1. Create a scene and show the theme.

Teacher: The teacher brought some pencils to prepare prizes for the children who studied hard. If each person has two pencils, four children will be awarded. How many pencils do you need? How to form? (Blackboard: 2+2+2+2=8) If you give five children a prize and a * * *, how many do you want? (Blackboard: 2+2+2 =10) Forty-six students in our class study hard, and each child is rewarded with two. How to make a list? While writing 2+2+2+2 on the blackboard, the teacher asked: How many "2" do you write like this? Can there be a simpler expression? This is the multiplication (blackboard writing topic) to be learned today.

2. Intuitive perception, forming appearances

(1) teaches multiplication symbols.

(2) Students put red flowers and write formulas.

Teacher: Put two flowers on the projector first, then two flowers, and finally two flowers. Q: Count how many 2 flowers are put in a * * * *? (Blackboard: 3 2) What method can be used to calculate? (Blackboard: 2+2+2=6) The addend in this continuous addition formula is 2, and we can rewrite it into a multiplication formula. Writing: 2×3=6, reading: 2 times 3; It can also be written as: 3×2=6, and read as: 3 times 2. (Teachers demonstrate, then read by name, read by the whole class)

(3) Students put small discs and write formulas.

Teacher: Would you please put a small disc on yourself and write down the formula?

It is required to discharge three small wafers first, three small wafers second and several small wafers first. How to calculate the formula of addition? Can you rewrite it as a multiplication formula? (According to the students' answers on the blackboard:

3+3=63×2=6 or 2×3=6

Teacher: If you put two more lines and one * * *, how many 3s will there be? How should the formula be listed? (According to the students' answers on the blackboard: 3+3+3 = 123× 4 = 12 or 4×3= 12.

(4) Look at the picture and write the formula.

Blackboard: 4+4 = 12, 4×3= 12 or 3×4= 12.

5+5+5= 15, 5×3= 15 or 3×5= 15.

3. Analysis and comparison, revealing the essence

(1) Teacher: Look at these addition and multiplication formulas on the blackboard carefully. What did you find? Guide students to infer that these addition formulas have the same addend, so they can be rewritten as multiplication formulas. It is easier to find the sum of several identical addends by multiplication.

(2) Discuss which of the following formulas can be rewritten as multiplication formulas and which cannot. Why?

2+2+33+3+3+35+56+6+6+7

4. Various trainings consolidate and deepen new knowledge.

(1) as shown in the figure.

*********************

Addition formula: multiplication formula:

(2) According to the formula, use the learning tool to swing it.

2×24×32×5

(3) Rewrite the first three addition formulas into multiplication formulas.

(4) Write an addition formula and rewrite it into a multiplication formula.

5. Summary (omitted)

Comments: This concept lesson follows the law of concept formation and uses such a way according to perception-representation-concept. The introduction of the concept can firmly grasp the existing knowledge base of addition with the same number, supplemented by vivid and intuitive teaching methods, which can kill two birds with one stone. From the very beginning, let the students touch the "same addend" in the real situation, and stimulate the students' desire to learn "multiplication" by calculating the total number of awards in the whole class. Then in the process of operation and practice, all kinds of senses work together on the basis of obtaining a large number of perceptual materials, forming a clear and rich representation, laying a solid foundation for students to understand multiplication initially. After the introduction of the new curriculum, students can be guided to analyze and compare perceptual materials such as addition formula and multiplication formula in time, and the essential attributes can be abstractly summarized. The simpler conclusion of finding the sum of several identical addends by multiplication is the result of abstract generalization. Through the first level, the teacher puts out three small red flowers by the students, lists the addition formula 22+2 = 6, and then guides the students to see what the characteristics of the addend in the formula are. Then ask the students to put four 3s in a square and five 4s in a small circle, list the addition formulas respectively, and observe the characteristics of addend in each formula. In the second level, the teacher leads to a new operation-multiplication from three addition formulas, explaining three sums of 2 addition and four sums of 3 addition. The sum of five plus four can be calculated by multiplication. At the third level, by comparing the addition and multiplication formulas, it is concluded that the multiplication calculation is relatively simple. The fourth level is the meaning of abstract multiplication. In this process from concrete to abstract, students' ability of abstract generalization is cultivated. There are both positive and negative examples in the analysis questions designed to consolidate new knowledge, which grasp the teaching difficulties and highlight the teaching key points, and help students really understand the meaning of multiplication, that is, multiplication is a simple operation to find the sum of several identical addends. Finally, the multiplication formula for finding the total number of pencils of 46 students is written, which expands the existing concepts of students in time. In the whole class, students actively participated in the whole teaching process.

(B) the area unit of the teaching segment and its ratio

1. Perception 1 square decimeter

(1) Student observation: The teacher draws a line segment with the length of 1 decimeter on the paper pasted on the blackboard, and draws a square with this line segment as the side length. Tell the students that the area of this square with a side length of 1 decimeter is l square decimeter. Then the teacher cut out L square decimeter square paper with scissors and stuck it on the blackboard.

(2) Students' operation: Cut out a square with L square decimeter, touch it with your hands, close your eyes and think about the shape and size of 1 square decimeter.

2. Perception 1 cm2

(1) Teacher: Who can cut out the square of 1 cm2 first? After the students cut out a square of L square centimeters, let them talk about how to cut it. Then let the students touch with their hands, close their eyes and think about the shape and size of L square centimeters.

(2) Put 1 square decimeter square paper and L square centimeter square paper on the desktop, have a look, compare them, close your eyes and think about their appearance and size.

3. Perception 1 m2

Teacher: Who can tell you how to cut out 1 square meter square paper? After the students finished speaking, the teacher put the pre-cut 1 square meter square paper on the blackboard, let the students have a look, close their eyes and think about its appearance and size.

4. Discussion: What are 1 square decimeter, 1 square centimeter and l square meter?

5. Discussion: the relationship between 1 square decimeter, l square centimeter and l square meter.

(1) Let the students look at 1 square decimeter and 1 square centimeter on the table. Think about how to measure how many L square centimeters are in 1 square decimeter? Students think it can be measured by putting a pendulum and drawing a picture. Students first align a vertex of two square pieces of paper, and then draw the plane position it occupies on the square paper of 1 cm2 along the edge of the square paper. Move the square paper of 1 cm 2, put it next to the drawn small square, and then draw its position along the edge. Move the box again ... draw one line like this, and then draw the second line. The second row is not finished yet. Some students divide each side of a square with L square decimeter into 10, connect two points on opposite sides, draw a line, count it, and work it out, and get 1 square decimeter = 100 square centimeter.

(2) Question: How do we know how much 1 m2 is? If you put the small squares of 1 square decimeter along the side of a square of L square meters, how many can you put in a row? How many rows can you arrange? Draw:

1 m2 = 100 square decimeter.

(3) Think about it and calculate how many square centimeters is L square meters? The students quickly came to the conclusion that:

1 m2 = 10000 cm2.

6. Integrate applications

(1) Give an example with dimensions of 1 cm2, L-square decimeter and 1 m2.

(2) Fill in the appropriate unit name. (omitted)

Comments: Through hands-on operation, students can increase their perceptual knowledge of what they have learned, get the representation of objects in operation, and deepen their understanding of what they have learned. It is out of this kind of thinking that the teacher here asked the students to put a pendulum, draw a picture, think for themselves and calculate for themselves, and really understood the meaning of 1 square meter, 1 square decimeter and l square centimeter and the progress between them, which was impressive and lasting. At the same time, it also cultivates students' practical ability. From beginning to end, the process of students acquiring knowledge is active.

(3) teaching fragments of prime numbers and composite numbers

1. Import

Teacher: All students have their own student numbers. Please find out all the divisors of this number representing your student number.

(Name feedback, the teacher writes down the approximate figures of these figures on the blackboard according to the speeches of students No.29, No.2, No.26 and 16 ... The rest of the students communicate with each other. )

2. Organize and reveal concepts

Teacher: Please look at these numbers carefully (finger blackboard). Can you classify these figures? Deskmates can discuss with each other.

Health A: I divide these figures into two categories, one is odd and the other is even. Odd numbers are 2 1, 7, 29, and even numbers are 6, 2, 26, 16.

Health B: I divide it according to the approximate number. Only two divisors 7, 29 and 2 belong to the same class, and more than two divisors 6, 16, 2 1 and 26 belong to the same class.

Student C: I divide 6, 7 and 2 into one category. These numbers are single digits, and 2 1, 16, 29, 26 are double digits.

Teacher: Are there any other divisions? (Students say no) All the above points make sense. We used to know odd and even numbers. Today we will focus on the divisibility of dividend. Numbers with only two divisors like this are called prime numbers, also called prime numbers; Numbers with more than two divisors are called composite numbers.

3. Discuss and establish concepts

Teacher: Please look carefully: What are the characteristics of prime numbers? What are the characteristics of composite numbers? Students who have difficulties can discuss it with their classmates around them.

Health: A prime number has only two divisors, L and itself, and the composite number has other divisors besides 1 and itself.

Teacher: Do you have any different opinions? Who said that again? Read what the book says.

4. Understand and consolidate concepts

Teacher: Now we know what a prime number is and what a composite number is. Besides these numbers on the blackboard, can you give some examples? Write it down in a notebook.

Students: 19, 23, 27, 3 1, 59, 6 1 is a prime number, 4, 15, 20, 18, 25, 10.

Teacher: Anything else? There are so many students who want to talk, but the blackboard is only this big. What should I do?

Health: indicated by ellipsis. (blackboard writing)

Teacher: Are these numbers quoted by these students prime numbers? Write on the blackboard. Let's judge.

Health: 19, 23 is a prime number, 27 is not.

Teacher: Why not a prime number?

Health: 27 is a composite number, because it has other divisors 3 and 9 besides 1 and itself. (The teacher adjusts the blackboard)

Teacher: Are these all composite numbers? Who can tell us why 12 is a composite number?

Application concept

(1) Teachers select materials from the surrounding environment, let students practice judgment and summarize the judgment methods (omitted).

(2) Discuss "1" and get that 1 is neither a prime number nor a composite number, because it has only one divisor.

6. Comprehensive exercises

(1) Find out which of these numbers on the blackboard are odd numbers. What is an even number? What did you find? (Some numbers are both odd and composite, such as 9,21,etc. ; Some numbers are even numbers and prime numbers, such as 2)

Teacher: Only 2 is both an even number and a prime number. Can other even numbers be prime numbers? Why? Check each other at the same table. Did you find the right one?

(2) Show the numbers from 2 to 50, and ask to find the prime number quickly.

When giving feedback, ask to introduce what good methods you have.

(3) Write the following numbers as the sum of two prime numbers.

6=()+()8=()+()

10=()+() 12=()+()

Teacher: What are the numbers 6, 8, 10 and 12 here?

Student: It is a composite number and an even number.

Teacher: Can you write these numbers into the sum of two prime numbers? The students write in their exercise books.

Teacher: Can all even numbers not less than 6 be written as the sum of two prime numbers? This is a guess, which is not easy to prove. This is the world-famous puzzle "Goldbach conjecture". Interested students can consult relevant materials after class.

Comments: This is an abstract concept class, and its biggest feature is that teachers can carry out the whole teaching process according to the characteristics of students' concept learning. At the beginning of the class, we should firmly grasp the basic knowledge of divisor, let students find the divisor of the number representing their student number, and reveal the concepts of prime number and composite number through observation and classification. After further observation and discussion, I will use my own language to say what are prime numbers and composite numbers, and initially establish concepts. On this basis, all students are required to give examples and make judgments to test and consolidate the concepts they have learned. The organization of comprehensive exercises, while consolidating the application of new knowledge in time, communicates old knowledge, so that students can clearly understand the differences and connections between odd numbers, even numbers, prime numbers and composite numbers, and make the concepts systematic.

In addition, this kind of classroom has the following three characteristics: first, teachers can sincerely regard students as the main body of learning and the master of the classroom, carry forward teaching democracy, and let every student actively participate in the teaching process, gain new knowledge in independent exploration and experience success. Second, pay attention to local materials, enrich the teaching content, and make the abstract teaching content vivid and close to students' life. Thirdly, knowledge learning can be used as a carrier to cultivate students' ability of active exploration, independent thinking and innovation.