1, do you know the actual length units of decimeter and millimeter? Creates a representation of decimeter and millimeter lengths.

2. Through actual measurement? Learn to choose the right length unit? Know the forward speed between length units? And improve the estimation ability.

3. Learning activities through hands-on operation and cooperative communication? Raise awareness of participating in learning? Experience the fun of learning. What are the difficulties in teaching? Gradually establish a clearer representation of decimeter and millimeter in practice? Simple unit conversion and accurate expression of some line segments and object lengths.

Teaching preparation? 1, courseware, ruler? 2. Student preparation? Colored paper, 1 cent coin, telephone card or bank card.

Teaching process?

First, import

Teacher? Let the students measure some objects about 10 cm by themselves? I feel that the length of many objects in life is 10 cm. How long is 10 cm? Draw it by hand.

Second, explore practice.

One? Know decimeter

1, measure a quantity

Teacher? Would you please measure the length of your pencil box with a ruler?

Teacher? Generally speaking? The pencil-box is about 20 cm long? The width is about 10 cm. ? Write on the blackboard while talking? 10 cm？

Teacher shows 10 cm color bar? We can also use another unit to express the length of the line segment of 10 cm, like this-decimeter? Blackboard writing project? Decimeter? 1 0cm is1decimeter? Write it on the blackboard after "10 cm"? Is it 1 decimeter? So, how much is 20 centimeters?

Students study together? 1 0cm is1decimeter.

2. I recognize it

1? Teacher? Would you please take out your ruler? See how long 1 decimeter is. 1 decimeter where can I go? Please point it out on the physical projection. That is to say, 1 decimeter is equivalent to how many centimeters of blackboard writing? 1 decimeter = 10/0cm? Students read together.

Ask? How many 1 decimeter are there on your ruler? how do you know

2? Experience?

Would you please extend your thumb and forefinger? Draw 1 decimeter with a ruler. What we are doing now is the length of an oak tree? An tussah is about 1 decimeter. Show it to your deskmate.

② One person rowed 1 decimeter? Did the other person measure it with a ruler? Let's see if the estimate is correct.

(3) take out colored paper? Estimated length 1 decimeter? 1 decimeter for discount? Test together? Let's see who has the best estimate.

Step 3 draw a picture

1? Teacher? Can you draw a line segment of 1 decimeter with a ruler? How are you going to draw it? Why don't you talk to your deskmate first? Then draw it on paper.

2? Communication? How did you draw it? Ask the students to report the physical projection.

3? Did the teacher say and draw? 1 decimeter can be drawn from scale 0 to 10? Can we start with 1 Where should this be painted? 1 1? Why? What if we start with 2? What about starting at 3?

Teacher? Just draw 10 squares? Is 10 cm? Yes 1 decimeter.

4? Would you please measure your deskmate? See if the drawn line segment is 1 decimeter.

Step 4 look for it

Four people tell each other which objects are about 1 decimeter long.

The whole class communicates.

Step 5 count

Teacher, show me the meter ruler? Who will count? How many centimeters is 1 meter? How do you calculate it? What happened, blackboard writing? 1 m = 10 decimeter? Students read together.

6. actual operation? "Thinking and Action" Question 4

Show courseware? Working with your deskmate? How many centimeters are the desks and stools? Besides, it is close to a few cents.

Let's visually observe it for a few minutes. Measure again.

Two? Cognitive millimeter

1, division? Have we measured the long and short sides of math books before? Now the teacher wants to ask you a favor? Measure the thickness of the math book.

Through measurement, we know that the thickness of the math book is less than 1 cm? If you want to know the exact thickness of a math book, you must measure it in units less than centimeters. Today, let's know a unit of length less than cm-mm? And write it on the blackboard? What about millimeters?

2. Group study

1? Teacher? When learning millimeters? The teacher wants the children to discover the knowledge about millimeters by themselves.

Show the learning steps?

① The length of each cell in the middle of 1 cm on the ruler is 1 mm? Please find it on the ruler.

(2) Point to the small square on the ruler with a pen tip and count? How many millimeters is 1 cm?

③ What objects around us are about 1mm in length or thickness? Please measure it.

2? Students study in groups of four.

3? Report? Do you think it's weird?

Summary? ① The length of 1 unit on the scale is1mm..

② How many millimeters is1cm? how do you know So 1 cm is equal to how many millimeters of board?

Books? 1 cm = 10 mm？ Students read together.

③ ? Show the real thing and measure it? 1 indicates the thickness of coins, the thickness of telephone cards or bank cards, and 10 is included in the book.

The thickness of each piece of paper is about1mm.

Ask? Is there anyone else?

3. organization? Now, please compare the length of 1mm with your finger. ? Teacher demonstration?

Deskmate gesture? Put a penny in and measure it, right?

4、 ? Show courseware? Do you know what can measure the length or thickness in millimeters? Ask the students to say.

Teacher? For example, measure rainfall and the length of small ants. ? The teacher's proper explanation?

Third, summary.

1，Q？ What did we learn about decimeters and millimeters today?

Teacher? Plus the rice and centimeters I learned earlier? We already know four units of length? What's the difference from big to small? Meters, decimeters, centimeters, millimeters. Today, we also know some relationships between these units. ? Students study together? 1 m = 10 decimeter 1 decimeter =10 cm1cm =10 mm?

2. organization? So now let's take a look at the question raised by Hong Hong. If the gold hoop is shorter than 1 cm, what unit of millimeter should be used? Is it shorter than 1 m but longer than 1 cm? The length exceeding 1 m can also be measured in decimeters.

[comment? Contact the imported story for review? Echo before and after. ]

Fourth, consolidate practice.

1, the second question of "think about it and do it"

Do deskmates talk about length with each other? Speak your mind. Answer by roll call.

2. Question 3 of "Think about it and do it"

Group discussion and communication? Then please report to the 1-2 group.

3. Question "Think about it and do it" 5

Student answer? Tell me what you think.

4. "Thinking and Action" Question 6

1? Student judgment? Collective feedback.

2? Students measure with a ruler.

5. Measure how wide your thumb is.