Teaching objectives
1. Make students go through the process of estimating and measuring the surface or plane graphic area of an object through their own choices, know the square centimeter and square meter of the area unit, and experience the square decimeter through migration.
2. Make students further understand the meaning of area, and initially realize that the area of a plane figure is the number of area units contained in this figure.
teaching process
First, contact life and introduce new knowledge.
Show photos and captions: The campus area of Wujiang Experimental Primary School is about two standard football fields; The campus area of Aide Bilingual Branch of Wujiang Experimental Primary School is about the size of four standard football fields.
Teacher: What do you know after reading these two photos and these two sentences?
Student 1: The area of Aide Bilingual Branch is larger than that of the headquarters.
S2: The area of Aide Bilingual Division is twice that of the headquarters.
Show photos and caption: The parachute of Shenzhou VI spacecraft is about half the size of a football field.
Students describe the parachute area of Shenzhou VI spacecraft in their own words.
Teacher: Students, we are not familiar with the school where Teacher Li works and the parachute of Shenzhou VI spacecraft. However, with the help of the football field, we have a general understanding of their area. Have you ever heard or used such an analogy? Today we will learn new knowledge by analogy.
[Thinking: Metaphor has initially infiltrated the concept that if there is a standard to describe or compare the size of an area, then the area can be quantified. For example, here, the mediation is the prototype of the regional unit. This metaphor is also very common in newspapers and periodicals, and is often heard in conversations, which is also conducive to students' natural and cordial feeling of learning new knowledge. ]
Second, explore independently and learn new knowledge.
1. Create situations and introduce concepts.
Teacher: If mom asked us how big the table was, what would you use as an analogy?
Health 1: I want to use a book as an example.
Health 2: I want to use leaves as an analogy.
Teacher: Then let's spread out the whole desktop with some items and see how many such items are in the area of the class desktop. (Instruct students to cover the class desktop with disposable paper cups, math exercise books, block letters, leaves and other items, and require that only the same item can be laid on the same class desktop. )
Teacher: Who can tell us what kind of things you use to lay the table? What is the area of the class platform?
Student 1: I spread out my math exercise books, and the area of my desktop is about the size of eight math exercise books.
Health 2: I paved it with leaves. The desktop area is about 15 leaves.
Student 3: I spread a big book, and the desk area is about the size of six big books.
Health 4: I spread paper cups, and my desktop area is about the size of 40 disposable paper cups.
Teacher: (The computer shows the process of unfolding four objects on the desktop) Let's review the process of unfolding objects just now. There are so many paper cups. How do you count it?
Health: First there is a line 10, and then there are exactly four lines, 4 10 = 40, so a * * * has 40.
Teacher: That's good! (Refer to the pictures of four paving methods) We use these items to spread on the desktop, which can vividly explain the area of the desktop. However, after reading these four paving methods and the results obtained, do you think there is anything wrong?
Health: These figures are all different.
Teacher: Yes, the same size desktop, how to show that the number of areas is different? Any good suggestions?
Health: spread it with the same thing.
Teacher: Students, do you still remember the scene when you studied length units? At that time, we used pencils, knives and hands to measure the length of desks, and the figures we got were different and not good. Later, we learned the length unit of centimeters and solved this problem. Therefore, in order to accurately measure or calculate the size of the area, it is necessary to use the square area with the same size as the area unit. (blackboard writing: area unit)
[Thinking: The essence of spreading things on the class desktop is to let students choose their own units to measure the area. Different units will lead to different measurement results, which leads to students' psychological demand for unified measurement units. Providing four kinds of articles for students to choose from enhances the contrast between different units and different results, and students' desire to unify the unit is also stronger, which can also highlight the essential characteristics as a unit: the same unit must have the same shape and size. Instruct students to count the number of paper cups, which implies the calculation method of rectangular area. Think back to the process of introducing length units and find a fixed point that introduces area units. ]
2. Know the square centimeter.
(1) learning.
Teacher: (showing the model of 1 cm2) This is the first area unit we will learn: 1 cm2. (Blackboard: 1 cm2) Please take out the same paragraph from the proofreading basket. Look, what shape is it?
Health: Fang.
Teacher: Please measure the side length of this square with a ruler.
Health: side length 1 cm.
Teacher: What is the side length? Is the square area 1 cm2?
Health: The area of a square with a side length of 1 cm is1cm 2.
Teacher: (blackboard writing: a square with a side length of 1 cm) Square centimeters can be represented by the symbol cm2 (blackboard writing: cm2) or read as square centimeters. Please write this symbol cm2 with a pen.
(2) remember.
Teacher: Let's remember our first new friend today! Hold up the model (demonstration) of 1 cm2, look carefully, remember by heart, close your eyes and think hard, and print 1 cm2 in your mind. Do you have 1 cm2 in your mind?
Health: (Qi) Yes!
Teacher: Come on, let's get a pen. Please take out our idea of 1 cm2 and draw it on paper. (Students draw 1 cm2. )
Teacher: Compare it with the model of 1 cm2. Is it right? What is wrong can be corrected again. (Students compare and correct. )
(3) looking for.
Teacher: What items in life have an area of about 1 square centimeter?
Health 1: The surface area of the button is about 1 cm2.
Health 2: The area of my decal paper is about 1 cm2.
Health 3: My nail surface is about 1 cm2.
Teacher: Let's pick up the model of 1 cm2 and compare it with your nails. Which nail surface of yours is about 1 cm2?
Health 1: My thumb nail surface is about 1 cm2.
Health 2: Mine is the middle finger.
(4) spelling.
Teacher: Please take out six more 1 cm2 squares from the school basket, make a rectangle with six 1 cm2 squares and put them on the table. If there are different spellings, you can spell one before the other. (Students are confused. )
Teacher: Look at each other at the same table. Is the spelling the same? How many square centimeters is the area of your rectangle?
Health 1: 6 square centimeters. Because it is composed of six squares of 1 cm2.
Health 2: Because they all have six 1 cm2.
Teacher: Are these two rectangles the same shape? What is this area like?
Health: Different shapes and the same area.
Teacher: That is to say, how many square centimeters a plane figure has depends on how many area units it contains; A plane figure has several area units, and the area is several.
(5) estimate the sum.
Teacher: Please take out a stamp from the school basket. What is the area of stamps?
Health 1: 8 square centimeters.
Health is 2: 20 square centimeters.
Teacher: How do you estimate it?
Health: The nail surface of my index finger is about 1 cm2. I drew it with my index finger nail just now, which is about 8 square centimeters.
Teacher: Your idea is very good, but we have a model of 1 square centimeter. Let's spread a 1 cm2 square on the stamp to see how big it is! Students find that a person's regional units are not enough, so they cooperate with their deskmates. )
Teacher: What's the area of stamps?
Health: (Qi) 12 cm2!
Teacher: Why?
Health: Its surface can be paved with 12 blocks 1 cm2.
Teacher: Please take out another business card. Estimate the area first, and then use the area unit to test. (Because the number of area units is not enough, instruct students to measure with the square area measuring tool printed with 1 cm. )
Teacher: Let's count the area of the calling card together. (The physical projector shows the calling card covered with measuring tools)
Health: Calculate the whole grid first, a row of 8 grids, ***6 lines, 6 8 = 48. The next two half cells or three small half cells can be combined into 1 cell, which is about 56 square centimeters.
[Thinking: Five levels of learning activities, with rich learning methods, smooth activity process and delicate guidance and help, guide students to experience the process of establishing the concept of 1 cm2. While establishing the concept, we should also pay attention to fully excavating the connotation of these links. For example, looking at the surface area of a plane figure or an object depends on how many area units it contains, which echoes the psychological needs of students when introducing area units; For another example, the process of calculating the phone card area is helpful to cultivate students' ability to solve practical problems flexibly and their rigorous and meticulous habits. ]
3. Yes 1 m2.
Teacher: How many square centimeters do you estimate the area of the blackboard? what do you think of it ?
Health 1: too small!
Health 2: There should be a larger unit area.
Teacher: There really is a bigger area unit. (Showing a square cloth of 1 square meter) Guess, what should this area unit be?
Health: square meters.
Teacher: Can you tell me the area of 1 square meter?
Health: A square with a side length of 1 m and an area of 1 m2. (blackboard writing)
Teacher: Can you use symbols to represent square meters? Write it down in a notebook. Please write m2 on the blackboard. )
Teacher: (Show four pieces of 1 m2 cloth and give them to each group) Students in each group discuss what to spread on the 1 m2 cloth first, and then actually spread one piece to see how many such articles can be spread.
Students spread articles in groups, three groups spread books, schoolbags and chairs respectively, and the other group stood on the cloth of 1 m2.
Teacher: Please send a representative from each group to introduce their articles.
Health 1: Our group spread 24 books on the cloth of 1 square meter.
Teacher: But you didn't cover it. How do you know you want 24 books?
Health 1: Because there are six books in one row, you can put four rows, and one * * * can put 24 books.
Health 2: We spread 9 schoolbags on 1 m2.
Health 3: 1 square meter can hold 4 chairs.
Teacher: Let's count how many people can stand 1 square meter.
Health: (Qi) 1, 23 13 people.
Teacher: What items in life have a surface area of about 1 square meter?
Health 1: (referring to the screen) The area of this screen is about 1 square meter.
Health 2: My desktop area is about 1 square meter.
Health 3: The screen area of some TV sets is about 1 square meter.
Teacher: What is the area of this blackboard?
Health: (Qi) 2 square meters.
[Thinking: Measure the area of the blackboard in square centimeters, so that students have the need to further explore larger units. The meaning and symbols of square meters are freely interpreted or written by students themselves, which is a direct application of the experience they accumulated when they first knew square centimeters. Let the students choose their own objects spread on 1 m2, which is an extension of the standing activities in the teaching materials and the activities of spreading objects on the desktop in previous classes. Finally, back to the blackboard area, the whole understanding process is seamless. ]
4. Know the square decimeter.
Teacher: What other units of area do you want to learn? (square millimeter, square decimeter, etc. ) How about learning another square decimeter? How big do you think 1 square decimeter is? How is the square decimeter represented by symbols?
Health: A square with a side length of 1 decimeter and an area of 1 square decimeter. (Write down dm2 on the blackboard)
Teacher: There is a model of 1 square decimeter in the school basket. Can you find it? (Students look for a model) Compare this model and draw the size of 1 square decimeter by hand. (Show and guide students to compare pictures)
Teacher: What items in life have a surface area of about 1 square decimeter?
Health 1: (Holding up the learning basket) The bottom of this basket is about 1 square decimeter.
Health 2: The area of the socket surface is about 1 square decimeter.
Third, consolidate practice and internalize new knowledge.
Teacher: Let's do some exercises to consolidate our new knowledge. Please look at page 79 of the textbook and consider doing the second question. Finish it on a book by yourself. (Students finish the exercise)
Teacher: Let's look at the area of the square desktop first, which is about 64.
Health 1: square centimeter.
Health 2: square decimeter.
Teacher: Who do you agree with?
Health: 64 square decimeters. Because the area of the calling card just now is more than 50 square centimeters, the square desktop is much larger than the calling card.
Teacher: Look at the envelope. The area is about 200.
Health: square centimeters.
Teacher: The area of the playground is about 3600.
Health: square meters.
Teacher: Finally, look at the first small question. Anyone who reads this question again should read something.
Student: The cover length of a math book is about 24.
Teacher: Who will answer?
Health 1: square centimeter.
Health 2: cm.
Teacher: I learned the area unit today. Why fill in the unit of length?
Health: 24 is the cover length of a math book.
Teacher: Look at the questions carefully! We know the new friend area unit, but we can't forget the old friend length unit! (Paste 1 square decimeter on the blackboard in the upper left corner of 1 square meter, and then paste 1 square centimeter in the upper left corner of 1 square decimeter) What do you think of the pasted area unit?
Health: They are very different.
Teacher: What's the relationship between them? We will study it further in the future.