Summary of all knowledge points in senior high school physics
1, large objects may not count as particles, and small objects may not count as particles.
2. A moving object may not be regarded as a particle, and a rotating object may not be regarded as a particle.
3. The frame of reference is not necessarily fixed, but an assumed fixed object.
4. Choose different reference frames. The motion of objects may be different, but it may also be the same.
5. n seconds on the time axis refers to the end of n seconds. The nth second refers to a period of time, that is, the nth1second. The end of the nth second and the beginning of the nth+1second are the same moment.
6. Ignore the vector of displacement, only emphasize the size and ignore the direction.
7. When an object moves in a straight line, the displacement is not necessarily equal to the distance.
8. Displacement is relative, so you must choose a reference system. When different reference frames are selected, the displacement of the object may be different.
9. The dot timer should be marked with dots of appropriate weight on the paper tape. If a short horizontal line appears, adjust the height of the vibrating needle from the carbon paper to slightly increase it.
10, when using the timer to dot, you should turn on the power first, and then loosen the paper tape after the dot timer is stable.
1 1. When using the EDM dot timer, pay attention to putting on two white paper strips correctly, and the toner box is sandwiched between the two paper strips; When using the electromagnetic dot timer, the paper tape should pass through the limit hole and be pressed under the carbon paper.
12, the word "speed" is a vague general term with different meanings in different contexts. Generally, it refers to one of the four concepts of instantaneous speed, average speed, instantaneous speed and average speed. We should learn to distinguish the meaning of "speed" from top to bottom. And "speed" usually refers to instantaneous speed, average speed and average speed commonly used in formula calculation.
13, focusing on understanding the vector nature of speed. Some students are influenced by the concept of speed understood in junior high school, so it is difficult for them to accept the direction of speed. In fact, the direction of speed is the direction of object movement, and the "speed" in junior high school is the average speed now.
14, the average speed is not the average speed.
15, the average speed is not the size of the average speed.
16, the speed of the object is large, but the acceleration is not necessarily large.
17, when the speed of an object is zero, its acceleration is not necessarily zero.
18, the speed of the object changes greatly, but the acceleration is not necessarily large.
19, and the positive and negative accelerations only indicate the direction, not the size.
20, the acceleration of the object is negative, and the object does not necessarily slow down.
2 1, when the acceleration of the object decreases, the speed may increase; When the acceleration increases, the speed may decrease.
22. When the speed of an object is constant, the acceleration is not necessarily zero.
23. The acceleration direction of an object is not necessarily the same as the speed direction, nor is it necessarily in the same straight line.
24. The displacement image is not the trajectory of the object.
25. Before solving the problem, make clear what the two coordinate axes represent, and don't confuse the displacement image with the velocity image.
26. The fact that the image is curved does not mean that the object moves in a curve.
27. When reading a physical quantity from an image, find out the size and direction of this quantity, and pay special attention to the direction.
28. The point where two lines intersect on the V-T diagram is not the intersection point, but the moment is equal.
29. People come to the wrong conclusion that "heavy objects fall fast" is mainly affected by air resistance.
Strictly speaking, a free-falling object is only affected by gravity. When the influence of air resistance is small, the influence of air resistance can be ignored, which is approximately regarded as free fall.
3 1. When recording the trajectory of free fall, the requirements for heavy objects are "large mass and small volume", and it is not accurate to emphasize only "large mass" or "small volume".
32. In free fall, the acceleration g is known, but sometimes it is not specified in the title. We should make full use of this implicit condition when solving problems.
33. Free fall is an ideal state without air resistance. The motion of real objects is sometimes greatly influenced by air resistance. At this time, air resistance can not be ignored. For example, in the final stage of raindrops falling, the resistance is great and cannot be regarded as free falling.
34. The acceleration of a free fall is usually 9.8m/s? Or 10m/s? , but it is not a constant, it varies with latitude and altitude.
35. The four important proportional formulas all start from free fall, that is, the initial velocity v0=0 is the condition for establishment. If v0≠0, none of these four proportional formulas holds.
36. All the formulas of uniform and variable speed motion are vectors, and attention should be paid to the direction of each physical quantity when solving the equation.
37. The direction of initial velocity v0 is often taken as the positive direction, but this is not necessarily the case, and the direction opposite to v0 can also be taken as the positive direction.
38, car braking problem should first judge when the car stops moving, don't blindly apply the uniform deceleration linear motion formula to solve.
39. Identify the critical conditions of tracking problems, such as displacement relation, velocity phase, etc.
40. When solving problems with speed images, it should be noted that the point where straight lines intersect is the point where the speed is equal, not the place where they meet.
4 1, one of the conditions to produce elastic force is that two objects contact each other, but there is not necessarily elastic force between the contacted objects.
42. When an object is subjected to elastic force, it is not caused by the deformation of the object, but by the deformation of the object applying elastic force.
43. The direction of pressure or supporting force is always perpendicular to the contact surface, regardless of the position of the center of gravity of the object.
44. Hooke's Law Formula F=kx x is the length of the spring, not the total length of the spring, not the original length of the spring.
45. The elastic force of the spring is equal to the force at one end, not the sum of the forces at both ends, nor the difference of the forces at both ends.
46. The elastic direction of the rod is not necessarily along the rod.
47. The function of friction can be both resistance and power.
48. Sliding friction is only related to μ and n, and has nothing to do with the size of the contact surface and the motion state of the object.
49, the direction of all kinds of friction has nothing to do with the direction of motion of objects.
50. The magnitude and direction of static friction are variable, so it is easy to make mistakes when analyzing related problems of static friction.
5 1, the maximum static friction is related to the contact surface and positive pressure, and the static friction has nothing to do with pressure.
52. Choose an appropriate proportion when drawing a diagram.
53. The two strings in the experiment should not be too short.
54, check whether the spring dynamometer pointer refers to zero.
55, in the same experiment, make rubber strip elongation node position must be the same.
56. When using the spring dynamometer to pull the string sleeve, make the spring of the spring dynamometer and the string sleeve in the same straight line, and the spring is parallel to the board surface, so as to avoid the friction between the spring and the shell of the spring dynamometer and the limit card of the spring dynamometer.
57. In the same experiment, the selected scale should be consistent when drawing the power diagram, and the scale should be used appropriately to make the power diagram slightly larger.
58. The resultant force is not necessarily greater than the component force, and the component force is not necessarily less than the resultant force.
59. The maximum value of the resultant force of the three forces is the sum of the values of the three forces, and the minimum value is not necessarily the difference of the values of the three forces. You need to judge whether it can be zero first.
60. The result of combining two forces into one force is unique, and the situation that one force is decomposed into two forces is not unique. There are many ways to decompose.
6 1, the two components of a force must have the same nature as the original force and must be the same force-bearing object. For example, when an object is stationary on an inclined plane, its gravity can be decomposed into the force that makes the object slide down and the force that makes the object press the inclined plane, but it cannot be said that it is the sliding force and the pressure of the object on the inclined plane.
62. When an object moves forward on a rough slope, it is not necessarily subjected to forward force. It is wrong to think that an object has a forward "impulse" when it moves forward.
63. All the ideas that inertia is related to the state of motion are wrong, because inertia is only related to the mass of an object.
64. Inertia is the basic property of an object, not a force. The external force on an object cannot overcome inertia.
65. When the force is zero, the speed of the object is not necessarily zero, and when the speed is zero, the force is not necessarily zero.
66. F = F in Newton's second law F=ma usually refers to the resultant force acting on an object, and the corresponding acceleration A is the resultant acceleration, that is, the vector sum of independently generated accelerations. Newton's second law still holds when only the acceleration produced by a certain force is studied.
67, the corresponding relationship between force and acceleration, in no particular order, the force changes at the same time the acceleration changes accordingly.
68. Although it can be concluded from Newton's second law that when an object is not subjected to external force or the resultant force of external force is zero, it will move in a straight line at a uniform speed or be at rest, it cannot be said that Newton's first law is a special case of Newton's second law, because the nature of the object, namely inertia, revealed by Newton's first law is not reflected in Newton's second law.
Newton's second law is widely used in mechanics, but it is not "universal" and has its limitations. Not suitable for high-speed micro-objects, only suitable for low-speed macro-objects.
70, using Newton's second law to solve the two basic problems of dynamics, the key is to correctly calculate the acceleration a, when calculating the resultant force, to make a correct force analysis, don't leak force or force.
7 1, when using orthogonal decomposition method to form equations, pay attention to the fact that the resultant force and component force cannot be calculated repeatedly.
72. Note that f =ma is a vector type. In application, we should choose a positive direction. Generally we choose the direction of external force, that is, the direction of acceleration, as the positive direction.
73. Overweight is not the increase of gravity, and weightlessness is not the loss of gravity. Overweight and weightlessness are only changes in apparent weight, but the actual weight of an object has not changed.
74. When judging overweight and weightlessness, it is not the direction of speed, but whether the acceleration direction is upward or downward.
75. Sometimes the acceleration direction is not in the vertical direction, but as long as there is a component in the vertical direction, the object is also in a state of supergravity and weightlessness.
76, two related objects, one of which is in a state of overload (loss), the overall pressure on the supporting surface will be greater than (less than) the specific gravity.
77, the international system of units is a system of units, don't understand the system of units as the international system of units.
78. The unit of force Newton is not a basic unit but a derivative unit.
79. Some units are commonly used rather than SI units, such as hours and kilograms.
80. Physical calculation often needs a unified unit.
8 1. As long as there is a resultant force that is not in a straight line with the speed direction, the object will move in a curve, regardless of whether this force is constant or not.
82. The speed direction of an object moving on a curve is the tangent of the locus where the point is located, not the tangent of the resultant force along the locus. Please pay attention to the difference.
83. Joint movement refers to the actual movement of an object relative to the ground, not necessarily the movement that people feel.
84. The combined motion of two linear motions is not necessarily linear motion, but the combined motion of two uniform linear motions must be uniform linear motion. The combined motion of two uniformly variable linear motions is not necessarily uniformly variable linear motion.
85. The synthesis and decomposition of motion is actually the synthesis and decomposition of physical quantities that describe motion, such as speed, displacement and acceleration.
86. Decomposition of motion is not separation of motion. Objects participate in one movement first, and then in another. Just for the convenience of research, the motion of an object is analyzed from two directions, and the sub-motion is isochronous, and there is no sequential relationship.
87, vertical throwing motion integral analysis must pay attention to the direction problem, the initial velocity direction is upward, the acceleration direction is downward, the equation can assume a positive direction, and then use positive and negative symbols to represent the direction of each physical quantity, especially the positive and negative displacement, which is easy to make mistakes and should be paid special attention to.
88. The acceleration of vertical throwing motion is unchanged, so the slope of its v-t image is unchanged and should be a straight line.
89. Attention should be paid to the concealment in the description of the topic, such as "the object reaches a place 5m away from the throwing point", which may not necessarily rise 5m from the throwing point, but may also reach there in the descending stage or 5m below the throwing point.
90. The time t in the formula of flat throwing motion is calculated from the throwing point, otherwise the formula is not established.
9 1. When calculating the speed change of a moving object in a certain period of time, we should pay attention to the method of vector subtraction. When the flat throwing motion is studied with the flat throwing vertical falling instrument, the result is that the free falling ball and the flat falling ball land at the same time, which shows that the vertical component motion of the flat throwing motion is free falling motion, but this experiment cannot show that the horizontal component motion of the flat throwing motion is uniform linear motion.
92. It is not that the greater the horizontal speed, the farther the range of oblique throwing objects will be. The range is determined by the initial velocity and the throwing angle.
93. The velocity of an object at the highest point of oblique throwing motion is not equal to zero, but equal to its horizontal component velocity.
94. The trajectory of oblique throwing is symmetrical, but the trajectory curve is asymmetrical.
95, in the case of radius uncertainty, can't judge the size of the linear velocity by the size of the angular velocity, also can't judge the size of the angular velocity by the size of the linear velocity.
96. Every point on the earth is moving in a uniform circle around the earth's axis, and its period and angular velocity are equal. The radius of each point doing uniform circular motion is different, so the linear velocity of each point is not equal.
97. Angular velocity relationship of each particle on the same wheel: Because the connecting line between each particle and the rotating shaft on the same wheel rotates at the same angle at the same time, the angular velocity of each particle is the same. Every particle has the same ω, t and n.
98, in the gear drive or belt drive (belt does not slip, friction drive contact surface does not slip) device under the condition of normal work, the linear velocity of each point on the belt and the rim is equal.
99. The centripetal force of uniform circular motion is the resultant force of objects, while the centripetal force of variable circular motion is not necessarily the resultant force.
100, when the centripetal force is provided by static friction, the magnitude and direction of static friction are determined by the motion state.
10 1, the rope can only produce tension, and the rod can produce both tension and pressure on the ball. Therefore, when calculating the force, we should first use the critical condition to judge the direction of the force exerted by the rod on the ball, or assume that the force is in a certain direction, and then judge it according to the obtained results.
Expanding reading: how to learn physics well
Memory: In the study of high school physics, we should memorize the basic concepts, laws and some basic conclusions, which is what we often call the most basic knowledge. Students often ignore the memory of these basic concepts and think that learning physics does not need to memorize these literal things. As a result, few students, even those in cram schools, can accurately state their physical concepts in the review of senior three. I can't absolutely say that the incompleteness of physical concepts has a great influence on your study in a certain exam or a certain stage, but I can definitely say that your understanding of physical problems has an inherent adverse effect on the formation of your knowledge of the whole physical system. You can't tell which question in an exam will lose points because of your inaccurate concept. Therefore, learning Chinese requires memorizing famous sayings and epigrams, learning mathematics requires memorizing basic formulas, and learning physics also requires memorizing basic concepts and laws. This is the first premise and the most basic requirement to learn physics well. Without this step, the following study is impossible.
Accumulation: it is the work after memory in the process of learning physics. On the basis of memory, we constantly collect a lot of information about physics knowledge from textbooks and reference materials, some of which come from a topic, some from an illustration of a topic, and some may come from a short reading material. In the process of collecting and sorting out, we should be good at analyzing and classifying different knowledge points, and find out similarities and differences in the process of sorting out, so as to facilitate memory. The process of accumulation is a process of struggle between memory and forgetting. However, it is necessary to make knowledge more comprehensive and systematic through repeated memory, and the relationship between formulas, theorems and laws is closer, so as to achieve the purpose of accumulation. Never repeat your homework like a bear breaking a stick, rote it and think nothing. The result will only be more memories than forgetfulness.
Synthesis: Physical knowledge is divided into chapters and sections, and the contents required by the physical examination outline are also piece by piece. They are both interrelated and different. Therefore, in the process of physics learning, we should constantly carry out small synthesis, and then carry out systematic synthesis after the third year of high school. This process requires students' ability, and chapters are interrelated, and different chapters can be compared with each other, so that the knowledge before and after can be truly integrated, so as to gradually find the connection of knowledge from synthesis and find the interest in learning physics knowledge.