Based on Newton's law of motion and the law of universal gravitation (see the law of universal gravitation), Newtonian mechanics studies the motion law of macro objects whose speed is far less than the speed of light. Special relativity studies the movement of objects whose speed is comparable to the speed of light. Quantum mechanics studies the movement of microscopic particles such as electrons and protons. In terms of research category, Newtonian mechanics is different from relativity and quantum mechanics. Newtonian mechanics is a part of classical mechanics. After I. Newton, J. - L. Lagrange and W R. Hamilton developed new mechanical systems one after another. Newtonian mechanics emphasizes that the quantities such as force and momentum have vector properties, and Newtonian equations are expressed in vector form, so Newtonian mechanics can be called vector mechanics; Lagrangian system and Hamiltonian system focus on the quantity of energy of the system, which has scalar properties, and can establish the dynamic equation of the system through the variational principle of mechanics, so Lagrangian system and Hamiltonian system can be collectively called analytical mechanics. Therefore, in terms of research methods and systems of mechanics, Newtonian mechanics is different from Lagrange system and Hamilton system; But from the basic principles of classical mechanics, Lagrange equation and Hamilton principle are equivalent to Newton's law. However, Hamiltonian principle can be applied to a wide range of physical phenomena. The Lagrangian system and Hamiltonian system (especially the latter) are widely used in the conservative systems in physics and astromechanics, which have great advantages. For example, the viewpoints and methods of these two systems are of great value to the theoretical research of perturbation theory of celestial mechanics and classical statistical mechanics.
Newton Born in England on January 4, 1643 Lincolnshire Near Grantham Wall Sop Village. Joined Britain in 1661 University of Cambridge holy Trinity College In 1665, he received a Bachelor of Arts degree. In the next two years, he avoided the plague in his hometown, where he formulated the blueprint for most important scientific creation in his life. Newton was elected to Cambridge in 1667 Trinity College, Cambridge University The college committee won a master's degree the next year. Cambridge University in 1669 Lucasian Chair of Mathematics Until 1701. In 1696, he was appointed as the supervisor of the Royal Mint and moved to London 。 Served in 1703 Royal Society president. In 1706, she was knighted by British Queen Anna. In his later years, Newton concentrated on natural philosophy And theology 。 On March 20, 1727, Newton died of illness in London at the age of 84. Note: Newton is Julian calendar December 25, 1642, namely Gregorian calendar （ Solar calendar ）January 4, 1643, so the correct date of birth is January 4. The origin of Newtonian mechanics
Newton's Mechanics is based on Newton's law of motion It was developed after the 17th century. Study directly based on Newton's law of motion particle The motion of the system is Newtonian mechanics. 
Newton Sir Isaac Newton tried to use inertia The concept of force and force describes the motion of all objects, so he finds that they are subject to certain conservation law 。 In 1687, Newton went on to publish his Mathematical Principles of Natural Philosophy Thesis. Here Newton created three laws of motion, which are still the way to describe force today. Newtonian mechanics correlation
Newtonian mechanics involves many aspects, and they all involve the most basic three Laws 。 Content: All objects always remain stationary or in a straight line at a constant speed when there is no force or the resultant force is zero motion state 。 Note: All objects have the tendency of maintaining static and moving at a uniform speed in a straight line, so the motion state of objects is determined by its Movement speed Determined, without external force, its motion state will not change. This property of objects is called inertia 。 So Newton's first law is also called Law of inertia 。 The first law also clarifies the concept of force. It is clear that the force is between objects Interaction It is pointed out that the force changes the motion state of the object. Because acceleration describes the change of the moving state of an object, the force is related to the acceleration rather than the speed. If you don't pay attention to this in your daily life, it is easy to produce illusion. be careful: Newton's first law It is not true in all frames of reference. In fact, it is only true in Inertial frame of reference Li Cai was established. Therefore, Newton's first law is often regarded as the criterion of whether a reference frame is an inertial reference frame. Content: The object is receiving Resultant external force The action of "" will produce acceleration. The direction of the acceleration is the same as that of the external force. The magnitude of the acceleration is proportional to the magnitude of the external force Inertial mass Inversely. Newton's second law It quantitatively describes the effect of force action and measures the inertia of objects. It is vector and instantaneous. It should be emphasized that the non-zero external force on the object will produce acceleration, which will change the motion state or speed of the object, but this change is related to the motion state of the object itself.
Limitation: This law is only applicable to low speed motion of macro objects.
Content: between two objects Force and Reaction force On the same line, the size is equal and the direction is opposite. Note:
（1） Force and Reaction force There is no priority or priority. It is generated and disappeared at the same time. (2) This pair of forces acts on different objects and cannot be offset.
(3) The action and reaction must be forces of the same nature.
(4) It is independent of the reference system.
The product of the mass m of a particle and its velocity v (mv). Momentum is a vector Symbol P means. Particle group The momentum of is the vector sum of the momentum of each particle in the group. Corporeal mechanical movement It does not occur in isolation. There is interaction between it and the surrounding objects. This interaction is manifested in the transmission (or transfer) of mechanical motion between the moving objects and the surrounding objects process Momentum measures mechanical motion from the perspective of mechanical motion transmission physical quantity This kind of transfer is carried out equivalently. How much mechanical motion (momentum) is transferred from object 2 to object 1, and object 2 will lose the same amount of momentum. The result of the transfer is that the total momentum of the two remains unchanged. from dynamics From the angle of view, force reflects Momentum transfer The situation of speed. Just like the real thing, electromagnetic field It also has momentum. for example photon The momentum of is p=h/(2 π) k, where h is Planck constant and k is wavelength , its size is k=(2 π)/λ (λ is the wavelength), and the direction is along the wave propagation direction. stay International System of Units In, the unit of momentum is kg · m/s (kg · m/s). Law of conservation of momentum
The law of conservation of momentum is the first law of conservation, which originated in the 16th to 17th centuries Western Europe Philosophers of Philosophical thinking 。 Looking at the moving objects around us, we can see that most of them, such as bouncing balls, flying bullets, moving clocks, and running machines, will stop. it seems universe The total amount of inter movement seems to be decreasing. whole universe Is it like a machine that will stop one day? But for thousands of years celestial bodies The observation of the movement did not find any sign of the decrease of the movement of the universe. Many philosophers who lived in the 16th and 17th centuries believed that the total amount of motion in the universe would not decrease. As long as a suitable physical quantity could be found to measure motion, the total amount of motion would be conservative. What is the proper physical quantity? France Philosopher, mathematician and physicist Descartes It is proposed that the product of mass and rate is a suitable physical quantity. But then, Netherlands Huygens (1629-1695), a mathematician and physicist, is studying Collision problems It is found that according to Descartes' definition, the total amount of motion of two objects is not necessarily conserved before and after collision. On the basis of summarizing the work of these people, Newton made an important modification to Descartes' definition, that is, he did not use mass and rate By using the product of mass and speed, we can find a suitable physical quantity to measure motion. Newton called it "quantity of motion", which is what we now call momentum. In 1687, Newton《 Mathematical Principles of Natural Philosophy 》It is pointed out in the book that the amount of motion obtained by subtracting the sum of motions in one direction from the sum of motions in the opposite direction does not change due to the interaction between objects; It also points out that the motion state of the common center of gravity of two or more interacting objects will not be changed due to the interaction between these objects, and will always remain stationary or do Uniform linear motion 。 The law of conservation of momentum is more applicable than Newton's law of motion
Modern scientific experiments and theoretical analysis show that: nature Medium, as large as the interaction between celestial bodies, as small as proton 、 neutron etc. Elementary particle The interaction between Law of conservation of momentum 。 Therefore, it is the most important and common objective law One is that it is more applicable than Newton's law of motion. Here's a Newton's law of motion that doesn't apply Law of conservation of momentum Examples of application. When we investigate the emission and absorption of light, we will see such a phenomenon: Cosmic space in Somewhere Sometimes it will suddenly emit very bright light, which is called supernova. But it soon faded. It takes millions of years for light to travel from such a supernova to reach the Earth. In contrast, the time from light emission to extinction of a supernova is too short. When light arrives from a supernova Earth time It gives the earth a slight push, while the earth cannot give the supernova a slight push at the same time, because it has disappeared. Therefore, if we imagine the interaction between the Earth and the supernova, it will not be the same size and opposite direction at the same moment. At this time, Newton's Third Law Obviously, it is no longer applicable. Nevertheless, Law of conservation of momentum It is still correct. However, we must also take light into account. When a supernova emits light, the star recoils and gains momentum. At the same time, the light also takes away momentum of equal size but opposite direction. When light reaches the earth after millions of years, it transmits its momentum to the earth. What should be noted here is that momentum can not only be carried by objects, but also ray radiation Spread together. When we consider the above, Law of conservation of momentum It is still correct. [1] Newtonian Classics Dynamics The establishment of the system has opened up a new world and a new era for scientific development. classical mechanics The wide spread and application of the Internet has had a significant impact on people's lives and ideas, and has promoted the development and progress of human society to a certain extent. However, the inherent shortcomings and limitations of classical mechanics also hindered the progress of human society to a certain extent, resulting in negative effects. Starting from the background of classical mechanics, this paper will further analyze the relationship between classical mechanics and reality The role played by and the adverse effects produced by. 17th century Europe , after many scientist In the astronomy On the basis of rich data on mechanics, British scientist Newton realized the integration of celestial mechanics and terrestrial mechanics, forming a unified mechanical system - classical mechanics. The establishment of the classical mechanics system is human knowledge natural And the first great leap in history and the great synthesis of theories, which opened up a new era and had a profound impact on the process of scientific development, human production, life and way of thinking. classical mechanics The establishment of natural science And become the model of other natural sciences. classical mechanics The establishment of the system benefits from the existing scientific achievements. Copernicus Galileo Kepler Descartes and others in astronomy, mechanics optics , mathematics and so on, laying a solid foundation for classical mechanics, especially Galileo and Kepler's classical mechanics The establishment of the system has an extremely important impact. Galileo Free fall Has found that inertial motion and Uniformly accelerated motion , which established the basic idea of Newton's first law and second law. Galileo's discovery of the law of motion of a projectile Universal gravitation His theory also has profound enlightenment. Kepler's discovery Laws of planetary motion It is the most important premise for Newton's theory of universal gravitation. Newton was very good at extensively absorbing the scientific achievements of predecessors and comprehensively using various knowledge to conduct interdisciplinary research Scientific research achievements Newton enriched the knowledge preparation for the establishment of classical mechanics system. Although classical mechanics is based on rich scientific experience, the establishment of classical mechanics is inseparable from Newton's personal reasons. Newton had a strong interest in science, a strong thirst for knowledge and exploration, and studied very hard from his youth. But he never stopped reading, liked to gain true knowledge through experiments, and personally designed and made many mechanical devices and supplies, which made him lay a broad and solid knowledge foundation, and also had innovative consciousness and practical ability. Although Newton was a genius with a high level of intelligence, his genius also came from his diligence. He is very devoted to research and often studies and works day and night. All these have cultivated and tempered Newton's scientific spirit and laid a solid foundation for future research.
classical mechanics The establishment of "Li" is also related to his era and society. After more than 100 years of religious and political reforms in the 16th century, Europe entered a period of political tranquility and economic prosperity in the second half of the 17th century. Production practice has raised many problems for mechanics research, which has given impetus to the development of science. After the 16th century Reformation Movement And the bourgeois revolutionary movement in the middle and late 17th century, British scientists had the most relaxed and free academic environment in the world at that time. The change of the academic environment has freed the research on mechanics from unnecessary constraints, and gave birth to the classical mechanical system. Personal factors, previous experience, loose academic environment and the development of production practice constitute the conditions and basis for the establishment of the classical mechanics system.
Influence of classical mechanics
It is not difficult to predict that the great success of classical mechanics will have an immeasurable impact on human society in all aspects.
（1） Yes Natural concept Impact of classical mechanics It has been widely spread and has profoundly changed people's view of nature. People often use the mechanical scale to measure everything principle To explain everything natural phenomena All motions are attributed to mechanical motion, and all motions are attributed to force law A moving machine. such Mechanical Materialist View of Nature At that time, it was progressive. Because it ascribes the reasons that play a role in nature to the role of the laws of nature itself, it is conducive to prompting scientists to explore the laws of nature. It can stimulate people to use analysis and anatomy to obtain more empirical materials from observation and experiment, which is also necessary for the development of science. But this way of thinking to a certain extent ignored Theoretical thinking The role of defect 。 （2） Impact on natural science
classical mechanics Content and research method For natural science, especially physics It has played a significant role in promoting, but there are also negative effects. The success of Newton's classical mechanics system and his mechanics research program made scientists think that classical mechanics It is the reliable and final foundation of the whole physics, even all natural sciences. In a quite long historical period, classical mechanics The famous book Mathematical Principles of Natural Philosophy became the norm that scientists followed together, and it dominated the development process of the whole natural science at that time. He studies problems scientific method And the principle has also been widely appreciated and adopted. Newton's scientific methodology and epistemology for studying classical mechanics, such as the combination of analysis and synthesis axiomatic method And the principle of scientific simplicity, the principle of seeking the unity of similarity in causality, the principle of universality of finding objects based on experiments and the principle of correctly treating inductive conclusions also have a profound impact on the development of science in later generations. Impact on social sciences
Classical mechanics not only has a great impact on natural science social sciences In particular Philosophy And the development of human thought, has also had a significant impact. Under the direct influence of classical mechanics, britain Hobbes and Locke Established and developed machinery Materialism Philosophy, and because of its powerful influence, made materialism win the right to speak from religious theology, and then formed a period of the most intense struggle between materialism and idealism in human history. after Kant And Hegel's research and development of dialectics and mechanical materialism, and Marx And Engels' absorption of the existing research achievements in philosophy, combined with the scientific development achievements at that time, finally established Materialistic dialectics 。 The establishment of materialistic dialectics benefits greatly from classical mechanics Establishment of the system. Modern science and philosophy originated from classical mechanics. It was precisely from Newton's establishment of classical mechanics that human beings began to move towards scientization and modernization in ideology, and its impact on the field of human thought was extremely extensive and profound.
Things are always dialectically unified and divided into two. Although scientists made great progress in natural science when they applied Newton's classical mechanical methods and achievements, people did not understand the scope of application of Newton's scientific achievements and made inappropriate exaggerations when they accepted and applied them. For example, some scientists thought that all the physical problems involved could be reduced to unchanging gravitation And repulsive force, so long as the natural phenomenon is transformed into force. As a result, "force" became a refuge for the lack of understanding of phenomena and laws, and all kinds of phenomena that could not be explained at that time were given the names of different forces. Therefore, the contents and research methods of Newton's classical mechanics have also had a great negative impact on the development of natural science. Classical mechanics has advanced human's understanding of the whole nature to a new level. Newton unified the movement in the sky and the movement on the ground, proving the unity of nature from mechanics. This is the first great leap and theoretical synthesis of human's understanding of natural history. It has opened a new era, It also has a profound impact on the process of discipline development and future generations of scientists.
The establishment of classical mechanics for the first time clarified the basic characteristics of all natural science theories, which marked the birth of modern theoretical natural science and became the model of other natural sciences. Newton used the methods of induction and deduction, synthesis and analysis to obtain a perfect mechanical system, which was called Scientific beauty It shows that when physicists study physics, they tend to choose a harmonious and self consistent system and pursue the most concise and ideal form. The establishment of classical mechanics has a profound impact on the development of natural science and technology and social progress. First, scientific research methods are applied to all branches of physics Classical physics The establishment of is of great significance; Second, classical mechanics and others Basic Sciences The combination has produced many cross disciplines and promoted the further development of natural science. Third, classical mechanics Science and technology It has a wide range of applications and has promoted the development of social civilization. [2] Scope of application and its limitations
The application of classical mechanics is affected by the motion of objects rate When the speed of object movement is close to that in vacuum light speed Many concepts of classical mechanics will change significantly when. As in classical mechanics Mass of object Not only unchanged, but also related to the speed or energy Not relevant, but relativity The research shows that the mass of the object will increase with the increase of the motion speed, and there is a close relationship between the mass and energy of the object. However, classical mechanics is still applicable when the speed of motion of an object is far less than the speed of light in vacuum. Newton's law of motion is not applicable to material structure and energy Discontinuity. At the turn of the 19th and 20th centuries, there were three major discoveries in physics, namely X-ray Discovery Electronics Discovery and radioactivity The discovery of quantum mechanics With the establishment of, new ideas different from the classical ones have emerged. For example, the research of quantum mechanics shows that microscopic particles are Particle property It is also shown as wave, particle energy Such physical quantities can only take discrete values, the speed and position of particles are uncertain, and the state of particles can only be described by the probability of particles appearing in space. However, the establishment of quantum mechanics is not a negation of classical mechanics. For the motion of macro objects, quantum phenomena are not significant, and classical mechanics is still applicable. The development of modern physics has not made classical mechanics lose its value of existence, but broadened people's vision. Classical mechanics will still shine in its scope of application. [3]
