Teaching objectives:
1, know the circle and know the names of each part of the circle;
2, master the characteristics of the circle, understand and master the relationship between radius and diameter in the same circle.
3. Learn to draw circles with tools;
4. Cultivate students' observation ability, practical ability and abstract generalization ability. Make students learn to apply what they have learned to solve simple practical problems;
5. Make students like beautiful circles and stimulate their interest in exploring the characteristics of circles.
Key points and difficulties:
Understand and master the characteristics of the circle.
Teaching preparation:
courseware
Teaching process:
First, pre-class activities
Students, how about taking a break before class and doing exercises between classes? erect
Section 1: Swing your arm (change direction after going)
Section 2: Turn your head.
Section 3: Turn around in the same place
Second, the introduction of new courses.
1, Teacher: What did you find in the practice before class? (doing circular motion)
2. Teacher: I just found that some students' arms don't turn like a circle. How can they turn more like a circle? (Hands straight, shoulders still)
3. Teacher: We can create circles in sports, and there are many circles in life. Look: enjoy the picture of the circle.
4. Expose the topic: understanding of the circle
5. Teacher: How many circles do we see on this dining table?
There is a lot of math knowledge in it. Do you believe it?
Third, hands-on operation.
(1) Teacher: Let's make this dining table.
[Media] Do it: work at the same table. Everyone draws a circle on white paper, and then cuts it out to form a round table model.
(2) Teacher: Let's talk about how to do it.
[Step 1] Our first step is to draw a circle. How did you draw it?
1. Tell me how you draw a circle with a compass.
Teacher: The teacher also draws a circle on the blackboard.
Separate the legs of the compass and determine the distance (radius) between them.
Fix a foot on a point (the center of the circle) with a needle tip.
Turn your feet with a pencil and draw a circle.
3. How is the teacher's circle drawing? What should I pay attention to when drawing a circle? (Needle tip fixed, foot spacing fixed)
4. Why are the two circles you drew different sizes? (The distance between feet is different)
[Step 2] We cut the drawn circle and asked: What is the difference between cutting and cutting a square and a triangle?
Teacher: What about the circle? Mathematically, we call it a curve, so a circle is surrounded by curves, which is quite different from a plane figure surrounded by line segments.
[Step 3]
How do you combine the cut circles? Where did these two pinholes come from?
Teacher: This point of the pinhole, which we call the center of the circle, can also be represented by the letter "O".
Teacher: Is there any other way to find the center of the circle? Take it off and try it on first. (hands-on operation)
Teacher: How did you fold it?
Possibility: ① Health: Fold in half and then fold in half, and the intersection point is the center of the circle. Teacher: How else to fold it?
② Fold in half, unfold, fold in half again, unfold again.
Teacher: Let's see how many creases there are here. And they all go through such a crease, which is called the diameter of the circle and is represented by the letter D (drawn on the blackboard).
Teacher: What else is in the circle? (Radius) Do you have it in the circle you folded? Point (draw on the blackboard). This is the radius.
Teacher: What are diameter and radius? Look at the self-study textbook p80.
Teacher: What's the diameter? Explain in the circle, explain outside the circle, and explain inside.
Let's point and say what the radius is.
[Media] Is it a radius that connects the center of a circle with a point on the circle? How many radii are there? Why? [blackboard writing]
You also need to draw a diameter and radius.
Look carefully, what else do you find?
① One diameter = two diameters.
Teacher: What else can I say? How did you know? How to express it in letters?
② All diameters and radii are equal.
Teacher: What do you think? What method can be used to prove it? You measure.
What did you measure? What about the result of quantity? What's your conclusion?
Teacher: We observe carefully and use our brains well. Now the teacher has a question, I don't know? All diameters are equal in length? (Same lap) Not bad? (Equal circle) What other conclusions do you think need this premise?
[blackboard writing]: In the same circle or equal circle
Third, application
Teacher: So we should think carefully and thoroughly when considering problems in the future, right? Let's look at a set of blanks.
1, filled in by [Media].
2. [Media] Please demonstrate again: Are the following sentences correct?
(1) The line segment with both ends on the circle is called the diameter.
(2) All radii are equal.
(3) A circle is a closed figure surrounded by curves.
Fourth, draw a circle.
Teacher: That's a good answer. Now the teacher wants to make a new request. Can you accept it?
Please draw a circle with a radius of 2 cm.
Teacher: Think about how to draw a radius of 2 cm. We can discuss it before painting. (original painting)
Teacher: How did you draw it? (The distance between the feet is 2 cm, then fix it and draw it. )
In short, how do you determine the radius of 2 cm?
What if you draw a circle with a radius of 3 cm?
Draw a circle with a diameter of 8 cm?
What connection did you find? (Radius = distance between two-foot compasses)
What determines the size of a circle? Where is the location?
Draw a circle with a diameter of 1 m.
(Wait a minute)
Teacher: Why not draw? What should I do (the compass is too small)? (nail, rope) How long is the rope? (50 cm) Why? Shall we have a try after class?
Verb (abbreviation of verb) abstract
Teacher: Today, we learned Yuan. Is there anything else worth asking about all kinds of knowledge from round tables to circles?
Teacher: These are all things we will learn in the future. The teacher has another question: who uses the western-style dining table at home? How do you feel? Relatively speaking, what about the round table?