1. The density formula can be used for relevant calculation.

2. Can solve simple practical problems with density knowledge.

capability goal

1. Cultivate students' ability to solve practical problems with physical and mathematical knowledge.

2. Cultivate students' abstract thinking ability by solving problems.

Moral education goal

1. Cultivate students' standardized problem solving, careful and good behavior habits.

2. Cultivate students' good qualities of overcoming difficulties and solving difficult problems.

3. Through the study of formula deformation and standardized format of arithmetic problems, students are trained to do their homework seriously, form neat and standardized homework habits, and enjoy them with beautiful homework.

Teaching suggestion

Textbook analysis

This section mainly uses density knowledge to solve practical problems, so that students can learn to use knowledge flexibly. The textbook first puts forward three practical questions for students to think about, to stimulate their enthusiasm for learning, and to guide students to use density knowledge to solve practical problems, so that students initially feel that density knowledge is very useful and can solve many problems. Then explain the density of various substances needed to solve practical problems by using density knowledge. The density tables of some substances are given. Then, taking these three problems as clues, the ideas and methods to solve these problems by using density knowledge are expounded. Teaching materials focus on inspiring students to solve problems by themselves, rather than giving answers, helping students to think and solve problems independently and cultivate their abilities. Finally, an example is used as a demonstration to further teach students how to use knowledge flexibly to analyze and solve problems.

Teaching suggestion

In this lesson, the formula of density is deduced by analogy speed formula of positive migration, and the methods of self-study, discussion and demonstration can be adopted.

Example of instructional design

First, the focus and difficulty analysis of teaching materials

1. Cultivate students' ability to use mathematical knowledge to solve physical problems through formulas.

In physics learning, mathematical methods are often used to calculate, analyze, reason and demonstrate physical problems, but it should be noted that solving physical problems by mathematical methods must be restricted by physical concepts and laws. Analyzing the physical process and meaning of the problem, clarifying the relationship between physical quantities, and clarifying the physical meaning and application scope of the formula are the basis for using mathematical knowledge to solve physical problems. We can't mathematize physical problems, nor can we mechanically apply mathematical laws. For example, we can't think that density is directly proportional to mass and inversely proportional to volume. Therefore, in the process of solving problems, we should pay attention to understanding the physical meaning of related content.

2. Transform the formula of.

The deformation of density formula can be explained by referring to the deformation of velocity formula. Through mathematical operation rules, students can master the basic method of formula deformation, and then guide students to understand the physical meaning of each formula.

Two. Class arrangement 1 class hour

3. Preparation of teaching AIDS, projectors and slides

Four. Design of teacher-student interaction activities

1. According to the formula, guide the students to discuss and analyze and get the sum.

2. Organize students to practice reading the density table and get familiar with the reading method of a certain material density by reading the table.

3. Practice answering comprehensive questions about density.

Teaching process design of verb (abbreviation of verb)

(1). Introduce new courses

First of all, several interesting practical problems are put forward, so that students can think about solutions and arouse their enthusiasm for learning.

Such as: 1. How to tell if a ring is pure gold? How do you know what the ore might be made of? 2. How do you know the quality of a rectangular stone tablet? How to know the air quality in the classroom? 3. How to know the volume of an irregular steel part? How to know the length of a large roll of thin copper wire? And so on. Then tell the students that these problems can be solved by density knowledge, and introduce the students into the new course of applying density knowledge to solve problems.

(2). New teaching

1. It can be used to identify substances.

In order to determine what an object is made of, we need to know the density of various substances. The density of some substances is given in the textbook. Please open your books and see what's the difference between these three tables. What are their characteristics?

Read the book, and then ask the students to answer the teacher's questions. Under the guidance of the teacher, we should mainly understand the following questions about densitometer.

A. The gas density table indicates "the condition of 0℃ at standard atmospheric pressure, which requires students to explain.

B The density of mercury in liquid is higher than that of ordinary metals.

C. the density of gas is relatively small.

On the basis of reading, ask students to read the density of several substances and tell their physical meanings.

In the teaching of densitometer, it should be explained that this is obtained by scientists through strict and accurate measurement, and it is constantly accurate with the continuous improvement and improvement of measurement technology.

Seeking quality

The huge rectangular granite tablet is too big to be weighed directly with a scale. How can we know its quality? Let the students say what they think. Then lead the students to discuss whether they can use the formula of density. How come? What quantities do I need to know first How do we get these quantities?

In the previous chapters, we studied the problem of speed. Please recall the calculation formula of speed.

What if we ask about distance and time?

You can distort the formula and get

Like the deformation of the velocity formula, the density formula can also be deformed by the same mathematical method. Let the students deform the density formula and then consider the deformed formula. What's the practical significance? And give an example. Students can discuss it.

For students with poor learning foundation, we can know the method of formula deformation through simple teaching, such as the formula deformation problem that can be solved more.

Students practice formula deformation and discuss the practical significance of deformation formula. The teacher patrolled the students and gave them guidance. After the student activities, ask the students to answer the previous questions.

We can know from the density formula that the mass of an object can be obtained by multiplying its volume by its density. This makes it inconvenient to measure the mass of some huge objects. We can measure its volume, find its density from the density table, and finally calculate its mass.

In other words, quality can be obtained through density knowledge.

Find the volume

The density formula can also be transformed into: if the mass and density of an object are known, the volume can be obtained. For example, some objects and volumes are irregular, so it is not convenient to measure them directly. We can measure their mass, find out their density from the density table, and finally calculate their volume.

4. Explain examples

Example: There is a steel ball with a volume of 3 16g. Is this copper ball hollow or solid?

Please use three methods to identify.

Students practice, teachers patrol students and give guidance. After the students practice, the teacher asks the students to answer and analyze the problem-solving ideas.

Please tell several students your own judgment methods.

We can find the density of this ball and compare it with that of copper. If it is equal, it is solid, but our calculation result is less than the density of copper, so it is hollow.

We assume it is solid, calculate its mass, and compare the calculated value with the actual mass of the ball. The result is greater than the actual mass of the ball, so the original ball is hollow.

According to the mass of a given copper ball, the volume is calculated, and the result is smaller than the known ball, so it is hollow.

So whose volume is the volume value we calculate?

Is the volume of the spherical shell.

According to students' analysis, there are three methods to judge whether the ball is hollow or solid: density comparison method, mass comparison method and volume comparison method.

Use projection to type the following standard problem-solving process. The teacher explained the problems found in the inspection and asked the students to correct them.

Known:

Find out whether the ball is hollow or solid.

Solution 1: density comparison method

This ball is hollow.

Solution 2: Quality comparison method

The copper ball is hollow.

Solution 3: Volume comparison method

The copper ball is hollow.

Please calculate the volume of the hollow part.

The volume of the hollow part is equal to the volume of the ball minus the volume of the shell.

As can be seen from the previous calculation, the density of this copper ball is exactly the same as that of iron. This tells us two questions.

One is the average density. What we have just calculated is actually the average density of this ball. If an object consists of more than two substances, the density of the object should be

The second is to identify substances by density. If we calculate that the density of an object is the same as that of the substance in the density table, we can only say that it may be this substance. If you don't know that it is a copper ball in the above example, the density value calculated by analysis will be mistaken for an iron ball. And as can be seen from the density table, the density of granite is between. If the density of a granite happens to be, can we say it is aluminum? Obviously not. Therefore, other characteristics of substances, such as color and hardness, are often used to identify substances by density. A more scientific method to identify substances should be chemical analysis or spectral analysis to identify chemical elements that make up substances.

3. Summary and expansion

The teaching of this lesson is actually to apply the density formula and its deformation formula to study and solve the problems of object mass, volume and density. In practical application, students should be reminded not to memorize the formula, but to understand the relationship between the three physical quantities in the formula and use it flexibly, especially the proportion problem (the following contents can be discussed while talking)

(1) The relationship between the mass and volume of two objects composed of the same substance (both objects should be solid).

Because the density of two objects A and B composed of the same substance is the same, it is concluded that the mass of two objects A and B composed of the same substance is also proportional to their volume, and the mass of the larger object is also large.

(2) The relationship between the volume and density of two objects A and B composed of different substances, if the mass is the same.

Because, that is to say, different objects with the same mass have high density and small volume, and the volume and density are inversely proportional.

(3) The relationship between the mass and density of two objects A and B with the same volume.

Because, that is, it tells us that different objects with the same volume have higher mass, and the mass is directly proportional to the density.

Investigation activities

Topic recognition shot put

Organizational form student activity group

Activity flow

Ask questions; Conjectures and assumptions; Make plans and design experiments; Conduct experiments and collect evidence; Analysis and demonstration; Evaluation; Exchange and cooperation.

The reference scheme uses density knowledge to identify whether the shot put used in physical education class is pure lead.

comment

1. Write a report on the investigation process.

2. Discover new problems.