Educational:
- to deepen the students' understanding of the force of friction, to reveal its nature, to show what types of friction are;
- with the help of an experiment, establish what the friction force depends on, establish a mathematical relationship between the friction force and the reaction force of the support;
- instill a culture of physical speech, the ability to build a graph based on experimental data, the ability to work with a device (dynamometer), take readings from the device, analyze and compare.
Developing:
- development of speech, logical thinking, ability to work, the ability to apply the knowledge gained in a non-standard situation, creativity, interest in the history of physics.
Educational:
- ability to work in a group;
- the ability to achieve a set goal on the example of biographies of scientists.
Method: problematic, research, reproductive.
Interdisciplinary communications: mathematics, literature, physics of the 7th grade.
Instruments: a wooden block, a wooden ruler, a dynamometer, a set of weights, glass, rubber.
Cabinet decoration.
Statement and brief biography of scientists at the stand. Annex 1.
"Knowledge, not born of experience, the mother of all certainty, is fruitless and full of mistakes."
Leonardo da Vinci
During the classes
1. Statement of the problem
“When I was a schoolboy, my friends and I took three bars of soap out of the house and rubbed them on the rails on the rise. That job took us three hours. But then we hid in the bushes and watched how the loaded train tried to climb the hill for half an hour, but all the time it rolled down. I returned home with a happy man, with a sense of a job well done. But at home my father was already waiting for me with a belt, I did not have time to ask what I would receive. My friends were more fortunate, their fathers did not work on the railway, unlike my dad. So I understood what it is sliding friction coefficient ”.
(From the Honored Teacher of Russia V.I.Tkachuk)
Question: "What did the student understand, and what exactly was it about in the memory?"
There is a discussion and a conclusion: about the action of the friction force.
Teacher: “The topic of our lesson is“ Friction force ”.
2. Historical background.
Leonardo da Vinci (06/15/1452 - 05/02/1519) - Italian artist, scientist and inventor.
Amonton Guillaume (31.08.1663 - 11.10.1705) - French physicist, Member of the Paris CP (1699).
Pendant Charles Augustin (06/14/1736 - 08/23/1896) - French physicist and military engineer, member of the Paris Academy of Sciences (1803).
3. Frontal conversation.
Friction, the hardest nut to crack in natural science, was discovered 400 years ago. Friction is encountered literally at every step, without it you cannot take a step; we hold a pen, friction in our hand, we write this very phrase; all sorts of objects stand on the table, do not slip - friction; nails hold a shelf with books, do not crawl out of the wall - friction, etc. etc.
When does friction occur? Where is the friction force directed? (When the surfaces of the bodies touch. The friction force is always directed in the direction opposite to the speed).
There is some kind of surface interaction mechanism. Usually they talk about small notches on the surface of bodies clinging to each other. The following fact leads to this idea: when cleaning surfaces, friction decreases - this is what lies afloat. In fact, the mechanism of interaction between contacting surfaces is much more complicated and needs to be analyzed at the molecular level. Since the friction force is electromagnetic in nature.
4. Friction. Brief summary.(Make an explanatory drawing. Write a definition. Cause of occurrence)
- Static friction force.
- Rolling friction force.
- Sliding friction force.
Friction force calculation formula: F = μN, where N = mg
About the force of friction
There is a friction force in the world.
It matters a lot!
There are three types of friction: sliding, resting, rolling.
Everyone is very important in their own right.
And in this world, of course, they are needed. (V. Sayapin)
5. Physical experiment.
Students complete assignments in groups and draw up a report. The strongest students do tasks 1 and 2, others do 3 and 4.
Experimental work. "Measuring friction force"
If you put a bar on a horizontal surface and act on it with sufficient force in the horizontal direction, then the bar will begin to move. In order for the bar to move evenly and in a straight line, it is necessary that the modulus of the traction force be equal to the modulus of the friction force.
This is the basis of the method for measuring the friction force.
Instruments and materials: tribometer, consisting of a wooden block with three holes and a wooden ruler, a school dynamometer, a set of weights for mechanics.
Exercise 1. Determine the dependence of the friction force on body weight.
- Determine the mass of the bar and weight from the kit.
- Having hooked the hook of the dynamometer to the hook of the bar, bring them in a uniform movement along the ruler (or the surface of the table), measure the pulling force. Note that during the movement of the bar, the dynamometer pointer fluctuates, therefore, the average value of the pointer position between its extreme deviations is taken as the measurement result. Enter the measurement result in the table.
- When loading the bar with one, two or three weights, measure the friction force in each case. Enter the data into the table.
| Test body | Weight m, g | Gravity F, N | Friction force F, N | Friction coefficient |
| Bar with one weight | ||||
| Bar with two weights | ||||
| Bar with three weights |
Task 2. Determine the coefficient of friction
Using the experimental points, build a graph of the dependence of the friction force on the force __________________________. This dependence is _________________. Since the scatter of the experimental points is inevitable, the graph of the dependence of the force F on the force _______________________ (a straight line passing through the origin of coordinates) must be constructed so that it passes as close as possible to all experimental points.
Graph F (N). µ = F / N
Task 3. Determine the dependence of the friction force on the surface area
1.Measure the length, width and height of the bar and calculate the areas of the base of the bar and the side surface.
| a = _______ cm | b = ________ cm | c = _________ cm |
| S = ____________ cm 2 | S = ______________ cm 2 |
2. Put the block with its side edge on a ruler and measure the friction force F = ____ N
3. Place the block with its base on a ruler and measure the friction force F = ____ N
Output:__________________________________________________________
Task 4. Determine the dependence of the friction force on the surface along which the body moves.
Dynamometer reading when moving a bar along a tree __________ N.
Dynamometer reading when the bar moves on a rough surface ___________ N.
Dynamometer reading when the bar moves on the glass _____________ N.
Dynamometer reading when a bar moves on rubber _____________ N.
Make a conclusion _________________________________________________
________________________________________________________________
________________________________________________________________
CONCLUSION: (what did you learn about friction force): _____________________________.
6. Discussion of the results of the assignments.
Conclusion: the friction force depends on the surface of movement, on the reaction force of the support and does not depend on the surface area.
7. Qualitative tasks.
- Which is easier: to move the body from its place or continue to move it along a horizontal surface? Why?
- Why are the paths sprinkled with sand in winter?
- Why are chains put on the rear wheels of cars in winter?
- Why is a protector applied on shoes, car tires?
- Why is oil being poured into a car engine?
- Why do sports skiers apply special lubricant to their skis?
- Why are bearings of wheels and pedals of bicycles lubricated with grease?
- How is an all-terrain hovercraft structured? What is the lubricant for him?
- Why do athletes wear spiked athletic shoes?
- The sword is the bone process of the upper jaw of the fish. It easily cuts the water and significantly improves the hydrodynamic characteristics of the fish. Here is a swordfish and sets records for the speed of movement under water - 130 km / h. But what would a sword be worth if not for the protein lubricant - mucin, which negates the friction of fish on water.
How does water friction arise? How do fish reduce resistance? - Give a physical justification for the proverb: “Mow the scythe while the dew is; the dew is gone and we're home. ” Why is it easier to mow with dew?
- Explain the sayings:
- If you don't grease, you won't go!
- It went like clockwork.
- You can't hold an eel in your hands!
- The skis glide according to the weather.
- You can't make a net out of waxed thread.
- A rusty plow is cleaned only after plowing.
- Petya examined the nail. The head had a notch in the form of a mesh, and under it, on the upper part of the rod, there were several transverse notches. “What is it for?” He asked the dad who was building the barn.
- It started to get dark. Robinson thought, "It would be nice to have a fire." But then he remembered: "There are no matches." What to do? How to light a fire without matches?
- Renovations were underway around the school. The worker put the ladder to the post and tried to climb it, but the ladder staggered, as the top step, resting on the post, slid off it, Little Johnny, passing by, saw this scene and advised: To prevent the ladder from slipping, replace the top step with a strong rope or a piece of rope. I have already done this: everything is fine. "
Is there a scientific basis for such advice?
8. Summing up the lesson and homework.
Prepare reports on the topics "Friction in wildlife", "Friction in everyday life and technology."
An essay on the topic “What would have happened if there had been no friction force”.
Friction force presentations.
9. Literature.
- Elkin VI “Unusual teaching materials in physics”. "Physics at school" library of the journal, №16, 2000.
- The wisdom of the millennia. Encyclopedia. Moscow, Olma - press, 2006.
- Non-standard crochet. Physics 7-11 grades. Publishing House Teacher ”, Volgograd, 2004.
- Semke A.I. Physics lessons in the 9th grade. Yaroslavl, Academy of Development, Academy Holding, 2004.
- Physics and Astronomy, a textbook for grade 7, edited by A.A. Pinsky, V.G. Razumovsky, Moscow "Education" 2002.
- Khramov Yu.A. Physics. Biographical reference book. Moscow "Science", 1983.
Class: 7
Lesson presentation
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Lesson type: combined.
Lesson type: Traditional with elements of laboratory work.
Lesson objectives: to reveal the concept of friction force, to explain the causes of friction force, to get acquainted with different types of friction force, to find out what factors the friction force depends on.
Tasks:
- Educational:
- to consolidate the already existing knowledge on the topic "Forces in nature";
- get acquainted with the force of friction;
- explain the causes of frictional forces;
- continue the formation of the ability to explain processes from the point of view of the structure of matter.
- Educational:
- the formation of communicative qualities, a culture of communication;
- the formation of interest in the subject under study;
- stimulating curiosity, activity in the lesson;
- development of working capacity.
- Developing:
- development of cognitive interest;
- development of intellectual abilities;
- development of skills to highlight the main thing in the studied material;
- development of skills to generalize the studied facts and concepts.
Forms of work: frontal, work in small groups, individual.
Means of education:
- Textbook "Physics 7" A.V. Peryshkin § 30, 32.
- Collection of problems in physics for grades 7-9, A.V. Peryshkin, chapter 15.
- Handouts (test sheets, practical exercises).
- Dynamometers.
- Wooden bars.
- Stripes of different types of surfaces.
- Friction Force presentation.
- A computer.
- Illustrations on the topic.
Lesson plan:
- Organizing time.
- Repetition of the material learned.
- Testing.
- Test check.
- Determination of the topic of the lesson.
- The force of friction in life and in nature.
- Writing the topic of the lesson in a notebook.
- Setting the goals and objectives of the lesson.
- Learning a new topic:
- Causes of friction force.
- Work in small groups to find out the factors on which the force of friction depends.
- Group reports on their work.
- Dependence of the friction force on the type of contacting surfaces.
- Dependence of the friction force on the force pressing the body to the surface.
- Difference between sliding friction force and rolling friction force.
- The friction force does not depend on the area of the contacting surfaces.
- Consolidation of the studied material.
- Summarizing.
- Homework.
During the classes
| Stage No. | Teacher work. | Student work | Notebook entries | Used slides, manuals, equipment, literature | Time |
| 1. | Greetings. | 1 minute. | |||
| 2. | Draws the attention of students to the handout sheets for the test, reminds the rules for filling them out. | Fill in the handout sheets for the test. Annex 1 | Handout sheets. | 1 minute. | |
| 2.1. | Reads test questions, comments on them if necessary. Collects handouts. |
Answer test questions. Hand over handouts. | Slides 2-7 | 5 minutes. | |
| 2.2. | Asks students to comment on their answer, and then names the correct answer and explains it, if necessary. | Think over the answers again, the students named by the teacher comment on their answers. | Slides 8-14 | 5 minutes. | |
| 3. | Asks to name the forces that were studied in the previous lessons. He says that the lesson will talk about another power. | They remember what forces they have already studied. Gravity, elastic force, body weight. | 2 minutes. | ||
| 3.1. | Shows on the screen slides demonstrating the importance of friction force in nature and life. Asks students to name the power in question. | They look at the slides, draw conclusions, name the strength. (As experience shows in the name, they are not mistaken). | Slides 15-16 | 2 minutes. | |
| 3.2. | Dictates the topic "Force of friction" and writes it down on the board. | Write down the topic of the lesson in a notebook. | Topic: "Friction force" - |
Slide 17 | 1 minute. |
| 3.3. | He gives a definition of the friction force and asks to write it down in a notebook. Defines the goals and objectives of the lesson. Distributes worksheets with group assignments. | They keep notes in a notebook. The teachers listen carefully. | Is a force that arises when one body moves on the surface of another, applied to a moving body and impedes movement.  |
Slide 17 | 3 min. |
| 4. | Asks students to help him explain new material. | Prepare to help. | |||
| 4.1. | Based on life experience, he shows that one of the reasons is uneven surfaces, demonstrates that in this case the friction force can be reduced using a lubricant. The other is the forces of interaction between molecules. Dictates the main provisions in the notebook. | They remember where in life they faced the force of friction, keep notes in a notebook. | Causes of friction force: 1. unevenness of the contacting surfaces. (With lubrication, unevenness can be reduced). |
Slides 18, 19, 20 | 5 minutes. |
| 2.mutual attraction of molecules of adjoining bodies | Slide 21 |
||||
| 4.2. | Says that the force of friction depends on a number of factors and asks students to find out what these factors are and how they affect the force of friction. Explains that the dynamometer shows the elastic force (traction force) and it will be equal to the friction force only in the case of uniform movement of the bar. | Students are divided into groups (the division into groups and the lists of groups were presented to the teacher before the lesson). Each group performs tasks that are written down on the handout. Appendix 2 They write down the results of their experiments on special sheets - tables. |
Slide 22. Handout sheets. Equipment: bars, weights, dynamometers, removable wheels, various types of surfaces. |
10 min. | |
| 4.3. | Announces the completion of the practical work, asks the groups to get ready to voice the results. | Prepare to report on the work done, choose a student who will go to the board. (It is best to discuss this before the lesson.) | The friction force depends on: | 1 minute. | |
| 4.3.1. | Listens to the answer, asks leading questions if necessary. Supplements the student's answer with examples from life ( grooved soles of winter shoes, studded sneakers, winter tires for cars and bicycles). | They find out that the friction force depends on the type of contacting surfaces, make the necessary notes in a notebook. | 1. The type of contacting surfaces. | Slide 23 | 2 minutes. |
| 4.3.2. | (wheels of trams and trains, as well as rails have a smooth surface, but the friction force is high due to the large weight of trams and trains). | They find out that the friction force depends on the force pressing the body to the surface, make the necessary notes in a notebook. | 2. The force pressing the body to the surface. | Slides 24, 25 | 2 minutes. |
| 4.3.3. | Listens to the answer, asks leading questions if necessary. Complements the answer with real-life examples (the use of drags in some tribes, the invention of the wheel, the ancient dragging of ships on dry land using logs, the use of special horizontal baskets made of intertwined rods during the construction of Stonehenge, the use of bearings to reduce friction force). | They find out that under equal loads, the sliding friction force is always greater than the rolling friction force, they make the necessary notes in the notebook. | 3. With equal loads, the rolling friction force is always greater than the sliding friction force. | Slides 26, 27, 28, 29, 30 | 2 minutes. |
| 4.3.4. | Listens to the answer, asks leading questions if necessary. Complements the answer with real-life examples (The ancient Egyptians, who erected pyramids of unprecedented size from carefully processed rectangular blocks, probably knew that the resistance when dragging such blocks does not depend on whether they lie flat, rest on the side edge or stand "on the bottom." scientist Guillaume Amonton at the end of the 17th century (1699) Charles Coulomb continued his work a century later, and now the law on the independence of the friction force from the surface area is called the Amonton - Coulomb law.) | Find out that the friction force does not depend on the area of the contacting surfaces. | The friction force does not depend on the area of the contacting surfaces. | Slides 31 | 2 minutes. |
| 5. | Questions: | Answers on questions. | Slide 32 | 3 min. | |
| 1. What force is called frictional force? | it is the force arising from the movement of one body on the surface of another, applied to the moving body and preventing movement. |
||||
| 2. What is the cause of the frictional force? | 1. Irregularities of the contacting surfaces. 2. Mutual attraction of molecules of adjoining bodies. |
||||
| 3. How can the friction force be reduced? | Lubricate mating surfaces or replace sliding friction with rolling friction. | ||||
| 4. What factors does the friction force depend on? | 1.from the type of contacting surfaces 2.from the force pressing the body to the surface 3. with equal loads, the sliding friction force is always greater than the rolling friction force. |
||||
| 5. What factors does the friction force depend on? | From the area of the contacting surfaces. | ||||
| 6. | Determining the meaning of friction force in life: what would happen if the friction force disappeared? Comments on the implementation of the lesson tasks, grading, gratitude to the distinguished students. | If there was no friction, we would not be able to walk on the ground (remember how our feet slide on ice), we would not be able to ride a bicycle, a car, a motorcycle (the wheels would turn in place), we would have nothing to wear (threads in fabric held by frictional forces). If there was no friction, all the furniture in the room would be knocked into one corner, plates, glasses and saucers would slide off the table, nails and screws would not stick to the wall, not a single thing could be held in hands, etc. etc. To this we can add that if there were no friction, it is not known how the development of civilization on Earth would have gone - after all, our ancestors produced fire by friction. | Slide 33 | 2 minutes. | |
| 7. | Homework, necessary comments. | Writing homework in diaries. Textbook Peryshkin A.V. - § 30, 32 Collection of problems Peryshkin A.V. - Chapter 15. |
§ 30, 32 chapter 15 |
Slide 34 | 1 minute. |
Used Books:
- A.V. Peryshkin textbook "Physics 7".
- A.V. Peryshkin "Collection of problems in physics 7-9 grades", Moscow, "Exam", 2006.
- V.A. Orlov "Thematic tests in physics 7-8 grades", Moscow, "Verboom - M", 2001.
- G.N. Stepanova, A.P. Stepanov "Collection of questions and problems in physics 5-9 grades", St. Petersburg, "Valeria SPD", 2001.
- IN AND. Grigoriev, G. Ya. Myakishev "Forces in nature", Moscow, "Science", 1988.
- kak-i-pochemu.ru
The peculiarity of the pedagogical system of multilevel continuous creative education NFTM-TRIZ consists in the fact that a student from an object of study becomes a subject of creativity, and educational material (knowledge) from a subject of assimilation becomes a means of achieving a certain creative goal, until recently, was my dream as a teacher. Today, slowly but surely, the dream is becoming a reality.
Introducing an element of creativity into the lesson, building bridges between physics and lyrics, linking boring physical laws with the accumulated life experience of students - has always been one of the important components of my pedagogical activity. But it is one thing to "cook" in your own boiler, and another, when at all levels of education there is continuous the formation of creative thinking and the development of the creative abilities of students, the search for highly effective creative solutions.
The German teacher A. Diesterweg said: “In a few years a student passes the road that mankind has taken for thousands of years. However, he should be led to the goal not with a blindfold, but with a sighted: he must perceive the truth not as a finished result, but must discover it. The teacher must lead this expedition of discovery, therefore, also be present not only as a mere spectator. But the student must exert himself, nothing should be given to him for free. It is given only to the one who strives. " How correctly and in unison with the requirements of the new educational Standard it is said!
With some kind of spiritual trepidation, I look forward to meeting with seventh-graders who are ready to set goals on their own, navigate the situation, think creatively, act ...
But then the teacher will have to accept in a new way the principle of Hippocrates "do no harm" as: help the child develop personality, gain spiritual and moral experience and social competence.
In the Federal State Educational Standard of Basic General Education (FSES LLC), the requirements for natural science subjects are noted, in particular,
Mastering the skills to formulate hypotheses, design, conduct experiments, evaluate the results obtained;
Mastering the ability to compare experimental and theoretical knowledge with the objective realities of life.
I will show how, using the block structure of a double creative lesson, these requirements can be implemented using the techniques and methods of NFTM-TRIZ, I will show on the example of a physics lesson in the 7th grade on the topic “Friction force. Types of friction. Friction in nature and technology. "
The principle of work is the education of the individual through creativity.
The task is to create pedagogical conditions for the identification of creative abilities and their development.
I took two aphorisms as an epigraph for the lesson (although, in my opinion, they reflect the entire line of development of creative thinking and abilities, therefore, they can take an honorable place in the design of the office):
Man is born to think and act.
Aphorism of the ancient Greeks and Romans
Ability, like muscle, grows with exercise.
Domestic geologist and geographer V.A.Obruchev (1863-1956)
Block 1... Motivation (5 min). To develop students' curiosity at the beginning of the lesson - experience.
On the display table are two deep bowls filled to the brim with water. The teacher invites two assistants to the blackboard and invites them to participate in the experiment. Gives one student a tennis ball, another - the same rubber. Objective: make the balls rotate in the water as fast as possible.
What are we seeing?
Which ball spins faster in water?
Why do you think a tennis ball spins faster than a rubber one?
The conclusion that we come to after a comprehensive analysis of the problem: a tennis ball rotates faster than a rubber one, because its surface causes less friction with water.
Friction is the interaction that occurs when one body touches another and prevents their relative movement. And the force that characterizes this interaction is the friction force. Today in the lesson we will reveal all the secrets of this amazing phenomenon - friction. Ready? Then get down to business!
Block 2. Content part (30 min)
On the tables for children: thread spool; elastic loop; smooth button, two matches, glue. The teacher suggests using a set of these tools to create a moving structure.
Work in groups (the teacher controls the process of search and communication activities), demonstration of what happened and a story about how they acted:
What ideas were born?
Why did you stop at this one?
How was it embodied?
What problems did you encounter?
How were they solved? Did you succeed in everything?
How did you work as a team?
Sample of a possible design:
Rice. 1
1 - thread spool;
2 - elastic loop;
3 - smooth button;
4 - a piece of a match threaded into a loop (it is better to glue it to the coil);
5 - match.
All groups worked as inventors, the result of the work of creative thought is a moving structure. The goal has been achieved. The coherence of the team, the ability to listen to each other, formulate and argue their opinion and correctly defend their position, played an important role in this. But all of you note that the speed of your car is not as high as you would like.
In order to understand how to make the resulting structure more high-speed, we need to figure out what prevents it from moving the way we want it.
The search will be carried out in 3 directions: the cause of friction, the types of friction, the factors that determine it. The following notes open on the chalkboard:
Friction reasons: Types of friction: Friction depends on:
I have no doubt that there are already ideas. There is a desire to express your point of view - we will listen with pleasure.
We work in shift teams according to the scenario: idea → experience → conclusion.
Each group receives equipment for setting up experiments: a wooden block with a hook, weights, a dynamometer, a wooden board 50 × 10 cm, boards of the same size, upholstered with linoleum, rubber, round pencils. And on the interactive whiteboard - tips in the form of pictures:
Rice. Fig. 2 Fig. 3 4
Rice. 5 Fig. 6 Fig. 7
Find pictures that show friction. Explain your point of view.
Pay attention to fig. 3, 4, 5. What do they have in common and how do they differ? (General - friction. But at the same time the hockey player slides, the cart rolls, and the piano stands still).
In nature and technology, there are three types of friction: rest, sliding, rolling (+ writing on the board). Try to define them. Find them in other pictures.
What is the reason for the emergence of the friction force? How do you think?
Place the weighted block on a wooden plank. Attach a dynamometer to it and, using force parallel to the board, move the load evenly. Record the dynamometer reading. What strength have we measured? (traction force equal to sliding friction force).
Repeat the experiment on linoleum and rubber. Draw conclusions
(1) one of the causes of friction is the unevenness of the contacting surfaces, which, when moving, cling to each other; 2) the friction force depends on the material of the contacting surfaces) → notes on the board.
Add weight to the bar. Repeat experiment. Formulate a conclusion. (The force of friction is directly proportional to the force of normal pressure) → writing on the board.
Place the kettlebell block over the pencils. Experiment. Output.
Guys, what do you know about grease? What is her role? What pictures does it show?
At one time, the great Italian artist and scientist Leonardo da Vinci, surprising those around him, carried out strange experiments: he dragged a rope along the floor, sometimes its full length, then collecting it in rings. He studied: does the sliding friction force depend on the area of the contacting bodies?
Before we know what conclusion Leonardo da Vinci came to, let's also try to answer this question. But here's an opportunity: we don't have a rope. How to be? Is it possible to do with the means at hand? We find a way out of the situation in the bar, which has different face areas. Comparing the force of sliding friction at three positions of the bar, we come to the conclusion that the force of sliding friction in all cases turned out to be the same, that is, it does not depend on the area of the contacting bodies. And what about Leonardo? (I read out the answer). And here it is - the joy of knowledge!
And now I suggest that you fill in 2 tables for the purpose of introspection of the material studied, compiling an oral story based on the resulting notes. In case of difficulty, refer to paragraphs 30 and 31 of the textbook.
Table 1
Studied physical phenomenon
table 2
The forces that I met
First you work independently, then in groups the notes are discussed, corrected, "polished".
But then it turns out that one problem arose for everyone: there is no formula for calculating the friction force in the textbook.
Guys, you already know that sliding friction depends on the weight of the body and the material of the contacting surfaces. The value characterizing the dependence of the friction force on the material of the contacting surfaces, their processing quality is called the coefficient of sliding friction μ. Thus, the formula for calculating the sliding friction force is: F tr = μmg.
I think that now you are ready to make your design fast, bringing it to perfection. This will be your homework assignment. The next lesson is the competition of your "cars". High marks await the winners. And now…
Block 3. Psychological relief (5 min)
Boys are divided into two teams by drawing lots, competing in tug-of-war. Girls are cheerleaders. They also have to explain what could be the reason for the team's victory or loss. What kind of friction and where did you encounter in this competition? Did it act as a helper or hindrance? What can you suggest to increase the friction of the soles on the floor? hands on the rope?
Block 4. Puzzle (10 min)
Tell me guys, which one of you loves to ski? My class and I sometimes spend weekends doing this wonderful activity! True, the memories of our first trip cause mixed feelings in us, tk. We suffered a lot: the skis all the time "tried" to roll back, it was worth incredible efforts to climb the smallest rise.
What do you think was wrong with us? - Grease! And why? It would seem that skiing requires less friction and that's it. No, not all. When skiing (classic style), two types of friction appear. Which? One is useful, and it must be increased, another is harmful, and it must be reduced. So, zoom in and out at the same time! It is clear how difficult it is to choose such a line so that, as they say, “the sheep are safe and the wolves are fed”. For each weather it has its own - this elusive line. Wrong - and the skis will either glide poorly or hold poorly when pushing off (recoil). On this occasion, the Finns have a proverb "Skis slide on the weather."
In proverbs - short sayings, teachings - national history, worldview, and everyday life of people are manifested. But all this is inextricably linked with physics. Today I offer you a few proverbs related to our topic (distributed into groups by lot). Your task: to read the proverb and answer the questions:
- What is its physical meaning?
- Is the proverb correct from the point of view of physics?
- What is its everyday meaning?
Proverbs:
Things went smoothly (Russian).
Skis glide according to the weather (Finnish).
Waxed thread is difficult to weave into a net (Korean).
You can't hold an eel in your hands (French).
If you don't grease, you won't go (French).
I walked around the watermelon rind, and slipped on the coconut (Vietnamese).
Mow the scythe while the dew is; dew down, and we are home (Russian).
Box 5. Intellectual warm-up (15 min)
Today, my young physicists, I will tell you the tale "Turnip" about the force of friction at rest, the mechanism of its occurrence, magnitude and direction. Listen carefully, because at the end you have to answer 10 questions easier than a "steamed turnip".
So listen.
Grandfather planted a turnip. The turnip grew big, very large, heavy, heavy, it grew in all directions, pressed the soil. That is why a very close contact of her tuber with the soil turned out, the earth penetrated into all the smallest cracks and protrusions. My grandfather went to pick a turnip. Pulls-pulls - cannot pull. He lacks strength: the turnip rests, clings to the ground with irregularities and protrusions, resists his movement. In places, the gap between the turnip and soil areas is of the order of the radius of action of molecular forces. There, the adhesion of soil particles to the turnip occurs, it prevents the turnip from moving relative to the ground.
The grandfather called the grandmother. The grandmother for the grandfather, the grandfather for the turnip, they pull, pull, they cannot pull: the thickened-rounded root is firmly held in the ground. The force of gravity pushes him to the ground. No, and the two of them cannot cope.
Grandma called her granddaughter. The granddaughter for the grandmother, the grandmother for the grandfather, the grandfather for the turnip, pull-pull - they cannot pull: still their total pulling force is less than the limiting force that arises on the surface of contact of the turnip with the ground. It is called the static friction force. Called by an external force, but always against an external force and directed. This power is ambiguous - it has many faces. It can vary within wide limits: from zero to a certain maximum value ... It can be seen that this maximum value has not yet come.
Granddaughter called Bug. The bug with four paws rested on the ground. There is also a static friction force between the paws and the ground. This power helps the Beetle in the same way as the grandfather, grandmother and granddaughter. If it were not for this force, they would not have been able to resist, they would slide on the ground, slide. A bug for a granddaughter, a granddaughter for a grandmother, a grandmother for a grandfather, a grandfather for a turnip, pull-pull - cannot pull. But in fact, the turnip has already moved by microns. The magnitude of these micro displacements is proportional to the applied force and depends on the properties of the soil itself. And the adhesion of the turnip to the ground and elastic deformations of the shear of the soil and micro protrusions of the turnip itself when trying to pull it out lead to an increase in the elastic force of the soil. And this emerging force of elasticity of the soil, in essence, is the force of friction at rest. She does not allow her to pull out the turnip in any way.
Beetle called the cat. A cat for a bug, a bug for a granddaughter, a granddaughter for a grandmother, a grandmother for a grandfather, pull and pull - they cannot pull: the external force turned out to be the smallest, but still less than the maximum possible value of the resting friction force.
The cat called the mouse. A mouse for a cat, a cat for a bug, a bug for a granddaughter, a granddaughter for a grandmother, a grandmother for a grandfather, pull-pull - pulled out a turnip.
Just do not think that the little mouse turned out to be the strongest! How many forces a little mouse has! But its small force was added to the total traction force, and now the resulting force even exceeded somewhat the maximum value of the static friction force: the sliding friction force has become more. Irreversible relative displacements have arisen. The "live chain" - from grandfather to mouse - pulled out the turnip, and she ... fell! The applied force turned out to be greater than the force of sliding friction of the turnip on the ground. Here, in the direction of greater strength, everyone fell. But this ... is already another fairy tale.
And now the promised questions are simpler than a "steamed turnip":
Block 6... Content part (15 min)
A little more and you will know everything about the force of friction.
Independent work with the textbook: study § 32, structure the text (diagram, table, etc.), discuss in a group and present the most successful option to the whole class, defending it. The work will be assessed according to the following criteria: an interesting form of presentation, the competence of the defender (a clear, understandable explanation, the ability to interest the audience, reasonably answer the questions asked, if any), support of the group. In the presentation of the result of the activity, there should be answers to three questions: "What am I doing?", "What am I doing?" and "How am I doing?"
Block 7... Computer intelligent support (10 min)
Video fragment of the cartoon "The Bremen Town Musicians" (They are going, singing "There is nothing better in the world than wandering friends around the world").
Rice. 8 Fig. nine
Find everything that is relevant to our topic, justify your choice. But you have to imagine it with the "eyes" of a physicist. One begins the story, the second takes over, then the third, etc. If necessary, we repeat the cartoon, stopping at the request of the respondent.
Box 8. Summary (5 min)
"Take your" photo "of the lesson or work"
Imagine that each of you is a photographer, and you need to take some “freeze-frames” from the lesson or the business you were just doing. The picture can be in color or black and white. A colored freeze frame reflects something you liked, which brought you joy from what you saw, heard, performed, constructed, etc. A black and white “freeze frame” should show what you didn’t like, failed, or upset.
Everyone depicts how he takes his picture: holding a camera in his hands, releasing the shutter and loudly commenting on the frame, explaining why he liked or did not like something. The camera must then be passed on to another student.
The last few "freeze-frames" are made by the teacher.
- Zinovkina M.M., Utemov V.V. The structure of a creative lesson on the development of the creative personality of students in the NFTM-TRIZ pedagogical system // Socio-anthropological problems of the information society. Issue 1. - Concept. - 2013. - ART 64054. - URL: http://e-koncept.ru/teleconf/64054.html
- Federal state educational standard of basic general education. - URL: http: //minobrnauki.rf]
- Experience "Friction" - Lessons in magic. - URL: http://lmagic.info/friction.html
- Balashov M.M.On nature: Book. for students of grade 7 - M .: Education. 1991.-64 p .: ill.
- Physics teaching that develops the student. - Book. 2. - Development of thinking: general ideas, teaching mental operations / comp. and ed. E. M. Braverman. A guide for teachers and methodologists. - M .: Association of Physics Teachers. 2005 .-- 272 p .; silt - (Personality-centered learning.)
- Class! Naya physics. - URL: http://class-fizika.narod.ru/
- Peryshkin A.V. Physics. 7th grade: textbook. for general education. institutions. - 8th ed., Stereotype. - M .: Bustard, 2004 .-- 192 p .: ill.
- Tikhomirova S. A. Physics in proverbs, riddles and fairy tales. - M .: Shkolnaya Pressa, 2002 .-- 128 p. - (Library of the journal "Physics at school"; Issue 22)
- Physics lesson in modern school: Tvorch. search for teachers: Book. for teacher / comp. E. M. Braverman; ed. V. G. Razumovsky. - M .: Education, 1993. - 288 s
- Physics teaching that develops the student. Book. 1. Approaches, components, lessons, tasks / comp. and ed. EM. Braverman: A Guide for Teachers and Methodists. - M .: Association of Physics Teachers. 2003 .-- 400 p .; silt - (Personality-centered learning.)
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Attention! Slide previews are for informational purposes only and may not represent all the presentation options. If you are interested in this work, please download the full version.
Target: to consolidate the knowledge gained about the forces in nature; to acquaint students with the force of friction; find out experimentally what the friction force depends on; consider the types of "dry" friction; compare rolling, sliding, resting friction; teach students to identify the type of friction; enter a calculation formula for finding the friction force (slide 2).
Required technical equipment: interactive whiteboard, computer, projector.
Software: PowerPoint, video player, presentation.
Design: The topic of the lesson and tasks for updating knowledge are presented on the board. On the folding halves, sayings about the force of friction are written (or printed).
Equipment: a wooden block with edges of different areas, but the same surface roughness; a set of weights, 100 g each; wooden, poorly sanded board; dynamometer, rollers (2 cylindrical objects, for example 2 pencils).
Explanatory note on the use of the presentation. (Annex 1)
During the classes
1. Organizational moment. Hello. Today in the lesson we will try to find out the meaning of some Russian sayings from the point of view of physics. (Slide 3). To do this, we use experiments to confirm or deny the possibility of the described events. But first, let's remember what we learned in previous lessons and what we need today.
2. Updating knowledge.
A) One student works at the interactive whiteboard: Depict body weight, elastic force and gravity. (The teacher pays attention to the point of application and the direction of the force).(Slides 4, 5)
B) At the blackboard, the teacher prepares assignments in advance. While the student is working at the interactive whiteboard, the whole class works independently in notebooks, the answers will be discussed when checked using the presentation.(Slide 6)
1. Where is the gravity greater? Where is more weight?
2. Where is the elastic force greater (k 1 = k 2)? What about the force of gravity if the bars are at rest? (Slide 7)
3. Where is the stiffness greater (m 1 = m 2)? What about the force of gravity if the bars are at rest? (Slide 8)
4. Determine and designate the resultant forces. Where will the body move in this case? And if you get rid of the force indicated in black, how will the body move? (Slide 9)
C) Two students (sitting at the same desk) receive an assignment and equipment: “Build a graph of body weight versus weight. Equipment: dynamometer, set of weights " Students present the results of the work to the class and draw conclusions after discussing all the questions.
The teacher observes how the students do the work and provides the necessary assistance. After 5-7 minutes, a check is organized. Emphasis is placed on the key points that students should have noted when completing the assignments.
3. New material
In previous lessons, you and I have repeatedly raised the issue that if no other bodies act on the body or the action of these bodies is compensated, the body either rests or moves in a straight line and evenly (slide 10). The physical quantity that characterizes the action of bodies on each other is called force. Let's conduct an experiment: pull a bar with weights with a dynamometer so that the movement is uniform. Why is this possible? Correctly, the traction force in this case is compensated by some other force that is not yet known to us? (Slide 11). Let's try to find out what kind of force it is, where it arises, where it is directed and what it depends on.
The teacher and assistants issue equipment (see above) to each school desk.
Conduct the same experiment yourself and think: where is the unknown force directed to?
This force is called frictional force. It is denoted by Ftr, measured in N. In connection with what does it arise? In connection with the contact between the bar and the desk, it means that it appears at the point of contact of two bodies. There are two reasons for the friction force (slide 12). When one body slides over the surface of another, the irregularities cling to each other, which creates some force that inhibits movement. But if you take 2 well-polished objects, for example, two glasses, then the friction force is also great, since in this case, forces of mutual attraction arise between the molecules of the contacting bodies, which are the cause of friction.
What do you think this force might depend on? Check your guesses. Possible assumptions. (Slide 13, 14)
(Better to organize the work in groups - each group tests one hypothesis and voices, comments on the result)
1. From speed (does not depend).
2. From the transported mass.
The more P, the more Ftr.
4. From surface roughness, etc.
The teacher helps the students to model the experiment so as to test all the assumptions made. After that, all conclusions are recorded.
In notebooks we write Ftr. (Slide 15)
- Directed in the opposite direction of movement.
- Occurs at the point where two bodies meet
- Depends: on body weight (mass) and surface roughness.
That. Ffr is calculated by the formula (slide 16): Ffr = µN, where µ is the friction coefficient depending on the type of rubbing surfaces, N is the support reaction force, i.e. elastic force arising in the support, under the influence of body weight.
We give the definition of Ftr - this is the force arising from the interaction of the surface of one body with the surface of another, when the bodies are stationary, or move relative to each other.
Now put rollers under the block with weights and measure the friction force. Compare it with the readings you made for the same weight in the previous experiment. What conclusion can be drawn? It is true that this frictional force is less. Now place the block with weights on a rough surface and try to move it. What is being observed? The force at first increases greatly, and when the bar starts to move, it becomes equal to the frictional force obtained during sliding. Those. in nature, there are three types of “dry” friction: sliding friction force, rolling friction force and static friction force.
Arrange signs between Fr. Rolling _____ Fr. Slip _____ Ffr. Rest. (Slide 17)
4. Anchoring
(Slide 18) Assign a type of friction force to each depicted situation. Give your examples of each type of friction force.
How can you increase and decrease the friction force?
Explain the meaning of the sayings on the chalkboard. Do they make physical sense? (Slide 19)
Additionally: Give examples of the manifestation of the action of the friction force.
Is there a benefit to frictional force? What is it?
What harm does friction force cause? Is it possible to fight this? How?
Homework: §30, 31, tasks 1 and 2, home experiment, get acquainted with additional material. (Appendix 2). ( Issued either in printed or electronic form). (Slide 20).
Bibliography
1. Peryshkin A.V. Physics. 7th grade: textbook. For general education. Institutions / A.V. Peryshkin. - 12th ed., - M .: Bustard, 2008.
2. Volkov V.A., Polyansky S.E. Lesson development in physics: grade 7. - 2nd edition. - M .: VAKO, 2009
, experimental activities, friction, types of friction, causes of friction
Lesson presentation
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Attention! Slide previews are for informational purposes only and may not represent all the presentation options. If you are interested in this work, please download the full version.
Lesson objectives:
Educational:
- students should know the concept of frictional force
- know the types of friction
- be able to experimentally establish what the friction force depends on
- students should be able to identify the causes of friction force
Developing:
- development of logical thinking
- development of skills to experiment
- Formation of skills to use devices
- Formation of skills to draw conclusions, analyze and compare the results of experiments
Educational:
- involve students in active independent activity
- fostering a culture of communication
Teacher equipment: Computer, multimedia projector, presentation, wooden block, dynamometer, set of weights (3), 2 round pencils, 2 glass slides.
Equipment for students: Dynamometer, a sheet of smooth paper, a block of wood, a set of weights (3), 2 round pencils, 2 glass slides.
Preparation for the lesson: Each table is provided with equipment, information sheets, and a self-assessment sheet.
Plan
- Organizational moment (2 min.)
- Knowledge update (2 min.)
- Motivational start of the lesson (1 min.)
- Learning new material (20 min.)
- Consolidation of what has been learned. Solving problems of a qualitative nature (5 min.)
- Test execution (4 min.)
- Summarizing. House. exercise. Reflection (5 min.)
During the classes
I. Organizational moment
Teacher: Hello guys! Sit down. (slide 1)
Today's lesson is a bit unusual for 2 reasons. I will lead it. My name is Lyudmila Ivanovna, and the second reason is that there are guests at the lesson. As for the rest, the lesson, as always, is the Lesson of gaining knowledge.
So, we begin our lesson,
Let him go to all of you for future use.
We will listen, answer,
Problems need to be solved.
How, why and why,
And you appreciate it!
In the “Interaction of Bodies” section, you explored the various forces that help us in life. In this lesson, we will study another power, no less important, but first, let's remember what you already know about powers.
II. Knowledge update
Continue the phrase:
- Strength is ...
- Types of forces:
- Force unit ...
- Force is measured by a device ...
- Force is a vector quantity. What does it mean?
- The force of elasticity arises ...
III. Motivational lesson start
Teacher: Guys, have you ever wondered, "Why does chalk leave a mark on the board?", "What role does saliva play when swallowing food?"
We can answer these questions by studying the lesson material.
But to the next question, you probably know the answer: "What physical phenomenon helps you to remove with an eraser an unwanted drawing made with a pencil in a notebook?" (Friction)
Teacher: Right. And for this you apply force to the eraser - friction force.
So guys, the topic of the lesson FRICTION FORCE.
Today we will be working on the next lesson map. Opposite the word THEME write down the topic of the lesson.
Based on the topic of the lesson, what questions would you like to get answers to today:
Students:
- What is friction force
- Types of friction force
- Where is it headed
- Where is it used
Today I will help you find out what the friction force is, I will introduce you to the types of friction force, we will establish the causes of the friction force and will experimentally see what the friction force depends on. And also we will develop logical thinking with you, we will learn to draw conclusions, analyze, compare the results of experience, independently in practice make sure which of the types of forces is greater.
IV. Learning new material
Teacher: You are familiar with the phenomenon of friction since childhood. On a hike, we say: “Not on rub legs". At school: “Co rub from the whiteboard ”, etc.
First experience:
Teacher: You have a block of wood on your table. Take it, put it in front of you and push. What happened to him?
Teacher: The body stopped .
Teacher: Why, what is it that slows it down?
Student:- Friction. Surfaces rub against each other and the body slows down.
Teacher: Friction force acts on the body.
Teacher: And how is it directed?
Student: Against the movement.
So: The force arising from the movement of one body on the surface of another, applied to the moving body and directed against the movement, is called the friction force.
Teacher: Back to the card. Read the definition and try to remember.
(Ask two or three people). Complete task 1.
Teacher: What have you learned?
After completing the next task, we will find out the causes of the friction force.
Second experience:
Take a piece of paper and a pencil. Draw any line on the piece of paper with a pencil. Now, try doing the same on glass. What are you seeing?
OUTPUT Student: There was a pencil mark on the paper, but not on the glass.
Teacher: What's the matter here?
Consider the surfaces of slate, paper and glass.
The surface of the paper is rough, like the lead. And the glass is smooth. When the pencil moves on the paper, the parts of the pencil are chipped on the nervousness of the paper, they remain on the paper. There are no such irregularities on the glass.
Teacher: So what is the cause of friction?
Student: In the roughness of the surfaces of contacting bodies.
Write in the second column next to the number 1
Teacher: Do experience 2
Third experience: Press the two pieces of glass closer together and try to move one relative to the other.
Student: This is not easy to do.
Teacher: So what's the deal? After all, there are no roughnesses, but still something interferes?
Student: Attraction of molecules of interacting bodies.
Write in the second column next to the number 2
Output: causes of friction
- Roughness of surfaces of contacting bodies.
- Attraction of molecules of interacting bodies.
Guys, there are three types of friction: sliding friction, rolling friction, static friction
Take your textbook, put a pencil on it, if it starts to slide, then there is a sliding friction force, if it rolls, then a rolling friction force arises.
What do you think, and when can the static friction force arise?
Which of these forces do you think is greater?
Let's check it out.
Put the block down, attach the dynamometer, load it with weights. Now attention: Try to move the bar, applying force to the dynamometer, and remove the maximum value at which the bar has not yet begun to move and at the moment when it is already sliding on the table surface. Compare the values on the card.
Place two round pencils under the block, take the reading from the dynamometer. Compare
Rest friction.
As the saying goes, every cloud has a silver lining. Friction not only harms movement, it also contributes to the stability of bodies. Without it, everything will roll and slide until it is on the same level. Nails and screws will slip out of the walls, fabrics will creep, not a single button will be sewn on, the threads will simply not stick either in the needles or in the fabrics. Little of. Without resting friction, we could neither walk nor ride. Remember how difficult it is to walk on ice.
(Perelman Ya.I. Entertaining physics. If there were no friction. P. 263)
Teacher: One of the London newspapers at the beginning of the 20th century wrote: (December 1927)
“Due to severe ice conditions, street and tram traffic in London is noticeably hampered. About 1400 people were admitted to hospitals with broken arms, legs ... "
Teacher: What should be done to prevent this from happening again? How can friction be increased?
Student: Sprinkle with sand, therefore increase surface roughness
Teacher: And they also say that the friction force also depends on the weight of the load.
Check it out by experience.
1. Front-end experience
A) Place one weight on the block and pull it evenly across the table surface. Note and record the dynamometer reading in the table opposite one weight.
B) Add one more weight to the block. Record the reading in the table.
C) Add a third weight to the block. Record the dynamometer reading.
D) Compare the results of measurements, and make those conclusions.
Conclusion: The greater the weight, the greater the frictional force.
Compare your findings with the entry in the table.
Teacher: In what ways can friction be reduced?
Student:- Remove irregularities, i.e. sand surfaces
Teacher: Wear of machine parts and mechanisms occurs due to friction. To reduce the friction of the contacting surfaces between them, introduce grease.
(slide 10) Ways to reduce friction
- Grinding
- Grease
- Reducing load
- Replace sliding friction force by rolling friction force
V. Consolidation of what has been learned. Solving problems of a qualitative nature
Teacher: You have questions in the card to fix. Read them, answer, you can consult with your deskmate.
Let's return the guys to the questions that we posed at the beginning of the lesson. We will answer them.
- Why are the needles carefully polished?
Answer: They reduce the sliding friction force and then it is easier to sew. - What role does saliva play in swallowing food?
Answer: The role of the lubricant is that friction is reduced and it is easier to swallow. - Why does chalk leave a mark on the chalkboard?
Answer: When the chalk is pressed against the board, a large frictional force is created, which tears off the chalk particles - a trace appears on the board.
In winter twilight nanny's fairy tales
Sasha loved. In the morning in a sleigh
Sasha sat down, flew like an arrow,
Full of happiness, from the icy mountain. N.A.Nekrasov (sliding friction force)
Vova rides along the edge of the forest
On my bike
And carries the jam
All for a treat. (rolling friction force)
Although the burden is sometimes heavy in her,
The cart is light on the move;
The coachman is dashing, gray time,
Lucky will not get off the irradiation. A.S. Pushkin (rolling friction force)
Cat for the Bug
A bug for a granddaughter
Granddaughter for grandmother
Grandma for grandpa
Grandfather for a turnip
Pull-pull, can't pull ... (static friction force)
Teacher: Now let's check how you are able to apply theory in practice. On the last page of the information card, work on options is suggested.
Vi. Test execution
Test work
Teacher: Take a pen and circle the correct answer.
| Option 1 | Option 2 |
| 1. In what units is the friction force measured? A. m B. N V. m / s 2. Which force is greater: the static friction force or the sliding friction force? 3. Why are rollers placed under it when moving a heavy load? 4. The sidewalks are sprinkled with sand on the icy surface, while the friction force of the soles of the shoes on the ice ... |
1. What device can be used to measure the friction force? A. ruler B. beaker B. dynamometer 2. Which force is smaller: the static friction force or the rolling friction force? 3. Why does any body set in motion eventually stop? 4. While the vehicle is slipping, gravel or slag is poured under the wheels. In this case, the friction force ... |
Teacher: Guys, take a pencil and exchange cards. We carry out mutual verification. The correct answer options are presented on the slide. Give a mark taking into account the criterion, it is also indicated on the slide.
Right answers:
| Question number | 1 | 2 | 3 | 4 |
| Option 1 | B | V | B | B |
| Option 2 | V | V | A | B |
Evaluation criteria:
- rating "5" for 5 correct answers
- score "4" for 4 correct answers
- score "3" for 3 correct answers
Have you checked it? Raise your hand to who is "5"? Put it down. And who is "4"?
Well done! Well, the rest have work to do.
The information card remains with you. You will paste it into your notebook.
Vii. Summarizing.
Let's summarize: What did you learn new in the lesson?
Have you achieved your goals in the lesson?
House. exercise
- §§ 30-32 (for all)
- Come up with an essay on the topic "If the friction force disappeared ..." (for those who wish)
Reflection
Self-esteem: Take your self-assessment sheet and answer the questions.
Self-assessment sheet
| № | Question | Yes | No | I am at a loss to answer |
| 1 | I know the types of friction | |||
| 2 | I know the unit of friction | |||
| 3 | I know where the friction is directed | |||
| 4 | I can determine the type of friction force | |||
| 5 | I can measure friction | |||
| 6 | I consider my work in the lesson to be effective. |
And just a second of your attention, guys, in memory of this lesson, I want to present you with a bookmark on the force of friction. I distribute them to you, and you answer the questions of the card.
Thank you for your cooperation!
The lesson is over.
Literature:
- Grinchenko N. А. Problems with vocational guidance content for rural schools // Physics at school, 2001, №2.
- Maron A.E., Maron E.A. Didactic materials. Physics grade 7 - M .: Bustard, 2002.
- A.V. Peryshkin Physics. 7 cl. - 3rd ed., Rev. - M .: Bustard, 2000.
- Perelman Ya. N. Entertaining physics. Book. 1, 2 - Moscow: Nauka, 1991.
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