1. Make students know the unit of length-decimeter through practical activities, and initially establish an intuitive expression of decimeter length.

2. Make students learn to choose appropriate length units and measuring tools in actual measurement, which will measure the length of some objects or line segments and improve the estimation ability.

3. Through hands-on operation and cooperative communication, students can further improve their interest in learning mathematics and appreciate the value of mathematics learning.

Teaching preparation

1. Teacher preparation: courseware, ruler, courseware, colored paper.

2. Students prepare: colored paper strips and scissors.

teaching process

First, check the import.

Which unit of length did we know last time? (mm) What units of length have we learned now? (Blackboard: meters, centimeters, millimeters) Can you draw the approximate length of 1 meter by hand? 1 cm? 1 mm? Which unit is better for us to measure the height of the classroom door? What unit should be used to measure the length of a small ant? In what unit is the length of this paper money measured? How many centimeters is it?

Note: Students have some experience in measuring the length of objects in their lives, and they also know the length units of meters and centimeters in their previous studies. By reviewing old knowledge and introducing new knowledge, students' knowledge reserve can be activated. ]

Second, explore practice.

1. Know decimeter.

(1) Take a test.

Requirements: How long are your notes measured with a ruler? (Students answer) (Show the color bar of 10 cm) "10 cm" We can also use another unit-decimeter. (blackboard writing: knowing decimeter) 1 0cm is1decimeter. How many centimeters is 1 decimeter? Please think about it. How many decimeters is 20 centimeters? How many centimeters is a decimeter?

(2) recognize it.

Please take out your ruler and see where 1 decimeter can go. Name demonstration communication: No matter from which scale to which scale, 1 decimeter is equal to how many centimeters? (blackboard writing: 1 decimeter = 10/0cm)

2 experience.

Please stretch out your thumb and forefinger and draw 1 decimeter with the help of a ruler. What we are drawing now is the length of one foot, and one foot is about 1 decimeter.

One person draws 1 decimeter, and the other person measures it with a ruler to see if the comparison is correct.

Take out the colored paper, estimate the length of 1 decimeter, and cut it according to 1 decimeter. Let's test it together and see who estimates it most accurately.

[Description: Students are required to estimate boldly and combine the estimation with the actual measurement. By counting a ruler and drawing by hand, it is more and more difficult to estimate the length of 1 decimeter on colored paper strips, which is beneficial for students to gradually deepen their understanding of decimeter and cultivate their preliminary estimation ability and consciousness. Although this classmate's estimate of 1 decimeter is not very accurate, it should be encouraged as long as it is close. ]

(3) Draw a picture.

① Requirements: Can you draw a line segment 1 decimeter with a ruler? How are you going to draw it? Talk to your deskmate first, and then draw on the paper.

② Communication: How to draw? Ask students to show the report with physical projection.

③ Guidance: (Draw while talking) 1 decimeter We can draw from scale 0 on the ruler to scale 10. So, can we start with the scale of 1? If so, where should I draw it? Why? What if we start with scales 2 and 3?

[Description: Let students know that there are different ways to draw the line segment of 1 decimeter with a ruler, which is not only conducive to further understanding the relationship between decimeter and centimeter, but also conducive to students' understanding of the diversification of problem-solving strategies. ]

④ Summary: As long as the square of 10 is drawn, it is 10 cm, that is, 1 decimeter.

Please measure your deskmate and see if the line drawn is 1 decimeter.

(4) looking for.

Talk to each other in the group about which objects are about 1 decimeter long, and then organize the whole class to communicate.

(5) count. Show me 1 piece of paper, how many decimeters? How many decimeters ... nine? How many centimeters? How many decimeters is 10? How many centimeters? Draw out, which length unit can be used to express? (1 m) (blackboard: 1 m = 10 decimeter = 100 cm)

Work at the same table: measure the height of the table and stool in centimeters, and then say it is close to several centimeters. (You can also ask students to estimate first and then measure.)

[Note: There is a gap between the data estimated by students and the results, but the actual measurement through estimation is beneficial for students to enhance their perception of the actual length and cultivate their estimation ability. ]

Third, summary.

1. Question: What did we learn today? (decimeter)

Question: Together with what we have learned before, we already know four units of length. Can you arrange these units in a row from the largest to the smallest?

[Description: Through the observation of ruler in teaching, the relationship between meter, decimeter, centimeter and millimeter is preliminarily communicated, and further summary can enable students to form a relatively complete understanding. ]

Fourth, consolidate practice.

1. Guide to finish the workbook # 1.

Let the students fill in the exercise book first, and then organize exchanges to inspire the students to explain the reasons for their choice. When necessary, students can show their own physical objects for observation.

2. Guide the completion of the workbook Question 2.

Let the students finish it independently first, and then tell the reason.

3. Guide the completion of "think about it and do it" question 6.

Let students judge freely first, and then inspire students to verify their guesses through actual measurement.

Summary: What did you get from this lesson?