1. Make students know the circle, learn to make the circle and master the calculation method of the circle area through teaching.

2. Cultivate students' hands-on operation ability, observation ability and imagination ability, and establish a preliminary concept of space.

3. Cultivate students' application awareness and ability to solve simple practical problems.

4. Make students know the close relationship between mathematics and human life, and experience mathematical activities full of exploration and creation.

Teaching emphasis: calculation method of annular area.

Teaching difficulties: understanding the formation process of the ring and forming the spatial concept of the ring.

Teaching method: self-help attempt teaching method

Preparation of teaching AIDS: multimedia courseware, small blackboard, two sets of round paper with radius of 6 cm and 2 cm respectively, scissors, ruler, compass and CD.

Preparation of learning tools: each student prepares circular pieces of paper, scissors, rulers and compasses with a radius of 6 cm, 10 cm.

Teaching process:

First, practice and introduce new knowledge.

1. Enjoy the picture: a wonderful circle.

2. Thinking: How to calculate the area of a circle? Please take out a CD with a radius of 10 cm. Who can tell you, can you work out the area of this circle? Guide the students to say the word formula, letter formula and list formula. )

3. Draw a picture. Can you draw a small circle in this circle? Try it? Students draw circles, teachers patrol and guide, and help students with difficulties. )

4. Do the math. Can you work out the area of a small circle? Say it.

5. Guess and cut. If you cut this small circle with scissors, what figure will you get? Where are the pictures? Hold up the cut graphics for everyone to enjoy. Regular script: ring

Thinking: Why are Figure 1 and Figure 3 not circular? (The ring has two concentric circles) and paste the picture.

Key point: If you remove a small concentric circle from a big circle, you get a ring.

Second, cooperative learning, exploring new knowledge

1. Say it. In daily life, which objects have rings? Students give examples and demonstrate with courseware.

2. Count: How many circles are there in the ring? What is the width of the ring?

Understand the characteristics of rings: there are two concentric circles with the same ring width.

3. Composition of circular ring: small circle, big circle, small circle radius, big circle radius.

(Courseware demonstration)

4. The area of the ring. The area of a ring is derived from the area of a circle. Ask the students to say and feel the area of the ring in their hands. Discussion: How can I calculate the area of this ring in my hand? Discuss in groups of four. (displayed on the blackboard)

5. Explore: the calculation method of annular area. Act it out first, and then discuss whose calculation method is the simplest.

Teacher: Demonstrate that when the small concentric circles are removed from the area of the big circle, the area of the circle is the area of the circle. Find the area of the outer circle and the inner circle first, and then find the area of the ring. What else can I do? Guide students to deduce a simple algorithm of ring area and express it with letter formula.

Thinking: What are the conditions for calculating the area of a ring?

6. practice. Judge.

(1) Cut a small circle inside the circle to get a ring. ( )

(2) For a circular ring, the radius of the outer circle is 4cm and the radius of the inner circle is 2cm. The formula for calculating the area of this ring is: 3. 14× 4-3. 14× 2 ().

7. An iron ring. The radius of the inner circle is 10 cm, and the radius of the outer circle is 20 cm. What is its area?

Third, apply new knowledge to solve problems.

1, can you calculate the area of the shadow?

(Half ring: r R= 10/0cm, r = 6cm)

2. The diameter of the circular roundabout is 50m, with a circular flower bed with a diameter of10m in the middle and other lawns. What is the area of the lawn?

3. Build a path with a width of 1m around a circular flower bed with a diameter of 4m. How many square meters is the area of this path?

4. Hands-on operation: 5 people do the five rings together.

Fourth, reflect on experience and summarize and improve.

What did you get from this lesson? Say it.

Verb (abbreviation for verb) assignment

Exercise 16, question 4.

Blackboard design:

Area product of ring

Large circle area-small concentric circle area = annular area