10 scientific laws and theories of physics
10, knocked down by many theories: the big bang theory.
Standard explanation: The Big Bang is a cosmological model that describes the initial conditions for the birth of the universe and its subsequent evolution. Today, it has been widely and accurately supported by scientific research and observation. At present, the general view of the Big Bang is that the universe evolved from the initial state with extremely high density and temperature a finite time ago (according to the best observation results obtained in 20 10, these initial states existed about 65.438+0.33 billion years ago to 65.438+0.39 billion years ago) and reached today's state through continuous expansion.
When anyone wants to try to get in touch with profound scientific theories, it is right to start from the universe, and the Big Bang theory, which explains how the universe has developed so far, is the best choice. The basic structure of this theory is in Edwin? Hubble and George? Lemaistre, Albert? This theory is based on the research of Einstein and many others. To put it bluntly, it is assumed that the universe began with a heavyweight explosion almost 654.38+04 billion years ago. At that time, the universe was confined to a singularity, which contained all the matter in the universe. The initial movement of the universe: continuous outward expansion, is still continuing today.
The Big Bang Theory can get such wide support without Arnold? Penzias and Robert? Wilson's credit. A horn antenna they set up received an indelible noise signal, that is, cosmic electromagnetic radiation, that is, cosmic microwave background radiation. It was the initial big bang that filled the whole universe with this detectable weak radiation, and the corresponding temperature was about 3 K. 9. calculating the age of the universe: Hubble's law
Standard definition: the red shift of light from distant galaxies is proportional to their distance. This law was formulated by Hubble and Milton? After nearly ten years of observation, Humenson formulated Vf=Hc for the first time in 1929. D (departure rate = Hubble constant? The distance from the earth), which is often cited as an important evidence to support the Big Bang today, has become the basis of the theory of cosmic expansion.
This involves one of the above-mentioned people, Edwin? Hubble. This man's contribution to cosmology can be traced back to his deeds: in the roaring and faltering years of the Great Depression in the 1920s, Hubble conducted a breakthrough astronomical research. He not only proved that there are other galaxies besides the Milky Way, but also found that those galaxies are moving away from the Milky Way, and the distance rate in his formula is the speed at which galaxies retreat. Hubble constant refers to the parameter of the expansion rate of the universe, and the distance from the earth is mainly these galaxies. But it is said that Hubble, who is regarded as the founder of galactic astronomy, dislikes the word "galaxy" very much and insists that it is an "extragalactic nebula".
As time goes on, Hubble constant will change, but it doesn't matter much. Importantly, it is this law that helps to quantify the motion of galaxies in the universe and calculate the distance of distant galaxies. The concept that "the universe is made up of many galaxies" and the discovery that the movements of these galaxies can be traced back to the Big Bang all make Hubble's law as famous as the astronomical telescope named after this man. 8. Changing the whole astronomy: Kepler's three laws
Standard interpretation: the laws of planetary motion, three simple laws observed by Kepler in planetary motion.
The first law: every planet moves around the sun along its own elliptical orbit, and the sun is at a focus of the ellipse;
The second law: in the same time, the connecting line between the sun and the moving planet sweeps the same area;
The third law: The square of the period of revolution of the planets around the sun is directly proportional to the cube of the semi-long axis of their elliptical orbits.
Scientists have struggled with religious leaders and their peers for centuries around the orbits of planets, especially whether they are centered on the sun. /kloc-in the 6th century, Copernicus put forward the Heliocentrism, which caused great controversy at that time, thinking that the planet was centered on the sun rather than the earth. What happened after that, Tycho? Blah and others have also discussed it. But it was Johannes who really established a clear scientific foundation for planetary kinematics? Kepler.
Kepler put forward three laws of planetary motion in the early17th century, describing how planets move around the sun. The first law, also known as the elliptic law; The second law, also known as the area law, in other words, explains this law. That is to say, if you track and measure the area formed by the connection between the earth and the sun with the movement of the earth for 30 days in a row, you will find that no matter where the earth is in the orbit and whenever the measurement is started, the result is the same. As for the third law, also known as the law of harmony, it enables us to establish a clear relationship between the orbital period of a planet and its distance from the sun. For example, a planet as close to the sun as Venus has a much shorter orbital period than Neptune. It is these three laws that completely destroyed Ptolemy's complex cosmic system. 7. The cornerstone of most theories: the law of universal gravitation.
Standard explanation: Newton's law of universal gravitation means that any two particles attract each other through the force in the direction of the connecting line. Gravity is directly proportional to their mass product and inversely proportional to the square of their distance, and has nothing to do with the chemical properties or physical states of two objects and intermediate substances. This theory can be expressed by a formula that has been written into today's high school physics textbook: F=G? [(m 1m2)/r2]
Although people take this for granted today, when Isaac? When Newton put forward the theory of universal gravitation more than 300 years ago, it was undoubtedly the most revolutionary event at that time. Newton's theory can be simply expressed as: any two objects, regardless of their respective masses, will exert forces on each other, and the greater the mass, the greater the attraction. In the formula, f refers to the universal gravitation between two objects, and Newton is the unit of measurement; M 1 and m2 respectively represent the mass of two objects; R is the distance between them; G is the gravitational constant.
This is a quite accurate law in many practical situations, but since the development of physics, people have known that Newton's description of gravity is imperfect. However, this law is still one of the most practical concepts in all sciences so far. It is easy to learn and involves a wide range, so that few people paid attention to it in the first period of general relativity. More importantly, the law of universal gravitation gives small human beings the ability to calculate the gravitational force between huge planets, which is especially useful in launching orbiting satellites and drawing lunar exploration routes. 6. Physical science has a basic theorem: Newton's law of motion.
Standard interpretation: Newton's first law is the law of inertia; Newton's second law established the relationship between mass and acceleration; Newton's third law is the law of action and reaction.
Or Newton. Whenever we talk about one of the most outstanding scientists in human history, we have to start with his most famous three laws of mechanics. Because these simple and elegant laws laid the foundation of modern physics.
A brief understanding of the significance of the three laws, the first let us know that the reason why the rolling ball can move on the floor must be driven by external forces. This external force may be friction with the floor, or a child's kicking. The second law is expressed by the formula F=ma, which also represents a direction vector. When the ball rolls across the floor, it will get a vector pointing in the rolling direction due to the acceleration. Through it, the force on the ball can be calculated. The third law is very simple and well known. It means nothing more than poking your finger at the surface of any object, and they will respond with equal force. 5. The thermodynamic foundation is basically complete: three laws of thermodynamics.
Standard interpretation: the first law of thermodynamics, heat can be transformed into work, and work can also be transformed into heat, that is, the law of energy conservation and transformation; The second law has several expressions. One is that it is impossible to transfer heat from a low-temperature object to a high-temperature object without causing other changes. The third law, when the thermodynamic temperature is zero (that is, T=0), the entropy of all perfect crystals is equal to zero.
British physicist and novelist Charles? Percy. Si Nuo once famously said, "A scientist who doesn't know the second law of thermodynamics is like a scientist who has never read Shakespeare." Si Nuo's speech was intended to criticize the separation and division of "two cultures" between science and humanities, but inadvertently made the second law of thermodynamics "win popularity" among scholars. In fact, Si Nuo's exposition does emphasize and appeal to all humanities scholars to understand its importance.
Thermodynamics is a science that studies the energy movement in a system. The system here can be an engine or a blazing core. Si Nuo summed it up as the following basic rules with his intelligence: You can't win, you can't make ends meet, and you can't quit the game.
How to understand these statements? First, let's look at the so-called "you can't win". Si Nuo means that since matter and energy are conserved, in the process of energy conversion, it is impossible for us to realize the equivalent conversion from one energy form to another without losing some energy. Just like if an engine is to work, it must provide heat energy. Even in a perfect closed space, some heat will inevitably escape to the outside world.
And this leads to the second law, "make ends meet." In view of the infinite increase of entropy, we can't return or keep the same energy state. Because entropy always flows from places with high concentration to places with low concentration. The existence of entropy is also the reason why perpetual motion machine can't appear.
Finally, the third law is "an unavoidable game". The absolute zero here, that is, the theoretically possible lowest temperature, generally refers to zero Kelvin (minus 273.438+05 degrees Celsius or minus 459.67 degrees Fahrenheit). The expression of the third law is that when the system reaches absolute zero, the molecules will stop all motion, that is, in the absence of kinetic energy, the entropy can reach the theoretical minimum. But in the real world, even in the depths of the universe, it is impossible to reach absolute zero. You can only be infinitely close to the so-called end point. 4. Great Wisdom in 200 BC: Archimedes Principle.
Standard explanation: Archimedes principle in physics, that is, Archimedes buoyancy principle, means that the resultant force of an object immersed in a static fluid is equal to the gravity of the fluid displaced by the object, and this resultant force is called buoyancy. The mathematical expression is: F float =G row.
There is a legend about how Archimedes discovered the physical breakthrough of buoyancy principle. When Archimedes took a bath, he saw that the water in the bathtub would rise with the immersion of his body. He was inspired and began to think. When he finally discovered the theory of buoyancy, the greatest philosopher in ancient Greece shouted excitedly, "Found it! Found it! " Streaking naked in the streets of Syracuse.
The ancient discovery of Archimedes, an ancient Greek scholar, has been widely used in all fields of human social production. According to the principle of buoyancy, the force acting on an object partially or completely submerged in liquid is equal to the weight of liquid discharged from the internal volume of the object. This is of great significance for calculating the density of objects, and then designing and building submarines and ocean-going ships. 3. Our own discussion: evolution and natural selection.
Standard definition: evolution, that is, evolution, refers to the change of genetic traits of a population between generations in biology. Natural selection, also known as natural selection, means that the genetic characteristics of organisms have certain advantages or disadvantages in the competition for survival, which leads to the difference between viability and reproductive ability, so that these characteristics can be preserved or eliminated.
Now that we have established some basic conceptual systems about why the universe came from scratch and how physics plays a role in our daily life, we can begin to pay attention to our own form, that is, how we become what we are today.
We know that genes will be copied to the next generation, but gene mutation will change their situation, and this changed new situation may be passed on in the population with species migration.
According to most scientists today, all living things on the earth once had a common ancestor. Later, with the development of time, some of them began to evolve into specific species with distinctive characteristics. With the passage of time, biodiversity has gradually increased and expanded among all organic organisms.
In the most basic sense, mutation mechanisms such as gene mutation have always existed in the process of biological evolution. These detailed changes in each stage will be preserved through the inheritance from generation to generation. Accordingly, biological populations have developed different characteristics, and these characteristics can often help organisms survive better. For example, frogs with brown skin are obviously more suitable for camouflage living in muddy swamp areas than frogs with other colors. This is called natural selection.
Of course, we can also apply the theory of evolution and natural selection to a wider range of organisms. However, Darwin's proposition that "the rich biodiversity on earth comes from natural selection in evolution" in the19th century is undoubtedly still the most basic and groundbreaking. 2. forever changed the way of understanding the universe: general relativity.
Standard explanation: Gravity is described here as a geometric property (curvature) of space-time, and this curvature of space-time is directly related to the energy and momentum tensor of matter and radiation in space-time, and its connection is Einstein's gravitational field equation (a second-order nonlinear partial differential equation group).
For those who have never studied or studied it, the standard interpretation of general relativity is the same as that of not reading it. Because it uses at least four groups of incomprehensible words when explaining the entry.
Its connotation and extension cover a wide range, and it seems that no paper form can be described. Here, let's take a look at what general relativity, which is called the highest level of modern gravity theory research, is saying. As a more general theory than Newton's gravity, mass is still an important attribute that determines gravity, but it is no longer the only source of gravity.
In Einstein's view, gravity is no longer the force described by Newton, and even the original concept of gravity has disappeared. Because Einstein regarded it as the curvature of spacetime around the object, the "motion of the object under the action of gravity" mentioned earlier comes down to the free motion of the object along the short-distance line in a curved space-time.
If we put the concept of "curved space-time" more clearly, we can imagine the astronauts in the space shuttle flying around the earth. For them, they fly in a straight line in space, but in fact, the space-time around the space shuttle has been bent by the gravity of the earth, which makes the space shuttle an object that can fly forward and rotate around the earth.
John, the chief expert of American relativity research? Wheeler explained that this so-called geometric property of space-time can be summarized as follows: space-time tells matter how to move, and matter tells space-time how to bend. Thus, the bending mode of cosmic starlight influenced by large celestial bodies can be displayed, which lays a theoretical foundation for the study of black holes. 1. Does God roll dice? Heisenberg uncertainty principle
Standard definition: German physicist Heisenberg proposed in 1927 that uncertainty in quantum mechanics means that in a quantum mechanical system, the position of a particle and its momentum (particle mass multiplied by velocity) cannot be determined at the same time.
"measure! In classical theory, this is not a problem to be considered. " The history of quantum physics says so.
That's because in classical physics, you, me, or anyone as an observer have no influence on this objective object waiting to be measured, or the influence is negligible. At that time, even if we didn't understand the truth, it didn't prevent the principle from staying there, waiting for us to learn more slowly.
But now we are about to step into the magic pool of the quantum world, where we as observers will bring some disturbances to the experimental phenomenon, so if we measure the momentum of an electron, the value we get is only relative to you as an observer. In the microscopic world, the so-called God rolls the dice with "probability".
Warner in those days? Heisenberg has made a breakthrough in this respect, and people can't get accurate information of two variables of particles at the same time, even with sophisticated instruments. Specifically, you can either know the position of the electron accurately, but you can't know its momentum at the same time, or vice versa. Similar uncertainties exist between energy and time, angular momentum and angle.
Maybe you don't understand the weirdness of this matter. As mentioned earlier, since the quantity in the quantum world is relative, it should be measurable as long as it exists. Since it can't be measured, it doesn't exist. Therefore, it is meaningless to talk about this physical quantity when the means of measurement are uncertain. The momentum of an electron only makes sense when you measure it.
This is more like a philosophical topic. Heisenberg's uncertainty principle was not so much discovered in experiments as discussed by Heisenberg and his teacher Bohr and others. When Bohr discovered that the electron has the properties of both particle and wave (the pillar of quantum physics, wave-particle duality), when we measure the position of the electron, we regard it as a particle with uncertain wavelength; When we want to measure momentum, we regard it as a wave, know the wavelength, but lose its position.
Even if you are extremely confused now, it's still no big deal. Bohr's famous saying is: "Anyone who is not confused about quantum theory must not understand." Similar to the phone bill man also said. So we have nothing to be depressed about. Einstein is in the same situation as us.
Five key points and three main lines to improve physics performance
First of all, study the syllabus and read through the textbooks.
Examination Outline is the basic requirement of teaching, which stipulates the scope and requirements of the senior high school entrance examination. It is one of the bases for the proposition of the senior high school entrance examination and plays an important role in the review of the senior high school entrance examination. Through the study of Examination Outline, we can make clear the requirements of the examination, understand the types of questions and the requirements for students' ability, make our review targeted and have a clear evaluation basis, which is conducive to grasping the breadth and depth of the review and making the review more targeted. While studying the syllabus, we should also read the textbook carefully, because the textbook is the fundamental basis for classroom teaching and one of the bases for the proposition of the senior high school entrance examination. Students must read the textbook carefully, paying special attention to the following aspects in the textbook:
(1) The formation process of physical concepts and laws and the scientific methods that follow. In recent years, in the physics test questions of senior high school entrance examination, the score of such questions should account for about 10%. In junior high school physics textbooks, the formation process of physical concepts and laws often adopts the "control variable method". For example, the formation process of concepts such as speed, density, pressure and specific heat capacity, ohm's law, factors affecting the evaporation speed of liquid, factors affecting the size of resistance, law of internal pressure of liquid, Archimedes theorem and other physical laws are all studied by "exploring variable method". In recent years, in the physics test questions of senior high school entrance examination, in addition to the "control variable method", the "equivalent substitution method" has also been assessed. For example, the effect of two forces acting on an object can be replaced by the effect of one force; In series-parallel circuit, the relationship between total resistance and each resistance, etc.
(2) Case analysis in teaching materials (including various illustrations, life examples and related scientific and technological development, etc.). ).
(3) Principles, research methods and processes of various experiments.
(4) The relevant history of physics. In many years of physics teaching, the author found that many students buried themselves in doing exercises in the process of reviewing for the exam, ignoring the most fundamental and necessary work-reading textbooks, which caused undue losses in the senior high school entrance examination and regretted it.
Second, organize the knowledge content and master it by classification.
The coverage rate of each knowledge point in the physics test paper of senior high school entrance examination is high, which is about 80%-90% in recent years, but the coverage rate of ten key knowledge points is 100%. These ten key knowledge are: calculation of specific heat capacity and heat, law of light reflection and imaging characteristics of plane mirror, law of convex lens imaging, ohm's law, characteristics of series-parallel circuit, concepts of electric power and force, density, pressure and balance of two forces. Physical knowledge covers a wide range, and basic concepts and theories are embodied in different teaching contents. Students should sort out the knowledge of each part according to the knowledge structure, form the connection between knowledge points, and extend it to the field of knowledge, so that the basic concepts can be firmly grasped and the basic theories can be interrelated. For example, when reviewing the knowledge of speed, we can transfer the thinking method of this physical concept to the formation process of other physical concepts such as density, pressure, power and specific heat capacity, and so on. That is to say, "the more books you read, the thicker you will be (the more knowledge you have)-the thinner you read (summarizing)-the richer your knowledge", so that you can be agile and handy in the exam.
Third, the classification of questions, master the method
At present, students have done a lot of mock exam questions, and many students are still struggling in the sea of questions. Many students and parents believe that in order to practice makes perfect, we must do more problems.
The author thinks that "the spirit is commendable and the way is improper". At present, it is unwise to do a lot of problems in a limited time. Students should analyze, compare and classify all kinds of questions in exercises, find out similarities and differences, and master problem-solving methods. Only by mastering the method can we understand the meaning of the question from multiple angles, broaden the thinking and methods of solving the problem, and give full play to our abilities in the exam.
Fourth, strengthen the cultivation of experimental research ability.
Physics is a subject based on experiments, and it is very important to pay attention to the cultivation of students' research ability in the new teaching reform. Both teaching materials and senior high school entrance examination questions over the years attach great importance to the examination of students' experimental research ability. In recent years, the scores of physics experiment in senior high school entrance examination have been rising, and the design mode has been explored from simple memory to experiment from the content of examination questions. This aspect is precisely the weak aspect of students, and they have lost more points over the years. Therefore, middle school students should strengthen review training. Generally speaking, in experimental research, students should pay special attention to the information provided in the topic, and make clear the research purpose, experimental principle, role and selection of experimental equipment, experimental operation steps, observation and analysis of experimental phenomena and analysis and induction of experimental results.
Fifth, pay attention to hot issues and master the exam dynamics.
In recent years, there are five hot topics in physics for senior high school entrance examination: (1) Estimation and estimation questions mainly involve practical cases directly related to what students have learned in real life. (2) dynamic and fault analysis (3) scientific method questions mainly examine the thinking methods in the process of forming physical concepts and laws; (4) Situational information questions provide more situational information in the test questions, and filter out useful relevant information according to the requirements of the test questions. (5) Open examination questions (including open results, open conditions, open process, etc. ) means that the methods and means of research can be changed from many angles and aspects, there is no fixed model and formula, the research results are not unique, and the forms of expression can be colorful.