This part of the content is based on students' study of plane figures such as triangles, parallelograms, rectangles and squares, and it is also the basis for further study of perimeter calculation of plane figures. This lesson plays a connecting role in the study of "spatial graphics" in primary school mathematics.

Analysis of learning situation:

"Perimeter" is abstract for junior three children, because in real life experience, students see, touch and use more shapes and sizes of graphics, but pay less attention to the feeling and attention to perimeter. In order to improve students' interest in learning and give full play to their main role, textbooks are introduced from familiar life scenes, which is in line with students' acceptance psychology.

Teaching objectives:

Knowledge and skills: By observing and operating specific scenes, people and objects, we can know the perimeter and understand its meaning. And can measure and calculate the perimeter of simple graphics.

Mathematical thinking: through the process of observation, measurement and other mathematical activities, students can develop the concept of space while gaining intuitive experience.

Problem solving: In learning activities, different strategies can be used to solve problems, which reflects the diversity of problem solving methods.

Emotion and attitude: Perceive the close relationship between perimeter and real life, and stimulate students' interest in learning mathematics.

Teaching emphases and difficulties:

Know the perimeter, understand the meaning of perimeter, and develop the concept of space.

Instructional design:

(1) Take a look and draw a picture.

1. Students, what season is it? Autumn is the season when leaves fall. The teacher brought some beautiful pictures of leaves to the students! What beautiful leaves! The lovely ant is very happy to see it! It says it can draw leaves, and it can draw beautiful leaves with one stroke! Look! (Show the courseware) Look carefully at how two little ants draw. Who draws well?

Teacher: Start from a point and then go back to the starting point. Mathematically, it's called a week. This outer edge is called the sideline.

Teacher: Draw a circle along the edge of the leaf, and a beautiful leaf pattern will appear. Now, who can tell us how ants draw?

Health: The little ant drew a circle along the edge of the leaf and finally returned to the starting point.

Teacher: Little ants can also be teachers. They taught us to draw beautiful leaves. Have you learned?

Please take out a piece of paper, choose a favorite leaf, and draw its outline along the edge of the leaf with a colored pen. Let's start!

2. all right! Who wants to show you how to draw? Please point with a pen and make it clear where to start and where to end. )

3. Summary: It seems that no matter where we started, we traced back a week along the edge of the leaves. Please see (dynamic demonstration). Do you know what the length of a leaf edge is mathematically called? The length of this week is called the perimeter of the leaves. (Blackboard Title: Perimeter)

4. Look at it again (show the picture). Can you draw the border below?

Choose the figure you like and draw it with strokes.

Just now, the students drew a circle along the edge line of the figure, and the length of this week is the circumference of the figure.

(2) find and touch.

1. Can you find an example from us to say what a circle is? Let you find your deskmate and feel its circumference, or you can find it at a lower level. (Guidance: class desktop perimeter, textbook cover perimeter, blackboard perimeter, ground perimeter, pool perimeter. )

2. Who can tell us the result you want? You can point when you speak.

(3) measure it.

1. You found a lot. It seems that perimeter is everywhere in our life and is widely used. For example, when we go to make pants, the tailor will measure how long your waist is in a week, which is usually called waist.

Now, please estimate how many centimeters is the teacher's waist circumference?

Is the estimate accurate? Who will measure it? (Pay attention to the guidance of measurement methods: How to measure waist circumference? ) tell everyone the measurement results.

According to this result, please estimate your waist circumference in centimeters.

Measure the cooperation at the same table.

Who will tell me about his waistline? It seems that the waist circumference of students is about 60 cm.

4. summary.

Through the previous study, the teacher found that students are good at observing and thinking, so I want to invite you to participate in the following competition. Are you interested?

There are 3 grades in * * *, and you will get corresponding points for each grade. The winner with the most points in the end is today! Have confidence? Let's meet the challenge with confidence!

(4) practice.

1. Look at the first level and measure and calculate the perimeter of the figure below.

There are 3 graphs here, please select 1 graph. Look at the second question on page 45 of the textbook and do it in the book.

Select a rectangle. Can you tell me how it is measured and calculated? Is there a different way? Everyone is very clever. We will study the calculation of rectangular perimeter later.

Who succeeded in the first level? Please add 100 to yourself!

Let's continue to break through the second level. How to measure the perimeter of leaves? Whoever breaks through this level will get 200 points.

3. the third level. (Question 3 on page 45 of the textbook)

The courseware shows pictures: Are their perimeters the same? (Name)

Let's look at the method of demonstrating the action. Who survived? Congratulations! 300 points each!

Think back, what method did you use to compare the perimeter of the graph just now?

Which group passed this level? Please add 200 points!

Now calculate how many points you got. Congratulations! Don't be discouraged by other students. Are you confident to catch up with them? I hope you can find out your own shortcomings and make up for them next time!

(5) class summary.

What have we gained today? Can you talk about your confusion?

(6) Homework after class:

Measure the circumference of the red scarf.

Blackboard writing: perimeter

The length of the leaf edge is the perimeter of the leaf.

The length of the graph week is the circumference of the graph.