Teaching objectives:

1. By measuring the length of the pencil, we can know how long 1 decimeter and 1 millimeter are, and develop the concept of space and hands-on operation ability.

2. Understand the relationship among meter, decimeter, centimeter and millimeter through observation and measurement.

3. Cultivate students' estimation ability through activities such as "estimation" and "measurement".

Teaching emphases and difficulties:

The key point is to establish the concepts of 1 decimeter and 1 mm and understand the relationship between length units.

The difficulty lies in the formation process of the concepts of millimeter and decimeter and their flexible application in actual measurement.

Teaching aid preparation:

Ruler pencil, the teacher hid a pencil 10 cm long in each classmate's drawer in advance.

Teaching process:

I. Review

What units of length have we learned? (m, cm)

Let's say the ballads together: when talking, we should compare meters with meters, so the length is about 1 meter, cm and cm, so the length is about 1 cm, and 1 meter is equal to 100 cm.

Second, the riddle wonderful tutorial

"Wearing flowery clothes, thin and long. If you write well, you need its help. " Students use their small brains and guess quickly. who is it?

Division; Pencil is everyone's good friend, and there is a lot of math knowledge hidden in the length of pencil! Today, let's compare who has discovered the most knowledge.

Third, create problem situations.

1, estimated.

Let's estimate first, how long is the pencil in the teacher's hand? The blackboard says: How long is the pencil?

How long is this pencil? (Quickly find your pencil friend in the drawer), make an estimate.

How do you estimate it? Tell your deskmate the result and method of your estimation. Health report.

Step 2 measure it

Is the student's estimate close to the actual length of the pencil? Take out a ruler and measure it quickly.

Fourth, learn new knowledge.

Activity 1: Understanding decimeter

1, revealing decimeter

The decimeter is a new unit of length, and 1 decimeter is equal to 10 cm long. Blackboard: 1 decimeter = 10/0cm

2. Perceived length 1 decimeter

(1) found it.

Can you find the length of 1 decimeter from the ruler? Show it to the students in your group. Who wants to say what scale you are looking for? The length is 1 decimeter.

(2) Measure a quantity.

Please measure the length from the tip of the middle finger to the palm of your hand. Which position is 1 decimeter? Show it to the students in the group.

Look, we have a small ruler 1 decimeter in our hands. We can use it to help estimate the length.

3. The relationship between decimeter and meter

Show me the meter scale: Can you find out from where to where the length is 1 decimeter on this meter scale? How many 1 decimeter are there on this ruler?

Health: There is 10 decimeter on this ruler.

Teacher's blackboard writing: 1 m = 10 decimeter

Step 4 feel a few decimetres

What is the length from 0 to 20? How long is the 2 decimeters in your hand? Which objects around us are about 2 decimetres long?

Student: pencil case, 20 cm long ruler, ruler.

5. Observe what objects around you or around you can be measured in decimeters. How many decimetres is it?

Activity 2: Know Millimeter

1. Measure: Measure your pencil with a ruler. (Not a whole centimeter)

Step 2 recognize it.

Please take out your ruler and observe it carefully. Did you find anything new?

Group students cooperate, communicate and explore.

Report: In addition to centimeter scale marks, there are many small scale marks on the ruler. These small scales divide centimeters into many small squares on average.

Teacher: The students watched carefully. The length of each cell between centimeters on the ruler is 1 mm.

Show me an enlarged view of the ruler:

Teacher: If you count carefully, what secrets can you find about millimeters?

Health: 1 cm has 10 cells, 1 mm has 10 cells. ..

Teacher: Then we can say1cm =10 mm. Blackboard: 1cm = 10mm

Teacher: Did everyone see it? Is there a long tick in the middle of other 1 cm?

Student: Yes, I also found that there are five small squares in front of the long scale line and five small squares behind it.

Teacher: Your discovery is very meaningful! Can we use this discovery to read the length faster?

3. Perceived length1mm.

(1) (Take out 1 min) What is the thickness of this coin? Measure it again.

Teacher: The thickness of shopping cards and telephone cards in life is also about1mm.

(2) Teacher's demonstration: Hold the coin gently with your forefinger and thumb, and slowly pull it out with your other hand to see how long 1mm is left between your fingers. you have

How do you feel?

Teacher: 1mm is relatively short, so you can't notice it without being careful, so you must be careful in measuring and drawing line segments!

4. Estimate an estimate

Looking around, which objects can be measured in millimeters in length or thickness? How many millimeters is it?

Solve the problem: Can you measure the length of the pencil more accurately now? Take a quick measurement and write down the measurement results. Then exchange measurements at the same table to check whether it is accurate.

Five, finishing

How many units of friends have we had? Can you line them up? And say why?

Practice (children learn so fast, now let the teacher test you, too)

1. Choose the correct unit to fill in the blanks.

The thickness of the shopping card is about 1 (), and the height is a little higher than 1 ().

A pencil is about 10 () or 1 ().

2. Simple conversion.

7m = ( )dm 3dm = ( )cm 500cm =( )m

40mm = () cm

Seven. Course summary

Tell me what you have learned from this course. Do you have any questions?

Attached book:

How long is this pencil?

Decimeter decimeter millimeter millimeter

1m = 100cm 1m = 100cm

1m = 10 decimeter 1m = 10 decimeter.

1 decimeter = 1 0cm1decimeter =10cm

1 cm = 1 0mm1cm =10mm