Summary of two knowledge points of compulsory physics in senior one.
First, curvilinear motion
1. In curve motion, the velocity direction of a particle at a certain moment (a certain position) is the tangent direction of that point on the curve.
2. Conditions for an object to move along a straight line or curve:
(As we all know, when an object is subjected to an external force F, an acceleration A is generated in the direction F)
(1) If the direction of f (or a) is the same as the direction of object velocity v, the object moves in a straight line;
(2) If the direction of f (or a) is different from the direction of the object's velocity v, the object moves in a curve.
3. When an object moves in a curve, the direction of the resultant force always points to the concave side of the trajectory.
4. Flat throwing movement: the movement of throwing an object horizontally at a certain initial speed, regardless of air resistance, and the object only moves under the action of gravity.
Second, the sub-movement:
(1) will move in a straight line at a uniform speed due to horizontal weakness;
(2) In the vertical direction, the initial velocity of the object is zero, and it is only affected by gravity, so the object is in a state of free fall.
5. Taking the throwing point as the coordinate origin, the horizontal direction is the X axis (the positive direction is the same as the initial velocity), the vertical direction is the Y axis, and the positive direction is downward.
6.① Horizontal speed? ② Vertical component velocity? ③ closing speed at the end of t seconds.
④ The direction of motion at any moment can be expressed by the included angle between the speed direction of this point and the positive direction of the X axis.
7. Uniform circular motion: particles move along a circle, and the length of the arc passed at the same time is the same.
8. Physical quantity describing uniform circular motion speed
(1) linear velocity v: the ratio of the arc length of particles passing through to the time taken to pass through, that is, v=s/t, in m/s; It belongs to instantaneous speed, which has both magnitude and direction. Direction is the tangent direction of each point on the circumference.
9. Uniform circular motion is a non-uniform curvilinear motion, so the direction of linear velocity is changing at any time.
(2) Angular velocity: ω=φ/t(φ refers to the rotation angle, φ is one revolution), and the unit is radian/second or 1/ second; For a uniform circular motion, the angular velocity is constant.
(3) period t, frequency: f =1/t.
(4) Relationship among linear velocity, angular velocity and period:
10. centripetal force: centripetal force means that an object moving in a uniform circle receives a resultant force pointing to the center of the circle. The centripetal force only changes the speed direction of the moving object, but does not change the speed.
1 1. centripetal acceleration: describes the speed of linear velocity change, and the direction is the same as the centripetal force direction.
12. Note:
(1) Because the direction is always changing, uniform circular motion is a variable acceleration motion with the instantaneous acceleration direction constantly changing.
(2) For an object with uniform circular motion, the centripetal force always points to the center of the circle, which is a variable force.
(3) The resultant force on an object moving in a uniform circle is centripetal force.
13. Centrifugal motion: An object with uniform circular motion will gradually move away from the center of the circle when the resultant force suddenly disappears or is insufficient to provide the centripetal force needed for circular motion.
Third, the law of universal gravitation and its application
1. law of universal gravitation: gravitational constant G=6.67× N? Square meter/kg 2
2. Applicable conditions: the interaction between two objects that can be used as particles; If it is two uniform spheres, R should be the distance between the centers of the two spheres. When the size of an object is much smaller than the distance r between two objects, it can be considered as a particle. )
3. Application of the law of universal gravitation: (mass m of central celestial body, radius r of celestial body, gravitational acceleration g of celestial body surface)
(1) Gravity = centripetal force (when one celestial body moves in a circle around another celestial body)
(2) Gravity = universal gravitation
Gravity acceleration of ground objects: mg = G g = G ≈9.8m/s2.
Gravity acceleration of high altitude objects: mg = g g = g
4. First cosmic velocity-The linear velocity (orbital radius can be regarded as radius of the earth) of satellites orbiting the earth near the surface of the earth is the largest among all satellites orbiting the earth.
Pass mg=mv2/R or pass = = 7.9 km/s.
5. Kepler's three laws
6. Calculate the mass of celestial bodies with the law of universal gravitation.
7. Calculate the revolution speed through the law of universal gravitation and the centripetal force formula.
8. Two special launch speeds greater than the surrounding speed: the second cosmic speed and the third cosmic velocity (meaning).
Work, power, mechanical energy and energy
1. Two elements of work: force and displacement of an object in the direction of force.
2. Work: Work is a scalar with only magnitude and no direction, but it can be divided into positive work and negative work, and the unit is Joule (J).
3. The problem that an object does positive work and negative work (it is simpler to understand α as the angle formed by F and V)
(1) When α=90 degrees, W=0. This means that when the direction of force F is perpendicular to the direction of displacement, force F does no work.
If the ball rolls on a horizontal table, the support of the table for the ball does not do work.
(2) When α; 0, W>0. This means that the force F does positive work on the object.
If a person pushes Xiangqian Che, this person's thrust F does positive work on the car.
(3) When α is greater than 90 degrees and less than or equal to 180 degrees, cos α
If a person forcibly blocks the car from moving forward, this person's thrust F will do negative work for the car.
When a force does negative work on an object, it is often said that the object overcomes this force to do work (take absolute value).
For example, a ball thrown vertically upward, in the process of upward movement, gravity has done -6J work to the ball, so it can be said that the ball has done 6J work to gravity. If you say "overcome", you can't say that you have done negative work.
4. Kinetic energy is scalar, with only magnitude and no direction.
5. The gravitational potential energy is scalar.
(1) Gravity potential energy is relative to the selected reference plane. Therefore, when calculating the gravitational potential energy, we should clearly choose the zero potential surface.
(2) Gravitational potential energy can be positive or negative, positive above zero potential surface and negative below zero potential surface.
6. Kinetic energy theorem:
W is the total work done by external force on the object, m is the mass of the object, and v is the final speed, that is, the initial speed.
Answer the idea:
① Select the research object and make clear its movement process.
(2) Analyze the stress of the research object and the work done by each force, and then find the algebraic sum of the work done by each external force.
(3) Remove the kinetic energy sum of the object in the whole process.
④ List the equations of kinetic energy theorem.
7. Law of Conservation of Mechanical Energy: (Only gravity or elasticity does work, and no external force does work. )
Think about solving problems:
① Select the research object-material system or object.
② According to the physical process experienced by the research object, analyze the force and work, and judge whether the mechanical energy is conserved.
③ Select a suitable reference plane to determine the mechanical energy of the research object in the initial and final state of the process.
④ According to the law of conservation of mechanical energy, solve equations.
8. Expression of power:, or P=FV Power: describes the speed at which a force acts on an object; It is a scalar, positive and negative.
9. Rated power refers to the maximum output power when the machine works normally, which is the nominal value on the nameplate of the machine.
Actual power refers to the actual output power of the machine during operation. Not all machines work at rated power. The actual power is always less than or equal to the rated power.
Extended reading: physics learning methods: six learning skills
First, we should lower the starting point and start from scratch.
We should change our ideas, and don't think that junior high school physics is good, but senior high school physics is good. Junior high school physics knowledge is very superficial, you can learn it with your head. In addition, through a lot of practice and repeated intensive training, your proficiency in physics will also be improved, and your physical performance will be steadily improved. It can be said that high marks do not mean good study. To learn physics well in senior high school, students need to have a strong interest in physics and good learning methods. These two conditions are indispensable. Therefore, we should change our ideas, study hard and make progress steadily!
Second, I have a strong interest in physics.
Interest is one of the driving forces of thinking, a powerful and lasting driving force for learning, and a potential driving force for learning physics well. There are many ways to cultivate interest. From the students' point of view, it should be noted that physics is closely related to daily life, production and modern science and technology. There are many physical phenomena around us and we use a lot of physical knowledge. For example, when speaking, the vibration of vocal cords forms sound waves in the air, and the sound waves reach the ears, causing the eardrum to vibrate and produce hearing; Atmospheric pressure is helpful when drinking boiled water, drinks and dipping a pen in ink. When walking, the static friction between the foot and the ground is helpful, and the walking process consists of continuous dumping action; Remove impurities from rice when washing rice and use buoyancy knowledge; A straight chopstick is inserted obliquely into the water, and it seems that the chopsticks are curved on the water surface; The formation of lightning and so on.
Consciously connecting with physical knowledge in practice and applying physical knowledge to practice let us know that physics is so closely related to us that it is useful. Can greatly stimulate the interest in learning physics. From the teacher's point of view, we should introduce the concepts and laws of physics through vivid practical examples and intuitive experiments that students are familiar with, organize students to carry out experimental operations, and let students feel the close connection between physics and daily life; Physics in senior high school introduces the history and progress of physics and its wide application in modernization, so that students can see the use of physics and make it clear that today's study is for tomorrow's application. According to the content of the textbook, students are often selectively introduced to some vivid physical allusions, anecdotes and mysterious stories of Chinese and foreign physicists exploring the physical world; According to the teaching needs and students' intellectual development level, some interesting and thoughtful questions are put forward. Teachers' efforts from these aspects can also make students have a passive interest in physics and stimulate their enthusiasm for learning physics.
Third, improve learning efficiency.
During study, time in the classroom is very important. So the efficiency of class determines the basic situation of learning. To improve the efficiency of lectures, we should pay attention to the following aspects:
1, preview before class can improve the pertinence of listening. The difficulty found in the preview is the focus of the lecture; We can make up for the old knowledge that we have not mastered well, learn new knowledge, reduce blindness and passivity in the process of listening to lectures, and help improve classroom efficiency. After preview, comparing and analyzing the knowledge you understand with the teacher's explanation can improve your thinking level, and preview can also cultivate your self-learning ability.
2, in the process of listening to lectures, we should concentrate, concentrate, and not be absent-minded. Concentration is to devote yourself to classroom learning, so that you can hear, see, feel, speak and touch. If you can achieve these "five goals", your energy will be highly concentrated, and all the important contents learned in class will leave a deep impression on your mind. Make sure you can concentrate on the class and don't be distracted. Be sure to take a ten-minute break before class. Don't do too intense sports or heated debates in high school physics, and don't read novels or do homework, so as not to snore and daydream after class, or even make your brain fall asleep. Therefore, we should make material preparation and mental preparation before class.
Pay special attention to the beginning and end of the teacher's lecture. At the beginning of a teacher's lecture, it is generally to summarize the main points of the last lesson and point out the content to be talked about in this lesson, which is a link to link old knowledge with new knowledge. Finally, he often summarizes the knowledge in a class, which is very general and is an outline for mastering the knowledge and methods in this section on the basis of understanding.
4. Take notes. Taking notes is not a record, but a concise record of the key points and difficulties in the above lectures, and recording the main points of the lectures and your own feelings or innovative ideas. In order to review digestion.
5. We should carefully examine the questions, understand the physical situation and process, pay attention to the ideas of analyzing problems and the methods of solving problems, and stick to it, we will certainly be able to draw inferences from others and improve the ability of knowledge transfer and problem solving.
Fourth, do a good job in reviewing and summarizing.
1, review in time. On the second day after class, you must do a good job of reviewing that day. An effective way to review is not only to read books and notes over and over again, but also to take retrospective review: first, combine books and notes to recall what the teacher said in class, such as the ideas and methods of analyzing problems (you can also write them in a draft book while thinking), and think as completely as possible. Then open the book and notebook, compare and make up what you don't remember clearly, so as to consolidate the content of the class that day, check the effect of the class that day, and put forward necessary improvement measures for improving listening methods and improving listening effect.
2. Review these chapters. After learning a chapter, you should review it in stages, and the review method is the same as timely review. We should review by recalling, and then compare books and notes to make its content perfect, and then do a good job in the general part of the chapter.
3. Make a chapter summary. The chapter summary should include the following parts. Knowledge network in this chapter. Main contents, theorems, laws, formulas, basic ideas and methods of solving problems, conventional typical problems, physical models, etc. Self-experience: In this chapter, you should record the typical problems you did wrong, analyze their causes and correct answers, and record the most valuable ideas or examples in this chapter, as well as the unsolved problems, so as to make up for them in the future.
4. Do a comprehensive review. In order to prevent the previous knowledge from being forgotten, every once in a while, it is best not to exceed ten days, and review all the previous knowledge, which can be done by reading books, taking notes, doing problems, reflecting, etc.
Fifth, correctly handle the exercises.
Many students pin their hopes of improving their physics scores on a large number of problems and engage in sea tactics. This is inappropriate. "Don't judge heroes by how many questions they do." The important thing is not to do more questions, but to achieve high efficiency and goals. The purpose of doing the problem is to check whether the learned knowledge and methods are well mastered. If you don't master it correctly, or even have deviations, the result of doing so many questions is to consolidate your shortcomings. Therefore, we should do a certain amount of exercises on the basis of accurately mastering the basic knowledge and methods.
As for the intermediate questions, we should pay attention to the benefits of doing the questions, that is, how much we have gained after doing the questions. This requires some "reflection" after doing the problem, thinking about the basic knowledge used in the problem, the main knowledge points, the physical laws used, whether there are other solutions, and whether the analytical methods and solutions of the problem have been used in other problem solving. If you connect them, you will get more experience and lessons.
Of course, it is impossible to form skills without a certain amount of practice (homework assigned by the teacher), and it is also impossible. In addition, whether it is homework or exams, we should put accuracy first, and put physics methods in senior high school first, instead of blindly pursuing speed, which is also an important aspect of learning physics well.
6. Pay attention to observation and experiment.
Physical knowledge comes from practice, especially from observation and experiment. We should carefully observe physical phenomena and analyze the conditions and causes of physical phenomena. It is necessary for physics students to do experiments well, learn to use instruments and process data, and understand the basic methods of studying problems with experiments. We should consciously improve our observation ability and experimental ability through observation and experiment. In short, as long as we are open-minded, eager to learn, proactive, practical and serious, work hard to understand knowledge, think more, study more, stress scientific learning methods, connect with life and production practice, and pay attention to the application of knowledge, we will certainly learn physics well in senior high school.