Please look at the screen and read this message on the screen. According to the statistics of relevant departments, due to the serious water leakage in urban water supply network in China, the annual tap water loss reaches 654.38+000 billion tons. What do you know from this message? How many 1 0 billion is it? Who knows how big a hundred million is? (10,000,000,10,000,000 ...) 100 million is a big number. How big is it? We can use familiar things around us to study and feel its size. (blackboard writing: how big is 100 million)

Task:

Teaching objectives:

1, through estimation, experiment, calculation, communication and other activities, let students experience the size of 100 million in specific situations, cultivate students' sense of numbers, and let students feel the close connection between mathematics and life;

2. Get some problem-solving strategies and methods to improve students' problem-solving ability;

3. Let students have a successful experience and receive the ideological education of thrift and environmental protection.

Teaching emphasis: let students feel the size of 100 million from different angles, and can express their feelings about 100 million with concrete things in combination with reality.

Teaching difficulties: cultivate students' strategies and methods to solve problems and improve their ability to solve problems.

Teaching aid preparation: students prepare: calculator, homework paper and math book;

Teacher prepares: rice (100 grains, 5 copies), 1 kg rice, balance, tape measure, the third chart, the following formula and courseware.

Process:

First, create problem situations to stimulate interest in learning.

Second, guide students to experience the process of estimation-verification, and experience how big 100 million is over time.

Teacher: This is an exercise book. The number of teachers 1, 2, 3, 4, 5, 6, 7, 8 ... At this rate, hundreds of millions of exercise books. How long do you think it will take? (Students estimate 3 hours, 5 hours, 24 hours ... and the teacher writes it on the blackboard.)

Teacher: What did the students estimate? We can verify it through experiments.

Discussion: How can we have time to make hundreds of millions of exercise books? Group discussion. (Count the time 100, 50, 20 ... exercise books, and then count the time of hundreds of millions of exercise books)

Experiment: each group chooses a representative to count 50 books, and the teacher records the time. It takes about 40 ~ 50 seconds to count 50 exercise books, about 80 seconds to count 100 student exercise books, and about 90 seconds to choose a median from them.

Teacher: Let's calculate the time needed for hundreds of millions of exercise books. (The courseware is shown in the following table)

figure

100

1000

10000

100000

1000000

10000000

100000000

Time (seconds)

90

Teachers and students discuss with each other and complete the above table.

Teacher: Through calculation, we know that the time of hundreds of millions of exercise books is 90 million seconds. Is this time long? It is obviously inappropriate to express such a long time in seconds. What kind of time unit do you think should be adopted? How to convert 90 million seconds into how many years? (First convert seconds into components, then hours, and finally into adults) Show me the formula in the book:

() 60 = () points

() ÷60= ()

() 24≈24 days

() 365 ≈ () years (learn to calculate and keep integers. )

Teacher: What do you think after reading this result? (student exchange)

Summary: hundreds of millions of exercise books, some students estimate that it needs ... some students estimate that it needs ..., but the actual result will take nearly three years. In the past three years, have we removed the time for eating and sleeping, that is to say, not eating, drinking or sleeping is three years. Students, how do you feel after watching it for so long? (100 million is too big, and hundreds of millions of homework books take too long ...)

Third, go through the process of estimation and verification again, and experience the size of 100 million with the help of length.

Teacher: Teachers often find that students like to play hand in hand during recess. Have you ever wondered how long it would be if 100 million children stood in a line hand in hand? Give students some time to think, or you don't have to answer.

Teacher: It's hard to imagine out of thin air. Students, you have all gone to the wrong place. The road from school to the main road is not long. The teacher told you that the total length of this road is about 1km. Think about it, is the length of 100 million children holding hands as long as the road from school to the end of the road? Estimate, how long is this? (Students estimate 2, 4, 3 thousand ... Teachers write on the blackboard)

Group discussion: How can we get the length of 100 million children holding hands?

(Measure the length of five children holding hands, 10 children, 100 children holding hands, and calculate the length of 100 million children holding hands. )

Teacher: Let's do an experiment together and measure the length of 10 children holding hands. The leader of each group will come up and take charge of the measurement in groups of three. Pay attention to the correct method. Other students stood hand in hand in the corridor, standing quickly and quietly. (The experiment collects data. Pay attention to the measurement from the first classmate's fingertip to the 10 classmate's fingertip in the experiment, and calculate the length of ten children holding hands, which is about 12m. )

Teacher: Just now, we measured 10. The length of children holding hands is about 12 meters. The following can be calculated. (Show the form, and calculate it jointly by teachers and students)

number of people

10

100

1000

10000

100000

……

100000000

Length (m)

12

120

Calculate again, how many roads are there from the school to Yangchatou?

Show the formula. Students use a calculator to calculate:12000000 ÷1000 =120000 (pieces).

Looking back, comparing the data estimated by students with the actual data, I once again feel the scale of 100 million.

Fourth, summarize the methods and guide the learning methods.

Teacher: Students, how did we know that 100 million is a big number just now? By counting and measuring, we first estimate and then calculate, and finally compare, we will know how big 100 million is. )

Teacher: Will you experience the size of 100 million again in this way?

Fifth, expand the method of learning large numbers, so that students can experience the size of 100 million by weight.

Teacher: Look at your desktop and see what research we can use to understand and feel the size of 100 million. (Weigh 100 grains of rice with a balance, and calculate the weight of 1 100 million grains of rice)

Students talk about how to do experiments with the methods learned above.

Group experiment: Students weigh 100 grains of rice, about 2.5 grams ... The team calculated the weight of 1 100 million grains of rice together and compared it with the previous estimated value in kilograms to further feel the size of 1 100 million grains of rice.

The courseware shows that (1) China has a population of1300 million. If everyone saves 1 grain of rice every day, how many grams of grain can China save every day?

(2) If everyone eats 400 grams of rice every day, how many days can one person eat the saved rice? About how many years?

The students answered one by one.

Question: What do you want to say after reading these two calculation results? To guide students, we should not only talk about the scale of 100 million yuan, but also talk about saving food and educating students ideologically. )

Sixth, class summary

Students, what did we learn together in this class today? How do we know how big 1 100 million is? What did you get? In fact, there are many things in life that can help us understand the size of 100 million. After class, I hope every student will be conscientious and pay attention to observation and thinking.

Blackboard writing:

How big is 100 million

Estimation and calculation

Hundreds of millions of exercise books (? 、? 、? ) hours and 3 years

Measurement 1 100 million children

The length of hand in hand (? 、? 、? ) 120000

Weight 1 100 million grains of rice (? 、? 、? ) 2500 kg

Teaching reflection:

1 and "100 million" are very large numbers, so it is difficult to understand students out of thin air. This lesson uses the methods of counting, measuring and weighing to experience and feel the size of "100 million" with familiar life examples, so as to cultivate students' sense of number and truly understand the size of "100 million".

2. This lesson embodies the purpose that mathematics comes from and serves life, educating students to look at everything in life from a mathematical perspective and educate students ideologically;

3. In classroom teaching, we pay attention to using modern information technology to guide students to use calculators to calculate, which breaks through the traditional teaching methods; In this class, students are always the main body of learning, and teachers are the organizers, guides and collaborators of students' learning activities, so that mathematics education is oriented to all students.