After students learn elasticity, they know that elasticity is the most basic natural force and is the premise and basis for the generation of friction. Elastic force is also the most important force in the force analysis of objects. Elasticity comes from deformation: "The size of the elasticity is related to the size of the deformation. The greater the deformation, the greater the elasticity. When the deformation disappears, the elasticity disappears" (required course in high school physics). But what is the relationship between elasticity and deformation? The high school physics textbook of the People's Education Press only gives a qualitative relationship. The reason is that the relationship between elasticity and deformation is relatively complicated. In order to reduce the difficulty and reduce the leap of knowledge, the course is set up as exploratory learning, and only the quantitative relationship between elastic force and spring elongation deformation is studied.
The teaching content of this class is novel and the form is relatively vivid. It includes explanations, experiments, blackboard performances, discussions, inductions, and exercises. It can be turned into a typical inquiry-based experimental teaching class. . We changed the perspective of the classroom and made some explorations in educating students on scientific research methods, allowing students to re-walk the path of exploration of scientists and appreciate the spirit of exploration of scientists.
Teaching objectives
1. Deepen the understanding of the relationship between elastic force and deformation, and know the conditions for the generation of elastic force;
2. Obtain the elastic force and spring elongation through experiments relationship;
3. Learn the scientific methods used in this topic;
4. Cultivate students’ spirit of exploration and teamwork, and stimulate students’ desire for knowledge;
< p>5. Improve students’ ability to analyze and solve practical problems, and experience the joy of success.Teaching focus
The relationship between the elastic force of the spring and the elongation of the spring.
Teaching Difficulties
How to process experimental data.
Teaching methods
Experimental method, conversation method.
Preparation before class
Teacher preparation: (spring scale, hook code, ruler, iron stand) 12 sets, CAI courseware, multimedia booth.
Student preparation: triangle board, pen, scratch paper.
Teaching Location
Physics Multimedia Laboratory.
Class schedule
1 class hour.
Teaching process
1. Review knowledge and introduce topics
Teacher: [Multimedia display] 1. What is elasticity? What is the direction of the elastic force? Give examples.
2. What are the conditions for elasticity to occur?
3. What is deformation and elastic deformation?
Student: Recall and answer.
Teacher: Correct the summary based on students’ answers and use multimedia to display the answers.
1. When a deformed object returns to its original shape, it exerts a force on the object in contact with it. This force is called elastic force.
For example: a book placed on a horizontal tabletop is subject to the elastic force exerted by the tabletop on the book. The direction of the elastic force is perpendicular to the tabletop and points toward the book; while the direction of the elastic force exerted on the tabletop is perpendicular to the tabletop and downward.
The electric lamp hanging under the wire is subject to the elastic force exerted by the wire on the electric lamp. The direction of the elastic force points along the rope to the direction of the rope contraction.
2. The conditions for the generation of elastic force are: two objects are in contact with each other and undergo elastic deformation.
3. The change in the shape or volume of an object is called deformation; when an object deforms, if the external force is removed, the object can return to its original shape. This deformation is called elastic deformation.
Teacher: [Show on the projection] If you pull the spring with your hand, the spring will stretch. The greater the force, the greater the stretch of the spring. When you let go of the spring, the spring will immediately return to its original shape. Ask students to analyze the experimental principles of the demonstration.
Student:...
Teacher: Analyze and ask questions
A spring will stretch when it is stretched, and when it is in equilibrium, the elastic force on the spring is equal to the external force. The greater the extension of the spring, the greater the elastic force. It can be seen: elongation (reason) → deformation (reason) → elasticity. So what is the quantitative relationship between elasticity and elongation? In this class, students will explore this relationship through experiments.
2. Experimental Research
Teacher: [Thinking Questions on Multimedia Projection]
1. What method is used to apply force to the spring?
2. How to determine the elasticity?
3. What data need to be measured? How to log data?
4. Can the spring be overstretched?
5. What is the elongation of a spring? What measurement is used?
Teacher: Divide the students into groups of four at two tables, read the text and discuss the questions, form a unified answer and write it on the scratch paper, and prepare to send representatives to answer.
Students: Read the text and actively discuss it.
Teacher: Patrol the laboratory and ask about the situation.
......
Teacher: Ask the students to answer one by one...
Teachers and students *** the same summary:
1. Use hanging The method of hooking the code applies tension to the spring;
2. According to the two-force balance condition, when the hooking code is balanced, the elastic force generated by the spring is equal to the gravity of the hooking code.
3. The data that need to be measured in the experiment include: the original length of the spring and the length of the spring corresponding to each hooked code. Data can be recorded in tables or ordered pairs of real numbers.
4. The tension applied to the spring should not be too large to prevent the spring from being over-stretched beyond its elastic limit.
5. Use a ruler to measure the difference between the length of the spring when it is hooked and the length when it is not hooked, which is the elongation of the spring.
Teacher: Give the instrument to the students , one set per 4 people.
Students: Students discussed and obtained the experimental method:
Fix the upper end of the spring on the bracket of the iron platform, and hang the hook code on the lower end. When it is at rest, the elastic force is equal to the gravity of the heavy object. Use this to measure the size of the elastic force F, and measure the elongation x (or total length) of the spring when the weight is suspended from the scale fixed on the vertical bracket.
Students: Students conduct experiments and record experimental data in lists.
Teacher: Inspect the laboratory, check and provide guidance, so that students can think further. Check the student statistical tables (there may be multiple tables) and display them on the experimental booth. Then the reference table is given as follows:
1
2
3
4
5
6
7
8
9
10
x
< p> x0x1
x2
Δx
0
Δx1
Δx2
m
0
m1
m2
F
0< /p>
F1
F2
Guide students to convert the data in the table into ordered real number pairs: (F, Δx)
1, ( F1, Δx1) 2. (F2, Δx2) 3. (F3, Δx3)...
It is helpful for students to use mathematical knowledge to draw points in the F-Δx rectangular coordinate system.
Teacher: Demonstrate the data processing method based on the measured data in the student-designed table.
[Multimedia display] Demonstration graphics:
1. With the elastic force as the ordinate and the extension of the spring as the abscissa, establish a plane rectangular coordinate system;
2. Draw points on the graph paper based on the measured data;
3. According to the distribution and direction of the points in the graph, try to draw a smooth curve (including straight lines). The points drawn may not be exactly right. on this curve, but be careful to have approximately the same number of points on both sides of the curve.
Students: Students process data...
Teacher: Randomly check the students’ data processing, select a few results to display on multimedia, and comment on them. If they are good, they will be affirmed, and if they are bad, they will be criticized. Revise and encourage.
Teacher: 1. Based on the F-Δx graph, guess the functional relationship of F-Δx;
2. What are the units of the constants in the functional relationship expression? The constant is determined by what in the image?
Students: Discuss and answer.
Teacher: [Projection display] 1. Guess the function based on the image: F=kx;
2. The unit of the constant in the function expression is: Newton/meter (N/ m), this constant is called the stiffness coefficient.
3. Summary based on the experiment
Teacher: Based on the experimental process, summarize the experimental steps.
Students: Students summarize on the scratch paper.
Teacher: [Multimedia display] Summary of several groups of students
1. Measure the elongation (or total length) of the spring and the tension (or the mass of the hooked code) ), make records in a list, and measure as many sets of data as possible;
2. Convert the recorded data into ordered pairs of real numbers;
3. Use force as the ordinate, and the spring The elongation is the abscissa, and points are drawn on the graph paper based on the measured data;
4. According to the distribution and direction of the points in the figure, try to draw a smooth curve (including straight lines). Connect the points and let as many points fall on the curve as possible. The points that cannot fall on the curve should be roughly symmetrically distributed on both sides of the curve.
5. Using the spring extension as the independent variable, write the function represented by the curve.
Teacher: Summarize the experimental conclusions.
Sheng: Within the elastic limit, the elastic force F of the spring is proportional to the length Δx of the spring extension.
IV. Experimental Expansion
Teacher: Students, we have explored the relationship between elastic force and spring elongation, and concluded that if the spring is compressed, the elastic force of the spring is related to What is the relationship between the length of spring compression?
Students: Students explore experiments...
The summary is: within the elastic limit, the size F of the spring force is proportional to the length Δx of the spring compression.
5. Analysis of Examples
Teacher: [Multimedia Display] Question: The relationship between the length L and the elastic force of a spring measured experimentally is as shown in the figure. Find:
(1) What is the original length of the spring?
(2) What is the stiffness coefficient?
Students: Students think and express their opinions.
Teacher: [Multimedia provides the solution process] Solution: The length of the spring when it does not produce elastic force is equal to the original length. From the figure, it can be seen that the original length of the spring is L0 = 15cm.
According to the definition of stiffness coefficient:
As can be seen from the graph, when the spring stretches Δx = (25cm-15cm) = 10cm, the elastic force ΔF = 50N, so N/m =500N/m.
6. Classroom exercises (potential development, thinking improvement)
Teacher: [Multimedia] Show the questions first, and then show the answers after the students have finished.
Example: When a student was exploring the relationship between elastic force and spring elongation, he drew four coordinate points a, b, c, and d on the graph based on experimental data.
(1) Based on the four coordinate points a, b, c, d, draw the F-Δx graph;
(2) From the graph, if the original length of the spring is 50cm , how much tension is needed to make the spring extend to 75cm (still within the elastic limit)?
Analysis and answers: (1) See the picture and judge that the four coordinate points are basically on a straight line, so that they are evenly distributed on both sides of the straight line, which can reduce accidental errors.
(2) In this question, k=600/20 (N/cm)=30N/cm. According to F=kΔL, the tensile force F=30×(75-50)N=750N.
7. Family Reinforcement Exercises
1. The experiment shows that the size of the spring force f and the deformation amount x of the spring have the following relationship: f = kx. The following statement is correct ( )< /p>
A. The k in the formula reflects a property of a specific spring
B. k is proportional to the external force exerted on the spring
C. x is the length of the spring after it is extended or shortened
D. Divide a certain spring into two sections, and the size of k is reduced by half
2. There are three identical springs with an original length of 10cm. After each spring is hung with a weight G, the spring stretches by 1cm. . Now connect the three springs in series to form a long spring, and then hang the weight G. The total length of the three springs is ( )
A. 31cm
B. 33cm
C. 36cm
D. 30.3cm
3. A light spring has its upper end fixed and an object of weight G suspended from its lower end. The length of the spring is L1. If the lower end of the spring is fixed and the same weight is placed on the upper end, the length of the spring is L2. The natural length of the spring is and the stiffness coefficient is.
4. A spring scale, because the original spring was damaged, a new spring was replaced. After testing, when no weight is hung, the reading is 2N. When a 100N weight is hung, the reading is 92N. Then, when the reading is 20N, the actual weight of the hanging weight is .
Teaching Instructions
The content of this lesson is simple and ultimately boils down to Hooke’s law: F=kx. If students are forced to memorize and train to cope with the exam, 98% of students will be able to master it, and at the same time, one teaching class will be saved. However, in middle school physics teaching, ideological exploration of teaching materials should be carried out. Provide students with multi-faceted education on physical science research methods, cultivate interest in experimental research, theoretical exploration, and devote themselves to scientific undertakings. This education should be infiltrated into specific classroom teaching. The teaching of exploring the relationship between elastic force and spring elongation not only focuses on cultivating students' ability to solve problems using F=kx, but also focuses on educating students in physical science research methods. In the teaching of this class, a general method of studying physical science is highlighted: "observe phenomena, preliminary analysis → experimental research → guess → draw rules → repeat experiments and test conclusions."
This kind of While teaching specific knowledge, scientific method education is carried out to enable students to understand the general methods of studying physical laws. Its importance is no less than the learning of specific physical knowledge, because it will benefit students throughout their lives.
Reference materials:
[1] "Dialogue on Physics and Culture" Jiang Shuigan, Beijing Science Press, 2002
[2] "Zhihong Optimization Design" Ren Zhihong Hainan Nanfang Publishing House 2004
[3] "Textbook Analysis and Refining" Ding Yaojian Jiang Qishi Beijing People's Education Press Yanbian Education Press 2002
[4] Full-time ordinary senior high school (compulsory) "Physics" Volume 1 People's Education Press
[5] "Encyclopedia of Chinese Middle School Teaching" (Physics Volume) Yan Jinfeng Shenyang Publishing House 1990