Tell me about Galileo.

Galileo galilei (1564- 1642) is a pioneer of modern experimental science and a great astronomer, mechanic, philosopher, physicist and mathematician in the late Italian Renaissance. He is also the pioneer of modern experimental physics and is known as "the father of modern science". He is an indomitable truth fighter. Engels called him "one of the giants who can break old theories and create new ones regardless of any obstacles". /kloc-0 was born in Pisa on February 5th, 564, and 1642/kloc-0 died in Pisa on October 8th. He is the author of Star Messenger, Letters about Sunspots, Dialogue between Ptolemy and Copernicus, and Dialogue and Mathematical Proof about Two New Sciences.

Is a person who loves thinking and dares to challenge tradition.

Galileo (1564- 1642), an Italian physicist, astronomer and philosopher, was a pioneer of modern experimental science.

1590, Galileo made a famous experiment of "two iron balls landing at the same time" on the leaning tower of Pisa, which overthrew Aristotle's theory that "the falling speed of an object is proportional to its weight" and corrected this erroneous conclusion that lasted for 1900.

1609, Galileo made an astronomical telescope (later called galileo telescope) and used it to observe celestial bodies. He found the unevenness on the surface of the moon and drew the first map of the moon himself. 161065438+17 October, Galileo discovered four moons of Jupiter, which provided conclusive evidence for Copernicus' theory and marked the beginning of its victory. With the help of a telescope, Galileo also discovered Saturn's rings, sunspots, the rotation of the sun, the profit and loss phenomena of Venus and Mercury, the balance between the moon and Zhou Yue on Sunday, and the fact that the Milky Way is composed of countless stars. These discoveries ushered in a new era of astronomy.

Galileo is the author of Star Messenger, Letters about Sunspots, Dialogue between Ptolemy and Copernicus, and Dialogue and Mathematical Proof about Two New Sciences.

To commemorate Galileo's achievements, people named Io, Europa, Ganymede and Callisto as Galileo satellites.

People rushed to preach: "Columbus discovered the new continent and Galileo discovered the new universe."

Detailed:

Galileo was a great Italian physicist and astronomer and a pioneer of the scientific revolution. In history, he first integrated mathematics, physics and astronomy on the basis of scientific experiments, expanding, deepening and changing human understanding of material movement and the universe. Galileo devoted his life to proving and spreading Copernicus' Heliocentrism. As a result, he was persecuted by the church in his later years and imprisoned for life. He overthrew the traditional speculative view of nature represented by Aristotle with systematic experiments and observations, and founded a modern science based on experimental facts and with a strict logical system. Therefore, he is called "the father of modern science". His work laid the foundation for the establishment of Newton's theoretical system.

Life and academic career

Galileo was born in Pisa on February 5th, 564. His father, Fen Cenzio Galileo, is proficient in music theory and acoustics, and has written a book "Music Dialogue". 1574 The whole family moved to Florence. Galileo was influenced by his father since childhood and was very interested in music, poetry, painting and machinery. Like his father, he is not superstitious about authority. /kloc-at the age of 0/7, he studied medicine at the University of Pisa according to his father's orders, but he was tired of medicine. After class, he listened with great interest to the lecture of the famous scholar O. Rich, who is a friend of our family. He taught Euclid geometry and Archimedes statics. 1583, Galileo noticed the swing of a chandelier in Pisa church, and then made a simulation (simple pendulum) experiment with a copper ball suspended by a wire, which confirmed the isochronism of the tiny swing and the influence of the swing length on the period, and thus created a pulse meter for measuring short time intervals. From 65438 to 0585, he dropped out of school because of family poverty and became a tutor, but he still worked hard to teach himself. 1586, he invented the buoyancy balance and wrote the paper "Small Balance".

1587, he took a paper on the calculation of solid center of gravity to the University of Rome to meet Professor C. Clavius, a famous mathematician and calendarist, and was greatly praised and encouraged. Clavius brought back his lectures on logic and natural philosophy from P Vara, a professor at the University of Rome, which was of great help to his future work.

From 65438 to 0588, he gave an academic lecture on the graphic conception of purgatory in A. Dante's Divine Comedy, and his literary and mathematical talents were greatly praised. The following year, he published several papers on the calculation of solid center of gravity, including some new statics theorems. Because of these achievements, the University of Pisa hired him to teach geometry and astronomy. The next year he discovered the cycloid. At that time, the textbooks of Pisa University were all written by Aristotelian scholars, and the books were full of theological and metaphysical dogmas. Galileo often expressed sharp objections and was discriminated and rejected by the school. 159 1 year, his father died of illness and the family burden increased, so he decided to leave Pisa. During the Padua period, Galileo transferred to the University of Padua to teach at 1592. Padua belongs to the principality of Venice, far from Rome, not directly controlled by the Vatican, and his academic thoughts are relatively free. In this good atmosphere, he often participates in various academic and cultural activities inside and outside the school, arguing with colleagues with various ideas and opinions. At this time, while absorbing the research results of mathematics and mechanics of N.F. tartaglia, G.B. Benedetti, F. Comentino and others, he often inspected factories, workshops, mines and various military and civil projects, made extensive friends with technicians in various industries, helped them solve technical problems, and learned production technical knowledge and various new experiences from them, which was inspired.

During this period, he deeply and systematically studied the falling body, projectile motion, statics, hydraulics and some civil and military buildings. Discovered the principle of inertia, invented the thermometer and telescope.

1597, he received a book "The Mysterious Universe" by J Kepler, and began to believe in Heliocentrism, acknowledging that the earth has two movements: revolution and rotation. But at this time, he was deeply impressed by Plato's most natural and perfect circular motion thought, and was not interested in Kepler's theory of planetary elliptical orbit. 1604 A supernova appeared in the sky, and the light lasted for 18 months. He took the opportunity to make several popular science speeches in Venice to promote Copernicus' theory. Because of the wonderful speech, the audience gradually increased and finally reached more than 1000 people.

1609 In July, it was rumored that a Dutch glasses worker invented a telescope for people to enjoy. He didn't see the real thing, so he thought of making a telescope with organ tube and convex-concave lens in the future. The magnification was 3, and then it was raised to 9. He invited Senator Venice to the top floor of the tower and looked at the distant view through a telescope, which surprised all the spectators. The Senate then decided that he was a tenured professor at the University of Padua. At the beginning of 16 10, he increased the magnification of the telescope to 33 times to observe the moon, the sun and the stars, and found many new discoveries, such as the uneven surface of the moon, the light emitted by the moon and other planets is the reflection of the sun, Mercury has four satellites, the Milky Way was originally a confluence of countless luminous bodies, Saturn has a changeable ellipse and so on, which opened up a new world of astronomy. In March of that year, he published the book Star Messenger, which shocked all of Europe. Later, it was discovered that Venus changed in profit and loss and size, which was a strong support for Heliocentrism. Galileo later looked back on his 18 years in Padua and thought it was the most productive and spiritual period in his life. In fact, this is also the greatest academic achievement in his life.

Galileo's fruitful achievements in physics and astronomy during his 20 years in Tuscany aroused his greater academic ambition. In order to get enough time to devote himself to scientific research, in the spring of 16 10, he resigned from the university and accepted the appointment of the Grand Duke of Tuscany as the chief mathematician and philosopher of the court and the honorary position of the chief professor of mathematics at the University of Pisa.

In order to protect science from church interference, Galileo went to Rome many times. 16 1 1 year, in order to win the recognition of his discoveries in astronomy from religious, political and academic circles, he went to Rome for the second time. In Rome, he was warmly received by elites including Pope Paul V and some senior bishops, and was accepted as an academician by the Lindsay Institute. At that time, the Jesuit priest acknowledged his observation, but disagreed with his explanation. In May this year, at the meeting of the University of Rome, several senior priests publicly announced Galileo's astronomical achievements.

In the same year, he observed sunspots and their movements, compared the movement law of sunspots with the projection principle of circular motion, and proved that sunspots are on the surface of the sun; He also found that the sun rotates. 16 13 published three communication articles about sunspots. In addition, in 16 12, the book "floating body dialogue in water" was published.

16 15 A perfidious cleric group and many people in the church who were hostile to Galileo jointly attacked Galileo's argument of defending Copernicus and accused him of violating Christianity. After learning the news, he went to Rome for the third time in the winter of, trying to save his reputation, pleading with the Vatican not to be punished for keeping Copernicus' views, and not to publicly suppress him and publicize Copernicus' theory. The Vatican acquiesced in the former request, but rejected the latter. In 16 16, Pope Paul V issued the famous "16 16 ban", forbidding him to reserve, teach or defend Heliocentrism orally or in writing.

1624, he went to Rome for the fourth time, hoping that his old friend, the new Pope urban VIII, would sympathize with and understand his wishes in order to maintain the vitality of emerging science. He had six audiences, trying to explain that Heliocentrism could be in harmony with Christian teachings, saying that "the Bible teaches people how to enter the kingdom of heaven, not how celestial bodies work"; And tried to convince some archbishops, but to no avail. Urbon VIII insists on "16 16 ban" unchanged; He is only allowed to write a book introducing Heliocentrism and geocentric theory at the same time, but his attitude towards these two theories must not be biased, and both should be written as mathematical hypotheses. In this year's efforts, he developed a microscope, "which can enlarge flies into hens."

In the following six years, he wrote a book "Dialogue between Ptolemy and Copernicus". 1630, he went to Rome for the fifth time and obtained the "publishing license" of this book. The book was finally published in 1632. This book is neutral on the surface, but actually defends the Copernican system, and in many places implicitly ridicules the Pope and the Bishop, which goes far beyond the scope of discussing only mathematical assumptions. The book has a humorous style and is listed as a literary masterpiece in the history of Italian literature.

Half a year after the publication of Dialogue, the Holy See ordered it to stop selling, arguing that the author had blatantly violated the "16 16 ban" and the problem was serious and needed to be examined urgently. It turns out that before Pope urban VIII, Galileo was provoked to say that in the Dialogue, he made some absurd and wrong remarks with the Simpleqiu and conservative mouth, which made him furious. The group that once supported him as pope strongly advocated severely punishing Galileo, while the Holy Roman Empire and the Kingdom of Spain believed that conniving Galileo would have a great impact on heresy in various countries and put forward a joint warning. Under these internal and external pressures and provocations, the Pope ignored his old friends and issued Galileo's order this autumn to be tried by the Roman Inquisition.

Galileo, who was nearly seventy years old and sickly, was forced to go to Rome in the cold winter and was interrogated three times under the threat of torture. There is no defense at all. After several tortures, on June 22nd, 1633, 10 cardinals jointly pronounced the sentence, mainly for violating the "16 16 prohibition" and biblical teachings. Galileo was forced to kneel on the cold slate and sign the "repentance book" written by the Vatican. The presiding judge announced that Galileo was sentenced to life imprisonment; The dialogue must be burned and it is forbidden to publish or reprint his other works. This judgment immediately informed the whole Catholic world that all cities with universities must gather to read it, so as to set an example for others.

Galileo is both a diligent scientist and a devout Catholic, convinced that the task of scientists is to explore the laws of nature, while the function of the church is to manage people's souls and should not infringe upon each other. Therefore, he didn't want to escape before his trial, and he didn't openly resist when he was tried, but he always obeyed the Vatican's disposal. He believes that it is extremely unwise for the Vatican to exercise its power outside the scope of theology, and it can only be privately dissatisfied. Obviously, G Bruno was burned to death at the stake, and T campanella was put on death row for a long time. What happened to these two outstanding Italian philosophers cast a terrible shadow on his spirit. The inquisition's decision was later changed to house arrest, and his student and old friend Archbishop A. Picolomini was appointed to take care of him in a private house in Siena. The regulations prohibit visitors and hand in writing materials every day. Under the careful care and encouragement of Piclomini, Galileo was resurrected, and he accepted Piclomini's suggestion and continued to study uncontroversial physical problems. So he still wrote his most mature scientific thoughts and achievements into Dialogues on Two New Sciences and Dialogues on Mathematical Proof with three dialogue characters in Dialogues and simple writing style. Two new sciences refer to mechanics and dynamics of materials. This manuscript was completed on 1636. Because the church banned the publication of any of his works, he had to entrust a Venetian friend to smuggle them out of the country and publish them in Leiden, the Netherlands on 1638.

Galileo had just stayed in Piccolomini's house for five months when someone wrote an anonymous letter accusing Piccolomini of being too kind to Galileo. The Vatican ordered Galileo to move to his former residence in Chetri, near Florence, in June 5438+February of that year, and his eldest daughter Virginia took care of him. The ban remained. She took good care of her father, but died before him four months later.

Galileo repeatedly asked to go out for medical treatment, but was not allowed. 1637 is blind. It was not until the next year that he was allowed to live in his son's house. During this period, in addition to the Grand Duke of Tuscany, there were also J Milton, a famous British poet and political commentator, and P Gasanti, a French scientist and philosopher. His student and old friend B. Castay also discussed with him the calculation of ground longitude by using wooden satellites. At this time, the Vatican's restrictions and surveillance on him have been obviously relaxed.

1in the summer of 639, Galileo was allowed to accept the smart and studious 18-year-old youth V. viviani as his last student, and he could take care of him. The young man made him very satisfied. 164 1 10 in June, Casta introduced his student and former secretary e torricelli to accompany him. They discussed with the blind old scientist how to design a mechanical clock by using the isochronism of pendulum, and also discussed the collision theory, the libration of the moon, the height of water column in the mine under atmospheric pressure and other issues, so he was still engaged in scientific research until his death.

Galileo died on1642 65438+1October 8, and the funeral was sloppy. It was not until the next century that his bones were moved to the cathedral in his hometown.

Learn to succeed.

New scientific ideas and scientific research methods Before Galileo's research achievements were recognized, physics and even the whole natural science was only a branch of philosophy and did not gain its own independent status. Philosophers at that time were bound by theology and Aristotle's dogma, thinking hard, and could not get objective laws in line with reality. Galileo dared to challenge the traditional authoritative thought, not by speculating on the causes of things, but by observing natural phenomena and discovering natural laws. He abandoned the theological view of the universe and thought that the world was an orderly whole that obeyed simple laws. To understand nature, it is necessary to carry out systematic experimental quantitative observation and find out its accurate quantitative relationship.

Based on this new scientific idea, Galileo advocated the research method of combining mathematics with experiment; This research method is the source of his great achievements in science and his most important contribution to modern science. The study of physical problems by mathematical methods was not initiated by Galileo, and it can be traced back to Archimedes in the 3rd century BC, the oxford school and Parisian schools in14th century and the Italian academic circles in 15 and16th century. They all made some achievements in this respect, but they didn't put the experimental method in the first place, so they didn't make a breakthrough in thought. Galileo's idea of attaching importance to experiments can be seen in a letter he wrote to Duchess Christina in 16 15: "I want to ask these clever and careful priests to seriously consider the difference between speculative principles and principles confirmed by experiments. You know, the opinions of professors who do experimental work are not determined by subjective will alone. "

Generally speaking, Galileo divided the research method of combining mathematics with experiment into three steps: ① Firstly, the main part of intuitive knowledge obtained from phenomena was extracted and expressed in the simplest mathematical form, and the concept of quantity was established; Secondly, another quantitative relationship that is easy to be verified by experiments is derived from this formula by mathematical method. ③ Then, this quantitative relationship is confirmed by experiments. His research on the law of uniform acceleration of falling objects is the best explanation.

The simplest assumption that can be made from the accelerated motion of a falling body may be that its instantaneous speed is proportional to the distance, which may also be proportional to the falling time. This is step ① of the research method. Through mathematical demonstration, it is not difficult to find that the first hypothesis is not valid for uniformly accelerated motion. So let's assume □□□ or □ =□□□, where □ is the acceleration.

Since the value of □ cannot be measured directly, the formula is converted into the form of measurable distance: □□ Then, at the end of □ 1, 2, 3, the distance the falling body moves, and step ② is completed.

The last step is to verify through experiments: because of the large acceleration of free fall, even in a short time, the falling distance will be large and difficult to measure. In order to "dilute" the acceleration and reduce the acceleration, Galileo designed an inclined plane rolling ball experiment to measure the relationship between the stroke and time of the bronze ball rolling down from the smooth groove on the inclined plane. He repeated the experiment with an accurate clepsydra 100 times. The results obtained are consistent with the quantitative relationship of □ -□ envisaged in step ②, with good repeatability, which confirms the correctness of the hypothesis that the falling body is uniformly accelerated.

It can be seen that the purpose of Galileo's scientific experiments is mainly to test whether a scientific hypothesis is correct, rather than blindly collecting information and summing up facts.

The innovation of physics concepts and principles, inertia principle and new concepts of force and acceleration make people intuitively experience that heavy objects need a lot of force, while light objects only need a little force. Aristotle drew a general conclusion from this: all objects have the nature of keeping still or looking for their "natural position", and thought that "everything that moves must have a promoter" and connected strength with speed by the law of proportion. Galileo put forward a new concept. He observed that when an object slides upward along a smooth inclined plane, the speed will be slowed down to different degrees due to the different inclination angles of the inclined plane. The smaller the inclination angle, the smaller the deceleration. If you slide on a level surface without resistance, keep the original speed and slide forever. It is concluded that "if a moving object has a certain speed, as long as there is no external reason to increase or decrease its speed, it will always maintain this speed-this condition is only possible on the horizontal plane, because in the case of inclined plane, the downward inclined plane provides the reason for acceleration, while the upward inclined plane provides the reason for deceleration;" Therefore, only the motion on the horizontal plane is constant "(dialogue between two new sciences, the third day, question 9, hypothesis 23). In this way, Galileo put forward the concept of inertia for the first time, and for the first time linked the external force with the "external cause of acceleration or deceleration", that is, the change of motion. Galileo put forward new concepts of inertia and acceleration and new laws of uniform acceleration motion of objects under the action of gravity, which laid the foundation for the establishment of Newton's theoretical system of mechanics. This new concept of inertia overturns the view of Aristotle school 1000 that the motion of objects is driven by elves or circuitous air from the outside for more than a thousand years, and also clarifies the vague "impulse" theory in the Middle Ages. This is the theoretical achievement of human long-term research on mechanical motion, which was supported by the supporters of seismology at that time. Although Galileo did not explicitly write the principle of inertia, he showed that it was an objective law of the nature of objects, and he skillfully used this principle when studying other physical problems. However, he failed to get rid of Plato's view that planets move in circles and believed in the existence of "circular inertia", so he failed to extend the concept of inertial motion to the motion of all objects. Two years after Galileo's death, Descartes expressed the complete principle of inertia.

Galileo attributed the change of speed and direction of an object or the generation of acceleration to the action of various forces, which is an objective understanding of the nature of force and the embryonic form of Newton's second law. The discovery of inertia principle broke the old idea that force is the cause of motion, but thought that force is the reason to change the state of motion. Newton spoke highly of Galileo's pioneering work in the first and second laws of motion in the book Mathematical Principles of Natural Philosophy (see Newton's laws of motion).

Galileo found in the study of trajectory that horizontal motion and vertical motion are independent and do not interfere with each other, but the actual trajectory can be synthesized by parallelogram rule. He completely explained the parabolic nature of trajectory from the uniform acceleration motion perpendicular to the ground and the uniform acceleration motion in the horizontal direction, which is a great gain in the research of motion synthesis and has practical significance.

When Galileo defended Copernicus's theory of ground motion with physical principles, he applied the principle of motion independence to explain the path of stones falling from the top of the mast to the bottom of the mast without deviating from the stern. He further put forward the concept of inertial frame of reference for the first time with the famous assertion that the motion law of the objects in the cabin is constant in uniform linear motion. This principle is called Galileo's principle of relativity by an Einstein, and it is the predecessor of special relativity.

The discovery of the periodic nature of the simple pendulum Galileo made an experimental study of the simple pendulum by observing the swing of the hanging lights in the church. It is found that the period of a simple pendulum is proportional to the square root of the pendulum length, but has nothing to do with the amplitude and weight of the pendulum. The discovery of this law laid a foundation for the vibration theory and the design scheme of mechanical timing device.

The finite speed of light and its measurement predecessors never had a clear understanding of whether the speed of light is limited. Galileo observed the lightning phenomenon, thought that the speed of light was limited, and designed a scheme of shielding the light to measure the speed of light. However, limited by the experimental conditions at that time, this measurement method actually measured the reaction of the experimenter and the action time of the human hand, rather than the propagation time of light. However, if there is a light source with regular light and dark changes, or a device controlled by high-speed machinery instead of human hands, the true speed of light can be measured. Later, the methods of measuring the speed of light, such as satellite food method, rotating gear method, rotating mirror method, Kerr box method and frequency conversion flash method, were all used for reference.

Development of several basic physical experimental instruments Galileo not only designed and demonstrated many experiments himself, but also developed many experimental instruments himself. He is rich in craft knowledge and exquisite in production technology. Many experimental instruments he created were very influential at that time and later generations. Here are some examples:

Buoyancy balance This is a direct reading instrument that uses buoyancy principle to quickly determine the proportion of gold and silver in gold and silver utensils and jewelry. This tool has been used in the trading of gold, silver and jewelry ships.

Thermometer Galileo's thermometer is an open liquid thermometer. The glass tube is filled with colored water and alcohol, and the liquid level is connected with the atmosphere (see Galileo thermometer). This is actually a mixture of thermometer and barometer, because he didn't have a clear understanding of the change of atmospheric pressure at that time. Nevertheless, its academic value is still great, and temperature has since become an objective physical quantity, rather than an uncertain subjective feeling.

The telescope made by Galileo can observe the positive image of an object. After improvement, its magnification is gradually increased from 3 times to 33 times; It not only points to the starry sky, but also can be applied to ship fortresses, and has made unprecedented rich discoveries. This telescope is simple in structure, but its magnification and resolution are greatly limited by spherical aberration and chromatic aberration.

Thoroughly overthrowing Aristotle's material view and the dominant view of nature in medieval Europe is Aristotle's theological view of nature, which has become a tool for feudal theocracy rulers to control people's thoughts. Aristotle believes that the earth and everything on it are composed of four elements: air, fire, water and earth. They are ugly, unclean and imperfect, with changes and birth and death. Fire and gas make up light things that flow upward, and water and soil make up heavy things that fall downward. Celestial bodies are pure, perfect and eternal objects composed of ether. And because "God hates vacuum", vacuum cannot exist. But Galileo found from the telescope that there are peaks and depressions on the surface of the moon, which are uneven and imperfect, and Venus also has profit and loss changes; There are still active sunspots on the surface of the sun; The naked eye can directly see the explosion of supernovae and its gradual darkening and disappearance. All these have broken Aristotle's thought that the sky is higher than the earth, and the nature of the celestial bodies in the sky is very different from that on the earth.

Galileo learned from the study of floating bodies through hydrostatics that all objects are heavy and not absolutely light. Celestial bodies are unified with the earth and everything on the ground in material structure. Vacuum may also exist and produce, and only in vacuum can the true nature of object motion be studied. This completely overthrew Aristotle's material view based on subjective speculation, thus fundamentally shaking the ideological rule of feudal theocracy.

Pioneer of scientific revolution

Galileo made epoch-making contributions to the emancipation of human mind and the development of civilization. Under the social conditions at that time, in order to strive for academic freedom that was not suppressed by power and old traditions, and for the growth of modern science, he waged unremitting struggles and made a loud voice to the whole world. Therefore, he is a pioneer of the scientific revolution, and can also be said to be the "father of modern science". Although he was finally deprived of his personal freedom in his later years, his will to create new science did not waver. His spirit and achievements in pursuing scientific truth will always be admired by future generations.

1799, Pope Paul II of the Vatican publicly rehabilitated Galileo on behalf of the Holy See, arguing that the persecution of him by the Holy See more than 300 years ago was a serious mistake. This shows that the Vatican finally admitted Galileo's claim that religion should not interfere with science.

It can be divided into the following three aspects:

① mechanics

Galileo was the first scientist to introduce experiments into mechanics. He determined some important mechanical laws through the combination of experiment and mathematics. 1582, after long-term experimental observation and mathematical calculation, he got the isochronous law of pendulum. Later, he dropped out of school on 1585 due to family financial difficulties. When he left the University of Pisa, he deeply studied the works of ancient Greek scholars Euclid and Archimedes. He wrote his first paper entitled "Balance" based on the principle of lever and buoyancy. Soon after, he wrote a paper on gravity, which revealed the essence of gravity and center of gravity for the first time and gave an accurate mathematical expression, so he became famous at one fell swoop. At the same time, he questioned many viewpoints of Aristotle.

During the period of 1589 ~ 159 1, Galileo made a detailed observation on the motion of falling objects. Theoretically and experimentally, it is denied that Aristotle, who has ruled for thousands of years, established the correct "law of free fall" on the "law of falling body motion", that is, under the condition of ignoring air resistance, balls with different weights fall to the ground at the same time, and the falling speed has nothing to do with the weight. According to V. viviani, a student of Galileo in his later years, the falling experiment was conducted in public on the leaning tower of Pisa: 1589, one day, Galileo dropped an iron ball weighing100lb and landed almost at the same time. The competitors present were dumbfounded and shrugged their shoulders in laughter. However, Galileo's works did not clearly indicate that the experiment was carried out on the leaning tower of Pisa. So it has been controversial for several years.

Galileo made a detailed study on the basic concepts of motion, including center of gravity, speed and acceleration, and gave a strict mathematical expression. Especially the concept of acceleration is a milestone in the history of mechanics. With the concept of acceleration, the dynamic part of mechanics can have scientific basis, while before Galileo, only the static part was described quantitatively.

Galileo informally put forward the law of inertia (see Newton's law of motion) and the law of motion of objects under the action of external forces, which laid the foundation for Newton to formally put forward the first and second laws of motion. Galileo was the pioneer of Newton's creation of classical mechanics.

Galileo also put forward the law of resultant force and projectile motion's law, and established Galileo's relativity principle. Galileo's contribution to mechanics is various. This is described in detail in his mechanical book Dialogue between Two New Sciences and Mathematical Proof written in his later years. In this immortal book, besides dynamics, there are many contents about mechanics of materials. For example, he expounded the bending test and theoretical analysis of beams, and correctly summarized the mechanical similarity relationship between the bending capacity and geometric dimensions of beams. He pointed out that for cylindrical beams of similar length, the bending moment is proportional to the cube of radius. He also analyzed the simply supported beam under concentrated load and correctly pointed out that the maximum bending moment is under load and is proportional to the product of its distance to two points. Galileo also analyzed the problems that should be paid attention to when applying the beam bending theory to practice, and pointed out that the size of engineering structures should not be too large, because they would be destroyed under their own weight. According to his experiments, he came to the conclusion that when the body size of animals decreases, the strength of their bodies does not decrease proportionally. He said, "A puppy may be able to carry two or three dogs of the same size, but I believe a horse may not be able to carry a horse of the same size."

② Astronomy

He was the first scientist who made great achievements in observing celestial bodies with a telescope. These achievements include: the discovery that the surface of the moon is uneven, Jupiter has four satellites (now called Galileo satellites), the rotation of sunspots and the sun, the profit and loss of Venus and Jupiter, and the Milky Way is composed of countless stars. He confirmed Copernicus's "theory of earth movement" with experiments, and completely denied Aristotle and Ptolemy's "theory of earth movement" which ruled for more than 1000 years.

③ Philosophy

Throughout his life, he insisted on fighting against idealism and scholasticism, advocated understanding the laws of nature with concrete experiments, and believed that experience was the source of theoretical knowledge. He denied the existence of absolute truth and absolute authority to master the truth in the world, and opposed blind superstition. He acknowledged the objectivity, diversity and infinity of matter, which is of great significance to the development of materialist philosophy. However, due to historical limitations, he emphasized that only material attributes that can be summarized as quantitative characteristics exist objectively.

Galileo "abandoned" Heliocentrism because he supported Heliocentrism's imprisonment. He said, "Considering various obstacles, the shortest line between two points is not necessarily a straight line." It is because of this idea that he temporarily gave up his support for eternity, instead of being as brave as Bruno, but he could continue to make contributions to science.

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