When talking about the meaning of ratio, traditional arithmetic textbooks only emphasize one case of ratio, that is, the multiple relationship between two similar quantities. But in practical application, another case of ratio is often used, such as the ratio of distance to time (speed), the ratio of mass to volume (density) and so on. Therefore, the current primary school mathematics textbooks not only talk about the ratio of the same kind of quantity, but also talk about the ratio of different kinds of quantity. Of course, compared with different kinds of quantities, it is only relevant. This is convenient for primary school students to understand the proportion of different categories that often appear in physics and other disciplines after entering middle school.

When it comes to the application of comparison, the biggest feeling is that it is scattered, discontinuous and not smooth. Proportion in measurement, proportion in human body, proportion in diet. The three pieces of content are independent of each other and have no close connection. These scattered pearls should be strung into a beautiful necklace. Carefully consider each link and design a teaching link.

Excerpts from the teaching process:

First, introduce new lessons from the application of life.

Please recall the following, where have you used comparison in your life?

Teacher: In fact, Bibi is widely used in life. In today's class, let's use Bibi's knowledge to solve problems in life (blackboard writing). Let's take a look at our campus life first.

Second, using ratio knowledge to solve practical problems

(a) ratio in measurement

1. Create a situation

Teacher: This is our beautiful school. (Show the picture) (Show the picture at the school gate) This is our school gate. There is a big tree at the school gate. If you want to measure the height of this big tree, do you have any ideas?

According to the students' answers, use the students' resources in time.

Teacher: Actually, the height of the object is related to the length of the shadow. Today, we will use shadows to measure the height of a big tree. What is the relationship between the height of an object and the length of a shadow? Let's do an experiment first to find the law.

2. Study the relationship between the length and shadow of bamboo poles with different heights.

3. Guide students to sum up the rules

4. Initially apply the law to solve the problem.

5. Use the law to solve problems.

(2) the proportion in human body.

Teacher: Bi is widely used. It exists not only in our campus life, but also in the human body we are familiar with (some students have talked about it before). Let's study Bi in human body together.

1. Students know their body shape.

Teacher: Actually, being overweight and thin is bad for your health. Overweight and thin students should strengthen exercise and pay attention to diet.

2. Interesting proportion in human body

(3) Proportion in diet

Quote: Just now, we learned about our body shape. We know that to keep a normal body shape, we should pay attention to exercise and diet. In fact, there are also proportional applications in diet.

1. The application of cooking proportion.

Quote: Fangfang cooked the meal and started washing vegetables and cooking. I found that the washing liquid for washing vegetables was used up, so I need to prepare some Amway washing liquid. Have you ever seen Amway wash bottles? The students I have seen introduce us.

2. The application of ratio in vegetable washing.

Fangfang wants to prepare 500 ml of vegetable washing liquid. How many milliliters of water should he use and how many milliliters of stock solution should he use?

When students can't solve it, show them: explain.

If there is only 50 ml of stock solution, how much ml of water should he add?

Students calculate the report and complete the form.

Observation: No matter how many milliliters of washing liquid are mixed, what can you find that has not changed?