Teaching objectives

① Establish the concept of perimeter.

② Let students "move" and experience the process of "doing mathematics" through activities such as observation and operation.

③ Cultivate students' habit of observation and thinking, so as to achieve the purpose of independent inquiry learning, active participation in learning and cooperative exchange learning.

Teaching focus

Understand the surroundings and cultivate the ability of observation, hands-on operation and cooperation.

Teaching difficulties

In a specific situation, the perceptual perimeter is closely related to real life.

Teaching preparation

Teaching courseware computer multimedia watercolor pen ruler rope leaf graphics card

First, the situation import:

Teacher: It's autumn, and Miss Qiu has come with a present. Want to know what it is?

Health: Yes.

Teacher: Then let's have a look! (Courseware shows fallen leaves)

Teacher: Yes, pieces of fallen leaves spread their wings like butterflies and danced around us. This is a gift from Miss Qiu. It landed gently on your desk. Do you like it?

Health: Yes.

Teacher: Then pick one of your favorite leaves and lift it!

The students picked their favorite fallen leaves and lifted them happily. )

Teacher: What shape are your leaves? Touch the outline of these leaves. Can you draw the shape of the leaves you like? Pay attention to draw along the edge of the leaves when drawing, and don't repeat the strokes. All right, let's get started!

The students began to draw the outline of the leaves. )

Teacher: Who can tell us how you describe it? Is there a different way?

Health 1: I hold the middle of the leaf with my hand, and then draw from the page handle with a watercolor pen, just along the leaf for a week, and it's finished.

Health 2: I started from the tip of the top of the leaf, which is just round.

Health 3: I drew the left side of the leaf first, and then the right side of the leaf, which happened to be the week of the leaf.

The teacher concluded: In fact, no matter what method you used just now, it took us a week to trace the length of this leaf, that is, the perimeter of this leaf. In this lesson, we will learn what a circle is.

Teacher's blackboard title: What is a circle?

Second, explore new knowledge.

1 reveals the concept of perimeter.

Teacher: The little ant also received a gift from Miss Qiu. Look, what is it doing? The courseware plays the animation of little ants circling the leaves. )

Question: How does the little ant run?

Health: Start from a point of the leaf, run around the edge of the leaf, and return to the starting point.

Teacher: The length that a small ant runs around a leaf is the perimeter of the leaf.

Teacher: Look, which of these two leaves draws the perimeter of the leaf? Why? (courseware plays pictures)

2. One shot:

Teacher: Can you draw such a figure? Ok, let's play a little game-a stroke, (experience from the starting point, draw a week, and then return to the starting point, the starting point and the end point coincide)

Student painting

Teacher: The length of a figure like this is the circumference of the figure.

3, practical activities: touch.

Teacher: Actually, we can also find the perimeter of many objects around us. Look, there is a plane on the teacher's desk. If you touch it along its edge, it will be the circumference of the desktop. (talk and demonstration)

Teacher: Can you, like me, find an object, choose such a plane, and then touch its edge carefully?

Students report to the front.

1: I chose the plane on my pencil case and touched the edge of the plane.

Health 2: I chose my rubber side, which is the edge of this side.

S3: I chose the cover of my math book, which is the dividing line of math writing.

Student 4: I chose the surface of my desk, which is the edge of the class desk.

Teacher: The length of the edge line of these faces we just touched is the perimeter of this face.

4, closed graphics

Teacher: Little ant is very happy to see that his classmates have learned so much knowledge. Look, another little ant is coming to compete with that little ant just now. (Show courseware)

Question: (1) Which of them runs Leaf Week?

(2) What's the difference between these two pictures?

Health: One is sealed and the other is not.

Teacher: Yes, the seal is called a closed figure with a perimeter. Unsealed graphics have no perimeter.

Demonstration: Fold a metal wire into a five-pointed star-shaped frame.

Question: Look at the picture in the teacher's hand. Where is its circumference? (Students come to the stage to point out)

Demonstration: Let go of the connector.

Q: Does this figure have a perimeter?

Discuss in groups, report the discussion results and briefly explain the reasons (encourage team members to supplement)

Teacher: Look, Miss Qiu will test the students and decide which of the following figures has circumference. Which ones are not? (Show courseware)

Summary: Like the figure in the teacher's hand, this line is closed, the length is the same as the edge of the figure, and the perimeter is actually a "line", not a "face" inside the line. So when measuring the circumference, use the length unit.

5, practical activities: measure a quantity.

Transition: In just a few minutes, students can not only accurately trace the perimeter of the figure, but also find the perimeter of many things around them, which is really amazing. In fact, there is a circle on our body. Do you believe it? Look, the teacher has a headdress in his hand. I invited two students to try it on in front. Please observe carefully. What will you find?

One student put it on just right, and another student put it on and slipped off. ) Why is this happening?

Health: Because the first one is big and the second one is small.

Teacher: If you want these two students to wear headdresses of appropriate size, you must first measure their head circumference, that is, the length of their first week.

The teacher demonstrates starting from a point, going around this classmate's first week, and finally returning to the starting point. Then measure the measured line on the meter ruler, which is the head circumference of this classmate. )

1, learn about measuring tools.

2, explain the measurement method

3. Choose a part of your body to measure.

4. Students report the measurement results.

5. Measure the circumference of the chart.

Teacher: You can measure the circumference of our body, so how to measure and calculate the circumference of a closed figure?

Look at a set of numbers. How many sides should we measure first to calculate the perimeter of this figure?

Health: A triangle must first measure the lengths of three sides, and then add up the lengths of these three sides to form the perimeter of the figure.

Teacher: How many sides should a quadrilateral measure first? How to calculate their perimeters?

Show a quadrilateral, let the students go to the front to measure and calculate the circumference of this figure.

Then show a set of figures: figures measuring the length of each side, including pentagons, hexagons, quadrilaterals, trapeziums and triangles. Ask the students to choose a figure they like and calculate their perimeter.

Through discussion, the students come to the conclusion that the sum of all sides of a figure is the circumference of the figure.