How long is this table?
Textbook analysis
How long is this table? It is the content of the sixth unit "Measurement" in the first volume of the second grade of the compulsory education curriculum standard experimental textbook "Mathematics" (Beijing Normal University Edition). The content of this unit has established a preliminary concept of space for students in the whole textbook, and narrowed the distance between mathematics and daily life with their observation and operation activities, and realized the close relationship between mathematics and life from another angle different from numbers. "How long is the desk" is the students' understanding of measurement from centimeters, including why, what, how and how to record. And the initial unit of length-centimeter, so that students can estimate a certain length by themselves and go through the process from knowledge to knowledge, just like peeling beans, from peeling to beans, and constantly clarify.
Student analysis
Although the students are young, they all know about rulers (every student has seen rulers). Based on their experience, they know what a ruler can be used for and how to use it (of course, it may be inaccurate and their knowledge may not be comprehensive). For example, in the topic of "Lian Lian", some students draw lines with a ruler, and they know that a ruler can be used to draw straight lines; Some students don't have scissors in paper-cutting activities. In order to tear the paper neatly, they pressed the edge of the paper with a ruler, which is also the straightness of the ruler. It can be seen that students are no strangers to rulers. When the whole class knows the length of an object together, some students try to measure it with a ruler first, which will drive other students to follow suit. Junior two students have the habit of imitating and being active. Students who know will teach students who don't know and even the whole class, and announce the results. Students who don't know will turn around, turn around and even get down from their seats, ask questions and see what others do. Faced with such students, we should give them time in teaching so that they can express themselves purposefully and acquire knowledge through argumentation and exploration.
The individual students in this class are active, intelligent and positive, and there may be some unexpected things that the teacher did not expect, which will make many changes in the design before class and cannot be carried out as planned. Therefore, teachers should face the changes of students and let them learn actively on the basis of cognition.
Design concept
In view of students' understanding, teachers should try their best to guide them to find problems and encourage them to solve problems through their own observation, thinking and cooperative inquiry. Cultivate their sense of cooperation and exploration in learning, as well as the ability to learn to learn. Combined with students' hands-on operation, fully mobilize the subjective initiative of learning, so that every student can integrate into it and experience the fun of thinking. For example, after students know the ruler in detail in the group, explain the function of the numbers on the ruler; The teacher pointed out that "the length from one number to the next is 1cm", so as to deepen students' understanding of centimeters in time, consolidate, affirm (or correct) the original viewpoint, and make use of this to make it extrapolate.
After knowing the ruler, it is practice and consolidation. When students measure the same object by themselves and get different answers, discuss and find out the reason: what is this? Is the starting position right? Whether the discussion can give students a result immediately or not, at least every student has thought about this problem and achieved the purpose of the discussion-participation and thinking. This is to let them explore a way to get information by themselves and cultivate a sense of cooperation at the same time. At this point, the teacher will summarize or prompt concisely, so that every student can understand and remember it smoothly. Compared with teachers restricting students' activities, it is much more vivid and positive to demonstrate first and then let students imitate. In short, the teacher takes the key step from the side guidance, and the rest is left to the students to try to complete.
Teaching objectives
1. I initially realized the necessity of establishing a unified unit of measurement and understood the diversity of measurement methods in real life.
2. Understand the length unit centimeter (cm) and establish the concept of 1 cm to estimate the length.
3. Learn to measure the length of an object with a scale and understand the meaning of centimeters.
4. Explore and master knowledge and experience the fun of learning in cooperative discussion.
Teaching preparation
Draw an enlarged ruler diagram; Make a slide ruler diagram to facilitate students to demonstrate their own measurement methods, and prepare various rulers (meter ruler, steel tape measure and tape measure) to broaden students' understanding of rulers.
teaching process
First, introduction.
It is natural to introduce the theme: let's see how long this table is.
Measure objects.
Second, teaching.
1. estimation: Let students try to estimate the length of their desks with their eyes or hands. After the estimation, raise your hand to exchange the results. If most students here say ×× "cm" skillfully, please pay attention to find out what the answer is in the later study.
This part of the arrangement allows students to have an uncertain sensory understanding of the length of an object in advance, and also cultivates students' preliminary estimation ability.
2. Measurement: After students estimate the figures, they will verify them. (First, avoid using a ruler and give an assumption. If you don't use a ruler, what else can you think of to measure the table? How to start the discussion and then report to each group? (Use pencil boxes, books, pens, etc. How long is the measuring table? I hope it is several pencil cases long and several books long. Ask more questions, and according to the students' answers, the teacher will summarize them in time.
Teacher: Why are the measured table lengths different? Are the tables really different in length?
Conclusion: Different tools will lead to different results. Only if the tools are the same, the results will be the same. So we will find a unified measuring tool to measure. After measurement, what do you think is the best unified tool? (Introduce the ruler and pave the way for introducing the ruler. )
It aims to make students realize the necessity of unifying measurement units and feel the diversity of measurement methods in life.
3. Know the ruler.
(1) Teacher: There are many kinds of rulers, not only the ones you use, but also these ones. Show all kinds of rulers, broaden the knowledge and let students know more about some rulers. End the introduction of the types of rulers with the sentence "They are used in different places". ) and in our study, the most commonly used is your student ruler (taken from students). At the same time, an enlarged ruler picture was posted on the blackboard. )
(2) Teacher: Then, please have a look. What are the rulers commonly used by students? Give this question to the students for discussion before the report. This can prevent some students from missing things without observing or observing carefully. )
Health 1: There are numbers.
Health 2: There are some small lines and cells.
Teacher: These are scale lines, and cells are divided by these scale lines. Please count carefully. There are several cells between each number and the next number, that is, between the two longest tick marks. Student 3: There is the letter cm.
Teacher: You observe very carefully. Get the attention of other students. )
Let's talk about the meaning of cm-C and m, which means that "cm" and "cm" can be replaced with each other, and point out that cm is a unit of length.
Blackboard: length unit-cm.
When students begin to estimate, the teacher will answer questions that may arise. Let the students say that our desk unit is ×× cm.
(3) Teacher: Did you find the "0" on the ruler? What do you mean, where is it? (health: the leftmost side of the ruler indicates the starting point. )
The teacher reminded: when measuring things, you usually start measuring from the starting point 0 scale line.
Teacher: What do you mean there are some numbers on the ruler? Draw the length in centimeters. Please find the part from "0 ~ 1" on the ruler. How many centimeters is it from 0 to 1? (Starting from students' experience and understanding. )
Students guess first, and then communicate with each other.
Teacher: The length of the next number is 1 cm, so 0 ~ 1 yes (student: "1 cm").
Draw a color stroke on the blackboard ruler to indicate that the range from 0 to 1 is 1 cm.
In the form of quick answers, ask the students to tell how many centimeters are between 5 ~ 6, 9 ~ 10, 0 ~ 2 and 0 ~ 6 respectively. Relieve, mobilize emotions, give timely praise, reward those who answer the most difficult questions correctly, and encourage everyone to think more. )
(4) On the basis of understanding, let the students feel "how long is 1 cm" with their hands, and then let the students say that what you have seen in your life is 1 cm long. The teacher gave more affirmation to the students' answers. )
4. measure things.
(1) Let the students take out a unified object (the big triangle in the learning tool), find the long side (just an integer), discuss it in groups and try to measure it before reporting. In the face of inconsistent results, we discuss the reasons and explain that it is best to start from 0. Then find someone to demonstrate on stage. When the students demonstrate, the teacher explains the requirements step by step with the demonstration: when measuring an object, first aim one end at the 0 scale line, and then see how many centimeters the other end is facing the scale line.
(2) Measure the short side of this big triangle (isosceles) again, not an integer. How much should the class read? Teacher: Which scale line is closer, about a few centimeters.
Third, practice.
This pencil is () centimeters long.
2. Open the book and read the third question on page 15 to judge who measured it correctly. Do it independently, communicate collectively, and tell the reason for the mistake. It is pointed out that the measurement from one full scale to another is also correct.
3. Group work, complete the 1 question on page 15, estimate first, and then calculate.
Fourth, summary.
Teacher: What have you gained after learning this lesson?
Student: By studying this lesson, I know how long my desk is and how to measure the length of objects with a ruler. The unit of length is centimeters, and centimeters can also be expressed in centimeters. When measuring, you should start from the scale of 0, or you can start from the whole scale, how long 1 cm is, and so on.
Reflection after class
After class, it was found that the existing foundation of students was beyond the teacher's expectation, which led to the failure of the originally designed classroom. Although the class changes flexibly according to unexpected situations, due to various reasons, the changed classroom grasp is not very successful, and many ideas that are conducive to students' development and can activate the classroom atmosphere have not played a incisive role. In the face of unexpected events, we should improve our ability to control the classroom, think carefully in many aspects when preparing lessons, and make constant changes.