light in his hand. He suspected that the goldsmith was adulterated, but the goldsmith swore with his head that he didn't, and weighed it to his face. The result is as heavy as the original gold nugget. The king still had some doubts, but he couldn't produce any evidence, so he called Archimedes and asked him to solve the problem.

After returning home, Archimedes closed the door, thanked the guests, thought hard, but was puzzled.

One day, his wife forced him to take a bath. The water overflowed when he jumped into the swimming pool. Archimedes heard the sound of running water and his inspiration came out at once. He jumped out of the pool and rushed into the street naked, shouting, "you guy!" Yulega! (meaning discovery) ". The lady was really anxious this time, muttering "really crazy, really crazy" and then chasing out. People in the street don't know what happened, so they all follow them.

It turns out that Archimedes found a solution to the crown problem by overflowing the bathtub: the same substance with the same quality is soaked in water, and the spilled water should have the same volume. If you put the crown in water, the volume of the overflowing water should be the same as that of the gold nugget with the same mass, otherwise the crown must be adulterated.

After Archimedes ran to the palace, he immediately found a basin of water, a piece of gold and a piece of silver, the same weight, and soaked them twice in the basin. The silver overflowed almost twice as much as the gold overflowed, and then he soaked the crown and the gold nugget in the basin respectively. The crown overflowed more water than gold. Obviously, the quality of the crown is not equal to the quality of the gold nugget. The crown must be adulterated. In the face of ironclad facts, the goldsmith had to bow his head and admit that the crown was indeed mixed with silver. The annoying mystery of the crown was finally solved.

One day more than 2000 years ago, an extremely tragic scene happened in the ancient city of Syracuse in ancient Greece. A Roman soldier broke into an old man's house. There is nothing valuable in this simple house, except an old man squatting on the ground, looking at a figure that seems to be his hand-painted. The old man who is absorbed in thinking has reached the state of ecstasy. He completely ignored the soldier with the sword, and when the soldier stepped on the figure on the ground, the old man flew into a rage and said, "Don't step on my figure." After being scolded by the old man, the soldier stabbed the sword in his hand in a rage. At this point, the world-famous old man completely disappeared from the world. Afterwards, the soldier was dealt with by military law, and the miserable old man could never come back. He is a legendary scientist: Archimedes. Although his body has passed away, many stories about him are still circulating in the world:

Archimedes was born in Syracuse in 287 BC. Syracuse is a famous ancient cultural city, and Archimedes' father is also an astronomer and mathematician. It can be said that the humanistic atmosphere of the ancient city and the excellent inheritance of his family have created such a wise mind. At the age of eleven, according to the custom of the ancient city, he was sent to the then world cultural academic center-the Royal School of Alexandria. There, he studied mathematics with the famous mathematician Ke Long at that time. During his study of mathematics, he also became interested in mechanics and astronomy. It can be said that his talent has already appeared at this time.

This direct manifestation is that when he was studying astronomy, he invented the planetarium driven by water. This planetarium can be used to simulate the movement between the sun, planets and the moon and explain the phenomena of lunar eclipse and solar eclipse, which can be said to be very advanced at that time. In addition, in order to solve the problem of land irrigation, he invented a cylindrical screw pump to pump water from the Nile to irrigate the land. This invention is called "Archimedes screw" by later generations, commonly known as "Archimedes pump"; The principle of water pump is the basic principle of today's helicopter. Today, people are still using this ancient Archimedes pump to irrigate fields, which is enough to show the greatness and spread of this invention.

In addition to the scientific and technological items he invented to solve daily life, what makes people relish is the story that he used his knowledge and courage to defend his home against foreign invasion:

The story of resisting foreign invasion with what he learned happened in his twilight years. Archimedes was 73 years old when the new Roman Empire invaded Syracuse, but he was not afraid. He still tried his best to use what he had learned all his life to resist foreign invasion. It is said that he used his knowledge of mathematics and physics to invent a mechanical device similar to a crane. This device can capture Roman warships from the sea and smash them into the water. After hitting the water hard, the warship naturally shattered and sank to the bottom of the sea. It is even said that there is a huge concave mirror where sunlight can be gathered. When it shines on the enemy's canvas, the canvas will burn quickly due to the concentration of energy, and the enemy's wooden hull will naturally burn.

It was because of Archimedes' invention that the Roman army could not cross the coast and advance into the ancient city of Silas. They were trapped outside the walls of the ancient city of Silas for nearly three years. It was also because of Archimedes' invention that the Roman army changed its long-term consumption strategy, and it was under this strategy that the ancient city of Silas was exhausted, so the opening scene happened.

(3) The widely circulated story of testing the authenticity of the crown was recognized by Archimedes Archimedes principle, which was invented by him. Legend has it that there was once a foreign country in Syracuse that had a crown made of pure gold. When it was successfully made, it was really exquisite and glittering, but Hu revealed to the emperor that the crown was not pure gold, and craftsmen secretly mixed some silver when making it. But there was no competent person around to test it, so the emperor invited Archimedes. In order to prevent the crown from being damaged, the emperor asked Archimedes to test whether it was mixed with silver without damaging the crown.

Archimedes knew that if he knew the proportion of the crown, he could know whether it was pure gold, and this required knowing the volume of the crown. But we know that the crown is an irregular object with potholes on its surface, so Archimedes tried his best to think for a while. His extreme research made him think about it while taking a bath in the bathhouse, so he had a historical opportunity to invent the law of buoyancy. When he was taking a bath, he found that the heavier his body was, the more water overflowed from the basin. At this time, he had a brainwave and thought of a good idea of measurement. It was later rumored that Archimedes forgot to wear clothes and ran out of the bathhouse shouting, "I found it, I found it." It can be seen how selfless Archimedes is to science.

So what is the specific principle for him to try to identify the authenticity of the crown? In other words, an object submerged in water will be subjected to upward buoyancy, which is equal to the weight of the water it displaces. Based on this, Archimedes calculated the contents of gold and silver. Because objects with the same weight, the greater the density, the smaller the volume. The density of gold is greater than that of silver, so when the weight of gold and silver is the same, the volume of gold must be smaller than that of silver; If solid gold nuggets and solid silver nuggets with the same weight are put into water, then the gold nuggets will discharge less water than the silver nuggets. The water discharged from the crown is between the two, which proves that the crown is not pure gold.

It can be said that Archimedes devoted his whole life to the development of science. Even before his death, he was still obsessed with a mathematical thinking, and a series of scientific laws he invented were still used by our descendants. It can be said that this is the best embodiment that the spirit still exists despite physical death!

Two thousand one hundred and ninety years ago, a great physicist appeared in Syracuse, Sicily, ancient Greece. His name is Archimedes (287-2 BC12 BC). Archimedes studied hard all his life, devoted himself wholeheartedly to science and was loyal to the motherland, and was respected and praised by people. Archimedes discovered the lever law and Archimedes principle named after him. And use these laws to design all kinds of machinery to serve the people and the motherland. The details of his life cannot be confirmed. But the story about his invention and defense of the motherland has been passed down to this day.

The establishment of lever law

People have used leverage since ancient times and know how to use it skillfully. When the pyramids were built in Egypt, slaves used levers to pry up heavy stones. The shipbuilder used a lever to erect a mast on the ship. People use shaduf to get water from wells and so on. But why can leverage do this? No one could explain the lever law before Archimedes discovered it. At that time, when talking about this issue, some philosophers insisted that it was "magic". Archimedes denied what "magic" it was. He knows that there are always natural reasons for all kinds of phenomena in nature. Lever also has its natural reasons, and he is determined to explain it. After repeated observation, experiment and calculation, Archimedes finally established the law of lever balance. That is, "the arm of force is inversely proportional to the force (weight)." In other words, it is: how many times is the small weight and how many times should the long arm be the short arm. After Archimedes established the lever law, he concluded that any heavy object can be lifted with little force as long as the appropriate lever length can be obtained. It is said that he once said such grandiloquence:

"Give me a fulcrum and I can lift the earth!"

King Syracuse heard this and said to Archimedes, "In the name of Zeus (Zeus is the king of gods in Greek mythology, in charge of heaven, thunder, electricity and rain), what you said is really strange, Archimedes!" After Archimedes explained the characteristics of lever to the king, the king said, "Where can I find a fulcrum to lift the earth?"

"There is no such fulcrum." Archimedes replied.

"So, it is impossible to convince people of the divine power of mechanics?" Said the king.

"No, no, you misunderstood, your majesty. I can give you other examples. " Archimedes said.

The king said, "You are too boastful! You can help me push the same heavy thing and see what you say. " At that time, the king had a problem, which was to build a very big ship for the king of Egypt. After the ship was built, the whole city of Syracuse was mobilized, and it was impossible to push it into the water. Archimedes said, "Well, I'll push the boat for you."

After Archimedes left the king, he used the principle of lever and pulley to design and manufacture a set of exquisite machinery. When everything was ready, Archimedes invited the king to watch the ship launch. He gave the end of a thick rope to the king to pull gently. Suddenly, the big ship moved slowly and slipped into the water smoothly. When the king and ministers saw such a miracle, they were as surprised as if they were watching magic! So the king persuaded Archimedes and issued a notice to the whole country: "From now on, no matter what Archimedes says, you must believe him ..."

The problem of weighing the crown

In the eyes of ordinary people, Archimedes is a "freak". In the words of Plutarch, a Roman historian, "He seems to be an enchanted man. He doesn't care about food or his body." Sometimes, the rice is put on the table and asked to eat, but he doesn't seem to hear it. He is still drawing his geometry in the ashes of the brazier. His wife should look after him at all times. For example, when he rubbed his body with oil, he just sat and oiled himself and forgot what he had done. His wife is more afraid of sending him to the bathhouse to take a bath. The joke was caused by a new crown of the king.

Not long ago, the king asked a craftsman to build him a golden crown. The king gave the craftsman the gold he needed. The craftsman's craft is very clever, and the crown produced is exquisite and unique, and the weight is as heavy as the gold given by the king at the beginning. However, someone reported to the king: "When making the crown, the craftsman swallowed some gold privately and mixed the same weight of silver." Hearing this, the king became suspicious, so he called Archimedes and asked him to try to determine whether the gold crown was mixed with silver and whether the craftsmen kept the gold for themselves. Archimedes was stumped this time. When he got home, he thought hard for a long time and couldn't find a way. I can't eat, sleep or take a shower every day, as if I were possessed.

One day, the king sent someone to urge him to report to the palace. His wife saw that he was too dirty and forced him to take a bath. When he was taking a bath in the bathhouse, he was still thinking about weighing the crown. Suddenly, he noticed that some water overflowed from the side of the bathtub when his body sank into it. At the same time, he felt that the deeper he went into the water, the lighter he was. So, he immediately jumped out of the bathtub, forgot to wear clothes and ran to the street of the crowd. He ran and shouted, "I found it, I found it, and the solution to the crown was found!" " "

After he entered the palace, he said to the king, "Please allow me to do an experiment, and then I can report the result to you." The king agreed. Archimedes put the gold, a piece of silver and the crown, which are as heavy as the crown, in the basin one by one, and saw that the gold nugget discharged less water than the silver nugget, while the crown discharged more water than the gold nugget.

Archimedes said to the king, "The crown is mixed with silver!" " "The king looked at the experiment and didn't understand. Let Archimedes explain. Archimedes said, "One kilogram of iron is bigger than one kilogram of wood. If you put them in water separately, the big wood will discharge more water than the small iron. I apply this principle to gold, silver and crowns. Because the density of gold is high and the density of silver is low, if gold and silver are equally heavy, the volume of silver must be greater than that of gold. Gold nuggets and silver nuggets with the same weight are put into water, and the amount of water discharged by gold nuggets is less than that of silver nuggets. The experiment just now shows that the crown discharges more water than the gold nugget, indicating that the density of the crown is smaller than that of the gold nugget, which proves that the crown is not made of pure gold. " Archimedes' methodical narration persuaded the king. The experimental results prove that the craftsman put the gold in his pocket.

This experiment of Archimedes is the embryonic form of "hydrostatics". However, he did not stop there and continued to study the floating body problem in depth. Results Archimedes principle, an important principle in natural science, was discovered. That is, when an object is immersed in a liquid, the volume of the displaced liquid is equal to the volume in which the object is immersed; Keep the buoyancy of the floating body equal to the weight of the liquid discharged by the floating body.

In 245 BC, in order to celebrate the grand Moon Festival, King Henon gave the goldsmith a piece of gold as a pure gold crown. Although the finished crown was as heavy as the previous gold, the king still suspected that the goldsmith had adulterated it. He ordered Archimedes to identify whether the crown was pure gold, but he was not allowed to destroy it. This seems an impossible thing.

In the public bathroom, Archimedes noticed that his arm was above the water. Vague thoughts flashed through his mind. He put his arm completely in the water, relaxed, and then his arm surfaced again. He stood up from the bathtub, and the water level around the bathtub dropped; When I sat down again, the water level in the bathtub rose again. He was lying in the bathtub, the water level became higher and he felt lighter. After he stood up, the water level dropped and he felt heavier and heavier. It must be the buoyancy of the water that makes him feel lighter.

This discovery made Archimedes very happy, and he decided to take this opportunity to do experiments on this new discovery. He put stones and stones of almost the same size into the bathtub at the same time and immersed them in the water. The stone sank into the water, but he felt it lighter. He had to press down the block of wood and soak it in water. This shows that buoyancy is related to the displacement (volume) of the object, but not to the weight of the object. How heavy an object feels in water is bound to be related to the density of water (the mass of water per unit volume). Archimedes found a solution to the king's problem here, and the key to the problem lies in density. If the crown contains other metals, its density will be different and the volume of the crown will be different under the same weight.

Putting the crown and the same weight of gold into water, it was found that the crown discharged more water than gold, indicating that the crown was adulterated. More importantly, Archimedes discovered the principle of buoyancy, that is, the buoyancy of liquid to an object is equal to the gravity of the object displacing liquid.