First unit negative number
first kind
Teaching objectives:
1. Make students know negative numbers in real situations, understand their functions, and feel the necessity and convenience of using negative numbers.
2. Let students know the reading and writing of positive and negative numbers, and know that 0 is neither positive nor negative. Positive numbers are all greater than 0, and negative numbers are all less than 0.
3. Make students experience the close relationship between mathematics and life, stimulate students' interest in learning mathematics, and cultivate students' ability to apply mathematics.
Teaching emphasis: the initial understanding of positive and negative numbers and reading and writing methods.
Teaching difficulty: Understanding 0 is neither positive nor negative.
Prepare teaching tools:
Multimedia courseware, thermometer, exercise paper, cards, etc.
Teaching process:
First, the game lead-in (feel the opposite phenomenon in life)
1. Game: Let's play a game to relax. This game is called "I am against me, I am against me, I am against myself". Rules of the game: If the teacher says something, please say something with the opposite meaning.
① Look up (look down); ② Go ahead 200 meters (walk back 200 meters); ③ The elevator goes up15th floor (down15th floor).
Let's take a more difficult test to see who has the fastest response.
I deposited 500 yuan (took out 500 yuan) in the bank. (2) knowledge contest, class five (1)20 points (20 points deducted).
(3) 10, the school canteen earned 500 yuan. (Thanks to 500 yuan). ④ Above zero 10 diopter (below zero 10 diopter).
3. Dialogue: A friend of Mr. Zhou likes traveling. 1In late October, he plans to take a walk in several tourist cities. As for me, I will help him pay attention to the lowest temperature in these places in the future so as to prepare clothes before going out. Please watch the weather forecast with me. (Weather forecast title)
Second, the teaching example 1
1, know the thermometer, and understand that positive and negative numbers are used to represent temperatures above zero and below zero.
Courseware shows the map: Click Nanjing to show the thermometer and pictures in Nanjing. First, let's look at the temperature in Nanjing.
This is a thermometer. Let's take a look at the thermometer first. Please observe carefully: how many degrees of refraction does such a small cell represent? What about the five squares? 10?
Now can you see how Nanjing was filmed? (It's 0℃ now. ) How do you know that? There is a 0, which means 0 degrees.
(2) Shanghai temperature: What is the lowest temperature in Shanghai? What are you thinking when you dial (the dial on the thermometer)? (Four squares above zero scale)
It is pointed out that the temperature in Shanghai is above 0℃, which is 4 degrees above zero. The teacher combined with the courseware to highlight that the temperature in Shanghai is above the zero scale line.
(3) Know the lowest temperature in Beijing: What's the temperature in Beijing? What about the 0℃ ratio with Nanjing? (Nanjing is below 0℃) Can you use a gesture to express its relationship with 0℃? Yes, the temperature in Beijing is below 0 degrees, which is 4 degrees below zero. Can you dial it on the thermometer?
(4) Comparison: Now we know the lowest temperatures in these three places. Observe the lowest temperatures in Shanghai and Beijing carefully. Are they the same? (No, one is above 0℃ and the other is below 0℃).
The temperature in Shanghai is above 0℃, which is 4 degrees above zero. We can record it as +4℃ and read it as+4 degrees. When writing, write a plus sign first (pointing out that it is a plus sign, not a plus sign, so the meaning and pronunciation are different) and then write a 4 (blackboard writing). Make a gesture with me. +4 can also be written directly as 4, omitting the plus sign. So when students say 4℃, it is +4℃. (blackboard writing)
The temperature in Beijing is below 0℃, minus 4 degrees. We can use -4℃ to represent MINUS 4 degrees (blackboard -4). Read with the teacher. When writing, you can write a minus sign first (which means minus sign, not minus sign) and then a 4. Please signal at the same table.
(5) Summary: Through the understanding of the temperature in the three cities just now, we know that when recording the temperature, we can use the number +4 or 4 to represent the temperature above zero, and the number -4 to represent the temperature below zero.
2. Try it: Students look at the thermometer, write down the temperatures in different places and read them out. (written on the card)
Listen to the weather forecast of CCTV and record the lowest and highest temperatures you hear in this city.
4. Summary: Through the study just now, we have come to a conclusion that the temperature above zero is represented by a positive number or a few directly, and the temperature below zero is represented by a negative number.
Third, learn the elevation expression method of Mount Everest and Turpan Basin (P4 Question 2)
1, students, do you know? Mount Everest, the highest peak in the world, has a great temperature difference from the foot of the mountain to the top of the mountain, which is related to the altitude. Recently, the State Bureau of Surveying and Mapping announced the latest elevation of Mount Everest. The teacher brought relevant web pages. Courseware appears on the web page with a simple text introduction. Who will read this introduction?
Today, the teacher also brought an elevation map of Mount Everest. Please have a look. This courseware dynamically demonstrates the elevation map of Mount Everest. What do you understand from the picture?
3. Let's take a look at the elevation map of Turpan Basin in Xinjiang. (Dynamically demonstrate the elevation of Turpan Basin).
What can you read from the picture? (Guide the students to communicate and answer that Mount Everest is 8844.43 meters above sea level; Turpan basin elevation 155 meters).
4. Mount Qomolangma is higher than sea level, and Turpan Basin is lower than sea level. Think again: can you record the altitude of these two places in a simple way?
(1) Communication: The elevation of Mount Everest can be recorded as +8844.43 meters or 8844.43 meters.
The elevation of Turpan basin can be recorded as-155 meters. (blackboard writing)
(2) Summary: With the sea level as the boundary, figures such as +8844.43m or 8844.43m can indicate the altitude, and figures such as-155m can indicate the altitude below the altitude.
Fourth, discuss in groups and summarize the positive and negative numbers.
1, through the study just now, we collected some data (courseware display). We can use these numbers to represent temperatures above zero and below zero, as well as altitudes above sea level and altitudes below sea level. Then look at these numbers. Are they the same? Do you want to help them classify?
2. Students exchange and discuss.
3. It is pointed out that because +8844.43 can also be written as 8844.43 meters, both the plus sign and the minus sign can be classified into one category. Ask a question: What kind does 0 belong to? (Guide students to debate and express their opinions)
If everyone agrees to be divided into three categories, the teacher can ask a question: I think 0 can be divided into four categories. How can you convince me?
(2) If students publish in three categories and some publish in two categories, they can be guided to argue with each other.
4. Summary: (Combined with the figure) We observed from the thermometer that 0℃ is the dividing line, the temperature above 0℃ is represented by a positive number, and the temperature below 0℃ is represented by a negative number. Similarly, taking the sea level as the boundary, we use positive numbers to indicate the height above sea level and negative numbers to indicate the height below sea level. 0 is like a dividing line, separating positive numbers from negative numbers. It belongs to no one. But for both positive and negative numbers, it is essential. We call numbers like+4,4 and +8844.43 positive numbers; Numbers like -4,-155 are called negative numbers; And 0 is neither positive nor negative. (blackboard writing) Positive numbers are all greater than 0, and negative numbers are all less than 0. In this lesson, we will know positive numbers and negative numbers with you. (blackboard writing: knowing positive numbers and negative numbers)
V. Connecting with life and consolidating practice
1. Exercise 1, questions 2 and 3
2. You know the temperature when water boils is _ _ _ _. The temperature when water freezes is _ _ _ _. The lowest temperature on the earth's surface is.
3. Discuss the positive and negative numbers in life
(1) passbook: What does -800 mean here? (On the basis of the original money, 800 yuan took it out as-800; Deposit in 1200 yuan as 1200 yuan or+1200 yuan).
(2) Elevator: What do 1 and-1 mean here? (bounded by the ground floor, we use 1 or+1 above the ground floor and-1 below the ground floor). What number should the teacher press to go to the 33rd floor now? Go to the third basement?
Sixth, the class summary
In this lesson, we know positive numbers and negative numbers together. In our life, above and below zero emittance, above and below sea level, score and loss have opposite meanings, and we can all use positive and negative numbers to express them.
Second lesson
Teaching content: Compare the size of positive and negative numbers.
academic goal