Design concept of centripetal force teaching plan in physics
This lesson is mainly to learn the dynamic characteristics of centripetal force of an object doing circular motion, so the teaching of this lesson is mainly to learn the knowledge of centripetal force from the perspective of dynamics.
The study of physical problems always begins with the simplest and most basic, so the teaching of this class begins with the simplest circular motion. Starting with uniform circular motion, the expression of centripetal force is obtained. Then it is further extended to the dynamic law of variable speed circular motion and general curve motion; Match? From special to ordinary? Cognitive law and teaching law.
In the teaching of centripetal force expression, this course adopts the scientific research method of first deducing the formula with Newton's second law theory and then verifying it with experiments. In this way, students can not only deepen their understanding of centripetal force formula, but also know the rigor of scientific research. Moreover, through theoretical analysis and experimental exploration, students can understand the source and nature of centripetal force and know two methods to find centripetal force: solving by force analysis and solving by formula. In addition, the experimental inquiry part adopts the combination of in-class experiments and playing recorded experimental videos, which not only allows all students to read and participate in the experiments on the spot, but also effectively saves classroom time.
In the teaching of variable-speed circular motion, this course adopts? Question (guess)? Discuss and analyze? Get the right rules? Teaching methods, let students really participate in the classroom, from? Quarrel? Draw a conclusion and gain knowledge. Reflection? Student-oriented? The idea of new curriculum standard.
Considering the tight class time and safety problems (students are prone to collision when waving sandbags), what are the teaching materials? Do it. Part of this lesson is arranged for students to finish after class (experimental equipment is distributed to each student), and students are required to experience the relationship with V,? Relationships, experiences? Control variable method? The idea.
Physics centripetal force teaching plan teaching material analysis
The content of this lesson is that students learn the knowledge of centripetal force, variable-speed circular motion and general curvilinear motion from the perspective of dynamics after learning the centripetal acceleration of circular motion from the perspective of kinematics; Its content is not involved in junior high school. Judging from the position and function of the textbook, the content of this lesson is an important part of this chapter, which not only inherits the knowledge of centripetal acceleration in the previous section, but also paves the way for the study of circular motion in the next section, and plays a connecting role; At the same time, the content of this lesson is also an important part of the knowledge examination of national examination and college entrance examination.
This section mainly requires students to understand the concept of centripetal force, know that centripetal force is named according to the function of force, master the expression of centripetal force, analyze the source of centripetal force and calculate the centripetal force in simple cases; Students are required to understand the expression of centripetal force from the perspective of Newton's second law, and know that the resultant force of variable-speed circular motion generally does not point to the center of the circle, and can be decomposed into tangential component and centripetal component; Knowing that the centripetal force formula is also applicable to variable-speed circular motion, we can use the centripetal force formula to quantitatively analyze the highest and lowest points for the problem of variable-speed circular motion in the vertical plane. Don't seek mastery? Equivalent circle? Dealing with general curvilinear motion; The tangential component and tangential acceleration of variable-speed circular motion and curve motion do not need quantitative calculation; It is not required to calculate the centripetal force of external force on objects that are not in the same line.
One of the ideas about experiments in this section is to try to use general equipment instead of special equipment for experiments. It would be better if you could use common items in your life for experiments. On the one hand, the purpose of thinking like this is to reduce the difficulties caused by equipment problems and let everyone do more experiments; On the other hand, it is believed that experiments with non-professional equipment, especially objects in life, will bring science closer to students, make students feel that science is around them and become interested in science [1]. So this lesson does not use the centripetal force demonstrator, but uses the conical pendulum to verify the expression of centripetal force. The advantage of this experiment is that the equipment is easy to get, and the analysis method of pendulum force is often used in the future. Mastering it skillfully is beneficial to the later study, and at the same time, it can let students know the source of centripetal force. Experiencing centripetal force is the effect force.
This lesson is different from the past, that is, it discusses the circular motion of speed change and the general curvilinear motion. The main purpose of this part is to make students understand projectile motion and uniform circular motion in a more general and broader background. This idea discusses with us the displacement of non-uniform linear motion and uniform linear motion. The starting point of time image is the same strain.
About textbooks? Do it. The arrangement is mainly to let students experience the relationship between centripetal force and linear velocity and angular velocity. Control variable method? The idea is similar to the centripetal force demonstrator experiment in the old textbook.
Analysis of the present situation of centripetal force teaching plan in physics
Because junior high school textbooks do not involve circular motion, students are not familiar with circular motion. However, through the study in the first few sections of this chapter, students have already known the conditions for objects to do curvilinear motion, and learned the linear velocity of circular motion and centripetal acceleration's related knowledge; In addition, through the compulsory study of 1, students have been able to correctly analyze the force of objects and master Newton's laws of motion in dynamics knowledge. Therefore, students can independently derive the expression of centripetal force according to Newton's law of motion and centripetal acceleration's formula; Students can also analyze the centripetal force source of circular motion and the problem of variable speed circular motion under the guidance of teachers. Besides, students have been able to use physical methods? Equivalent model? 、? Control variable method? 、? Infinitesimal method? And can other ways of thinking to study physical problems guide students to adopt in the study of this course? Equivalent model? Inquiry experiment; Adoption? Control variable method? Empirical centripetal force formula; Adoption? Infinitesimal method? Dealing with general curvilinear motion.
In this class, students may be interested? Conical pendulum experiment? It is difficult to analyze and understand the tangential acceleration of circular motion with variable speed. Therefore, in the teaching process, students should be given enough time to discuss and explore, communicate with each other, draw conclusions and acquire knowledge; Of course, teachers can also help students break through space barriers, build models and deepen their understanding through multimedia.
Teaching objectives of centripetal force teaching plan in physics
Knowledge and skills
1. Understand the concept of centripetal force and its exact meaning.
2. You should know that centripetal force is named according to the action of force.
3. Experience the existence of centripetal force and analyze the source of centripetal force.
4. Know what factors are related to centripetal force, and can calculate centripetal force in simple situations.
5. Know the function of centripetal acceleration and tangential acceleration of circular motion with variable speed.
6. Know that in general curvilinear motion, the centripetal force formula can be used to find the centripetal force and centripetal acceleration of a particle at a certain point.
Teaching plan process and method of physical centripetal force
1. Derive the expression of centripetal force by using dynamics knowledge.
2. Through the experiment of roughly verifying the expression of centripetal force with a conical pendulum, we can understand what factors are related to the magnitude of centripetal force, analyze the source of centripetal force, and realize that centripetal force is the effective force. Do it. In order to understand the meaning of the formula
3. Further understanding is the reason for acceleration. Through Newton's second law, we can understand the respective characteristics of uniform circular motion, variable circular motion and general curvilinear motion.
Emotion, attitude and values [2]
1. Cultivate students' hands-on habits and improve their ability to analyze and solve problems in experiments.
2. Experience the happiness of success, realize the significance of the experiment and stimulate the interest in learning physics.
3. experience? From special to ordinary? Physical research method based on
4. appreciate? Theoretical derivation to experimental verification? Think scientifically and develop a rigorous scientific attitude.
Emphasis and difficulty of centripetal force teaching plan in physics
Teaching focus
1. The application of Newton's second law in centripetal force is realized by the experiment of conical pendulum and the measurement of related physical quantities.
2. Make clear the significance, function, formula and source of centripetal force.
Teaching difficulties
1. Conical pendulum experiment and measurement of related physical quantities
2. The tangential component and centripetal component of the circular motion of variable speed.
Teaching process of centripetal force teaching plan in physics
Introduction of new lesson
Teacher: In the first two classes, we learned the kinematic characteristics of circular motion and how to describe circular motion with linear velocity and centripetal acceleration. In this lesson, we will learn the dynamic characteristics of circular motion. centripetal force
Activity 2 Teaching a new lesson
[new course teaching]
First, centripetal force
Teacher: We always start with the simplest and most basic problems, and the simplest circular motion is uniform circular motion, so let's study uniform circular motion first. Let's watch a video.
Play the video: the rope pulls the ball in a uniform circular motion on a smooth horizontal plane.
Teacher: What forces are acting on the ball?
Health: The ball is pulled by gravity, support and rope.
Teacher: Yes, so what is the relationship between the direction of the resultant force and the direction of centripetal acceleration?
Health: The same.
Teacher's activity: Play the teacher's stress map when students answer.
Teacher: That's right. We can know this from Newton's second law. Last class, we already knew that an object with uniform circular motion has centripetal acceleration. According to Newton's second law, this acceleration must be caused by the resultant force pointing to the center of the circle. This resultant force is called centripetal force. It is the centripetal force that constantly changes the linear velocity direction of the ball, making it move in a circle instead of flying in a straight line.
Writing on the blackboard: first, centripetal force
1, definition: the resultant force acting on a circular moving object pointing to the center of the circle.
Teacher: If you know the direction of centripetal force, you have to know its size. Please speed up according to centripetal force.
The formula of degree is combined with the expression of centripetal force derived from Newton's second law.
Student activities: the expression of derived centripetal force.
Teacher's activity: Deriving the expression of centripetal force with students (performance)
∫Fn = m = v2/r = r？ 2
? You can get the simultaneous expression: Fn=m v2/r =mr? 2
Write on the blackboard: 2. Expression: Fn=mv2/r, Fn=mr? 2
Comments: Students' thinking lies in the stimulation of teachers, and students' enthusiasm for learning lies in the mobilization of teachers. By designing questions, students can express their opinions and ask questions, and cultivate their language expression ability and problem analysis ability.
Activity 3 activity experiment exploration
Second, experiment: roughly verify the expression of centripetal force with a conical pendulum.
[Experiment and Exploration]
Teacher: Above, we have theoretically derived the expression of centripetal force, and any theory must stand the test of experiments. Let's design an experiment to verify the expression of centripetal force.
Teacher: Show the experimental equipment and demonstrate the experiment: Let the ball make a circular motion on the paper.
Teacher: What forces are acting on the ball?
Health: The ball is pulled by gravity and rope.
Teacher: The ball moves in a circle. Who will provide the centripetal force? Is it gravity? Is it the tension of the rope?
Health: No, it should be the combined force of gravity and tension.
Teacher's activity: Play the teacher's stress map when students answer.
Teacher: That's right. We know that centripetal force produces centripetal acceleration and centripetal acceleration points to the center of the circle, so the direction of resultant force also points to the center of the circle. So how to calculate this resultant force? Suppose the rope is perpendicular to the vertical? Horn.
Students discuss in groups: f =Fn =mgtan? = Manager/hour (teacher performance)
Teacher: It can be seen that to calculate the resultant force, it is necessary to measure the mass m, the circumferential radius r and the distance h from the suspension point to the center of the ball.
Teacher: We got it through force analysis. How to verify the expression of centripetal force next?
Student activities: group discussion
According to the centripetal force formula Fn=m v2/r =mr? 2 Calculate Fn and compare whether the results obtained by the two methods are equal.
Teacher: So what other physical quantities need to be measured according to the formula? V and? Can it be measured directly?
Student activities: group discussion
Health: Can't you directly measure V sum? But it can be obtained indirectly by measuring the time t of the ball moving n times? .
Teacher's performance: Fn=m v2/r =mr? 2=mr(2？ Nt )2
Comments: Can students think about whether it can be measured? (The principle of simplicity and operability of penetration test, so that students can understand it? Equivalent transformation? Thought)
Teacher: That's good. Let's finish the experimental measurement together. Please record the experimental data.
Play the video: the experimental process recorded by the teacher in the laboratory
Student activities: reading and recording data.
Teacher (after the students read the H value): Is the H we measured the H in the formula mgr/h?
Student activities: group discussion
Student: No, you have to subtract the radius of the ball.
Teacher: Yes. In addition, in fact, when the ball moves in a circle, it will leave the paper and the center of gravity will rise by a small height, but this height is very small and we can ignore it. Therefore, the distance from the suspension point to the center of gravity of the ball can be considered as H in the formula. Please take notes.