The word physics comes from the Greek physis, which means nature, so in Europe, the word paleophysics is the general name of natural science. Physics is a science that studies the basic structure of matter and the most common motion forms and laws of matter, and it is a science based on experiments. The whole history of physics tells us that human physical knowledge comes from practice. Through the demonstration experiments made by teachers in the classroom and the group experiments made by students in the laboratory, we can gain perceptual knowledge, thus accurately establishing physical concepts, verifying physical laws and deepening our understanding of physical laws, enhancing our ability to observe physical phenomena and analyze problems, and understanding the methods of scientific experiments.
Learn physics concepts and laws well.
To learn physical concepts well, we must deeply understand the physical essence revealed by these physical quantities. A profound understanding here means doing the following for each physical quantity: What is its physical meaning? The so-called physical meaning refers to the introduction of this physical concept to describe what the nature of matter is. For example, the strength of the electric field describes the nature of the force of the electric field; Momentum describes the state of motion of an object. (2) How is it defined and what is the mathematical expression defined and determined? (3) Whether it is a vector or a scalar. Because the operation of vector and scalar is different, it is not just a question of whether the physical quantity is vector or scalar. (4) What is its unit? (5) What is the relationship with other physical quantities in the definition formula and judgment formula? For example, the electric field intensity e has nothing to do with the defined electric field force f and the electric quantity q of the test charge; Density ρ has nothing to do with mass m and volume ν; The resistance R of a conductor is directly proportional to the length L of the conductor and inversely proportional to the cross-sectional product, and the proportional constant is resistivity ρ and so on. (6) It is different from other similar physical quantities such as temperature, heat, specific heat, heat energy and internal energy; Similarities and differences of electric potential, electromotive force, potential difference, voltage and voltage drop.
Learning physical concepts well also includes correctly understanding physical relations. For example, is static, the balance of objects and the balance of forces the same? In order to balance a force and a pair of forces, the reaction forces are equivalent and in opposite directions, but what are their differences? (Say at least three o'clock). Wait a minute.
Physical laws are often expressed by algebraic expressions in addition to words. To learn the laws of physics well, we should know how this law is summed up through experiments, what is the physical meaning of each term in the expression, what is the meaning of the symbols in it, what is the meaning of the left and right parts of the equation, and what is the applicable scope and conditions of this law. It is very common for middle school students to confuse formulas. Only by understanding the applicable conditions of the formula can we correctly choose the formula and overcome the confusion of the formula. For example, υt=υ0+at is only applicable to the linear motion with uniform change in middle school, and the flat throwing motion is a curve motion with uniform change, so it cannot be used. For another example, when choosing the law of conservation of momentum, we should first see whether the resultant force of external force on the research system is equal to zero, so as to decide whether the equation can be established by the law of conservation of momentum.
There are three expressions of physical concepts and laws, one is language, the other is formula symbol, and the third is image. Image expression plays an important role in physics. We should overcome the tendency of attaching importance to formula expression, ignoring language description and ignoring image expression. When studying physics, we should pay attention to three aspects of learning and training at the same time.
Laying a good foundation is the key to the rise of a tall building. Only by deeply understanding and mastering the basic concepts and laws can we talk about the ability to solve problems. Listening to lectures, reading books and observing examples are all around the word "understand", and only practice can solve the word "understand". Then, how to do physics exercises will help us learn knowledge well and grow our talents? What is the correct way to do physics exercises? I think it can be summed up in eight words: phenomenon, concept, law and method. Specifically, in the face of a physical exercise, we must first carefully examine the problem, which is the basis of success. It is necessary to find out what kind of physical phenomenon this problem depicts, find out the changing process of the phenomenon (that is, the physical process) and express it with a schematic diagram. Middle school students don't like to use charts to express problems, so they should consciously correct them. Mechanical problems include stress diagrams, optical problems include light path diagrams, electrical problems include circuit diagrams, and thermal problems include process diagrams. If we can draw the schematic diagram of physics exercises correctly, the problem will be solved by one third. Second, think about what physical concepts should be used to describe this physical phenomenon, which are known, which are unknown and which are the answers to be sought. Third, think about the organic connection between these concepts, that is, choose the physical laws correctly. At this time, it is necessary to consider the scope and conditions of application of the selected laws, so as to confirm how many laws are available. Fourth, because there are often several laws available to solve a physical problem, we should further consider which law is the simplest and what mathematical method is the simplest. It is "unscrupulous" to solve physical problems with mathematical tools. Geometric methods are usually simpler than algebraic methods. But to be clear, neither method is omnipotent, and comprehensive application is the shortcut. Experience tells us that the correct choice of physical laws cannot solve the problem, and the difficulty often lies in mathematics. After solving the required answers to the questions through the ideas of phenomena, concepts, laws and methods, we must also estimate the rationality of the answers.
To sum up, learning physics knowledge well is inseparable from paying attention to and doing experiments well, learning concepts and laws well and doing exercises well. There is no place in the world where pies fall from the sky, and there is no cure-all medicine. Learning is hard and honest work, no pains, no gains.
(2) In our colorful world, sound plays an important role. What would the world be like without sound? Let's imagine what kind of world it would be. Is it interesting? Cold? Quiet? or ...
Man is the master of the world. First of all, what effect will sound have on human beings? Then let's talk about the influence of sound on human beings first! What will happen to human beings if there is no sound? If there is no sound, people can't make a sound when they speak, just like people who lose their voices speak in sign language. Why do people need ears? There is no sound to listen to. Is it for decoration? How can there be such beautiful music now? If there is no sound, what is the point of the whole world dying in a dead universe? If there is no sound, how can students study and read at school? How can there be music, English, information ... courses? How will you express what you want to express? Do you rely on sign language? I really can't imagine what teaching would be like at that time.
Pangu, the ancestor of China, created human beings because he thought the world was too quiet and lifeless. Now, if there was no sound, there would be no laughter. Then why are there humans? What's the point of having humans? We are not Beethoven, nor do we have Beethoven's skills. Even if we can't hear, we can bite a stick with our teeth and feel the sound according to the vibrating skull. But if there is no sound, not even sound waves, even Beethoven can't feel the sound, let alone play the piano. If there is no sound, how can there be a telephone now? If relatives are far away, how will they talk? Can you sign language after such a long distance? If … if … if too much, I think these ifs are impossible. In short, human beings need sound.
It's hard to imagine how human beings would survive without sound! Of course, this is not just human beings; Animals also need sound, and even animals can't live without sound; For example! Bats can be said to be a special kind of animals. Although it has a pair of eyes, it can always see if it can't hear, but do you know it is called "blind" in the animal kingdom? Its eyes are not worthy of the name, because it relies on its ears. Listen to ultrasonic waves with your ears to identify positions and avoid obstacles. If there is no sound, the bat can't hear the sound, can't catch the food and can't fly, then does it still have a chance to survive? Of course, bats are not the only animals, and other animals cannot do without sound. Here is an example to emphasize that "the earth cannot live without sound".
Without sound, people seem to live in a vacuum, quiet and silent. There is no wind, no rain, no reading, but more birds, songs and laughter. Therefore, the universe in which human beings live now has no color and no sound.
Excuse me, will two be all right? I don't know if it is written correctly! schoolmate