Zhang Ya wuhuan primary school

Teaching objectives:

1. Combine specific things or figures, and know the circumference through practical activities such as observation and operation.

2. Be able to measure and calculate the perimeters of triangles, parallelograms and trapeziums.

3. Be able to perceive the close relationship between the perimeter and life in combination with specific situations.

Teaching emphasis: know the perimeter, know the meaning of perimeter, and establish the concept of perimeter.

Teaching difficulties: understanding the meaning of perimeter and developing the concept of space.

Teaching methods: exploration and discovery.

Teaching preparation: multimedia courseware, ruler, soft ruler, marker, box cover and envelope.

Teaching hours: one class hour.

Teaching process:

First, create situations and introduce new lessons.

Teacher: Students, the teacher is going to test you. Write a word on the blackboard and see if you know it. Zhou is on the blackboard. )

Health: Yes. It is "Zhou"

Teacher: Are there any classmates or friends named Zhou around you?

Health: Yes, Zhou.

Teacher: "Zhou" can be used as a surname and has other meanings. Can you use the combination word "Zhou"?

Health 1: around.

Student 2: Weekend.

Health 3: One week.

Health 4: circumference.

Teacher: It's great that students use "Zhou" to form so many words. Now the teacher will use the word "week" in the class just now to make sentences. Xiaoming ran around the playground for a week. Do you know what "a week" means in this sentence?

Health: One lap.

Teacher: Yes, it means round. Just now, some students formed the word "wai". Do you know what perimeter is?

Health 1: "perimeter" is the perimeter.

Health 2: "circumference" is the length of a week.

Teacher: What is the circumference? Today, let's learn "What is circumference".

(blackboard title: what is the circumference? )

Second, feel exploration and learn new knowledge.

1. Say, draw.

Teacher: There is a little ant who is a painter. He is going to draw a picture today. Do the students want to see it?

Health: Yes.

Multimedia demonstration: the little ant climbs the leaves for the first time. )

Students, did you just observe how the little ants crawl?

Health 1: Little ants are crawling on the edge of leaves.

Health 2: Little ants crawl around the leaves.

Teacher: Teacher, let's play it again. Students, open your eyes and observe carefully how the little ants crawl. (Multimedia demonstration: Little ants climb the leaves for the second time, marked in red. )

Teacher: We watched it again. Now, who can tell me how the little ants climb?

Health: Little ants are crawling around among the leaves.

Teacher: Then we can also use the word just now: the little ant crawled around the leaves for a week. Right?

Health: Yes.

Teacher: The red line on the edge of the leaf is the trace left by the little ant. This is the perimeter of the leaf. (If multimedia shows little ants. ) Now the teacher has another question, how to measure the perimeter of leaves? In the past research, what is the first measurement tool that we think of?

Health: Ruler.

Teacher: Can you measure the circumference of leaves with a ruler now? The teacher draws on the picture with a ruler. )

Health: No.

Teacher: What should we do?

Health 1: measured with a soft ruler.

Health 2: Measure with a round ruler.

Health 3: Wrap a thread around the leaf, and then measure the length of the thread, and you will know what the circumference of the leaf is.

Teacher: Yes, I see. He wants to wrap the thread around the leaves first. At this time, what is the length of the line?

Health: circumference.

Teacher: So in the end, what do we need to do?

Health: Measure the length of the rope.

Teacher: Students are really smart. They not only found the perimeter of leaves, but also came up with a good method to measure the perimeter of leaves. Now, do you want to be a painter like a little ant?

Health: Yes.

Teacher: Now open page 44 of the book. There are two beautiful leaves in the middle, one is green and the other is yellow. Which leaf do you like? Draw a beautiful border with crayons. (Students finish independently, and teachers patrol. Find a good painting and a contextual exhibition evaluation. Students who draw quickly can be encouraged to draw the boundary between two leaves. )

Teacher: (Show and comment on the works of painting veins. Students, do you think his paintings look good?

Health: Beautiful.

Teacher: He drew not only the edge of the leaf, but also the veins on it. Students, do you think this painting is suitable?

Health 1: Suitable.

Health 2: Not suitable.

Teacher: Just now, when the little ant painted, he only painted the edges of the leaves, not the veins. Do you think it is necessary to draw veins now?

Health: No need.

Teacher: Yes, we only ask to draw the edges of leaves, so we don't draw veins. Students, there are three pictures on page 45. What do you think they look like? (Multimedia display pictures. )

Health: Bridges, rabbits, cars.

Teacher: Next, let's choose a drawing edge, but this time I have raised my requirements to see who can draw the edge of a painting with one stroke. Who dares to challenge? Come on stage and show it. Tell me about the process of projecting and showing paintings. )

Teacher: Look, class, how great he is! He drew it in one stroke! Can you draw a picture with one stroke?

Health: Yes.

Teacher: Choose a picture you like and draw a border. Students who draw fast can draw more. (Students finish independently, and teachers patrol. )

Teacher: Huh? The teacher found that some students who like painting painted eyes and noses on rabbits. Do you think this painting is suitable? Why?

Health: Not suitable. Because only the edges are drawn, the rabbit's eyes and nose are not the edges of the picture.

Teacher: (Show and comment on a painting of the interior lines of a car. ) Students, do you think this classmate painted correctly?

Health: No, you don't have to draw the lines inside.

Teacher: How clever! Students, you have just drawn so many pictures. Did you find out what the border you drew from these pictures?

Health: circumference.

Teacher: Yes, the edge of the leaf is the perimeter of the leaf, the edge of the bridge is the perimeter of the bridge, the edge of the rabbit is the edge of the rabbit and the edge of the car is the perimeter of the car.

2. Find and touch.

Teacher: In life, the surface of many objects has the same circumference as the picture just now. (Multimedia display of envelopes, pot covers and other pictures. Let's see, what's on the left?

Health: Envelope.

Teacher: Can you find out where the perimeter of the envelope is? Teacher, here is an envelope. Who can touch it? Touch the perimeter of the envelope by name. Students usually touch it from the upper left corner. )

Teacher: (pointing to the upper right corner of the envelope. ) Can you touch it from here? Who will touch it? (Touch by name. )

Teacher: (pointing to both sides of the envelope. ) Can you touch it from here?

Health 1: Yes.

Health 2: No.

Teacher: Can the teacher touch it? Look carefully at where the teacher started and where he ended. The teacher began to contact from the point just pointed out. Did the teacher touch the perimeter of this envelope just now?

Health: Yes.

Teacher: In other words, we can get in touch from this point. What about here? What about here? (refers to any point around the envelope. )

Health: Anything will do.

Teacher: That is to say, no matter where you start, you can touch its circumference. Think back, where did the teacher start to touch and where did he end?

Health: Start from that point and go back there.

Teacher: Then we can say that no matter where we start, the perimeter of the figure is the first connection. Let's look at the picture on the right again. What is this?

Health: pot cover.

Teacher: Does the pot cover have a circumference?

Health: Yes.

Teacher: Can you point it out? (The student pointed out. ) I brought a box cover today. Now the teacher feels its circumference. (I touched half a circle for the first time. ) watch the teacher's touch carefully?

Health: No, I haven't touched enough.

Teacher: Then I'll touch it again. (I touched it more than once the second time. ) Did you get it right this time?

Health: No, there are too many.

Teacher: Then who can find the right one? (Touch by name. In addition to these things, there are many things in life that have perimeters on their surfaces. Can you find them in the classroom? Answer by name and point out the surface circumference of the object. )

Health 1: door.

Student 2: Multimedia screen.

Student 3: Books.

Teacher: Each of us has a book. Let's take out our math books and touch them. (touch it first. Besides, what else do you have?

Health 4: The table. Students touch their desks. )

Health 5: Pencil box.

Teacher: (Pick up a pencil box. ) I want to ask you, which side do you want to touch? The teacher shows different sides of the pencil box for students to touch. ) We found that the circumference of the pencil case may be different on different sides.

Teacher: Students, we just drew a picture and touched it, and found out the perimeter of many objects. Do you know what the circumference is now?

Health: It's the length of a week.

Teacher: What is the length of a week?

Health: This is the length of a graphic week. (Teacher writes on the blackboard: The length of a figure in one week is its circumference. )

Teacher: (Multimedia displays closed and unsealed graphics. Students, can you find the perimeter of these pictures? Please point it out.

Health: The first picture has no circumference.

Teacher: Why?

Health: The starting point and the ending point of the sideline can't be connected.

Teacher: The first figure that can't be connected like this has no perimeter. The first connected graph like that is called a closed graph. The length of a closed figure is its circumference. The blackboard is closed. )

3. measure and say.

Teacher: Perimeter is widely used in life. For example, if we want to lace the blackboard, we need to know the circumference of the blackboard. For example, children need to measure their head circumference for physical examination. The head circumference mentioned here is the circumference of the first week. (Multimedia shows the picture of measuring the head circumference. ) look at the picture. What measuring tools are needed to measure the head circumference?

Health: Soft ruler.

Teacher: What should I find first to get the measuring tools?

Health: Zero scale.

Teacher: I'm going to measure the head circumference of a classmate in our class now. Who wants to come up? (Name. ) I also need a classmate to help me read. Who will come? (Name. The teacher measured her head circumference. ) read data.

Health: 54. (about 50 cm. )

Teacher: What's missing?

Health: 54 cm.

Teacher: That's right this time. When reading, you should not only read the data, but also add units. Different units mean different distances. Do you know how to measure head circumference now?

Health: I see.

Teacher: Now take out your soft ruler and measure his head circumference for your deskmate. And record it. (Students interact, measure the head circumference by hand, and visit the teacher for guidance. Report by roll call when finished. )

Teacher: How many centimeters do we find the students' head circumference?

Health: About fifty centimeters.

Teacher: Everyone's physique is different, so the head circumference will be different. Of course, there will be errors in measurement. After you go home today, you can also measure the head circumference of your family and friends with the method you just learned. Besides, you can also measure your waistline.

Third, practice to consolidate new knowledge.

Teacher: Through the previous study, the teacher found that the students are good at observation and diligent in thinking, so I would like to invite you to participate in the following quiz. Do you dare to meet the challenge?

Health: Dare.

1. Teacher: (Multimedia presentation P45 Question 2. ) Here are three pictures. What is the first picture?

Health: Triangle.

Teacher: Now we are required to measure and calculate its circumference? Think about it, class. Can you measure it directly with a ruler? (Multimedia projection, the teacher gesticulates with a ruler. )

Health: No.

Teacher: What should we do?

Health: You can measure the length of each side with a ruler.

Measure the length of each side and mark it on the diagram. Pay attention to the zero scale and one end of the line segment, and let the students read the correct units. )

Teacher: Do you know its circumference now?

Health: I don't know.

Teacher: What else should I do?

Health: Add up the three figures.

Teacher: That is to add up all its sides, right?

Health: Yes.

Teacher: Add another one. (Multimedia projection, the teacher writes the formula, answers, and emphasizes that the unit must be written in the end. ) There are two left. Please work in groups. The two groups on the left do the second and the two groups on the right do the third. (Students finish independently, and teachers patrol. )

Teacher: (Each team will make a presentation and comment, and report the data, calculation process and circumference of each side respectively. The second figure is a rectangle. In retrospect, what are the characteristics of rectangles?

Health: The opposing sides are equal.

Teacher: That is to say, the two looks are equal and the two widths are equal. So how many sides do we only need to measure when measuring a rectangle? What is the difference?

Health: Two. One is long and the other is wide.

Teacher: After the measurement, we only need to add up each side of them to know what their circumference is. Students, you have successfully passed the first level, so let's meet the challenge of the second level. Teacher Zhang is going to the bookstore to buy books at the weekend. Now look at the big screen. (Multimedia display circuit diagram. Please find out where Teacher Zhang's home and bookstore are first.

Student: Teacher Zhang's home is in Blue Point and the bookstore is in Red Point.

Teacher: Mr. Zhang is going to the bookstore. How many ways are there?

Health: Two.

Teacher: Look carefully. How can we close the distance?

Student 1: Teacher Zhang starts from home, first goes south, then goes east to the bookstore.

Student 2: Teacher Zhang starts from home, first goes east, then south, then east, and finally south to the bookstore.

Teacher: If you think the first method is the shortest, please raise your hand. (Students raise their hands. Please raise your hand if you think the second way is the shortest. (Students raise their hands. What do some students who don't raise their hands think?

Health: I think the two roads are equally close.

Teacher: Let's see which way is the shortest. (Multimedia presentation. ) Now I'll move this circuit diagram. What graphics do you find after moving?

Health: It was moved into a rectangle.

Teacher: We know that the opposite sides of a rectangle are equal, the two paths on the upper line are equal, and the left and right paths are equal, so the first path is as close as the second path. Congratulations to the students who have carefully observed. Let's go on to the third floor. (Multimedia display P45, questions 3 and 1. ) Compare these two pictures, which one has a long week?

Health 1: the length of the first picture.

Health 2: The second picture is long.

Health 3: The same length.

Teacher: Let's see who holds the truth. (Multimedia demonstration of the moving process, explained by the teacher. Next is the last level. Do the students dare to continue to break through?

Health: Dare.

Teacher: (Multimedia shows two pictures of P45 question 3 and question 2. ) Which one is the circumference of these two pictures? Through the practice of the last question, many students will answer the same length. Multimedia demonstration, explained by the teacher. Please raise your hand if you win all four levels in the competition. (Students raise their hands. ) You are really something. Give yourself a round of applause, okay? (Students applaud and encourage. )

Fourth, class summary, summary and improvement.

Teacher: Students, through the study of this class, the teacher believes that you must have gained a lot of knowledge. Who can tell me what you have learned?

1: I know that the length of a closed graph is its perimeter.

Health 2: I learned how to measure the perimeter of leaves.

Health 3: I learned to calculate the perimeter of triangle, rectangle and trapezoid.

Health 4: I will find out the circumference of an object in my life.

Teacher: Autumn is the season when melons and fruits are fragrant, and autumn is the season of harvest. Look, the grapes on the grape rack are ripe, and the fruit farmers are blooming happily. Here you are. The teacher gave you this big and sweet grape. I hope you will bear bigger and sweeter fruits in your future study, ok?

Health: OK.

Blackboard Design: What is the perimeter?

The length of a closed figure is the perimeter.