Eureka !
Lesson by Boon Boonprayoon
A Thai barge displaces water as it hauls construction material on the Chao Phraya river in Ayutthaya. Wat Phutthaisawan, built in 1352, can be seen in the background. PHOTOS BY KEN MAY
It is staggering when we think about great scientists and mathematicians and how they uncovered the facts about how nature works.
One of the great discoveries about nature is Archimedes’s theory of displacement and buoyancy. Actually, we do experience the law of displacement and buoyancy everyday.
Take this summer for example. Most of us feel like we are burning in the strong sun and sticky weather, so one of our favorite activities at this time is swimming. Once we jump into the pool and reach the bottom, we slowly rise up to the surface of the cool blue water. That is not just because we can swim. Even those who cannot swim—if they don't panic, will gradually be lifted up to the surface of water, too.
eureka - useed when you are very pleased becasue you avhe found the answer to a problem
staggering - so great, shocking or surprising that is difficult to believe; astounding น่าตกตะลึง แทบไม่น่าเชื่อ
uncovered – to discover something that was previously hidden or secret ไขความลับ
relevant – closely connected with the subject you are discussing or the situation you are thinking about เกี่ยวข้องกัน
gradually – slowly, over a long period of time ค่อยเป็นค่อยไป
บทความวันนี้เกี่ยวกับประวัติของ Archimedes ผู้ค้นพบทฤษฎี Eureka ที่เราได้เรียนกันมาตั้งแต่ชั้นมัธยม นั่นคือการแทนค่าเพื่อวัดน้ำหนักของวัตถุด้วยของเหลว หลายต่อหลายคนมักมองว่าการเรียนหรืออ่านบทความทางวิทยาศาสตร์เป็นเรื่องยุ่งยากและไกลตัว แต่อันที่จริงแล้่ววิทยาศาสตร์คือกฎของธรรมชาติ และเราอยู่ในโลกที่ทุกอย่างเกี่ยวข้องกันเนื่องด้วยกฎธรรมชาติทั้งนั้น ดังนั้นดิฉันจึงอยากให้คุณลองอ่านและคิดกันเล่นๆ ในช่วงปิดเทอมว่ามีอะไรบ้างในชีวิตประจำวันของเราที่สามารถเอาทฤษฎีของ Archimedes มาใช้ได้
Whatever floats your boat
An explanation of how ships stay afloatDave Canavan
A Thai barge of the same style and size as the
one above floats high on the water after being emptied of cargo.It amazes me that airplanes can fly, but in the same way, I am amazed by how ships can float. It is especially staggering when you consider that the largest ship ever built, a Supertanker named “Knock Nevis”, is 458.45 meters long and 68.9 meters wide. The ship has a mass of 564,763,000kg, which doesn’t include the weight of over four million barrels of petroleum that it can carry. The fact that a ship this size can still float is astonishing!
The explanation, however, is relatively simple and is based on work by a renowned mathematician known as Archimedes.
Archimedes
Archimedes was born about 287BC in Syracuse, an independent Greek state in Sicily. He is known for many inventions and theories and is surely one of the greatest mathematicians of all time. He is widely known for accurately approximating Pi.
Archimedes also created a water-pump known as the Archimedes screw, developed principles of levers and invented many war machines. However, one of his most famous ideas was his theory on displacement.
When an object is immersed in a fluid, the fluid gets pushed out of the way. The volume of fluid displaced is equal to the volume of the immersed object.
A popular story describes Archimedes’ discovery of how to measure the volume of an object by means of displacement. Archimedes was commissioned by King Hiero II to find out if a crown made by a local goldsmith was pure gold. The King suspected that the goldsmith had stolen some of the gold and replaced it with cheaper and less dense silver.
Archimedes could not damage the crown, but he needed to calculate the density of the crown. While getting into a bathtub, the water level rose because his body displaced the water. He therefore deduced that the displaced water was equal to the volume of his own body weight, and this observation was key to solving the problem.
He then jumped out of the bath and ran through the streets naked, having forgotten to get dressed, shouting “Eureka!” -- meaning “I have found it” -- in Greek.
He placed the crown in water and measured its volume, which he then compared to a known quantity of gold. He recorded the volume of water displaced, and then by dividing the mass of the crown by the volume of the crown, he worked out the density.
He found out that the density of the crown was less than the density of gold; therefore Archimedes could prove that the goldsmith had cheated the King by adding silver to the crown.
staggering - so great, shocking or surprising that is difficult to believe; astounding น่าตกตะลึง แทบไม่น่าเชื่อ
mass - a large amount of a substance that does not have a definite shape or form มวลสาร
renowned - famous and respected; celebrated, noted มีชื่อเสียง
independent (state) - having their own government; self-governing รัฐอิสระ
accurately - อย่างแม่นยำ
lever - a long piece of wood, metal, etc. used for lifting or opening something by somebody placing one end of it under an object and pushing down on the other end ไม้คาน เหล็กงัด
displacement - the amount of a liquid moved out of place by something floating or put in it, especially a ship floating in water การแทนที่ การเปลี่ยนตำแหน่ง หรือปริมาณการขับน้ำ
immerse - to put somebody /something into a liquid so that they or it are completely covered แช่หรือจุ่มทิ้งไว้
commission - to officially ask somebody to write, make or create something or to do a task for you ได้รับหน้าที่ งานที่ได้รับการจ้างทำ
goldsmith - a person who makes, repairs or sells articles made of gold ช่างทอง
calculate - o use numbers to find out a total number, amount, distance, etc.; work out การคิดคำนวน
density - the quality of being dense; the degree to which something is dense ความหนาแน่น
quantity - an amount or a number of something ปริมาณ
Buoyancy
Buoyancy is an upward force exerted on an object placed in a fluid (usually water) by the surrounding fluid. Every time you immerse yourself in water, such as when you swim, you experience buoyancy. This is why you feel lighter when you swim, despite your mass remaining the same.
To feel the pressure of buoyancy, simply place a deep plastic bowl in a full sink and push down. You will clearly feel the force pushing back against your hand.
It is this upward thrust that keeps boats afloat. Archimedes stated, "A body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid." Therefore, a ship will continue to sink until it has displaced its weight in terms of water mass.
However, the shape of an object is a factor that should be taken in consideration. A solid lump of metal will clearly sink. This is due to the density of the metal being much greater then the density of water. If, however, the metal is shaped into the design of a ship, the density will change. The inside of a ship is comprised mostly of air, which is less dense than water. Therefore, the average density of a ship includes a combination of both steel and air.
This allows the ship to be submerged only slightly into the water before the mass of the ship has been displaced -- making the ship float. Every square centimeter of the ship that is submerged in the water has the upward water pressure, buoyancy, acting upon it. If the ship sinks into the water before the mass of the ship is displaced, then the ship will continue to sink until it hits the bottom of the sea.
The density will change depending on the type of water. Salt water exerts a greater upward pressure than fresh water, making objects more buoyant. Warm water works in the opposite way because it is less dense, so ships are less buoyant in the tropics.
You can try buoyancy yourself at home if you have any plasticine. Roll the plasticine into a ball and place it in water. You will see that it sinks. Now mold the plasticine into a boat shaped model and try again. If you get the design right, your plasticine will float because you have displaced the amount of water to an mass equal to the plasticine without totally submerging it. Clever!
David Canavan has an MSc in Behavioral Ecology and teaches science, math and ICT at Garden International School. David is fascinated by science and loves animals, especially the dangerous kind; the more dangerous the better. You may contact David at davidc@gardenbangkok.vcom .
buoyancy - the act of floating, able to float or able to keep things floating กำลังลอยตัว (buoy [v] - ทำให้ลอยขึ้น)
exert - to use power or influence to affect somebody /something ใช้กำลังความสามารถอย่างเต็มที่
thrust - sudden strong movement that pushes something /somebody forward ผลัก ดันไปข้างหน้า
lump - a piece of something hard or solid, usually without a particular shape ก้อน
comprise of - consist of ประกอบด้วย
submerge - to go under the surface of water or liquid; to put something or make something go under the surface of water or liquid จมลงใต้น้ำ
plasticine - a soft substance like clay that is made in different colors, used especially by children for making models ดินน้ำมัน
get something right - true or correct as a fact ทำได้อย่างถูกต้อง






