Teaching objectives:
(1) knowledge and skills: let students feel the meaning of the circle through their own personal experience; Through group cooperation and exploration, the perimeter of plane figure is obtained by various appropriate methods; Cultivate students' ability of observation, comparison and operation.
(2) Process and method: Put large graphics in class to attract students' interest, let students actively participate in personal experience, and let students perceive the meaning of perimeter by walking, watching, drawing and measuring.
(3) Emotion, attitude and values: speak with your own personal experience, actively participate in the exploration of knowledge and put forward your own opinions.
Emphasis and difficulty in teaching: understanding the meaning of perimeter.
Teaching aid preparation: all kinds of graphic cardboard and exercise paper.
Teaching process:
Before class, a figure was put in the middle of the classroom. )
First, create situations and introduce new lessons:
T: Are the children particularly surprised today? The teacher surrounded a big shot in the middle of our classroom. Please observe this number carefully and tell us what you find.
Students are in appearance, straight line curve and symmetry. )
T: Observe very carefully. Children should observe everything carefully as they do today. Well, then we observed that the teacher wanted to invite a child for a walk. Teacher's demonstration: let a child follow the teacher and walk around the edge of the figure from a point to let other children pay attention. (Students leave)
T: Did you walk well? (Great! ) Your observation is better. The teacher rewarded everyone with a question: What did the child walk along this figure just now? In mathematics, we call the edge or outline of this figure "perimeter" (blackboard writing: the perimeter of the figure)
Second, cooperation and communication, * * * and exploration:
Teaching perimeter
So, can you tell what the circumference is in your own words? (student exchange. )
Teacher's demonstration: let's start from any point, walk around its sideline for a week, and then return to this point, then the length of this week is its circumference.
(1) The teacher showed some plane figures () and posted them on the blackboard. Ask the students to choose a figure they like to draw its perimeter.
(2) Look at things around you. Can you point out their boundaries? We also found the circumference of the surface of the object.
T: We find that not only the figure has a perimeter, but also the surface of the object has a perimeter.
(3) Print one, draw one: Use the object on your desk, select one of its faces, and draw the perimeter of the figure on this face by printing one.
(1) It is found that the graphics in the middle of printing are not closed; The teacher also prepared two figures. Please draw their perimeters: why not? Let's start from a point and walk around the edge of the graph. We can't go back to this. This graph is called an unclosed graph. What kind of figure do you think has a perimeter? So in mathematics, we can summarize it in a more concise sentence: the length of a closed figure is its circumference.
Please decide which of the following figures can calculate the perimeter (yes, please sit down, no, please raise your hand. )
(B) the method to explore the perimeter
Teacher: Now that we know the circumference, please try to find out.
Leave this task to your team of four.
Group activity: The teacher put the basic plane graphics displayed on the blackboard into the envelopes of each group, and asked four people in each group to explore the method of finding the circumference.
Communication: Tell me, what did your group ask for? (Measurement, rope circumference, symmetry ...)
Summary: We just found that a figure can be measured with a ruler when it is flat and with a rope when it is bent. We also found that a symmetrical figure only needs half. ...
Third, application migration, consolidation and improvement:
(1) I want to know the perimeter of this leaf. What should I do?
(2) I use two equal-length ropes to form a triangle and a quadrilateral. Whose week grew up?
(3)T: So, can you find the perimeter of the surface pattern of the object just printed by these methods?
The great people who are led to the ground in the classroom can be found in different ways according to the characteristics they find in the classroom. )
(4) The desktop of Xiao Ming's book is a rectangle with a length of 120cm and a width of 50cm. If a square with a side length of 5 cm is cut off from its two corners, what will happen to the pattern? ※? (pictured)
Fourth, summarize and reflect, expand and sublimate:
T: What have you gained from studying together in the same class?