The teaching content of this course is based on students' understanding of rectangular and other plane graphics, and it is also the last common plane graphics in primary schools. The idea of textbook arrangement is to reveal the circle with the help of physical objects, so that students can feel the close relationship between circle and life, and then guide students to draw a circle, initially feel the characteristics of the circle, and master the method of drawing a circle with compasses. On this basis, guide students to understand the related concepts of circle and master the basic characteristics of circle. Teaching this part can broaden students' knowledge, enrich their learning experience of space and graphics, and further develop their concept of space. The study of knowledge also lays the foundation for future study.

Second, student analysis

Students often come into contact with circular objects in daily life, and they have a preliminary understanding in the lower grades, but they are all intuitive appearances. In primary school, students' spatial concept is relatively weak and their practical ability is relatively low; In view of long, square, etc. They are all straight-line plane figures, and circles are curved plane figures. It is estimated that students will have some difficulties in hands-on operation and cooperative exploration.

Third, learning objectives.

1. Let students master the characteristics of a circle and understand and master the relationship between radius and diameter in the same circle. Can draw circles with compasses.

2. Empirical mathematics is closely related to daily life. We can use the knowledge of circle to explain the phenomena in life or use the phenomena in life to explain the characteristics of circle.

3. Enable students to acquire basic mathematical knowledge and skills through imagination and verification, observation and analysis, hands-on operation, cooperation and communication, cultivate their interest and awareness in understanding the physical characteristics of things around them, and enable them to use their learned mathematical knowledge to solve simple problems.

Fourth, the teaching process

(a), from the game, build a circle, a preliminary understanding of the names of the various parts of the circle.

1. Do you like playing games? Let's play a game of "finding friends". Now, if everyone stands in front of me like this, whoever runs to the teacher first will be the teacher's good friend. Do you agree to stand like this? So how to stand is fair and reasonable? Group discussion.

After the discussion, the student representatives spoke. Show the courseware, why is it fair and reasonable to stand like this? It is fair and reasonable to draw the conclusion that the distance from each student to the teacher is equal.

A good "prologue" of a class is like a "magnet", which can firmly attract students and make them quickly enter the "role". Let students "find friends" through games, and then lead out the content to be learned, which is appropriate and natural, so as to firmly grasp the students' hearts from the beginning, stimulate their interest in learning and emotional needs, and mobilize their desire to further explore learning. ]

2. Teacher: Have you ever seen a circle in your life? Where have you seen it?

Let students find the circle in life, let students feel that there is mathematics everywhere in life, and stimulate students' desire to explore knowledge. ]

The teacher also brought some pictures of objects with circles. Please enjoy them. Do you think these circled things look good? Computer demonstration of pictures with circular objects

[Students feel the beauty of patterns combined with various circles, and at the same time successfully reveal the theme of inquiry: knowing circles. ]

3. What is the biggest difference between a circle and a rectangle or a square that I have learned before? Name the students.

Teacher's summary: In the past, these were plane figures surrounded by line segments and circles were plane figures surrounded by curves. Today, let's get to know the topic of circle and blackboard writing.

4, abstract the circle, and introduce the names of each part of the circle.

Go back to the courseware of "Finding Friends" at the beginning and introduce the names of all parts of the circle.

(1), the students stand in the circle and the teacher stands in the circle. Like this, outside is outside the circle. Everyone is equivalent to a point in the circle, and the teacher is also equivalent to a point in the circle. This is mathematically called the center of the circle and is represented by the letter O.

(2) As everyone said just now, the distance between everyone and the teacher is equal, that is, the distance from a point on the circle to the center of the circle is equal. The line segment connecting the center of the circle and any point on the circle in this way is called radius, which is generally represented by the letter R. Are there only these points on the circle?

(3) What is the maximum distance between two points on the observation circle? Students speak after discussion. Abstract: The distance from the center of the circle to both ends of the circle is called the diameter of the circle, which is generally represented by the letter D.

With the help of courseware, these abstract concepts such as center, radius and diameter are vividly explained to facilitate students' understanding. ]

(2) Using round paper to explore the basic characteristics of the circle.

Ask the students to explore the following questions independently with the circular pieces of paper in their hands:

1. Can you find the center, radius and diameter of a circle on circular paper?

2. Can you find out the characteristics of the radius and diameter of the circle by folding in half, drawing and measuring?

Through students' observation, operation and hands-on drawing, folding and measurement, it is concluded that the intersection point of the crease is the center of the circle, from which countless radii can be drawn and countless diameters can be drawn through the center of the circle. You will also find that in the same circle, all diameters are equal, all radii are equal, and d=2r? r=d/2 .

["Children's wisdom is at your fingertips." The process of hands-on operation can not only make students learn lively, but also make students understand what they have learned more deeply and remember it more firmly. When dealing with this link, by allowing students to explore, practice and actively cooperate in sufficient independent space and activity opportunities, it is beneficial for students to gain a positive and profound experience, experience the joy of success and experience the formation and development of knowledge. Here, students' learning is not only a "text course", but also an "experience course". ]

(3) Learn to draw a circle with compasses to further understand the circle.

Can you draw a standard circle? Students will say that they should use compasses to plan. Let the students draw a picture on the paper first and exchange the drawing methods. On this basis, teachers and students summed up the basic steps and methods of drawing a circle:

(1) when drawing a circle, first separate the two feet of the compass to determine the distance between the two feet (that is, the length of the radius) to determine the size of the circle.

(2) A foot with a needle tip is fixed at a point. (Determine the position of the circle)

(3) Spin one foot into a circle with pencil lead, and you draw a circle.

Ask the students to draw a circle with a radius of 2 cm and 3 cm, and then observe what you find. Students will find that a circle with a radius of 3 cm is big and a circle with a radius of 2 cm is small. That is, the radius determines the size of the circle.

2. Let the students draw circles in different positions: draw a circle with a radius of 3cm in the middle of a piece of paper, and draw another circle in the upper left corner, lower right corner and upper right corner of this paper. How to draw? It is concluded that the center of the circle determines the position of the circle.

Let the students draw a circle, which is the difficulty of this lesson. I seized the opportunity to let the students draw circles at will at first, and summed up the method of drawing circles layer by layer. Then I asked the students to draw circles with radii of 2cm and 3cm, and let the students return the theory to practice and draw circles with what they have learned, so as to achieve the application of circle knowledge. Classroom teaching has received good feedback. ]

(4) Consolidate exercises and improve the understanding of circles.

1, can you find the radius and diameter of the circle below? Unit: cm

Tuloue

(None of these graphic problems directly give the radius and diameter of a circle, but students need to find out what the radius and diameter are by carefully observing the relationship between a circle and a rectangle or a square. )

2. If you draw a slightly larger circle on the playground, can you still use a compass? How to draw? Pay attention to what?

Please use what you learned today to explain why the wheel should be round. Where should the axle be installed?

The ultimate goal of learning mathematics is to apply mathematics to solve practical problems. Through practice at different levels, students can flexibly learn and use newly formed knowledge and help them to understand it deeply? , so as to cultivate students' comprehensive ability to explore and solve practical problems by using knowledge; At the same time, practice pays attention to the connection with life, so it is also effective for students to participate in this practice. ]

(5) Summary

Today we have a preliminary understanding of the circle, blackboard writing: understanding of the circle. Did everyone get anything? Some people say that because of the circle, our world has become so wonderful. In the future, we will come into contact with a lot of knowledge about circles in our lives. At that time, you must feel how amazing the circle is.

(6) after-school development

How many methods are there to measure the diameter of 1 yuan coin? Give it a try.

The extension of problems is the continuation of activities and learning. Walking out of the classroom and into life with questions is also a continuation of students' real learning and understanding of mathematics. Through the problem of "measuring the diameter of 1 yuan coin", let students consciously take their mathematics knowledge out of books and bring it into life. On the one hand, it can expand and extend the knowledge learned, on the other hand, it can extend the positive factors of students' learning to their after-school life, which can promote students to develop good problem consciousness and mathematics consciousness, and then cultivate innovative consciousness, and can also continuously stimulate students' interest in learning and good learning mood. ]