The following are three periods of the development of physics.
Physics is produced, formed and developed with the development of human social practice, and it has gone through a long development process. Throughout the development history of physics, according to the characteristics of its different stages, it can be roughly divided into three stages: the embryonic stage of physics, classical physics and modern physics.
(A) the embryonic period of physics
In ancient times, due to the low level of production, people's understanding of nature mainly relied on insufficient observation and intuition and speculation on this basis to grasp the general nature of natural phenomena, so the knowledge of natural science basically belonged to the description of phenomena, the summary of experience and speculative speculation. At that time, the knowledge of physics was contained in the unified natural philosophy.
The first thing that developed in this period was mechanics closely related to production practice, such as simple machinery, lever principle and buoyancy law in statics. In Mo Jing, the description of the concept of power ("power and shape are also exciting"); In optics, I have accumulated knowledge of direct light, refraction, reflection, pinhole imaging, concave-convex mirror and so on. Mo Jing has eight records about optical knowledge. Euclid's works in ancient Greece (450-380 BC) also discussed the law of linear propagation and reflection of light, and also studied the refraction of light. In electromagnetism, phenomena such as friction electrification and magnet attracting iron were found, and on this basis, the compass was invented. Acoustics, due to the development of music and the creation of musical instruments, we have accumulated a lot of knowledge about music rhythm and singing. In terms of material structure and interaction, the hypotheses such as atomism, primordial qi, yin-yang and five elements, and ether are put forward.
During this period, although observation and speculation are the main means and methods for people to understand nature, there are also some methods similar to studying physical phenomena through experiments. For example, Shen Kuo's acoustic vibration in Meng Qian Bi Tan and the experiment of artificial magnetization with natural magnets in Song Dynasty, and Zhao Youqin's large-scale optical experiment in Gexiang New Book is a typical example.
In short, from ancient times to the end of the Middle Ages (Europe usually refers to the 5th to15th century as the Middle Ages), due to the development of production, although a lot of physical knowledge was accumulated, some conditions were prepared for the emergence of experimental science, and some experiments were done, but these were not systematic natural science research. In this period, physics is still in its infancy.
(2) the period of classical physics
At the end of 15th century, the appearance of capitalist relations of production promoted the great development of production and technology. The Renaissance, which swept through western Europe, liberated people's thoughts and inspired people's spirit of exploration. Modern natural science was born under this historical condition of material and thought. The research method of combining systematic observation experiment with rigorous mathematical deduction was introduced into physics, which triggered the "scientific revolution" in the17th century, mainly in the fields of astronomy and mechanics. The establishment of Newtonian mechanical system marks the birth of modern physics. Throughout the eighteenth century, physics was in a stage of gradual digestion, accumulation and preparation. New scientific ideas, methods and theories have been spread, improved and expanded. Newtonian mechanics completed the analysis work and established analytical mechanics; Optics, thermodynamics and electrostatics have also completed their basic work and become several basic disciplines of physics. People use mechanical models to understand various physical phenomena, which makes the mechanistic view of nature become the dominant idea of physics in the18th century. /kloc-in the 0/9th century, physics has made rapid and important development, and the connection and transformation between various natural fields have been widely discovered. New mathematical methods have been widely introduced into physics, and complete and analytical theoretical systems such as wave optics, thermodynamics and molecular motion theory, classical electromagnetic field theory have been established one after another, perfecting classical physics. The unity of nature revealed by the great achievements of physics provides an important scientific basis for dialectical materialism's view of nature.
(3) the period of modern physics
/kloc-A series of major discoveries in physics at the end of the 9th century made the theoretical system of classical physics encounter an insurmountable crisis, which led to the revolution of modern physics. Due to the development of production technology, the creation of precision and large instruments and the change of physics thought, the physics theory in this period showed a rapid development trend. From low speed to high speed, from macro to micro, the research object goes deep into the vast universe and material structure, and great changes have taken place in the understanding of the structure, motion law of the macro world and the motion law of the micro matter. The establishment of relativistic quantum mechanics overcame the crisis of classical physics, completed the transformation from classical physics to modern physics, made a qualitative leap in the theoretical basis of physics and changed people's physical world picture. After 1927, quantum field theory, nuclear physics, particle physics, astrophysics and modern cosmology have developed rapidly. The promotion of physics to other disciplines has produced a series of new physics departments and marginal disciplines, providing new ideas and methods for modern science and technology. The development of modern physics has aroused people's understanding of matter, motion, space, time, law of causality and even life phenomena, as well as great changes in their understanding of the nature of physics theory. Now more and more facts show that physics is brewing a new major breakthrough to uncover the mysteries of micro and macro. The theoretical achievements of modern physics have been applied to practice, and many new technical sciences have emerged, such as atomic energy, semiconductors, computers, lasers, aerospace and so on. These emerging technologies are vigorously promoting the new scientific and technological revolution and promoting the development of production. With the development of production and new technology, in turn, it has strongly promoted the development of physics. This is the dialectical relationship between the development of physics and production.
The structure of physics theory
The development history of physics has gone from low level to high level, and now the structure of L physics theory has been basically established.
The structure of physical theory is controlled by constants g, c and h.
The first level: Newtonian mechanics (g, h, 1/c=0)
The second stage: Newton's gravity theory (h, 1/c=0, g is not 0).
Einstein's special theory of relativity does not include gravity (h, g = 0, 1/c is not 0).
Quantum mechanics (g, 1/c=0, h is not 0)
The third stage: Einstein's general theory of relativity (h=0, g, 1/c is not 0).
Quantum mechanics of relativity (G=0, h, 1/c is not 0)
Newton's quantum gravity (1/c=0, h, g is not 0)
Gion
Amount of time
Virtual function of time quantum
Ultimate: relativistic quantum gravity theory (1/c, h, g are not 0)
Edit the nature of physics in this paragraph.
Physics is a regular summary of people's understanding of material transformation in inanimate nature. There should be two kinds: movement and transformation. One is the extension of early human sensory vision, and the other is the result of modern people inventing scientific instruments for observation and measurement. Physics can be divided into microscopic and macroscopic parts from different research angles and viewpoints. Macroscopically, the whole effect is directly considered without analyzing the individual effect of particle swarm, which has appeared in the earliest stage. With the development of science and technology, the theory of microphysics has been gradually improved.
Secondly, physics is a kind of intelligence.
As born, a German scientist who won the Nobel Prize in Physics, said: "It is not so much because my published work contains the discovery of a natural phenomenon as because it contains a scientific thinking and methodological basis on natural phenomena." Physics is recognized as an important science, not only because it profoundly reveals the laws of the objective world, but also because it has formed a unique and effective system of ideas and methods in the process of development and growth. Because of this, physics has become the crystallization of human wisdom and the treasure of civilization.
A large number of facts show that the ideas and methods of physics are not only valuable to physics itself, but also have important contributions to the development of the whole natural science and even social science. According to statistics, since the middle of the 20th century, more than half of the Nobel Prize winners in chemistry, biology, medicine and even economics have a physics background. This means that they have learned wisdom from physics and achieved success in non-physical fields. On the other hand, there has never been a case in which a scientist who is not a physics major won the Nobel Prize in physics. This is the power of body intelligence. No wonder some foreign experts pointed out that a nation without sports literacy is a stupid nation!
In short, physics is a summary of laws and a theoretical understanding of the scientific nature of experience.
Edit the mechanical concepts in this paragraph.
mechanics
A branch of physics. It studies the law of mechanical motion and balance of objects and its application. Mechanics can be divided into statics, kinematics and dynamics. Statics mainly discusses the conditions for an object to maintain its equilibrium under the action of external force. Kinematics is a description method to study the mechanical motion without interaction between objects, and it does not involve the cause of motion. Dynamics is to discuss the relationship between the force and motion of a particle system under pressure. Mechanics can also be divided into particle mechanics, rigid body mechanics and continuum mechanics according to the nature of the studied object. Continuous media are usually divided into solid and fluid. Solids include elastomers and plastomers, while fluids include liquids and gases.
From16th century to17th century, mechanics began to develop into an independent and systematic discipline. Galileo put forward the law of inertia through the study of projectiles and falling bodies, and used it to explain the motion of objects and celestial bodies on the ground. At the end of 17, Newton put forward three basic laws of mechanical motion, which made classical mechanics form a systematic theory. According to Newton's three laws and the law of universal gravitation, the laws of falling bodies and the orbits of planets on the earth are successfully explained. In the next two centuries, with the research and promotion of many scientists, it finally became a classical mechanics with perfect theory. 1905, Einstein put forward the special theory of relativity. For high-speed moving objects, we must use relative mechanics instead of classical mechanics, because classical mechanics is only an approximate theory that the speed of an object is much less than the speed of light. In the 1920s, quantum mechanics developed. According to the duality of particles and photons, the microscopic phenomena that classical mechanics cannot explain are explained, which limits the application scope of classical mechanics in the microscopic field.
classical mechanics
The basic laws of classical mechanics are Newton's laws of motion or other mechanical principles related to Newton's laws and their equivalents. It is mechanics before the 20th century, and it has two basic assumptions: one is that time and space are absolute, the measurement of length and time interval has nothing to do with the observer's movement, and the transfer of interaction between substances is instantaneous; The second is that all observable physical quantities can be measured infinitely accurately in principle. Since the 20th century, due to the development of physics, the limitations of classical mechanics have been exposed. As the first hypothesis, it actually only applies to low-speed motion compared with the speed of light. In the case of high-speed movement, time and length are no longer considered to be irrelevant to the observer's movement. The second assumption only applies to macroscopic objects. In microscopic systems, all physical quantities cannot be accurately determined at the same time in principle. Therefore, the laws of classical mechanics are generally only approximate laws when macroscopic objects move at low speed.
Newtonian mechanics
It is based on Newton's law of motion and developed after17th century. Newton's law of motion is directly regarded as the starting point of studying the motion of particle system, which is Newtonian mechanics. It takes particles as the object and focuses on the concept of force. When dealing with the problem of particle system, it is necessary to consider the force on each particle separately, and then infer the motion of the whole particle system. Newtonian mechanics holds that mass and energy exist independently and are conserved separately, which is only applicable to the range where the speed of motion of an object is much less than the speed of light. Newtonian mechanics mostly adopts intuitive geometric methods, which is more convenient and simple than analytical mechanics in solving simple mechanical problems.
analytical mechanics
Classical mechanics is divided into Newtonian mechanics and analytical mechanics according to different historical development stages and research methods. 1788 Lagrange developed the work of Euler D'Alembert and published Analytical Mechanics. When analyzing mechanical problems, the whole mechanical system is taken as the object, and the configuration of the whole mechanical system is described by generalized coordinates, with the emphasis on the concept of energy. When the mechanical system is subject to ideal constraints, the motion problem of the system can be solved without considering the binding force. Analytical mechanics mostly adopts abstract analytical methods, which shows its superiority in solving complex mechanical problems.
theoretical mechanics
It is a combination of mechanics and mathematics. Theoretical mechanics is an integral part of mathematical physics and the basis of various applied mechanics. It generally uses calculus, differential equations, vector analysis and other mathematical tools to thoroughly explain Newtonian mechanics and systematically introduce analytical mechanics. Because mathematics is more deeply applied to the field of mechanics, mechanics is more theoretical.
Motor functionalism
The motion of an object is described by purely analytical and geometric methods, and the physical reasons for the motion of the object can be ignored. That is to say, the change of relative position between objects with time is studied from the geometric aspect, and the cause of motion is not involved.
mechanics
In this paper, the relationship between the force acting on the particle system and the motion under the action of the force is discussed. Based on Newton's law, various basic principles of dynamics are put forward according to different needs, such as D'Alembert's principle, Lagrange's equation, Hamilton's principle, canonical equation and so on. According to the current state of the system, the interaction between internal components and the interaction between the system and its surrounding environment, the motion that will occur can be predicted.
elastic mechanics
It is a subject that studies the stress, deformation and displacement caused by external force or temperature change in elastomer, so it is also called elasticity theory. Elasticity usually discusses the linearity of an ideal elastic body. Its basic assumptions are: the object is continuous, uniform and isotropic; Objects are completely elastic; There is no initial stress in the body before the load is applied; The deformation of the object is very small. According to the above assumptions, the mathematical derivation of the relationship between stress and deformation is often called mathematical elasticity. In addition, there is application flexibility. If the deformation of the object is not very small, it can be studied by nonlinear elastic theory. If the internal stress of an object exceeds the elastic limit, the object will enter an incomplete elastic state. At this time, plastic theory must be used to study.
continuum mechanics
It studies the motion law of deformable objects with continuous mass distribution, and mainly discusses the mechanical laws that all continuous media generally follow. Such as conservation of mass, theorem of momentum and angular momentum, conservation of energy, etc. The comprehensive discussion of elasticity and fluid mechanics is sometimes called continuum mechanics.
The meaning of force
The interaction between objects is called "force". When an object is acted on by other objects, it can get acceleration (change of speed or momentum) or deformation, which is called "force". It is an important basic concept in physics. In the scope of mechanics, the so-called deformation refers to the change of the shape and volume of an object. The so-called change of motion state refers to the change of object speed, including the change of speed or direction, that is, the generation of acceleration. Force is the interaction between objects (or substances). When an object is subjected to a force, there must be another object that exerts this effect on it. The former is the stressed object and the latter is the applied object. As long as there is a strong action, there must be an object of force and an object of force. Generally speaking, an object is subjected to a force, but no force object is specified, but the force object must exist. No matter the force between objects in direct contact or the force between objects in indirect contact; No matter the force between macroscopic objects or microscopic objects, they can't exist alone without objects. The action of force, like the movement of matter, is realized through time and space. Moreover, the change of motion state or shape of an object depends on the cumulative effect of force in time and space. According to the definition of force, for any object, the force is in the same direction as the acceleration it produces, and its magnitude is proportional to the acceleration it produces. The acceleration produced by two forces acting on the same object is the vector sum of the accelerations produced by two forces acting on the object respectively.
Force is a vector, and the magnitude, direction and action point of force are important characteristics to express the action of force, which are called the three elements of force. The composition and decomposition of forces obey the parallelogram law. According to the international system of units (SI), for an object with a mass of one kilogram, the force with an acceleration of 1 m/s 2 is 1 Newton, and the symbol is n. (1 kg force = 9.80665 Newton. 1 Newton = 105 dyne)
There are many kinds of forces. According to the action of force, there are pressure, tension, supporting force, buoyancy, surface tension, repulsion, gravity, resistance, power, centripetal force and so on. According to the nature of force, there are gravity, elasticity, friction, molecular force, electromagnetic force, nuclear force and so on. Middle school is generally divided into field force (including gravity, electric field force, magnetic field force, etc.). ), elasticity (pressure, tension, tension, etc. ) and friction (static friction, sliding friction, etc. ).
Three elements of force
The magnitude, direction and action point of force are collectively called "the three elements of force". Directed line segments are often used to represent forces. The length of the line segment is proportional to the force, the arrow indicates the direction of the force, and the starting point of the line segment indicates the action point of the force. Expressing force in the above way is called "the schema method of force" These three elements must be considered when considering the problem of force.
Material ties
It is one of the contents of physics, and it is a science that studies the mechanical and thermal properties of gas, liquid and solid states of matter. Physiology originally refers to the study of the mechanical and thermal properties of three states of matter. With the study of the properties of matter, it has gradually expanded from mechanics and heat to electromagnetism and optics, and the scope of physics is too wide. Now it is no longer a separate subject, but its contents are included in relevant departments respectively.
physical change
It means that the state of a substance has changed, but generally speaking, the composition of the substance itself has not changed. Such as the change of position, volume, shape, temperature and pressure, and the mutual transformation between gas, liquid and solid. The transformation from gas to liquid is called liquefaction, from liquid to solid is called solidification, from solid to liquid is called melting, from liquid to gas is called gasification, from solid to gas is called sublimation, and from gas to solid is called solidification. There is also the interaction between matter and electromagnetic field, the interaction between light and matter, and the interaction and transformation between microscopic particles (electrons, nuclei, elementary particles, etc.). ) These are all physical changes.
material
Matter is a physical object and field that constitutes all objects in the universe. For example, air and water, food and cotton cloth, coal and oil, steel and copper, aluminum, synthetic fibers and plastics are all substances. In the world, all the objective existence around us is matter. The human body itself is a substance. In addition to these physical objects, light, electromagnetic fields, etc. It is also a matter, which appears in the form of a field.
There are many kinds and forms of substances, and the properties of substances are also diverse. Gaseous substances, liquid substances or solid substances; Simple substance, compound or mixture; Metals and nonmetals; Minerals and alloys; Inorganic and organic matter; Natural substances and synthetic substances; Inanimate matter and living matter, as well as solid matter and field matter. Although there are many kinds of substances, they all have their own characteristics, that is, they exist objectively, can be observed, and all have quality and energy.
target
An individual composed of matter and occupying a certain space is called an object. The objective reality of its existence can be felt through human sensory organs.
nervous
The force of a flexible object (such as a stretched rope or rope) on other objects that stretch it, or the force between internal parts of a stretched flexible object. For example, a rope AB can be regarded as consisting of two sections, A C and C B, where C is any section of the rope A B, and the interaction between AC section and CB section is tension. The tensile force per unit area on the cross section of the rope is called tensile stress.
Unit of force
In the meter-kilogram-second system, the unit of force is Newton. The force is usually measured in units of weight. If the elongation of a 500-gram weight hanging on the spring scale is the same as that of pulling the spring scale by hand, then the pulling force of the hand is the same as the gravity of the 500-gram weight. Therefore, the same force as the weight of 500 grams is expressed by the force of 500 grams. But in fact, grams and kilograms are both mass units, and the weight units such as grams and kilograms are a kind of gravity unit of force, which cannot represent all, and the values are different when calculating, so they are powerful absolute units. According to the definition of Newtonian mechanics: force = mass × acceleration. When a particle with a mass of 1 kg produces an acceleration of 1 m/s 2 in the direction of force, the force is called 1 kg m/s 2 = 1 Newton. Because particles are influenced by the gravity of the earth, the acceleration of gravity when falling is g = 9.8m/s 2, so the weight of particles with mass of 1kg is w = mg =1× 9.8kg m/s 2 = 9.8n. ..
newton
It is the unit of force in the international system of units. The force that makes an object with a mass of 1 kg obtain an acceleration of 1 m s-2 is called1Newton. The symbol is represented by n, (1 Newton = 105 dyne).
gravity
The gravitational field near the source of the gravitational field is called gravity field, and the force exerted by the gravitational field on an object is called gravity. Gravitational field The force that matter attracts each other because of its mass is called universal gravitation, or gravity for short. There is a gravitational field around an object, and objects in the gravitational field will be attracted. The physical object that produces the gravitational field is called the field source of the gravitational field. There are various explanations about gravity, for example, it is the sum of the gravity of one object in the universe by other objects; Gravity is the attraction of the earth to objects; Gravity is the force exerted on objects by the gravity of the earth; Every particle in the universe has gravitational interaction with other particles, and gravity is directly proportional to the product of the mass of two particles and inversely proportional to the square of the distance between them. This interaction is called "gravity".
Although there are some differences between the above methods, they all emphasize that its essence is gravity. Because all objects in the gravitational field are affected by gravity, the essence of gravity is gravitational interaction. For an object near the ground, because other celestial bodies are far away from it, other objects on the earth have little gravity on it, so the gravity of the object refers to the gravity of the earth, and its direction points to the center of the earth. The farther away from the ground, the less gravity. The gravity of the same object in different parts of the earth is slightly different, and it gradually increases from the equator to the poles, because the earth is a flat sphere, and its radius at the equator is greater than that at the poles. Objects on the earth make uniform circular motion with the rotation of the earth, and the centripetal force required for the uniform circular motion comes from the gravity of the earth. Both centripetal force and gravity are components of gravity. Because of the different landforms and geological structures in different parts of the earth, the gravity of objects in different parts of the earth will change, and the gravity of objects will also change accordingly. This change in gravity can be used for exploration (detecting the reserves of coal, iron, copper and oil). ).
weight
Near the surface of the earth, the magnitude of gravity on an object is called "weight". An object on the earth's surface will be subjected to inertial centrifugal force generated by the earth's rotation in addition to its own gravity. The resultant force of these two forces is called the weight of the object. Traditionally, people think that the gravity of an object is its own weight. There are many explanations for weight, such as weight is gravity; The weight of an object is the gravity of the earth on the object; Weight is the magnitude of gravity on an object; Weight is the force that tightens the vertical suspension rope or presses on the horizontal support when the object is at rest.
Some of the above statements emphasize that weight is gravity, not vector, and their essence is gravity. Some emphasize that gravity is not a vector, and weight is the magnitude of gravity, not a scalar. There is also a definition of weight based on measurement rules. These different definitions are just different interpretations, and there is no right or wrong.
The weight of an object with a mass of 1 kg at the sea level of latitude 45 is called 1 kg force. Different objects have different weights, and the same object has different positions on the earth and different weights. An object with 1 kg is said to have a weight of 0.973kg force at the equator and1.26kg force at the North Pole. The mass of the same object in different positions is constant, but the closer it is to the poles and the closer it is to the ground, the greater the mass will be (which shows that the centrifugal force of the earth's rotation will make the object lighter).
Edit the research methods of physics in this paragraph.
For physical theory and experiment, the definition of physical quantity, the hypothesis selection of measurement, the mathematical expansion of theory and the comparison between theory and experiment are all in line with the experimental law and the only goal of physical theory.
People can solve the problem through such a combination, that is, prediction guides scientific practice. This is not a great materialistic thought, but actually the purpose and structure of physics theory.
Edit the thoughts and theories of physics in this paragraph.
The relationship between physics and metaphysics
On the basis of continuous reflection on the objective principle of non-empiricism produced by metaphysics, the theory of physics can be judged by its own scientific terms. Without relying on the idea that they may be subordinate to the philosophical school. Among the physical attributes described, simple attributes are selected, while other attributes are the imagination and combination of clustering. Through appropriate measurement methods and mathematical skills, we can further understand the true colors of things. There is a certain correspondence between the quantities selected in the experiment. A relationship can have many experiments, but an experiment can't correspond to many relationships. In other words, a rule can be embodied in multiple experiments, but multiple experiments may not necessarily embody only one rule.
For physics, whether theoretical predictions are consistent with reality is the only criterion for judging truth.
Physics is a natural subject with a long history. As an important branch of natural science, physical science not only plays an important role in promoting the progress of material civilization and deepening human understanding of nature, but also has an indispensable influence on the development of human thinking. From natural philosophy in Aristotle's time to classical mechanics in Newton's time, and then to relativity and quantum mechanics in modern physics, all these are tangible manifestations of physicists' scientific quality, scientific spirit and scientific thinking. With the development of science and technology and the progress of society, physics has penetrated into all fields of human life.