In the teaching process 1 What is the circumference of the class (1) ⊙ Create a situation and introduce a new lesson Teacher: Students, which one of you took part in the 400-meter race in the school sports meeting? What is the route of the 400-meter race? Booked student: Run around the playground. Teacher: A circle starts from the starting point and goes back to the starting point. The length of a circle on the playground is its circumference. In this class, the teacher will study what is a circle with everyone. (blackboard writing: what is perimeter) ⊙ actively explore and measure the perimeter of 1 Draw a picture and feel the meaning of the circle initially. (1) The courseware shows two pictures on page 45 of the textbook: leaves and the cover of the math book. Teacher: Please take out your colored pencils and draw the edges of these two pictures in the book. Use a ruler where you should use it. Students operate and check and correct each other with their deskmates after completion. (2) say it. Teacher: Who can tell us how he describes it? Do you know what a sideline is? Let the students talk and demonstrate. It is clear that the "sideline" is the route drawn around the leaves and the cover of the math book. (3) touch it. Ask the students to find anything around them, point out or touch their sideline. For example, the edge of the desk, the edge of the pencil box, the edge of the blackboard, etc. 2. Know the circumference. (1) Let's have a look. The courseware shows two pictures in the middle of page 45 of the textbook. Question: What are the ants and pencils doing? what did you say ? What did you learn from it? Please report after observation. The little ant crawled around the leaves for a week, and the length it climbed was the circumference of the leaves; The pencil draws a circle along the edge line of the cover of the math book, and the length of the cover of the math book is its circumference. Ask the students to communicate in groups. First, point to each other with your partner on the map and say what the circumference is. Then take turns pointing to the two pictures shown in the courseware and say. ② Emphasize the meaning of "one week". Teacher: What is a week? Where to start? Where does it end? Students answer the teacher's summary: starting from a point, moving along the edge of the figure, and finally returning to this point, this is a week. Design intention: By looking, drawing, talking and pointing, arouse students' senses in all aspects and experience the practical significance of perimeter in all directions, so as to deepen students' understanding of the concept of perimeter and correctly establish it. 3. Explore the method of measuring the perimeter of graphics. (1) Take a look and discuss. ① The courseware shows leaves and math books, so that students can observe and think: How can we know their perimeters? Do you have any good ideas? Let the students think independently first, and then talk about their own methods and the reasons for choosing this method. Initially determine which methods can be used. (2) the actual operation, a quantity. Teacher: Now, please find a good partner, choose the right tool and measure it. Students carry out practical operations and teachers patrol for guidance. (3) Report the methods and results of communication measurement. Teacher: Please tell us how you measured it. Why did you choose this method? How to get the measurement results? Preset health 1: When measuring the perimeter of leaves, because the shape of leaves is irregular, it cannot be measured directly with a ruler. You should first wrap a soft rope around the edge of the leaves, and then measure the length of the rope with a meter ruler. Health 2: When measuring the perimeter of the cover of a math book, because the cover of the math book is rectangular, you can measure the length of each side with a ruler and then add up the length of each side. Teacher: In the process of measurement, how to ensure that the measured data is more accurate? Students express their opinions, and the teacher concludes: In the process of measurement, we should use the correct measurement method, measure several times more, reduce the error as much as possible, and ensure the correctness of the results.