1. Understand the meaning of decimeter, centimeter and millimeter, and establish the corresponding concept of length.

2. Remember the forward speed between these units.

3. The length of some shorter objects can be estimated.

4. Measure the length of shorter objects.

Emphasis and difficulty of (engineering) teaching

1. Teaching emphasis: Understand the practical significance of 1 decimeter, 1 cm and 1 mm.

2. Difficulties in teaching: establish specific concepts of decimeter, centimeter and millimeter.

(3) Teaching preparation

1. Preparation of teaching AIDS: physical projector, meter ruler, transparent plastic ruler, one penny and two pencils.

2. School tools preparation: each student has a ruler, a penny, a thread and a long nail.

teaching process

1. Build a bridge.

(1) Children, if you want to know how tall a person is, how long the blackboard is and how wide the math book is, what methods can you use? (measured with a ruler)

(2) How did you come up with the idea of measuring with a ruler? (There are scales on the ruler)

(3) Show me the meter ruler: How long is the child's gesture about one meter?

(4) Estimation: How long is the blackboard? The teacher measured that the blackboard was more than 3 meters long.

The extra part is less than 1 meter. how much is it? We need help for units smaller than meters.

2. Practical operation.

(1) Know the centimeter.

① Put a plastic ruler on the physical projector and let the students observe that the length from the "0" scale line to the scale line marked "1" is 1 cm. (blackboard writing: cm cm)

② Students find the length of 1 cm (finger width, rubber thickness, maximum width of 1 cent coin ...) on their own ruler and measure it with a ruler.

③ Measurement: How long is the nail? (3 cm)

(4) Show me two pencils, one is 10 cm, and the other is 1 cm or more. It is estimated that these two pencils are about several centimeters long.

(2) Know decimeter.

① This pencil is 10 cm long, or it can be called 1 decimeter long (blackboard writing: decimeter dm), so 1 decimeter = () cm.

(2) As above, students look for the length of 1 decimeter on the ruler, and find the articles with the surrounding length (width) of about 1 decimeter, which can be actually measured. (Between the two buttons of the shirt, the palm is wide ...)

③ Count on the instrument scale. How many decimetres is 1 meter? That is a few 10 cm. 1 decimeter = 10/0cm, then 1 m = () cm.

④ Think about it: How long is 1 meter, 1 decimeter and 1 cm?

Game: Bo; When you say I'm gesturing, it means 1 the person at the same table says 1 meter (or 1 decimeter, 1 cm), and the other person gestures immediately.

(3) Know millimeters.

There is also a pencil that is more than 1 cm. How long is it? We need to know the smaller unit of length-millimeter (blackboard writing: millimeter one)

② 1mm is difficult to draw by hand, so let's use pencil lead.

(3) It's hard to find items with the length of 1mm, right? (1 cent thickness of coin, thickness of math exercise book ...)

(4) Guess, and then count -() mm = 1 cm on the ruler.

3. Inductive application.

What unit did we learn today? (Length unit) (Completed project)

Can you arrange these units from big to small?

Do you know the relationship between them? (Forward speed)

(2) See what the textbook says. (Textbook page 85-86)

(3) Exercise: Page 87 of the textbook "Exercise" 1, 2,3. (Observe first, estimate the length of each item, and then measure)

(4) Exercise: "Exercise" on page 87 of textbooks 4, 5 and 6. (Six of them are deskmate cooperation questions)

(5) Take out the thread, how long is the cooperation at the same table? (1 m2, 4cm, 6mm)