1. Aristotle's mechanics
Mechanics, which originated in Greece, was systematically summarized in Aristotle's Physics. According to this speculative and humanistic sports viewpoint, ordinary sports are divided into three categories. The first category is the movement of objects on the ground; The second category is the movement of objects falling in the air; The third category is celestial movement. Aristotle explained the reason for the movement. The motion of objects on the ground is mandatory. If you push a pile, it will move, but if you don't push it, it will not move, so force is the reason to keep the object moving. The second and third kinds of sports belong to natural sports. The earth is the center of the universe and the natural destination of all air moving objects. The greater the weight of an object, the greater its tendency to the natural position, so the greater its falling speed; Celestial bodies are made of special materials and have special properties. The celestial body is the place of God, so the movement of the celestial body is along the most perfect curve-circle, at the most perfect speed-at a constant speed. This explanation that can't stand the test of facts is obviously wrong, but it actually influenced and ruled people's minds for 2000 years, and it was not completely corrected until the times of Galileo and Newton. This is not only related to the low level of productivity development, but also related to the social structure at that time. In ancient Greece, it was considered a despicable thing to engage in experimental operations, which should be done by slaves or servants. People with status and "knowledge" did not move, but talked and demonstrated endlessly. Legend has it that Aristotle often gives lectures to his disciples while walking in the garden, so the Aristotelian school is also called a bard. Therefore, the fatal weakness of ancient Greek physics is the lack of attention to quantitative experiments. Even simple experiments can prove that Aristotle's law of falling objects is wrong.
Scholasticism is an ideological system that appeared in medieval western Europe. In order to fool and rule people's thoughts, the church distorted and castrated the reasonable and positive parts of Aristotle's theory and publicized its negative parts, so that the "reformed" Aristotle's philosophy conformed to religious teachings and its works became the authority second only to religious teachings. Lenin once hit the nail on the head and pointed out: "Monvism stifled the creatures in Aristotle's theory and made the dead immortal." Because this processed and reformed philosophy originated from Catholic colleges, it is called scholasticism. This kind of philosophy is keen on starting from abstract concepts, demonstrating religious teachings with complex reasoning, and advocating that reason obeys faith. I'm not interested in experiments and observations, and I don't believe that human feelings are the guide to understanding the essence of things. This philosophy has had a far-reaching impact on the development of science in the history of science. This is particularly prominent in Galileo's struggle with the church.
Leonardo da Vinci (1452~l5 19), a legendary figure of Italian Renaissance who was a century earlier than Galileo, was an all-rounder of scientists and artists. He studied the physiological structure of human body through anatomy, observed celestial bodies and studied astronomy. He is proficient in painting and sculpture, and is good at machinery and civil architecture. In short, his interests are wide, involving many disciplines and technologies. In his activities, there is a remarkable feature: he attaches importance to practice. He said: "when studying a scientific problem, I first arrange several experiments, because my purpose is to decide the problem according to experience, and then point out under what reasons objects will have such an effect." This is all the methods that must be followed in studying natural phenomena ... We must refer to the experience in various situations and environments until we can draw the universal laws they contain from these many examples. " Not only that, he also attached great importance to the important role of the combination of mathematics and experiment in the process of exploring natural laws, and understood the importance of quantitative experiments in scientific methods. He thinks that there is nothing certain in science that cannot be used in mathematical science. He used this method when studying the strength and force of beams and columns, and obtained quantitative results. These insights and practices of Leonardo da Vinci played an important role in inspiring Galileo to establish experimental natural science.
2. Galileo's life and main scientific activities
1564 February 15 Galileo was born in the ancient Italian city of Pisa. His father is a ruined aristocrat who is good at music and mathematics. In his childhood, Galileo showed extraordinary manufacturing and observation abilities, and made his own moving toys and machines. From 65438 to 0572, he began to receive formal education and studied in Santa Maria Monastery. 1581September was admitted to Pisa University to study medicine according to his father's wishes. However, he is not interested in medicine. An accidental opportunity led his interest and attention to mathematics and physics. 1583, the Grand Duke of Tuscany (Pisa belongs to this principality) came to Pisa for the winter. Among his entourage was a very talented court professor Ostilio Matteo Ricci (1540 ~ 1603), who was a friend of Galileo's family. In a math lecture given by Ricky, Galileo who was present was fascinated. Since then, his interest in mathematics has soared. Because of his extraordinary understanding of mathematics and his extraordinary logical thinking ability, he was accepted as a pupil by Richie and guided him to read many mathematical works, especially Archimedes and Euclid. This made Galileo have considerable attainments in mathematics, which played a great role in the establishment and success of his later experimental natural science.
Galileo's love for mathematics caused his father's opposition, and his family was embarrassed. 1583, he left the University of Pisa without a degree and returned to Florence to help his father run the shop. In his spare time, he spent all his time studying mathematics and doing experiments, and began to study by himself and independently.
Legend has it that in 1583, he discovered the law of "synchronization of pendulum" in the phenomenon of swinging on the chandelier of Pisa Cathedral and applied it to practice. Regarding this legend, KINOMOTO SAKURA Sakura, a Japanese researcher in the history of science and science education, once disagreed, on the grounds that the chandelier of Pisa Cathedral was made after 1583. This legend was described in Galileo's Biography by vincenzo viviani (1622 ~ 1703), a student accepted by Galileo in his later years. However, it is well documented that Galileo invented the pendulum pulse meter, which can accurately measure the pulse rate according to the pendulum law. A doctor from the University of Padua mentioned this kind of pulse meter in his book 1607, and attached drawings.
During 1585~ 1589, I worked as a tutor and taught mathematics. 1586, he published his first paper, Hydrostatic Scale, which showed his talent in experiments. This scale is made according to the lever principle and buoyancy principle of Aki Shuide, and can accurately and conveniently measure the specific gravity of metals. At the same time, he also wrote an article about the center of gravity, which was introduced by Richie to the Grand Duke of Ferdinand I. In order to pursue his career, Richie instructed Galileo to write letters to some influential nobles and scientists to introduce his research results in order to get support. In the process, he got to know the Marquis Guido Baudo, who loves science and courtesy. Marquez appreciated his knowledge and talent and expressed his willingness to support and help his research work.
Due to the recommendation of Marquis Guido Baudo, he was hired as a newly added professor of mathematics in Pisa University in 1589, mainly teaching mathematics and astronomy, and he was still keen on studying sports in his spare time. The central problem of his research is the falling body motion under the action of gravity, and he questioned Aristotle's law of falling body and the theory of motion causes. Aristotle's theory of falling body motion can be summarized as two points: first, the speed of falling body is proportional to its weight; Second, the speed of a falling body is inversely proportional to the density of the medium it passes through. Galileo bluntly criticized this as nonsense. He respected Archimedes very much and was deeply influenced by the "buoyancy principle". He tried to explore the law of falling body motion with Archimedes theory, and put forward that the falling speed of an object is directly proportional to its density. When falling in water or air, the falling speed is directly proportional to the density difference between the object and the medium. His hypothesis is reflected in his long paper "On Movement" written in 1590. Giovanni battista benedetti (1530 ~1590), a Venetian mathematician, was contemporary with Galileo and had a great influence on Galileo. He was a famous momentum theorist at the University of Padua. He criticized Aristotle's theory of falling body motion in the Theory of Mechanics published by 1585. He proposed that in a vacuum, objects of different sizes composed of the same substance fall at the same time and at the same distance, that is, their terminal velocities should be the same. This is completely different from Aristotle's conclusion that the falling speed is proportional to its weight. In order to prove this point, he refuted Aristotle's argument by logical reasoning: a heavy object and a light object are tied together and let them fall. According to Aristotle's theory, heavy objects fall fast, light objects fall slowly, and heavy objects are constrained by light objects, so the speed of their falling together must be between their respective falling speeds; On the other hand, the weight of two things tied together should be greater than the weight of specific objects, so they fall faster than either of them. Thus, Aristotle's theory of falling body motion is self-contradictory and can't stand scrutiny. Benedetti's concise and convincing reasoning, in some articles introducing Galileo's discovery of the law of falling objects, is often wrongly described as the ideal experiment first proposed by Galileo, which is really misinformed. E.j. dixter haweis (e.j. dijksterhuis, 1892~), a professor of the history of science in the Netherlands, solemnly put forward this view in his History of Science and Technology co-authored with R. J. Forbes(L900 ~).
There is a legend about falling objects. 1590, Galileo, like all other teachers, philosophers and students on the leaning tower of Pisa, repeatedly dropped two spheres with different weights at the same time, refuting Aristotle's theory of falling objects with the fact that the two spheres looked at the ground at the same time. Although this legend is legendary and widely circulated, it is said that even the wooden balls used in Galileo's experiments are displayed in some museums in Pisa and Florence, but the evidence is insufficient. It is not mentioned in Galileo's well-preserved notes and works, or in the conversations and articles of Galileo's contemporary scientists. This legend first came from Vivian, a student of Galileo, who described it in the Biography of Galileo published by 1654. There are two different views on this legend in history: one thinks that the leaning tower of Pisa experiment is credible and true; The other is that there is no such thing at all, just a legendary description made by Vivian to expand the influence of her teacher. Of course, there are also views that this matter is undecided.
The first view is held by a group of physical historians headed by favaro, editor-in-chief of the national edition of Galileo's Works (its twenty volumes), including the famous British philosopher A.N. Whitehead, who listed the leaning tower experiment of Pisa and the Michelson-Morey experiment in 188 1 year as the two most famous "decisive" experiments in the history of science.
There are a group of physical historians headed by Volfel, editor-in-chief of Galileo's Works National Edition, who hold the second view, including the famous scientific historian butterfield.
There are indeed falling objects experiments in history. This man is Stevin (1548 ~ 1620), a Dutch engineer and mechanic, that is, Lester Vinouse. In "Statics" published by 1586, he introduced a falling experiment he did: "Let's take two shot putters, one of whom is ten times heavier than the other, and fall from a height of 30 feet at the same time and land on a board or something that can make a clear noise. Then, we will see that the light shot put does not take ten times as long as the shot put, but falls on the board at the same time.
Some works and biographical dictionaries on the history of physics with rigorous materials, extensive contents and accurate descriptions, such as C.C. Gillispie (ed. ), Dictionary of Biography of Science, Sons by Charles Scribner, new york, 1970 ~ 1980, refer to Galileo's Leaning Tower of Pisa.
The golden age of Galileo's scientific research was from 1592 to 16 10. With the full help of Marquis Guido Baudo, Galileo went to Venice on 1592 and was hired as a professor of mathematics at the University of Padua. Venice is located on the Adriatic Sea, far away from the Roman inquisition, less controlled by the church and relatively free in academic atmosphere. Due to the development of navigation, trade and handicrafts, Venice was rich in economy and was one of the powerful countries in the Mediterranean at that time. Padua belongs to the Republic of Venice, and Padua University was one of the famous universities in Europe at that time. It is famous in Europe for advocating free research and free thought, and people with various beliefs and new ideas are welcome to give lectures. This kind of environment and atmosphere is very beneficial to Galileo's scientific research activities and a good opportunity to give full play to his outstanding talents. This period is the golden age of his scientific career, the most fruitful period and the happiest period in his life. His scientific world view was formed here.
During this period, Galileo studied many problems, especially mechanical problems. Such as falling body motion, pendulum and inclined plane motion, projectile motion, force composition and so on. In addition, the problems of fluid and heat are also studied. Galileo thermometer was invented during 1592~ 1593. 1609, he was attracted by the news that the Dutch Hans Leppershey (about 1570~ about 16 19) invented the telescope, so he turned his interest and attention from mechanics to optics and astronomy, and was sentenced to life imprisonment by the church in 1633. Most of his research work and discoveries in mechanics were completed during this period and published in his later years.
Galileo mainly taught Euclid's mathematics, Ptolemy's astronomy and Aristotle's mechanics in Padua. Amateur lectures on fortification and military engineering, combined with mathematical knowledge, mechanical experiments and national defense engineering, are very popular among students' aristocratic children.
1597, designed a proportional gauge and compass with military use, and set up a factory to produce and sell these instruments. Before that, he invented the air thermometer according to the property that gas expands with heat and contracts with cold. In use, I found that the temperature measurement was inaccurate, and I was busy with other work at that time, so I couldn't improve it further. I didn't discuss the improvement with student evangelista torricelli (1608 ~ 1647) until my later years. Under his guidance, Torricelli invented the mercury barometer in 1643.
When studying the problem of falling objects, he found that the speed of falling objects in the air is not only related to their weight and density, but also to their size and shape. He realized that the air resistance to falling objects and the assumption that the falling speed of objects is proportional to the density difference between objects and air is wrong. The mistake is that the air resistance is not considered. He believes that if there is no air, the falling speed of objects in a vacuum may have nothing to do with weight and density, and all objects fall at the same speed. He observed that when an object began to fall from a static state, its speed was increasing. He is convinced that this increase in speed is carried out in an extremely simple and obvious way, because he believes that nature essentially acts in the simplest way. With the increase of falling time, the falling distance of the object also increases sharply. He assumes that the falling distance s is proportional to the square of the falling time t, so how can the speed increase to satisfy the above relationship? From the letter he wrote to his friends in 1604, we can see that he put forward the hypothesis that the speed is proportional to the distance traveled, repeating the mistake made by Albert of Saxony (about 13 16~ 1390) more than two centuries ago. Based on this assumption, after mathematical calculation, it is impossible to draw the conclusion that "the falling distance S is proportional to the square of the falling time T", and there are many contradictions. It was not until about 1609 that the correct relationship between speed and falling time was seen in his notes and articles, and it was proved graphically that from this relationship of speed change, the conclusion that "falling distance s is proportional to the square of falling time t" could be drawn. Therefore, Galileo did not get the correct law of the falling body of the leaning tower of Pisa in 1590, as in the legend, but experienced a tortuous and repeated process.
Galileo hopes to test whether these relations are correct through experiments, so as to further verify his hypothesis. However, the process of free fall is too fast to be measured under the conditions at that time. In order to "dilute gravity" and fully slow down the motion, he verified the relationship that "the falling distance S is proportional to the square of the falling time T" by studying the simple pendulum motion and the carefully designed inclined plane experiment, and found the correct law of the falling body motion. In "Dialogue between Two New Sciences" published by 1638, the law of falling body is described in detail for the first time, pointing out that the distance traveled by an object from a static free fall is proportional to the square of the falling time, which is actually the acceleration of gravity. But Galileo did not give an approximation of the acceleration of gravity. The first person who put forward this approximate value of 9.8m/s 2 was christiaan huygens, a Dutch physicist, mathematician and astronomer (1629 ~ 1695).
Galileo's inclined plane experiment is the key experiment to prove the correctness of his hypothesis that the distance of free fall is proportional to the square of falling time. This is completely different from some popular sayings. Galileo discovered the law of falling body through inclined plane experiment, and concluded that the distance is proportional to the square of time from the measured distance and the time spent. This is not only contrary to historical facts, but also inconsistent with the research methods used by Galileo at that time. His method is: according to empirical reasoning, put forward the initial hypothesis, deduce it with mathematical tools, draw a conclusion, and then verify the hypothesis through experiments. This method is now called deduction. In this method, the position and function of the experiment is not to discover the law, but to prove the deductive conclusion, thus proving that the original hypothesis is correct and effective. This method has played an important role in the development of many future scientists and physics.
During his stay in Padua, Galileo made great contributions not only to mechanics, but also to astronomy and the development of Copernicus Heliocentrism.
/kloc-during the period of 0/594, Galileo stayed at home because of arthritis and read books about Copernicus and Heliocentrism. The image of the universe structure described by Copernicus aroused his strong interest and began to study astronomy. In a letter to a friend in Pisa in May 1597, he expressed his support for Copernicus' Heliocentrism for the first time. In August of the same year, I received Kepler's first book, The Mystery of the Universe. In his reply to Kepler, Galileo once again publicly claimed that he was a follower of Copernicus, and claimed that he had found some physical arguments conducive to confirming the earthquake. His interest in Copernicus is not based on mechanics, but on astronomy. The appearance of new stars since 1604 has triggered a debate on Aristotle's theory of sky compactness. In this debate, Galileo publicly supported Copernicus' theory, delivered three informative speeches and prepared to publish an astronomical book. However, his plan was disrupted by an accident and failed to come true. 1606, Meyer, a German in Padua, and his student capra plagiarized the proportional gauge invented by Galileo, translated his Italian instruction into Latin, lied that they invented it themselves, and refuted Galileo as a plagiarist. Galileo sued both of them to defend his right to invention. At that time, Meyer had returned to Germany, while capra was expelled from school. 1607 published "A Self-defense against capra's Defamation and Deception" with argumentative style, and since then began to write with argumentative style as a fighting weapon, and achieved great success.
1609 In July, he heard from a friend that Lipsch of the Netherlands invented the telescope. In August of the same year, it was rumored that he made the first telescope with a magnification of three times. He used an organ tube as a lens barrel with a plano-convex lens and a plano-concave lens with a diameter of 5.6 cm embedded at both ends. He went to Venice and presented it to the Grand Duke. Telescope soon showed its practical value in military and navigation. In recognition of his achievements, the Grand Duke of Venice made him a tenured professor at the University of Padua and gave him an extra salary. He was not satisfied with the success of the first telescope. Through continuous efforts and improvement, by the end of 1609, he had increased the magnification to 32 times, which was the limit of galileo telescope. What makes sense is not that he made the first high-powered telescope, but that he aimed the telescope at the vast starry sky for the first time, which initiated a new era of studying celestial motion with telescopes and founded telescope astronomy.
He first observed the moon and found that the surface of the moon was not as smooth and perfect as described by scholastic philosophers, but as uneven as the surface of the earth, with mountains and deep valleys and rotating around the earth axis. He named the two main mountains on the moon "Alps" and "Apennines" respectively, and drew the first map of the moon in the world. According to the change of light and dark stripes on the moon, he speculated that the moon itself is not luminous, and its bright light is the result of reflecting sunlight. He then observed the planets and found that the planets seen in the telescope were much larger than those seen by the naked eye, but there was little difference between the two stars, which inferred that the stars were far from the ground. The Milky Way is made up of countless stars, which proves Bruno's assertion that the universe is infinite is correct. 161065438+1October 7 is the greatest day in Galileo's life and an important day in the history of astronomy. After several days of observation, he found that Jupiter has four satellites, which rotate slowly around Jupiter, which is more like a picture of a small solar system in the Copernican system.
This is an important support of Copernicus' theory. It shows that Aristotle's celestial world is unchanged, and there are only seven planets, and the statement that one is not much and one is not much is completely untenable. 16 10 In March, he wrote a book "Star Messenger" based on the above observations, which was published in Venice and caused a sensation. Kepler spoke highly of this book. With the consent of Galileo, Kepler reprinted it in Frankfurt, Germany in the same year. In order to support Galileo, Kepler wrote the article Dialogue with Star Messenger, pointing out that Galileo's discovery was completely consistent with his planetary theory.
Galileo is in Padua. He always misses his hometown Florence. In order to return to his hometown, he dedicated Astral Messenger and a telescope to Cosimo del Medici II, Archduke of Tuscany in Florence, and named Jupiter's satellite "Medici Star". 16 10 In July, he was appointed by the Grand Duke of Tuscany as a court professor of mathematics and philosophy, and served as an honorary professor at the University of Pisa. In the same month, Galileo discovered that Saturn was an olive-shaped "Samsung" and mistakenly thought that Saturn had two extremely close satellites. It was not until 46 years later that Huygens correctly suggested that this was caused by Saturn's rings.
Galileo returned to Florence in September of 16 10 to continue his astronomical observation. It was at the end of this month that Venus' profit and loss phenomenon was discovered, and later it was discovered that Mercury had a similar phenomenon. From the phase changes of Venus and Mercury are different from those of the Moon, it is inferred that Venus and Mercury revolve around the Sun in the orbit between the Sun and the Earth. This is undoubtedly a strong evidence for Copernicus.
16 1 1 year, he visited Rome, was received by Pope Paul V, and met with Marquis Federico Ceci (1585 ~ 1630), who founded it in 1603. Yan Li Institution (Yan Li is a bobcat, named after it, which is a metaphor for the profound and powerful power of science. ) is an academic group composed of top Italian scientists at that time, and it is the first influential scientific organization in the history of scientific development. Because of Galileo's academic achievements and reputation, he was elected to the society and became the sixth member.
16 12, Galileo published a paper on hydrostatics, expounding his development of Archimedes' principle and his attack on Aristotle's physical principle. Offended the followers of scholasticism and Aristotle. 16 13, he published a pamphlet "letters about sunspots", describing his observation on the activities and shape changes of sunspots since 16 10. In the book, Copernicus' theory is clearly expounded for the first time, and the preliminary concepts of conservation of angular momentum and inertia are put forward. His views attracted malicious attacks and slanders from opponents in the church and Aristotle's followers, accusing him of preaching heresy and betraying the Bible. 1665438+On February 26th, 2006, the Inquisition tried Galileo, and issued the following decree: "It is foolish, philosophically illusory and pure heresy to think that the sun is motionless in the center of the universe, because it violates the Bible", officially declaring Copernicus's Theory of the Operation of Celestial Bodies as a banned book, and warning Galileo not to use it.
From then on, Galileo lived in seclusion in a villa on the outskirts of Florence, doing some research work that did not violate the church's warning. The mechanical research interrupted by the appearance of telescope 1609 is still going on. He studied the accelerated motion and correctly defined the uniform accelerated motion.