1, class, what season is it? (Autumn) Yes, it's autumn now. It's cold and leaves are falling gently from the trees. (Post a leaf model) You see, the teacher also brought you a big leaf today. Do you like it? A little ant also likes this leaf very much. Look, it uses this leaf as a playground. Please watch carefully and see how this little ant moves on the edge of this leaf. What did you find through observation? (Little ants crawling around the leaves), what can a circle say? (a week). Today, in this class, we will study this problem for about a week. (blackboard writing: one week)

Second, practice and feel the circumference.

1, touch it

(1) Please take out the leaves collected before class, choose one you like best, and touch its face first. How do you feel? (Slippery) Then can you touch its sideline like a small ant climbing a leaf?

(2) Students touch the leaves.

(3) Who wants to come to the front and talk about how you touched the edge of the leaves for a week?

(4) Students perform, (say and touch).

Step 2 draw a picture

(1) Just now, you touched the leaves for a week. Can you find the week of leaves? Please take out your colored pencils and draw a picture!

(2) Students draw leaves. After painting, do the deskmates look at each other beautifully?

(3) Who wants to come to the front and describe the week of this big leaf? Ask a student to draw a leaf model in front of him. Can you tell us how you drew it? Ask the students to point out and say where they started and where they ended. ) Take down the leaf model. Do you think it looks good?

(4) Do you draw like him? Please raise your hand if there are different ways? Ask a classmate to describe it. )

Summary: As you can see, no matter how you draw, you always draw along the edge of the leaf, right?

Step 3 look for it

(1) In life, the surface of many objects is like a leaf for a week. Can you find the faces of these objects around us?

Look, touch and say between your deskmates.

(2) Group report. What kind of face do you want? Where is the week when you touch it? )

Step 4 draw a picture

(1) The students are really looking for a lot. To encourage you, the teacher also prepared some graphic gifts for you. Do you want it? But the teacher has one condition. Only by drawing its week correctly can you get these gifts. Please open the envelope on the desk, choose a figure you like, and draw the edge of this figure with colored pencils. Start painting!

(2) Teacher: Can you receive gifts? Now let's check each other in the group and see if your little friend has drawn it correctly. If he draws it correctly, he will get a gift. If he makes a mistake, please help him correct it.

(3) Who got the gift? Show it to everyone! The teacher congratulated everyone.

Just now, we had many interesting activities. We learned that leaves have a week, textbook covers have a week, and plane graphics have a week. So, what are their names this week? (blackboard writing: add "long" after "week") Shall we give him a name?

(circumference), you are so clever. You think like a mathematician. In mathematics, mathematicians call the length of a plane or plane figure of an object perimeter.

Step 5 measure it

(1) Measure the circumference of the cover of a math book.

Do you want to know the circumference of the cover of the math book? Please select the appropriate measuring tools in groups. One person is a recorder, the rest are small strategists, giving advice to your group, and you can also be a small assistant to help your group complete the task. Start measuring! After the measurement, the team reports the measurement results.

(2) Measure waist circumference

Not only the surface and plane figures of objects have circumferences, but also our bodies have circumferences. For example, if you want to buy pants, you need to know the length of the waist. It's called a circle. Who can estimate the teacher's waistline? (Students speak freely) Is the estimate accurate? To actually measure, who will measure the teacher's waist? Ask the waistlines of two teachers. (Guide the measurement method while measuring), and tell everyone the measurement results after measuring. Do you want to know your waistline? Help each other at the same table, first estimate and then measure, and the measurement results should be recorded on the record card. Report after measurement.

6. distinguish.

(1) Just now, we know that the curved surface and plane figure of an object have perimeters. Do you think these figures have a perimeter? (Courseware shows: several closed figures and unclosed figures) Answer by name.

(2) Summary: It seems that only closed figures have perimeters.

7. talk about it

Just now, we had many interesting activities. Now, can you talk about the circumference in your own words? (Write "What is it" in front of "perimeter" on the blackboard)

Third, expand understanding and stimulate thinking.

1, compare.

Just now, the little ant told the teacher that it had encountered a difficult problem. Do you want to help it? (thinking). (Courseware shows: question 3 on page 45) Which week is the following picture long? (Students talk about their opinions in groups, and then verify them through courseware operation)

2. Measurement and calculation.

(1) We helped the little ant solve the problem. The little ant thanked us very much and brought us presents. (Showing the box of wisdom) These gifts are hidden in this box. Do you want it? (Thinking) But this box has a combination lock. Only by unlocking the code can we open the box. Do you want to unlock the code? These passwords are hidden in the second question on page 45 of our book. Please find them quickly! (The courseware shows the second question on page 45)

(2) In order to unlock the password quickly, let's divide the work. (The first and second groups measure the triangle perimeter, the third and fourth groups measure the rectangle perimeter, and the fifth group measures the trapezoid perimeter) Here we go!

(3) Who will solve the first password? Let's quote the length of each side of the triangle first, and then what is its circumference? How to calculate it? )。 The solution of the second and third passwords is the same as above.

3. cut it and compare it.

(1), the password is unlocked, and the smart box is opened for us. You see, the little ant brings us another question of wisdom. Only by solving the problem of wisdom can we get the gift from the little ant. Let the students read the questions quickly. Whoever knows the answer first will raise his hand.

A rectangle, cut diagonally, becomes two figures. Are the perimeters of these two figures the same? )

(2) giving gifts. (One star of wisdom per person)

Fourth, sum up the harvest and experience success.

Students, what have you gained from this class? Are you happy? The teacher is also happy for your success, and you will learn more math knowledge in the future. I hope you can experience the happiness of success in your study.

Verb (short for verb) Task:

Draw a leaf after class and try to measure its circumference.