The Teaching Objectives of 8th grade Physics Volume I "Density and Social Life" published by People's Education Press.
Knowledge and skills
1. Try to solve simple problems with density knowledge. It can explain some physical phenomena related to density in life.
2. Understand the law of material density changing with temperature.
3. Understand the value of density in identifying substances.
Process and method
1. Through classroom experiments and reviewing life experience, we can understand the causes of wind formation and the abnormal expansion of water, so as to fully understand the law of object density changing with temperature.
2. By calculating the density of substances, we can understand the method of identifying substances with density knowledge.
Emotions, attitudes and values
By understanding the relationship between density knowledge and social life, we can promote the close combination of science and technology with society and make science and technology apply to and serve society.
Emphasis and difficulty in teaching
focus
Variation law of object density with temperature; A method of identifying substances by density.
difficulty
Explain the phenomena related to density in life; Density calculation.
teaching tool
Video: Windmill Kingdom? Dutch scenery lens (including the scene of windmill working); Tornado fragments.
teaching process
First, the introduction of new courses.
Play windmill kingdom? Dutch scenery and the scene of tornado, organize students to watch the windmill work scene and the harm of tornado carefully. Why can the windmill turn? How do tornadoes form?
Second, the new curriculum teaching
1. The important value of density in social life.
Students think about the use of substances with different densities in social life.
Teachers guide students to give examples.
Teacher's instruction (1) People use the wind to distinguish full seeds from dry seeds, that is, they use the knowledge of density. ② In production, people choose suitable materials according to different needs, and choose alloy materials with high strength and low density when manufacturing airplanes and spacecraft.
③ In our daily life, we make different utensils with different densities of materials.
(4) Identify the types of substances and their purity or concentration, and often use the knowledge of density.
The knowledge generalization density of teachers is closely related to people's social life.
2. Relationship between density and temperature
(1) wind formation
Students observe the tornado wall chart.
Students think about how the wind is formed.
The teacher pointed out that the air rises because the heated volume expands and the density becomes smaller. After the hot air rises, the cold air with low temperature flows from all directions to form wind. Wind energy is one of the available energy sources for human beings.
(2) Abnormal expansion of water
(3) the change of water freezing amount
Students think about what happens to the volume of water when it freezes.
The teacher suggested that the density of water is 1.0? 103 kg/m3, and the density of ice is 0.9? 103 kg/m3.
The teacher gave an example of a car with water as the coolant. In the cold winter, drain the water from the radiator to prevent the water from freezing the machine. In winter in the north, exposed water pipes should be wrapped with something, otherwise they will freeze and crack, causing damage to water supply equipment.
For example, in the cold winter, the river freezes, but the water at the bottom of the deeper river keeps a water temperature of 4℃, and fish can still swim freely in the water.
Students discuss the relationship between water density and temperature.
The teacher concluded that the density of substances is related to temperature, and most substances follow it? Thermal expansion and cold contraction? Law, some substance followed? Thermal contraction and cold expansion? Law. At 4℃, water has the smallest volume and the largest density.
3. Density and substance identification
The teacher asked two cubes with the same shape. Do you know what material they are made of?
Students answer (1). If you see them, you will know what they are made of.
(2) By measuring their density, we can judge what materials they are made of.
(3) Please ask scientists to measure with advanced instruments.
The teacher concluded that under our existing conditions, the most feasible way is to measure their density and identify which substance is made according to the density.
Guide students to read textbook examples and master the method of identifying substances by calculating density and the standard format for solving physical calculation problems.
The teacher asked, if you know the mass and volume of an object, can you judge whether it is hollow or solid?
The student's answer (1) can calculate the density of an object and compare it with the density of the substances that make up the object. If the density of an object is less than that of a substance, it is hollow; if the density of the two is equal, it is solid.
(2) It can be assumed that the object is solid, and the mass of this substance of the solid object can be calculated and compared with the mass of the object, and a conclusion can also be drawn.
(3) It can be assumed that the object is solid, and the volume of these substances with known mass can be calculated. Compared with the volume of the object, it can also be concluded that the object is hollow or solid.
The teacher concluded (1) that there are three methods to judge whether an object is hollow or solid: comparative density method, comparative volume method and comparative mass method.
(2) When calculating, you must first write the formula, then substitute the data, and then write the unit after the data, and you must have the necessary text description.
Third, the class summary
Guide the students to summarize what they have learned in this section and talk about their own gains and experiences.
Fourth, detect feedback.
1. After water with a volume of 100 cm3 solidifies into ice, the volume of ice ()
A. more than 100 cubic centimeter B. less than 100 cubic centimeter
C. It is still 100 cm3 d, which cannot be judged.
Answer a
There are several piles of rice, so we should compare the quality. Good quality? Refers to rice with fewer hollow grains and more full grains), which of the following methods is not feasible ()
A. Same volume, relative mass
B. Same mass, relative volume
C, comparing the masses of a certain number of particles
D. Comparing particle sizes
Answer d
3. Two iron balls and aluminum balls with equal mass and volume are impossible under the following circumstances ()
A. the iron ball is hollow. The aluminum ball is hollow.
C. both balls are empty.
Answer d
4. The wishful golden hoop used by the Monkey King, the great sage of Qitian in China's classic The Journey to the West, turned out to be one of the East China Seas? Fix the Poseidon needle? . What does this book say? This stick is more than 20 feet long and weighs 13 500 Jin. . Its volume is about 0.86 cubic meters in international units. (1 kg =0.5 kg)
(1) Calculate the density of Ruyi Golden Hoop; What metal is it made of?
(2) The size of this golden hoop can be changed at will. When the Monkey King used it to exorcise demons, its volume was only 1/20. At present, the densest substance on the earth is osmium, with a density of 22.5? 103 kg/m3, can you find the material to make the golden hoop on the earth at this time?
The answer (1) is that the mass of the golden hoop is m= 13 500 kg =6 750 kg.
The density of the golden hoop? ===7.85? 103 kg/m3, probably made of iron.
(2) At this time, the volume V'=V=0.043 m3, and the mass remains unchanged. What is the density of the golden hoop? === 157? 103 kg/m3 because 157? 103kg/m3 & gt22.5? 103 kg/m3, so there is no such substance on the earth.
Density and teaching objectives of social life teaching design
I. Knowledge and skills
1. Understand the relationship between density and temperature, and explain simple density problems related to social life;
2. Identify substances by density knowledge;
3. Can solve simple practical problems with density knowledge.
Second, the process and methods
1. Through experimental exploration activities, it is concluded that a certain mass of gas has higher temperature and lower density; When the temperature is low, the density becomes larger;
2. Learn to use density as an important attribute to identify substances.
Third, emotional attitudes and values
Cultivate students' rigorous scientific attitude and fully connect density knowledge with social life.
Emphasis and difficulty in teaching
1. Understand the relationship between density and temperature, and explain simple density problems related to social life;
2. Use density knowledge to identify substances.
teaching tool
courseware
teaching process
[introducing new lessons]
Situation import:
Density is the basic property of matter, and each matter has its own density. Density plays an important role in our social life. For example, knowledge of density can be used to identify whether a ring is pure gold. In field exploration, the exploration team can determine the deposit type and its economic value by collecting information such as sample density. In agricultural production, salt water can be used for seed selection. We know that these are all based on the characteristics that the density of different substances is generally different. Let's enjoy several groups of pictures (multimedia playback):
Figure 1: Ring Figure 2: Ore Figure 3: Salt Water Selection
Introduction: As can be seen from the video, the problem of seed selection is solved with the knowledge of density. Do you know what we can do with density in life?
Students think and answer.
[Promote new courses]
Teacher: From the discussion just now, we can see that the knowledge of density is closely related to people's social life, so is the density of all objects constant? Is there a relationship between density and temperature?
1. Density and temperature
Play video: tornado
Figure 4: Video screenshot-Tornado
Enlightenment: Is the formation of wind and tornado in our daily life related to the density knowledge we have learned?
The students are talking about it.
Demonstration experiment 1: Blow two balloons at room temperature. Put them near a pile of ice and the flame of an alcohol lamp.
Observe and think: After a while, what do you find? Why?
Teacher's analysis: the balloon on the ice becomes smaller and the balloon falls; The balloon placed near the flame of the alcohol lamp became bigger and the balloon rose. Experiments show that gas expands when heated. Because of density, a certain mass of gas, after its volume expands, its density decreases.
Demonstration experiment 2: Make a paper windmill according to the textbook drawing 1 1.5- 1. If the windmill is placed near the lighted alcohol lamp, it can turn.
Observe and think: Do you know what drives the windmill?
Student analysis.
Conclusion: The density of a certain mass of gas decreases due to volume expansion.
[Thinking and discussion]
1. How is the wind in life formed?
Student analysis.
Summary: The wind in life is that when air is heated, its volume expands, its density decreases and rises. After the hot air rises, the cold air with low temperature flows from all directions to form wind.
2. Is the density of gas, liquid and solid affected by temperature in daily life?
Student analysis.
Summary: Gas is greatly affected by temperature, while solid and liquid are less affected.
Teacher: It is very important to protect water pipes in winter in northern China. If the protection is not good, the water in the water pipe will freeze, which will not only affect the normal domestic water use, but also freeze the water pipe and cause damage to the water supply equipment. Then, why does the tap water pipe freeze and crack?
The students are talking about it.
Revelation: What do most things in life follow? Thermal expansion and cold contraction? Law, but there are also substances that are the same? Thermal contraction and cold expansion? .
Introduce the characteristics of water.
Guide the students to infer why water becomes bigger when it freezes.
Solve the problem: Why are water pipes easy to freeze and crack in winter?
Teaching guidance: inspire students to follow the tap water pipe? Thermal expansion and cold contraction? Law, when water freezes, obey it? Thermal contraction and cold expansion? From these two aspects, analyze and answer. )
Revelation: What is the significance of the abnormal expansion of water in winter to living things?
Students think, discuss and answer.
2. Density and substance identification
Thinking and discussion
Ask a question: how to tell if a ring is pure gold?
Guide students to think: from the density table, we can see that the density of various substances is certain, and the density of different substances is different. As long as the density of the ring is measured and compared with the density of gold in the density table, whether the ring is pure gold can be identified.
Guide students to think: how to measure the density of rings?
On the basis of the students' answers to the questions, it is concluded that after measuring the density of the ring, it is compared with the density of gold in the density table. When measuring the density of the ring, you can measure the mass with a balance, measure the volume with a measuring cylinder, and calculate the density according to the density formula.
Guide students to think: Is the ring quality measured by measuring cylinder accurate? So is the measured annual ring density accurate?
Students discuss and answer.
(Courseware display example)
Example: The gold medal of Binzhou Middle School Sports Meeting has a mass of 45.39g and a volume of 5. 1cm3. Is it pure gold? If it's not pure gold, what is it made of?
Student activities: think and solve problems independently.
Description: Educate students to use what they have learned to solve problems around them. Apply what you have learned)
Let two students calculate on the blackboard, and the other students calculate in their exercise books. After the completion, the teacher comments and pays attention to the standardization of the students' problem-solving format.
Teacher: Just like the above question, we can also use density knowledge to identify the quality of milk and wine, and identify minerals in geological exploration. In addition, we can also use density knowledge to identify whether the shot put used in physical education class is made of pure lead.
Let students learn how to identify substances by calculation. When calculating the density, if the unit is g/cm3, it can be converted into/m3, and then the type of substance can be determined according to the density table.
Summary: As can be seen from the previous density table, the density of some different substances is the same. For example, alcohol and kerosene are both liquids with a density of 0.8? 103?/m3。 By judging their odor, we can distinguish alcohol from kerosene on the basis of knowing their density. It can be seen that the important attribute of density can be used to identify substances, but many methods are often used to accurately identify substances.
(Instruction: Can teachers use it? China ancient gold and silver appraisal technology? Expand students' knowledge)