1. Understand line segments, rays and straight lines with the help of real scenes. Can correctly read line segments, rays and straight lines with letters.

2. Cultivate the ability to operate, observe, discover, summarize and generalize.

3. Experiencing mathematics is closely related to daily life and feeling the important role of mathematics. Further develop the concept of space in activities.

Teaching focus:

Identify and distinguish line segments, rays and straight lines.

Teaching difficulties:

Understand the meaning of straight lines and rays.

Teaching tool: physical display platform

Teaching process:

(a) Creating scenarios and introducing new courses

(B) Group cooperation, in-depth exploration

1, identifying line segments

(1) Establish the mathematical model of the line segment and know the endpoint.

(3) Draw a line segment

Teacher: Please draw the line 1 in your exercise book. The teacher draws pictures on the blackboard with reference to students with different drawing methods, and looks at each other's line segments in the same place and feeds back qualified questions. Such as: draw a curve, don't click on two endpoints, draw a direction, etc.

Follow-up: Who do you think painted it right? Why? How about not adding two endpoints? What are the functions of the two endpoints? What do you think should be paid attention to when drawing line segments?

Emphasize that the ` direction of the line segment can be adjusted freely.

(4) reading the line segment

Teacher: Who can help the teacher name this line segment on the blackboard? How to read it?

According to the students' answers, name the two endpoints, name the line segment, read it, and read it on the blackboard: read it: line segment AB (or BA) points out that there are two ways to read it.

Important: When reading a line segment, you can read it from any endpoint.

(5) Find the line segment

Teacher: Actually, there are many line segments around us. Please find the 1 line segment, point out its two endpoints with your hands, and talk to your deskmate.

Peer interaction refers to two student reports.

2. Know Ray.

(1) Establish the ray mathematical model.

The courseware demonstrates that the light bulb of a flashlight emits a beam of light. Q: What do you see?

(2) Drawing and reading rays

Teacher: What are the characteristics of rays? How to draw? How to read it? Think before you try, and then communicate with your deskmate after you finish.

The teacher found problems during the patrol and asked a group of deskmates to perform on the blackboard.

Teacher: What confusion did you encounter when drawing rays just now? How to solve it? What about reading rays?

Guide the students to make it clear in the debate that we should draw an endpoint first, and then draw a straight line in any direction, pointing out that we only need to draw a part of the straight line because the ray is infinite. For the convenience of reading, the endpoint of the ray should be represented by the capital letter A, and then any point on the ray should be represented by B, but it can't be taken at both ends. It can be read as: Ray AB, Ray BA can't be read, and when reading the ray, you should start reading from the endpoint. There is only one way to read.

(3) looking for rays

Teacher: Think about it. What objects have you seen emit rays in your life?

Guide the students to say: laser, searchlight, infrared ray, sun, light bulb, etc.

Teacher: Don't forget, all living things on earth are also rays from the sun.

Step 3 know the straight line

(1) Establish a mathematical model of a straight line.

(2) Draw a straight line and read it.

Teacher: What are the characteristics of straight lines? How to draw? How to read it? Please think twice before you act, and then communicate in groups of four.

The teacher found problems during the tour and asked four people to perform on the blackboard.

Teacher: Who has different ideas? Follow-up: Are Point A and Point B the endpoints of a straight line? Why?

Guide the students to make it clear in the debate that we only need to draw a part of the line, because the line is infinitely long. For the convenience of reading, two points on a straight line should be arbitrarily represented by a and b, not the two ends. It can be read as: straight line AB (or BA). When reading a straight line, you can read it from any end. There are two ways to interpret it.

(4) Find a straight line

Teacher: Actually, there is no real straight line in life. For example, a straight road can be regarded as a straight line only when you can't see its head extending infinitely to both ends. Think about it, is there a similar example in life?

Examples are: high-voltage lines, railways, highways, etc.

(C) practical activities, summing up the characteristics

Compare the differences and connections of the three lines;

Teacher: Today, we know three kinds of lines. Please observe their similarities or differences carefully.

Refers to students saying, the rest of the students complement.

It is pointed out that there seems to be both difference and connection between the three lines.

Courseware demonstration: the straight line extends infinitely to both ends; Intercept 1 line segment on a straight line; A line segment can get a ray by removing 1 endpoint and extending to one end indefinitely; Line segments and rays are also part of a straight line.

(D) comprehensive use to enhance perception

Teacher: Today, we met three good friends: straight line, ray and line segment. Let's play games with them, shall we?

The first level: guess riddles and type the name of the first line.

1, start and end (line segment)

2, no beginning and no end (straight line)

3, a beginning without an end (thunder)

Level 2: Which of them is right?

1, Xiao Ming said: The line I drew is 4 cm long. (right)

2. Xiaohong said: The ray length I drew is 1 meter. (error)

Xiaoli said: The straight line I drew is 2 meters long. (error)

Level 3: Try to draw a straight line.

1, draw a straight line after a little bit.

Draw a little at random first, then draw a straight line, and the teacher will lead the students to finish.

Experience: After a little, you can draw countless straight lines.

2. Draw a straight line after two o'clock.

Students' operational experience.

Follow-up: Can you draw again?

After summing up two points, you can only draw a straight line.

Level 4: What did you find?

There are many roads from Hushan to Fox Cave, which is the shortest? (Summary: Of all the connecting lines between two points, the line segment is the shortest)

(5) detection.

True or false:

(1) The straight line AB is 30cm long. ( )

(2) One end of a line segment can extend indefinitely. ( )

(3) The line segment CD is 5cm long. ( )

(4) The two ends of the light can extend indefinitely. ( )