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1 Brockbank/ Kessinger Amanda Brockbank and Ethan Kessinger Physics, Period 5 Exploration 1: Ancient Physics Any study of Ancient Physics must begin with the Babylonians. In fact, our entire modern world would look completely different if it were not for the Babylonians. They created the first written language, which started a pattern of ideas being recorded and allowed ideas to pass on to others when they were gone its original form. Ideas were passed along before, but the accuracy was dependent on the person trusted with the information. If people forgot or died before they were able to explain their inventions/discoveries, then it was lost forever. The Babylonians also had a very accurate counting system. In trade as well as in science, the Babylonians had a system that was consistent throughout the society. This was a very important precursor to physics. Aristotle had very specific ideas on the physical world. His theories were taken as fact for centuries. The problem with Figure 1 shows the Babylonian language. This stone has survived the tests of time and is a great example of how permanent written word was. this was that Aristotle did not use tests and experiments to come up with his ideas; Aristotle matched his ideas of the physical world with his philosophy. Aristotle started out with preconceived notions, and found evidence and models that would support those notions. Universities taught Aristotle physics for so many years, which hindered these people from exploring the depths of physics. When a person is taught that something is 2 Brockbank/ Kessinger true, they will not question the validity of the hypothesis nor will they look for other explanations. According to Aristotle, our planet was made up of four elements: Earth, Fire, Air, and Water. Everything, living and nonliving, was made up of a combination of these elements. A human for example was made up of all four elements. The Air made up the human’s lungs and also served as its “breath of life.” The Fire kept the human warm (which is Aristotle’s way of saying a human’s homeostasis). The Water made the humans blood. Finally, the Earth made the human strong and also contributed to the human’s weight. In order to explain how water became blood, Aristotle proposed that the concentrations of each element made the human look and function the way that it did. In Aristotle’s mind, all four elements were pure. However, our Earth and the air that we breathe are not pure. They are mostly Earth and mostly Air, but there are small concentrations of other elements. Aristotle actually thought that there were five elements. There were the four elements on our planet, and there was one element that made up outer space. Quintessence, outer spaces element, made up asteroids, starts, and all other space matter. Archimedes was also a Greek physicist, but he viewed Figure 2 is a Roman copy of a bronze Greek sculpture of Aristotle made during his lifetime. Since the ancient artist was carving 3-dimensionally instead of trying to capture 3 dimensions on canvas, the Greek sculpture would have been a much more accurate depiction of Aristotle than paintings of him. Bronze also holds up a lot better than canvas, so even though all we have today is a replica of the statue, we can assume it is very accurate. physics in a very different way than Aristotle did. While Aristotle used philosophy and separated nature with mathematics, Archimedes combined the two. He is viewed by most as the first mathematical physicist. The other 3 Brockbank/ Kessinger difference between Aristotle and Archimedes is that Archimedes used his knowledge to make practical inventions. His most prolific invention was water screw. This was used in his time, and is still used in some 3rd World countries, to move water from low-lying areas to ditches for irrigation. This was a very important invention because of its simplicity. Archimedes used his knowledge of motion to create a device that moved water out of “A double or triple helix built from wood strips around a heavy wooden pole.” Archimedes is also said to have invented a mirror that when directed at the sun shot a blast of fire in a specified direction. However, most modern historians view this as a myth. Even if his burning mirror did not exist, Archimedes did make several instruments of war. He also discovered the physical law of buoyancy, known today as the Archimedes principle. Archimedes’ principle states that “any body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward, or buoyant, force the magnitude of which is equal to the weight of the fluid displaced by the body.” This is the first time that scientists were able to explain the phenomenon of buoyancy and how it was the inverse of gravity. Because of this, Archimedes is a very influential physicist whose ideas and research continue to be used. In the field of astronomy, Ptolemy was by far the most influential person of this time. He did many things in his lifetime, and was a noted mathematician and geographer. However, his astronomical contributions, such as codifying the Greek geocentric view of the universe, and rationalizing his generations ideas on the apparent motions of the planets. Claudius Ptolemaeus, now universally recognized as Ptolemy, lived in Alexandria around 87 AD to around 150 AD. While he authored several scientific treaties, his most remembered work was The Algamist. In this, he focused on many different things. He challenged Aristotle’s cosmological outline, 4 Brockbank/ Kessinger determined latitude lines, followed the motion of the sun, and looked at eclipses. The level of his research and hypothesis are incomprehensible when you look at the lack of information available at this time for him to build off of. In 13 books, Ptolemy’s The Algamist used kinematic to explain solar, lunar, and planetary motion. This book gave all scientists a much clearer picture of the physical world. Islamic scientists especially used Ptolemy’s information effectively, and this led to their vast contribution to physics. Islamic scientists are often famous for their contributions to the mathematic world, such as the discovery of the number zero, and the coining of the term algebra. However, there were three scientists who also made large contributions to the study of the physical world; scientists whose discoveries paved the way for physicists such as Newton and Bacon. The first of these scientists was named Abu Raihan al-Biruni. Though he studied a wide range of topics in his life, some of his most significant findings were the very beginnings of what we now know as gravity. He defined the concept of gravitation as “the attraction of all things towards the center of the earth.” Given the fact that al-Biruni lived from 973 to 1048, this definition is impressively close to the modern definition, which is, “the force of attraction between any two masses.” Though the concept of specific gravity is present in Archimedes work, Al-Biruni was the first to define it. He was also one of the first to apply the concept of specific gravity to an experiment: after measuring the specific gravity and the volume of gemstones, alBiruni found a direct correlation between the two measurements. Up until that point, the general belief about gravity in relation to astronomy and planets was that which Aristotle had hypothesized centuries earlier: heavenly bodies do not have gravity. Al-Biruni challenged this 5 Brockbank/ Kessinger concept, saying that if gravitation, previously defined by him, pulls everything towards the center, and then there must be gravity between the planets in order to keep them from falling towards that center. While this is not fully correct, he was still one of the first physicists to think critically about gravity and its application in the universe. Al-Biruni made important discoveries and observations about other aspects of the physical world that would come to be important in future scientist’s work. He was the first to notice that the speed of light is far greater than the speed of sound and was the first to realize acceleration is connected to non-uniform motion, which is a part of Newton’s second law. He also was the first to observe that movement and friction cause heat. Applying this to the world, he hypothesized that a lack of movement explains why it is so cold near the geographic poles. The earth and the water form one globe, surrounded on all sides by air. Then, since much of the air is in contact with the sphere of the moon, it becomes heated in consequence of the movement and friction of the parts in contact. Thus there is produced fire, which surrounds the air, less in amount in the proximity of the poles owing to the slackening of the movement there. Again, not all of his concepts about physics were completely correct. However, early physicists like al-Biruni were more important because they were hypothesizing and providing a stepping stone for future scientists to build upon. Following al-Biruni came Abu'l Fath' Abd al-Rahman al-Khazini, who also played a major role, among other things, in furthering the work on gravity. Of his three major works, two are on astronomy. The first, al-Zidj al mu`tabar al-sandjari al-sultani (Sinjaric Tables), gave the positions of 46 stars, calculated from the data given in the Almagest and gave a description of a 24 hour water clock he had built for astronomical purposes. This is one of the earliest recorded examples of an astronomical clock. His second book, Risala fi ‘l-alat (Treatise on Instruments), was a seven part book describing different astronomical instruments. However, his most 6 Brockbank/ Kessinger influential book was called Kitab Muzan al-hikma (The Book of the Balance of Wisdom), which was on hydrostatics and gravity. Using what had previously been published in these subjects, Kitab Muzan al-hikma was superior to anything written up to this point. Most importantly, alKhazini, in this book, was the first to propose the gravity of a body varies with its distance from the center of the earth. Like much of al-Biruni’s works, this was not completely accurate. It was, however, one of the first notions of changes in gravity and weight with relation to the center of the earth. Al-Khazini derived this concept beginning with a strict definition of specific weight, saying, “the magnitude of weight of a small body of any substance is in the same ratio to its volume as the magnitude of weight of a larger body (of the same substance) to its volume." This is the exact definition we use today. One reason Al-Khazini was able to come up with such an accurate definition is that he was the first to show any knowledge that air had weight and this weight increases in density with a change in altitude. It is known that he was aware of this because he also discovered that water is denser when it is closer to the earth’s center, a fact that would later be proven by Roger Bacon in the 13th century. In order to come up with this, he first had to define weight. Al-Khazini called weight “a force inherent in solid bodies which causes them to move, of their own accord, in a straight line towards the center of the earth and towards this centre alone.” Once more, this is not absolutely correct, but it is fairly close. Using all of the aforementioned facts, Al-Khazini theorized that the gravity of a body changes as it gets closer or farther from the center of the earth. In his book, he says: For each heavy body of a known weight positioned at a certain distance from the centre of the universe, its gravity depends on the remoteness from the centre of the universe. For that reason, the gravities of bodies relate as their distances from the centre of the universe. The farther is a body from the centre of the Universe, the heavier it is; the closer to the centre, the lighter it is. For that reason, the gravities of bodies relate as their distances from the centre of the Universe. 7 Brockbank/ Kessinger This concept of gravity was the starting point for our modern concept of gravitational potential energy. Al-Biruni and al-Khazini’s discoveries and methods changed the way science was thought about. They were the first to apply experimental scientific methods to the fields of hydrostatics and dynamics, which they unified to create the scientific field of hydrodynamics. They also were the first scientists to study the science of gravity, (which would be further developed in medieval Europe) generalizing the theory of centers of gravity and applying them to three dimensional bodies. Without these two scientists who are often overlooked, the work done by Newton and others would potentially never have occurred. A third Islamic scientist, who actually did his work earlier than the previous two, was influential in a very different field: optics. Before Abu Ali al-Hasan ibn al-Haitham, there were two main theories on vision: the first, supported by Ptolemy and called the emission theory, said that rays were emitted by the eye towards the object. Al-Haitham argued this was impossible through the use of the stars: he said the distance from a star to the eye was too far for this to be feasible. The second theory, called the intromission theory and supported by Aristotle, said that physical forms emitted by the object enter the eye. Al-Haitham also thought this was inaccurate. Instead, he argued that vision was different rays of light coming from each point on the object to the eye, a much closer definition than either of the previous two. Through experimentation with lens’, mirrors, refraction and reflection, he also found that light travels in a straight line. This was all recorded in his book, Kitab al-Manazir (The Optics Thesaurus), an extremely influential book for its time that introduced many of our modern concepts on optics, including the anatomy of the eye. Eventually, a commentary was written by Kamal al-Din Abu’l- Hasan al-Farisi, which was more frequently used by subsequent scientists than its predecessor. 8 Brockbank/ Kessinger Al-Haitham made two other major contributions to the scientific world. The first, which we still use today, was the use of the scientific method to obtain results. The second, which is seemingly unrelated to optics, though still relevant, is that he was the first to theorize that a body is in motion until something stops it. This is the beginnings of the concept of inertia, but alHaitham did not have any experiments to prove it, leaving the door open for Newton. During the European Middle Ages, several factors contributed to the little exploration of physics. The first was that the Church controlled all aspects of citizens’ lives and was against science. Secondly, the economic recession that happened because of the Great Famine led most people to solely focus on finding enough food to survive. Thirdly, The Bubonic Plaque killed 30% of the European population and isolated the remaining people in their own regions. Without consistent communication, building ideas off or others’ experiments could not effectively happen. This began to change with the European Crusades. Europeans who traveled to the Middle East were exposed to the ideas of these Islamic scientists for the first time. These ideas, new and exciting to the European Crusaders, were brought back to Europe and translated so that they were accessible to educated Europeans, giving way to a whole new group of scientists who emerged during the Renaissance. Four major scientists appeared, making their most significant contributions in the field of astronomy: Nicolaus Copernicus, Galileo Galilee Tycho Brahe and Johannes Kepler. Copernicus, a polish scientist, lived from 1473-1543. Though there were other ideas, the common belief of the time was in the Ptolemaic system, which, put generally, stated that the earth is the center of the universe and all other planets moved in ‘epicycles’ around it. Copernicus, however, disagreed with the Ptolemaic concept of equants and deferents. He says, Yet the widespread [planetary theories], advanced by Ptolemy and most other [astronomers], although consistent with the numerical [data], seemed likewise to present 9 Brockbank/ Kessinger no small difficulty. For these theories were not adequate unless they also conceived certain equalizing circles, which made the planet appear to move at all times with uniform velocity neither on its deferent sphere nor about its own [epicycle's] center…Therefore, having become aware of these [defects], I often considered whether there could perhaps be found a more reasonable arrangement of circles, from which every apparent irregularity would be derived while everything in itself would move uniformly, as is required by the rule of perfect motion. This first challenge of Ptolemaic ideas was a part of his Commentariolus, a small manuscript that was only circulated, never printed in Copernicus’ lifetime. It is believed that Copernicus’ opposition to Ptolemy’s idea of equants is what prompted him to write Commentariolus. He was exposed to and saw the flaws in Ptolemy’s system because at the time, he was working for the church (one main reason he waited to publish his idea until right before his death) to reform the calendar. The reason he had to reform this calendar was due to Ptolemy’s system. It is unknown when Commentariolus was written, though based on later works, it is guessed that it was probably sometime between 1508 and 1514. It was intended as an introduction to a later work, as in it he says it is the “the mathematical demonstrations intended for my larger work should be omitted for brevity's sake…” In it, he listed assumptions that he believed to solve the problems of the current beliefs in astronomy. These included the concepts that the earth is only the center of gravity and the moon’s orbit rather than the center of the universe, that all planets encircle the sun (which is not in the center of the universe), the universe is much larger than it was previously assumed to be, and the motion of the heavens, including the sun, is all due to the motion of the earth. It also dealt with the correct order of the known seven planets (this was before Galileo, so everything known about the universe had to be able to be viewed with the naked eye.) Elaborations on his theory, called the heliocentric system, explained the motion of the planets much more simply, and were published in his book, De revolutionibus (On the Revolutions), published right around Copernicus’ in 1543 for fear of punishment from the church. The first 10 Brockbank/ Kessinger book sets out the order of the planets, one of the strongest pieces of evidence for a heliocentric universe. Copernicus says, “[The sphere of the fixed stars] is followed by the first of the planets, Saturn, which completes its circuit in 30 years. After Saturn, Jupiter accomplishes its revolution in 12 years. The Mars revolves in 2 years. The annual revolution takes the series' fourth place, which contains the earth…together with the lunar sphere as an epicycle. In the fifth place Venus returns in 9 months. Lastly, the sixth place is held by Mercury, which revolves in a period of 80 days.” This made the planets a unified system, established a relationship between the planet’s distance from the sun and their periods, and corrected Ptolemy’s concept that since the universe was geocentric, the sun, Mercury, and Venus all had the same period. This provided an explanation for retrograde motion: Since earth is closer to the sun, it has a faster orbit. Thus, it will sometimes overtake other planets farther from the sun, making it look as though the other planets are moving backwards. Copernicus’ heliocentric system was not perfect (he believed planets move in perfect circles at a constant speed), nor was he able to prove it, but it was an extremely important concept that would forever change the way astronomers looked at the solar system. Galileo, who followed Copernicus’ ideas, is considered by many to be the father of modern science, because he represents a turning point scientific history: Figure 3 is a picture from Copernicus' original publication. It shows that all bodies in our solar system, with the exception of the moon, orbit around the sun. when observational experiments were used in addition to thought and reason to prove nature’s laws. He is most famous for discoveries in two fields: motion and astronomy. His studies on motion began as a contradiction to Aristotle, who believed that heavier 11 Brockbank/ Kessinger objects will always fall faster than lighter ones. To prove Aristotle wrong, Galileo dropped two balls of different weights from the leaning tower of Pisa. As he suspected, both balls hit the ground at the same time. Had Aristotle been correct, the heavier one would have hit the ground first. In 1638, Galileo published a book that mathematically described his concepts of motion in addition to the concept of friction. The key piece of Galileo’s discoveries in astronomy was his invention of the telescope in 1609. Using this, he was able to view things that no one had before, and would be some of the strongest evidence for a heliocentric system, something in which Galileo strongly believed. The strongest piece of evidence for Copernicus’ theory was the discovery that Venus went through phases like the moon, proving that it reflects the sun’s light and thus revolves around the sun. Other important discoveries Galileo was able to make due to the presence of the telescope include seeing the mountains and craters of the moon, viewing the rings of Saturn, and observing the moons of Jupiter, proving Earth is not the only planet with a moon. Another astronomer who expanded on the ideas of Copernicus was named Tycho Brahe. He did not fully agree with Copernicus, nor did he disagree. Rather, he saw advantages in both systems. He believed that physics would be undermined if Earth were not the center of the universe, because heavy bodies fall to the center of the earth. On the other hand, the heliocentric system had its advantages, such as a better explanation of lunar motion and explanation of retrograde motion. So, Brahe created his own system. He put earth at the center of the universe, so Aristotelian physics still made sense. The moon, sun, and stars revolved around the earth, but the other planets revolved around the sun. This system was adopted by various astronomers throughout the 17th century that could neither accept Ptolemy’s ordering of the planet, nor agree 12 Brockbank/ Kessinger with Copernicus’ system for one reason or another (often, including in the case of Brahe, it was for religious reasons). Brahe made a number of other important contributions to astronomy. He revolutionized astronomical instruments, was the first to observe celestial bodies throughout their orbits thus discovering that planets do not always move in perfect circles, made corrections for atmospheric refraction, and proved, through observations of comets that the atmosphere could change, contradicting previous Aristotelian beliefs. Following Brahe was Johannes Kepler. Though Brahe was Kepler’s mentor, Kepler believed in the heliocentric system of Copernicus. However, he wanted to improve upon Copernicus’ concepts. His first effort at this was trying to find a geometrical reason for the distance between each planet and the sun. Unfortunately, this got him nowhere. His next try was much more successful. By analyzing the orbits of various planets with a focus on Mars, Kepler was able to establish three laws of planetary motion. First, planets move in an elliptical orbit around the sun, rather than a perfect circle. Second, planets “sweep out” equal areas over equal amounts of time. Third, the square of the time of a revolution is proportional to the cube of their distance from the sun. These laws were influential in more than the astronomical world: Newton used them to establish universal gravitation. Kepler also made advances in the field of gravitation. He disagreed with Aristotle’s theory on gravity, saying “gravity is a mutual tendency between material bodies toward contact, so the earth draws a stone much more than the stone draws the earth. Heavy bodies are attracted by the earth not because it is the center of the universe, but simply because it contains a lot of material, all of which attracts the heavy body.” He realized that the tides occur because of gravity, stating that "If the earth ceased to attract the waters of the sea, the seas would rise and 13 Brockbank/ Kessinger flow into the moon..." and went on to add: "If the attractive force of the moon reaches down to the earth, it follows that the attractive force of the earth, all the more, extends to the moon and even farther..." Both of these statements are extraordinarily accurate applications of the concept of gravity. He did, however, fail to realize that gravity plays a role in determining the motions of the planets because he believed that a force must be acting upon the planets to keep them in motion. Galileo disproved this years later through the use of projectiles. Newton then used this information on projectiles and applied it to planetary bodies, a concept that is one of the beginnings of the Newtonian Revolution. The history of physics involves all aspects of ancient life. Without contribution made by the Babylonians in written word and measurement, mathematical contributions from Euclid and Pythagoras, and astronomical contributions by Thales all the way through Hipparchus, Physics would not be important. Our history of Aristotle, Archimedes, Ptolemy, the European Middle Ages, Early Islamic science, and the European Renaissance focus mostly on physics, but cannot be completely understood without this other knowledge. The most important conclusion is that all discoveries prior to the Newtonian Revolution were important because they allowed for Newton to expand on them and allow the study of Physics to exponentially grow at an unbelievable rate since that time. 14 Brockbank/ Kessinger Works Cited “Islamic Scientists." 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