The main contributions can be divided into the following three aspects: ① Mechanics Galileo was the first scientist to introduce experiments into mechanics. He combined experiments with mathematics and determined some important laws of mechanics. 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." 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 of the church, advocated using concrete experiments to understand the laws of nature, 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 all kinds of obstacles, the shortest line between two points is not necessarily a straight line". It is precisely because of this idea that he temporarily gave up for eternal support, instead of being as brave as Bruno, he could continue to contribute his strength to science. Galileo and His Scientific Discoveries There are two schools of physical theory in ancient Greece, one is represented by the philosopher Aristotle, and the other is represented by the natural scientist Archimedes. Both of them are famous scholars in ancient Greece, but their scientific conclusions are different because of their different viewpoints and methods, forming a sharp opposition. Aristotle's view is basically idealistic, and he draws conclusions by subjective thinking and pure reasoning, so it is full of fallacies. Archimedes' view is basically materialistic, and he relies entirely on scientific practice to draw conclusions. However, since 1 1 century, with the support of the Christian church, Aristotle's works have attracted the attention of scholastic philosophers, who rejected Archimedes' physics and regarded Aristotle's physics as a classic, and all scholars who violated Aristotle's physics were regarded as "heresies". But Galileo was skeptical about Aristotle's physics. On the contrary, he paid special attention to the study of Archimedes physics. He attaches importance to integrating theory with practice, observes various natural phenomena and thinks about various problems. When Galileo was eighteen, he once went to the church in Pisa. He noticed that the ever-burning lamp hanging in the church was regularly swung from left to right by the wind. He timed them according to the pulse and found that the reciprocating time was always equal. In this way, he discovered the synchronicity of pendulum. Later, the Dutch physicist Huygens made a hanging pendulum clock according to this principle, which was called "Galileo clock". According to Archimedes' theory, Galileo studied the hydrostatic balance for rapidly determining alloy composition, invented the "small balance" for measuring material density, and wrote a paper called "small balance". Later, he devoted himself to studying the geometry of the center of gravity of objects, and published the article "Center of Gravity of Solids" in 1588, which attracted the attention of academic circles. The following year, on the recommendation of a friend, he was hired as a professor of mathematics by the University of Pisa. Aristotle believes that two objects fall at the same height, and the heavier object falls first than the lighter one. But after repeated research and experiments, Galileo came to the opposite conclusion: the falling speed has nothing to do with the weight. 1590, Galileo made a falling experiment on the leaning tower of Pisa, which proved that Aristotle's statement was wrong, which shook Aristotle's theory that ruled people's thoughts for more than 2000 years for the first time. However, some famous scholars invited to watch denied what they saw with their own eyes, and they attacked Galileo. Galileo was expelled from Pisa in 159 1 year. In the history of science, Galileo was not the initiator of the falling body experiment, but Stevin. But Galileo's experiment on the leaning tower of Pisa had a far-reaching impact. 1592, Galileo came to teach at the University of Padua in Venice and began the golden age of his scientific activities. During this period, he studied many physical problems, such as slope motion, force synthesis, projectile motion and so on. He also studied liquids and heat and invented the thermometer. 1609, Galileo made an astronomical telescope and used it to explore the mysteries of the universe. He found that the surface of the moon was uneven, with mountains and deep valleys. Jupiter has four satellites revolving around it, and Venus, like the moon, has both gains and losses. Saturn has a halo; The sun has sunspots and can rotate. The Milky Way in Qian Qian is made up of thousands of dim stars. These findings provide strong evidence for the views of Copernicus and Bruno. This dealt a serious blow to the creed of the church. The following year, he published "Star Messenger", which introduced the sky phenomenon he observed and publicized his views. This book caused a great sensation in Europe, so Galileo was called "Columbus in the sky". 16 13 years, he published an article about sunspots in Rome. The book clearly points out in the form of letters that Copernicus' theory is correct and Ptolemy's theory is wrong. Galileo angered the church and began to be tried by the Inquisition. Under the pressure of the Holy See, Galileo continued his scientific research, and became more convinced of the correctness of Copernicus' theory through long-term observation and study of celestial movement. 1632 65438+ 10 In Florence, Galileo published Dialogue on Ptolemy and Copernicus. In the book, he talked for four days in the form of a dialogue between three scholars. Discuss three questions: 1, which proves that the earth is moving; 2. Enrich Copernicus' theory; 3. the tides of the earth. Dialogue summarizes Galileo's scientific discoveries in his long-term scientific research practice, declares the bankruptcy of Ptolemy's geocentric theory, fundamentally shakes the supreme authority of the church, and thus promotes the development of materialism. Once published, this book was welcomed by readers. But it was opposed by the Roman church. Galileo was imprisoned for a long time. 1636, Galileo secretly completed another masterpiece in his life, Dialogue between Two New Sciences. The book was published in the Netherlands on 1638. This masterpiece is also written in the form of a three-person dialogue. The first day is about the strength of solid materials, which refutes Aristotle's view that the speed of falling objects depends on the weight. "The Next Day" is about the reason of connection, and it discusses the proof of lever principle and the strength of beam. On the third day, we discussed uniform motion and natural acceleration motion. The fourth day is about the discussion of projectile motion. This masterpiece fundamentally denies Aristotle's theory of motion.