course content

Compulsory Education Curriculum Standard Experimental Textbook (West Normal University Edition) Page 64~66 of Grade Four Exercise 13 1~4.

Teaching objectives

1. Know what an angle is, and can point out angles, edges and vertices; The angle can be expressed by common symbols, and the degree of the specified angle can be measured by a protractor.

2. Cultivate students' observation ability and operation ability, and develop students' spatial concept.

Prepare teaching AIDS and learning tools

Teachers prepare multimedia courseware and video display platform; Each student prepares a round piece of paper; Some special horns; protractor

teaching process

First, the introduction of new courses.

Teacher: We studied X-ray before. Please identify a point and draw two rays in different directions with that point as the endpoint.

After the students operate, select the representative homework of the students to display on the video display platform.

Teacher: What did you find?

Lead the students to answer: I found that the figure composed of two rays introduced by a point is an angle.

The teacher wrote the students' answers on the blackboard

Teacher: Look at the corners drawn by the students. Are they the same size?

Students find that some corners are big and some corners are small.

Teacher: Which of these angles is bigger and which is smaller? Besides observation and overlapping comparison, we can also solve this problem by measuring the angle.

(blackboard writing topic)

[Comment: This teaching link starts with students' original knowledge, so that students can understand the meaning of angle from the operation process of drawing angle, that is, "drawing a graph composed of two rays from one point"; The angle of students' painting is large and small, which subtly leads to the measurement of angle. ]

Second, implement the new curriculum.

1. Special angle.

Teacher: You need a protractor to measure the angle. Let's make a simple protractor. Please take out your round paper and fold it in half. Into what?

Students answer after folding in half: semicircle.

Teacher: What angle does this semicircle form when it is folded in half?

Students answer after the operation: turn into a right angle.

Teacher: What is a right angle?

Student: 90 degrees.

Teacher: Fold this 90-degree right angle in half again (student operation). What is the angle now?

Student: It's 90÷2=45 (degrees).

Teacher: Please spread the paper into a semicircle. What did you find?

Student: There are some creases on the semicircle.

Teacher: Draw these creases. Can you find the angles of 0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees from left to right on the crease of this semicircle?

After the students find it, please show it to everyone and tell them how to find this corner.

Teacher: Let's write 0 as 0 and 45 as 45. Please mark the corresponding degrees on the semicircle in this way.

After the students operate, display the students' semicircular pieces of paper on the video display platform (as shown in Figure 4? 5)。 Figure 4? five

Teacher: Such a simple protractor has been made. Students can compare the corner of the book cover on this protractor to see if it is 90. After the teacher demonstrates while talking, the students compare the books on the semicircle.

Teacher: Can you tell me what we should pay attention to when comparing?

Guide the students to aim at the line marked with 0 when they say the quantity, and the vertices of the angles should aim at the vertices of several angles on the semicircle.

Teacher: We call the line marked with 0 the scale line, and the endpoints of several angles on the semicircle are called angle measurement. Figure 4? six

Teacher: Let the students measure the angle of a triangle in this way. Can you find a 45-degree angle? Then put a right angle and a 45 angle on the triangle to see how many degrees this angle is.

After the students measure the angle, the key point is how to measure it, so that students can master how many degrees the 0-degree scale coincides with one side of the angle, and the center of the protractor coincides with the vertex of the angle, and then look at the other side.

[Comment: Take this teaching link as a simple protractor method, so that students can know the protractor in the process of doing it and master the method of measuring the angle, so that the teaching of knowledge is not limited to "teaching", but embodied in the process of "doing", which can better reflect the curriculum concept of "doing mathematics" and fully mobilize the enthusiasm of students to acquire knowledge actively. ]

2. Average angle.

The teacher took out an angle of 25 and asked the students: Can you measure the degree of this angle with the protractor in your hand?

Student: No.

Teacher: This requires us to have a more accurate protractor.

Multimedia courseware shows protractor.

Teacher: Look, what's the difference between this protractor and the protractor in your hand?

Students intuitively found that this protractor has many scales, including internal and external scales.

Teacher: Here, the semicircle is divided into 180 parts, and the angle of each part is1; This protractor has two scales inside and outside and two zero scale lines, which is convenient for students to measure the degree of angle from two directions.

Teacher: The measured horn of 1 is 25, where the symbol of the horn is usually "∞", so it can be recorded as ∠ 1 = 25. Please remember the other angles you measured in this way. Students remember the angle.

Teacher: What should I pay attention to when measuring the angle?

Students answer after discussion (omitted)

Instruct students to complete the second question in class activities.

[Comment: This teaching link is mainly from a special angle to a general angle, which leads to the need for a more accurate protractor. On this basis, the emphasis is on the understanding of protractor and angle measurement, and the students' mastery of angle measurement methods can be improved through their specific operations. ]

3. Make an active corner.

Instruct students to make activity corners, and then let them rotate an edge to form corners of different sizes.

Teacher: in the process of making the activity corner, what do you find to be the relationship between the size of the corner?

After the students answer, please judge Figure 4. 7. Then use a protractor to measure the size of the two angles, and guide the students to draw the conclusion that the size of the angle mainly depends on the size of the corner mouth, and has nothing to do with the length of the side. Figure 4? seven

[Comment: This link is mainly to judge the size of the angle by doing the activity angle, so that students can understand the relationship between the size of the angle and the size of the angle opening and prepare for the next class. ]

Third, class assignments.

Instruct students to complete the exercise 13, question 1~4.

(This case is provided by Lu Ping. )