Physics lesson friction force. Open lesson in physics "Friction force". Ways to increase friction
Municipal budgetary educational institution
"Magnielchik secondary secondary school them. G.N. Volkova "
Physics lesson "Friction force"
(7th grade)
The purpose of the lesson:
to form students the concept of friction strength (causes, patterns)
Tasks lesson:
Educational:
The formation of the ability to plan and conduct physical experiences, explain physical phenomena
Formation of students and skills to contribute to the independent discovery of new knowledge, the use of new ways to search for information, the development of problem thinking.
the formation of the ability to systematize the studied, disclose the relationship between the studied theoretical material and the phenomenon in life, to form the ability to interact with the group form of work.
Developing:
Development of logical thinking.
Development of communicative skills and skills when working in the classroom
Development of interest in solving problems.
Improving interest in physics.
Educational:
Education of interest in the subject
Education of a conscientious relationship to work
Type of lesson: lesson for the formation of new knowledge.
During the classes:
1. Organizational moment.
Hello, dear guys!
So, we start our lesson,
Let him all go to you.
Today is a special lesson!
Today we have to open another mystery of nature.We will meet today with mysterious strength - friction force!At the lesson, we need to find out: friction ally or human enemy.BUT B. beginning it is necessary to repeat the knowledge gained on the topic.
2. Check the knowledge gained in previous lessons
- A boy weighing 35 kg put on the shoulders backpack weighing 5 kg. What force is the boy puts on the floor?
3. Statement of the lesson:
The theme of today our lesson:"Friction force » (Slide 1).Write down the date and theme of the lesson in the notebooks. Now we need to study, in my opinion, one of the most important forces - the strength of friction, which is stronger than storms, winds and bad weather. And I think you will agree with me at the end of the lesson.
4. Study of the new material
With the phenomenon of friction and friction strength, we are familiar with childhood. We all happened to go out in Hollyyeditsa: how much effort was required to keep from falling, how many funny movements had to do to resist!
Experience 1: Observation of friction phenomenon.
On the table is a wooden bar. Push him and watch his movement.
What can you say about body speed?
What power arises? (Friction force).
As a result, she arises? (When contacting the surfaces of the tel).
Conclusions:
The friction force is the force arising when contacting the surfaces of the bodies, and preventing one body from the surface of the other.
Designation of friction force F. tr. (Slide 2).
What are the causes of friction force? We can answer these questions, according to the results of experiments.
Experience 2. : Take 2 pieces of sandpaper. Fold them and try moving relative to each other. Name the causes of friction(Slide 3).
Experience 3: Take 2 glass plates, press them with each other, and then slide one plate relative to the other. What do you watch? Why are the plates hard to move? Name the causes of friction(Slide 4).
Conclusions:
surface roughness.
molecular interaction (according to the basic ICT laws)
Where direction is the force of friction?
Output : - The friction force is directed to the side opposite to the movement(Slide 5).
What does friction force depend on? Experience 4: The strength of friction depends:
from the weight of the moving body;
from the kind of rubbing surfaces;
The friction force does not depend on the area of \u200b\u200bcontacting surfaces.(Slide 6).
Three types of friction forces can be distinguished:(Slide 7).
Experience 5. Friction of rest F. Tr.Pok. (in order to move off any body, you need to make any power)(Slide 8).
Experience 6. Sliding frictionF. Tr.Colzh (Sledge) (Slide 9).
Experience 7. . Rolling friction F. Tr. Kach (wheels) (slide 10).
F. tr.Pok. > F. tr.Colzh >> F. tr.Kach
Experience 8. The friction force, which is stronger than storms, winds and bad weather (two books that have sheets intertwined, it is not possible to pull out).(Slide 11).
Life experience tells us that friction is very important in our lives and plays both a positive and negative role.
Our attitude towards friction is contradictory: on the one hand, a struggle is being conducted: the rubbing surfaces of the machines are grouped, simple sliding bearings are replaced by ball or roller, rich lubricants are used, lubricants are created.(Slide 12).
On the other hand, if the friction disappeared? Friction helps when walking, could not touch without friction of the train, cars.(Slides 13-14).
In the absence of friction of nails, the screws slip out of the walls, could not hold one thing in their hands, the whirlwind never stopped, the sounds did not slander.
Wisdom and life experience every people concludes in sayings. For example:
not fit, you will not go;
the case went like oil;
what circle is easily rolling;
ski slide on the weather;
rusty plow only on the smelting is cleared;
there is no such person who would not have slipped on ice at least once. (slide 15).
How can I use the studied phenomenon in life? Give your examples. The friction phenomenon is used in the technique:
for moving movement;
when processing metals and other materials;
when welding with friction;
when sharpening instruments;
for fastening materials, parts of structures;
when grinding, polishing materials, etc.
What evaluation can be given the role of friction in life? Given the negative role of friction, it is necessary to reduce it. For this you need:
Select materials with low friction coefficient;
Improve the quality of the processing of rubbing surfaces;
Replace the friction of sliding friction of rolling;
Use lubrication.
5. Physical pause
Before you begin to solve problems, we will conduct a physical pause.
Why in winter the tracks sprinkle with sand?
Why is oil poured into the car engine?
Why do sportsmen skiing on skis apply special lubricant?
Why the bearings of the wheels and pedals of bicycles are lubricated with solidol?
Why do the athletes wear sports shoes with spikes? (slide 16).
9. Fixing the material studied. (from Lite 17)
Students perform a test task. Answers are shown using the Signal Cards on the Teacher's team.
1. What power does not allow a heavy wardrobe from the spot?
A. Slip friction forces.
B. Power of friction of rest.
B. Power.
2. Parachutist, the mass of which is 70 kg, evenly descends. What is the power of air resistance?
A. 700 N.
B. 0 N.
B. 70 N.
3. When lubricating rubbing surfaces, friction force ...
A. does not change.
B. increases.
B. decreases.
4. How is the friction force point when the bar moves on the table to the right?
A. Right.
B. Left.
V. Vertically down.
5. The sidewalks sprinkle with sand. At the same time, friction soles of shoes about ice ...
A. does not change.
B. decreases.
B. Increases.
10. Conclusions. (we conclude with the study) (5 min) (slides 21-22)
11. The results of the lesson:
HOMEWORK. § 32-34 (slide 23)
Thank you, children, for lesson!
Sabasev Sergey Vitalevich
, experimental activities, friction, types of friction, Causes of friction
Presentation to the lesson
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Objectives lesson:
Educational:
- students need to know the concept of friction force
- know the types of friction
- be able to experimentally install, from which the strength of friction depends
- students should be able to establish the causes of friction force
Developing:
- development of logical thinking
- development of skills experiment
- Formation of skills to use appliances
- Formation of skills to draw conclusions, analyze and compare the results of experiments
Educational:
- attract students to active independent activities
- education of culture of communication
Equipment for the teacher: Computer, multimedia projector, presentation, wooden bar, dynamometer, cargo set (3), 2 round pencil, 2 slot glasses.
Equipment for students: Dynamometer, smooth paper sheet, wooden bar, cargo set (3), 2 round pencils, 2 slot glasses.
Preparation for lesson: Each table is issued equipment, information sheets, a leaf of self-esteem.
Plan
- Organizational moment (2 min.)
- Actualization of Knowledge (2 min.)
- Motivational principle of lesson (1 min.)
- Study of a new material (20 min.)
- Fastening learned. Solving quality challenges (5 min.)
- Test execution (4 min.)
- Summarizing. House. the task. Reflection (5 min.)
During the classes
I. Organizational moment
Teacher: Hello guys! Sit down. (Slide 1)
Today, the lesson is a little unusual for 2 reasons. I will lead him. My name is Lyudmila Ivanovna, and the second reason is visiting guests at the lesson. And the rest of the lesson as always - the lesson for receiving knowledge.
So, we start our lesson,
Let him all go to you.
We will listen, respond,
Takes must be pulled.
How, why and why
And you evaluate it!
In the section "Interaction of Body", you studied various forces that help us in life. In this lesson, we will study one more power, no less important, but first, remember that you already know about the power.
II. Actualization of knowledge
Continue phrase:
- Strength is ...
- Types of forces:
- Force measurement unit ...
- The force is measured by the device ...
- Strength is a vector value. What does it mean?
- The force of elasticity arises ...
III. Motivational principle of lesson
Teacher: Guys, have you ever wondered, "Why makes the chalk leaves the mark on the board?", "What role does saliva play when swallowing food?", "Why do needles polish carefully?"
We will be able to answer these questions by studying the lesson material.
But the next question you probably know the answer: "What physical phenomenon helps you remove an eraser without a desirable drawing made by a pencil in a notebook?" (Friction)
Teacher:Right. And for this you attach strength to the eraser - the strength of friction.
So guys, the topic of the lesson FRICTION FORCE.
Today we will work in the next lesson map. Opposite words SUBJECT Write down theme lesson.
Based on the topic of the lesson, what questions you would like to get answers today:
Pupils:
- What is the force friction
- Types of friction force
- Where she is directed
- Where is the application
Today I will help you to find out what kind of friction will be introduced with the types of friction force, we will establish the causes of the friction force and experimentally see what the friction force depends on. And we will also develop logical thinking with you, learn to draw conclusions, analyze, compare the results of experience, yourself in practice, make sure which kind of strength is more.
IV. Studying a new material
Teacher: With the phenomenon of friction you are familiar with childhood. In the campaign we say: "Not on trite legs". At school: "with trite from the recording board "etc.
Experience the first:
Teacher: You have a wooden bar on the table. Take it. Put in front of yourself and push. What happened to him?
Teacher: The body stopped .
Teacher: Why, what slows it?
Pupil:- friction. Surfaces rub each other, and the body slows down.
Teacher: The body has the power of friction.
Teacher: And how is it directed?
Pupil: Against movement.
So: The force arising from the movement of one body along the surface of another attached to the moving body and directed against the movement is called the force of friction.
Teacher: We return to the card. Read the definition and try to remember.
(Ask two or three people). Perform task 1.
Teacher: What did you know?
By following the following task, we will learn the causes of the friction force.
Second experience:
Take a sheet of paper and pencil. Spend any line on a pencil sheet. And now, the same try to make on the glass. What do you watch?
OUTPUT Pupil:The paper remained on the paper from the pencil, and there is no glass.
Teacher: What is the case?
Consider the surfaces of the griffel, paper and glass.
The surface of the paper is rough, like in the griffel. And the glass is smooth. When the pencil is moving on paper, it is cleaned by a pencil pieces about the nervous paper, they remain on paper. There are no such irregularities on the glass.
Teacher: So, what is the cause of friction?
Pupil: In the roughness of the surfaces of contacting bodies.
Write down in the second column next to the number 1
Teacher:Perform experience 2.
Experience the third: Press each other's row more than two glass and try moving one relative to the other.
Pupil: It is not so easy to do.
Teacher: So what's the deal? After all, there are no roughness, but still something interferes?
Pupil: Attraction of molecules of interacting bodies.
Write down 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: friction slip, rolling friction, friction of rest
Take your tutorial, put a pencil on it, if he begins to slide means, the stronghold of slip friction occurs if it rolls, then the strength of rolling friction arises.
What do you think, and when may the strength of friction of rest arise?
What do you think, which of these forces is more?
And let's check it.
Put the bar, attach the dynamometer, load it with the weights. And now attention: Try to move the bar, making an effort to the dynamometer, and remove the maximum value at which the bar did not start moving at the moment when it already slides on the surface of the table. Compare the values \u200b\u200bin the card.
Put two round pencils under the bar, remove the reading from the dynamometer. Compare
Friction of rest.
As they say, there is no humus without good. After all, it does not only harm movement, it also contributes to the stability of the tel. Do not be it, everything will roll, and slide until it turns out on the same level. Nails and screws will slip out of the walls, the fabric will spread, no buttons cannot be seeded, the threads simply will not be kept in the needle, nor in the tissues. Little of. Without friction, we could neither walk, do not ride. Remember how difficult it is to move in ice.
(Perelman Ya.I. Entertaining physics. If there were no friction. P. 263)
Teacher: One of the London newspapers in the early 20th century wrote: (December 1927)
"As a result of a strong farmer, street and tram movement in London is noticeably difficult. About 1400 people enrolled in hospitals with hand fractures, legs ... "
Teacher: What should I do to not happen again? How can the friction be increased?
Pupil:Sprinkle with sand, therefore enlarge surface roughness
Teacher: And they say also that the strength of friction also depends on weight of cargo.
Check it out on experience.
1. Front experience
A) Put one cargo on the bar and pull it evenly over the surface of the table. Note and write down the dynamometer readings into the table opposite the same cargo.
B) Add another cargo to the bar. Write down the testimony in the table.
B) Add the third cargo on the bar. Record the dynamometer readings.
D) Compare the results obtained, and make the output.
Conclusion: the more weight, the more friction force.
Compare your conclusions with the entry in the table.
Teacher: What ways can the friction be reduced?
Pupil:- Remove unevenness, i.e. Collect surfaces
Teacher: Wearing machine parts and mechanisms occurs due to friction. To reduce the friction of contacting surfaces between them are injected lubrication.
(Slide 10) Ways to reduce friction
- Grinding
- Lubricant
- Reducing the load
- Slip friction force replace rolling friction force
V. Fixing the studied. Solving quality challenges
Teacher: You have questions for consolidation in your card. Read them, answer, you can consult with a subsidement on the desk.
Let's go back to the guys to the questions we set at the beginning of the lesson. Reply to them.
- Why do needles polish carefully?
Answer: Reduce the force of friction of sliding and then easier to sew. - What role does saliva play when swallowing food?
Answer: The role of lubrication, friction is reduced and easier to swallow. - Why make the chalk leaves the mark on the blackboard?
Answer: When the chalk is pressed to the board, create a greater friction force, which tears the chalk particles - the mark on the board occurs.
In winter twilight nanny fairy tales
Sasha loved. In the morning in Salazki
Sasha sat down, flew the arrow,
Full happiness, from the mountain ice. N. A. Nekrasov (Slip friction force)
Along the edge of Vova rides
On his bike
And lucky jam
Everyone for treats. (rolling friction force)
Although it's hard at her burden,
The cart on the move is light;
Ditch dashing, gray time,
Luck does not get off the irradiation. A. S. Pushkin (rolling friction force)
Cat for bug
Bug for granddaughter
Grandmother's grandmother
Grandma behind Ditch
Dedka for Rust
Pull-pull, stretch can't . (rest friction)
Teacher: And now check how you know how to apply the theory in practice. On the latest page of the information card, work is offered options.
Vi. Test execution
Test work
Teacher: Take the handle and circle the correct answer option.
| Option 1 | Option 2. |
| 1. Which units are the friction force measured? A. M. B. N. V. M / s 2. What is the force more: the strength of friction of peace or the power of friction slip? 3. Why when moving heavy loads under it put rollers? 4. In the Hollyeditsa, the sidewalks sprinkle with sand, while the friction force soles of shoes about ice ... |
1. What device can be measured by the power of friction? A. Laina B. Menzurka V. Dynamometer 2. What power is less: the strength of peace friction or rolling friction force? 3. Why is any body given in motion in the end, stops? 4. During the challenge of the car under the wheels, gravel or slag are plundered. At the same time the force of friction ... |
Teacher: Guys, take a pencil and exchange cards. We carry out the mutual test. The correct answers are presented on the slide. Put the rating with regard to the criterion, it is also specified on the slide.
Right answers:
| Question number | 1 | 2 | 3 | 4 |
| Option 1 | B. | IN | B. | B. |
| Option 2. | IN | IN | BUT | B. |
Criteria ratings:
- rating "5" for 5 correct answers
- evaluation "4" for 4 loyal responses
- rating "3" for 3 loyal responses
Checked? Raise your hand to "5"? Lower. And who "4"?
Well done! Well, the rest is over what to work.
The information card remains with you. You go into your notebook.
VII. Summarizing.
Let's summarize:What did you know the new on the lesson?
Have you achieved your goals in the lesson?
House. the task
- §§ 30-32 (for all)
- Invent an essay on the topic "If the friction force had disappeared ..." (for those who wish)
Reflection
Self-esteem:Take a sheet of self-esteem and answer questions.
Sheet of self-esteem
| № | Question | Yes | Not | Difficult to answer |
| 1 | I know the types of friction force | |||
| 2 | I know the unit of measurement of friction force | |||
| 3 | I know where the friction force is directed | |||
| 4 | I can define the type of friction force | |||
| 5 | I can measure friction force | |||
| 6 | I consider my work in the lesson effective |
And another week of attention, guys, in memory of this lesson, I want to give you a bookmark about the strength 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. A. Tasks with vocational guidance for rural schools // Physics in school, 2001, №2.
- Maron A. E., Maron E. A. Didactic materials. Physics Grade 7 - M.: Drop, 2002.
- Pryrickin A.V. Physics. 7 cl. - 3rd ed., Act. - M.: Drop, 2000.
- Perelman Ya. N. Entertaining physics. Kn. 1, 2 - M.: Science, 1991.
The purpose of the lesson to get acquainted with the force of friction; Find out whether the friction force is really stronger than storms, winds and bad weather; experimentally establish the causes of friction force; To find out what kind of friction force exists, as well as find out the positive and negative role of friction strength in a person's life.
Experience 1 Observation of the friction phenomenon on the table is a wooden bar. Push him and watch his movement. Attach the dynamometer to it and pull uniformly. Replace the cylinder bar and do the same. What can you say about body speed? How did she change in experiments?
Experience 2 and 3. Clarification of the causes of friction. We establish 2 reasons for the friction and the presence or absence of similarities between the friction force and the force of elasticity. Experience 2: Take 2 glass plates, press them to each other, and then slide one plate relative to the other. What do you watch? Why are the plates hard to move? Drip pipette on one plate 2-3 water droplets and repeat the experience. Why did it make it even harder to shift the plate? Experience 3: Take 2 pieces of sandpaper and magnifying glass. Consider the surface of these bodies. Fold them and try moving relative to each other. Name 2 causes of friction.
Friction force causes from what the mutual attraction of molecules of contacting surfaces depends the quality of processing of contacting me the surfaces of the substance grease the magnitude of the pressing force of the KI Type of force of the friction force of friction slide friction force rolling force of friction rest roughness comes
I offer questions in poetic form: "Well, friends, tell me why live fish is difficult to keep in your hand? Well, who, guys, knows: why in winter roads are sprinkled to us? Skates with the sands of Egorka somehow climbed onto the slide. Well, now I understand: Shut off Egorch down?
Our attitude towards friction is very controversial. On the one hand, a merciless struggle is conducted with friction: rubbing the surfaces of the machines are carefully polished, simple sliding bearings are replaced by ball or roller, rich lubricant is used, there is a lot of work on creating new ideal lubricants. On the other hand, what would we do if the friction suddenly disappeared? Even when walking friction provides us with a big service - it is so difficult to go on slipping ice. Cars and trains without friction could not touch. And if some kind of body moves, slides to stop it, you need to make an effort.
Do you need to get rid of friction? In the absence of friction, the nails and the screws would slip out of the walls, not one thing could not be held in their hands, no whirlwind would never stop, no sound, but I would have sounded an endless echo, it would be unrepreneurously reflected, for example, from the walls of the room. A visual lesson that convinces us in the great importance of friction gives us every time a holled. We are covered on the street. We turn out to be helpless. Wisdom and life experience every people concludes in sayings. For example: you will not fit, you will not go; The case went like oil; eel in the hands do not hold; What circle is easily rolling; ski slide on the weather; From the hosted thread, the network does not spit; Cleaning rope log houses;
Conclusions: The friction force is the force arising when the single body moves along the surface of the other. Types of friction forces: peace friction force, sliding friction force, rolling friction force. Causes of the appearance of friction force: - intermolecular interaction of surfaces of contacting bodies; -Howness of contacting surfaces of friction force: - aimed to the opposite movement; - has a point of application - a set of points of contact of the surfaces of interacting bodies; - weakly depends on the rate of relative movement of interacting bodies; - dependent on the genus of rubbing surfaces, i.e. from the material and on the quality of surface treatment of interacting bodies; - depends on the strength of normal pressure and grows with its increase; - does not depend (in large limits) from the area of \u200b\u200brubbing surfaces.
Thank you for a good job. And maybe in the distant future, any of you will be a great scientist, and we will all be proud of it. For, as the great M.V. Lomonosov wrote, there can be own platonists and fast intelligence of the Russian Earth to give birth to! Thank you, children, for lesson!
Class: 7
Presentation to the lesson
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Type of lesson: combined.
Type of lesson: Traditional with elements of laboratory work.
Objectives lesson:disclose the concept of friction force, to explain the causes of the friction force, to get acquainted with various types of friction force, find out what factors the friction force depends.
Tasks:
- Educational:
- consolidate the existing knowledge on the topic "Forces in Nature";
- get acquainted with the force of friction;
- explain the causes of the friction force;
- continue the formation of the ability to explain the processes in terms of the structure of the substance.
- Educational:
- formation of communicative qualities, culture of communication;
- formation of interest in the subject studied;
- stimulation of curiosity, activity in class;
- development of performance.
- Developing:
- development of cognitive interest;
- development of intellectual abilities;
- development of skills to allocate the main thing in the material studied;
- development of abilities to summarize the studied facts and concepts.
Forms of work: Frontal, work in small groups, individual.
Means of education:
- Textbook "Physics 7" A.V. Pryony § 30, 32.
- Collection of tasks in physics for 7-9 classes, A.V. Pryskin, Chapter 15.
- Distribution material (test sheets, practical tasks).
- Dynamometers.
- Wooden bars.
- Strips of different types of surfaces.
- Presentation "Friction force".
- A computer.
- Illustrations on the topic.
Lesson plan:
- Organizing time.
- Repetition of the material studied.
- Testing.
- Check test.
- Definition of the lesson.
- The power of friction in life and in nature.
- Record the topic of the lesson in the notebook.
- Setting the goals and objectives of the lesson.
- Study of a new topic:
- Causes of friction force.
- Work in small groups to clarify the factors on which the force of friction depends.
- Reports of groups of their work.
- The dependence of friction force on the type of contacting surfaces.
- The dependence of the friction force from the force presses the body to the surface.
- The difference between the force of friction of sliding and the strength of rolling friction.
- The friction force does not depend on the area of \u200b\u200bcontacting surfaces.
- Fastening the material studied.
- Summarizing.
- Homework.
During the classes
| Stage number | Work teacher. | Work of students | Entries in notebook | Used slides, benefits, equipment, literature | Time |
| 1. | Greeting. | 1 min. | |||
| 2. | Draws the attention of students to the handouts to the test, reminds the rules for filling them. | Fill out the dispensing sheets to the test. Attachment 1 | Disposal sheets. | 1 min. | |
| 2.1. | Reads the test questions, if necessary, comments on them. Collects dispensing sheets. |
Answer test questions. Roll down handpers. | Slides 2-7 | 5 minutes. | |
| 2.2. | Requests the student to comment on their answer, and then calls the correct answer and explains it if necessary. | Once again, they think about the answers, the disciples mentioned by the teacher comment on their answers. | Slides 8-14. | 5 minutes. | |
| 3. | Requests the forces that have been studied at previous lessons. It suggests that the lesson will talk about another force. | They remember what time they have already studied. Gravity strength, strength of elasticity, body weight. | 2 minutes. | ||
| 3.1. | Shows the slides on the screen, demonstrating the value of friction strength in nature and life. Requests students to name the strength of which is in question. | Consider slides, draw conclusions, call strength. (As experience shows in the title, they are not mistaken). | Slides 15-16. | 2 minutes. | |
| 3.2. | The topic "Power of friction" dictates and writes it on the board. | Record the topic of the lesson in the notebook. | Topic: "Friction force" - |
Slide 17. | 1 min. |
| 3.3. | Gives the definition of friction strength and asks to write it to the notebook. Defines the purpose and objectives of the lesson. Cleaned sheets with group tasks. | Wear entries in the notebook. Carefully listen to the teachers. | - This is the force arising from the movement of one body along the surface of the other attached to the moving body and preventing the movement.  |
Slide 17. | 3 min. |
| 4. | Requests the disciples to help him explain the new material. | Prepare to help. | |||
| 4.1. | Relying on life experience shows that one of the reasons - the irregularities of surfaces demonstrates that in this case the friction force can be reduced using lubricant. Other - the interaction forces of molecules. Dictates the basic positions in the notebook. | They remember where in life they came across the force of friction, lead records in the notebook. | Causes of friction force 1. The irregularities of contacting surfaces. (With the help of grease irregularities can be reduced). |
Slides 18, 19, 20 | 5 minutes. |
| 2. Mutual attraction of molecules of contacting bodies | Slide 21. |
||||
| 4.2. | It suggests that friction force depends on a number of factors and asks students to find out what these factors and how they affect the force of friction. Explains that the dynamometer shows the force of elasticity (thrust force) and it will be equal to the power of friction only in the case of a uniform movement of the bar. | Pupils are divided into groups (division into groups and lists of groups was presented to the teacher before lesson). Each group performs tasks that are written on handouts. Appendix 2. The results of their experiments they are recorded on special sheets - tables. |
Slide 22. Disposal sheets. Equipment: Bars, loads, dynamometers, removable wheels, various types of surfaces. |
10 min. | |
| 4.3. | Announces the completion of practical work, asks the groups to get ready to voice the results. | Preparing to report on the work done, choose a student who will go to the blackboard. (It is best to discuss it even before the lesson). | The friction force depends on: | 1 min. | |
| 4.3.1. | Heads the answer, if necessary, asks leading questions. Complements the student's response by examples from life ( corrugated sole of winter shoes, studded sneakers, winter tires in cars and bicycles). | It turns out that the friction force depends on the type of contacting surfaces, make the necessary entries in the notebook. | 1. The type of touching surfaces. | Slide 23. | 2 minutes. |
| 4.3.2. | (The wheels of trams and trains, as well as rails have a smooth surface, but the friction force is large due to the high weight of trams and trains). | It turns out that the friction force depends on the strength pressed the body to the surface, make the necessary records in the notebook. | 2. Forces pressed the body to the surface. | Slides 24, 25 | 2 minutes. |
| 4.3.3. | Heads the answer, if necessary, asks leading questions. Complements the answer examples from life (The use of volokus in some tribes, the invention of the wheel, dragging in antiquity of ships with a case with the use of logs, the use of special horizontal baskets from twisted rods during the construction of Stonehenge, the use of bearings to reduce friction force). | It turns out that with equal loads, the sliding friction force is always more rolling friction force, make the necessary entries in the notebook. | 3. With equal loads, the rolling friction force is always greater than the stroke of the slip. | Slides 26, 27, 28, 29, 30 | 2 minutes. |
| 4.3.4. | Heads the answer, if necessary, asks leading questions. Complements the answer examples from life (The ancient Egyptians who have erected unprecedented pyramid from thoroughly treated rectangular blocks, probably knew that the resistance when dragging such blocks does not depend on whether they lie to the pier, rest on the side face or stand "on the pop.". For the first time, this phenomenon was interested in French The scientist Gilo Amonton at the end of the 18th century (1699) his work of the century later continued Charles Pendant and now the law on the independence of the friction force from the surface area wears the name of the Amonton Law - Coulomb.) | It turns out that the friction force does not depend on the area of \u200b\u200bcontacting surfaces. | The friction force does not depend on the area of \u200b\u200bcontacting surfaces. | Slides 31. | 2 minutes. |
| 5. | Questions: | Answers on questions. | Slide 32. | 3 min. | |
| 1. What is the force called friction force? | this is the force arising when the single body is moving along the surface of the other attached to the moving body and preventing the movement. |
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| 2. What is the cause of friction force? | 1. The irregularities of contacting surfaces. 2. Mutual attraction of molecules of contacting bodies. |
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| 3. How can I reduce the power of friction? | Lubricate in contact with surfaces or replace the force of friction of rolling friction force. | ||||
| 4. From what factors the friction force depends? | 1. From the type of touching surfaces 2. From force pressering the body to the surface 3. With equal loads, the sliding friction force is always greater than the rolling friction force. |
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| 5. From what factors does the friction force do not depend? | From the area of \u200b\u200bcontacting surfaces. | ||||
| 6. | Determining the value of friction force in life: What would happen if the friction force disappeared? Comments on the performance of the lesson tasks, estimates, thanks to distinguished students. | If there were no friction, we could not walk on the ground (remember how the legs slide on the ice), it would not be possible to ride a bike, a car, a motorcycle (wheels would be ruined in place), we would have nothing to wear (tissue threads keep friction forces). If there were no friction, all the furniture in the room would have gotten up in one corner, plates, glasses and saucers would sculpted from the table, nails and screws would not keep in the wall, none things could be kept in hand, etc. etc. This can be added that if there were no friction, it is not known how civilization will go on Earth, because our ancestors mined friction fire. | Slide 33. | 2 minutes. | |
| 7. | Homework, necessary comments. | Recording homework in diaries. Tutorial Pereshkin A.V. - § 30, 32 Collection of tasks Pryskin A.V. - chapter 15. |
§ 30, 32 Chapter 15. |
Slide 34. | 1 min. |
Used Books:
- Pryrickin A.V. Textbook "Physics 7".
- Pryrickin A.V. "Collection of tasks in physics 7-9 classes", Moscow, "Exam", 2006.
- V.A. Orlov "Thematic tests in physics 7-8 classes", Moscow, "Verbum - M", 2001.
- G.N. Stepanova, A.P. Stepanov "Collection of questions and tasks in physics 5-9 classes", St. Petersburg, "Valeria SPD", 2001.
- IN AND. Grigoriev, G.Ya. Myakyshev "Forces in Nature", Moscow, "Science", 1988.
- kak-i-pochemu.ru.
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Purpose: consolidate the knowledge gained in nature; introduce students with friction force; experimentally find out what friction force depends on; consider the types of "dry" friction; Compare rolling friction, slip, rest; Teach students to determine the type of friction; Introduce the calculated formula for finding friction force (slide 2).
Required technical equipment: Interactive board, computer, projector.
Software: PowerPoint, video player, presentation.
Registration: The board shows the topic of the lesson and tasks to actualize knowledge. The printed halves are written on the folding halves (or printed) about the strength of friction.
Equipment: Wooden bar with grains of different areas, but the same surface roughness; Set of loads of 100 g; Wooden, badly ground board; Dynamometer, rollers (2 cylindrical stem, for example 2 pencils).
Explanatory note on the use of the presentation. (Attachment 1)
During the classes
1. Organizational moment. Hello. Today, at the lesson, we will try to find out the meaning of some Russian sayings from the point of view of physics. (Slide 3). For this, we will confirm or refute the possibility of the described events. But first remember what we studied in previous lessons and what you need today.
2. Actualization of knowledge.
BUT) One student works for an interactive boards: Portray body weight, strength of elasticity and gravity. (The teacher pays attention to the point of the application and the direction of force). (Slides 4, 5)
B) At the board, the teacher prepares the tasks. While the student works at the interactive board, the entire class works independently in notebooks, the answers will be discussed when checking using the presentation.(Slide 6)
1. Where is the strength of gravity more? Where is more weight?
2. Where is the force of elasticity more (k 1 \u003d k 2)? What can be said about the strength of gravity if the bars rest? (Slide 7)
3. Where is the rigidity greater than (M 1 \u003d m 2)? What can be said about the strength of gravity if the bars rest? (Slide 8)
4. Determine and designate the resultant forces. Where in this case will the body move? And if you get rid of the strength marked with black, how will the body move? (Slide 9)
C) Two student (sitting at one desk) get a task and equipment: "Build a graph of body weight dependence on the mass. Equipment: Dynamometer, Truck Set " Students represent the results of the work of the class and conclude after discussion of all issues.
The teacher watches how students perform work and provides the necessary assistance. After 5-7 minutes, the check is organized. Focus on the key points that should have been noted by students when performing tasks.
3. New material
In previous lessons, we have repeatedly affected the question that if there are no other bodies on the body or the effect of these bodies is compensated, the body either rests or moves straight and evenly (slide 10). The physical value that characterizes the effect of bodies on each other is called force. Let's carry out an experiment: dynamize a dynamometer of a bar with weights so that the movement is uniform. Why is it becoming possible? That's right, the force of thrust in this case is compensated for some more force, we have not yet known yet? (Slide 11). Let's try to find out what it is for the power where it occurs where it is directed and depends on.
A teacher with assistants issues equipment (see above) to each desk.
Spend the same experiment yourself and think: where is the force unknown to us?
This force is called friction force. The FTR is indicated, is measured in N. In connection with which it occurs? In connection with the contact of the bar and parties, it means that there arises in the place of contact of the two bodies. The causes of the friction force are two (slide 12). When one body slides over the surface of another, irregularities cling to each other, which creates some power, delaying movement. But if you take 2 well-polished items, for example, two glasses, the friction force is also high, since in this case there are mutual attraction forces between molecules of contacting bodies, which are the cause of friction.
What do you think this power can depend on? Check your guesses. Possible assumptions. (Slide 13, 14)
(It is better to organize the work by groups - each group checks one hypothesis and voiced, comments the result)
1. From speed (independent).
2. From the mass transferred.
The more P, the more FTR.
4. From surface roughness, etc.
A teacher helps to simulate the experiment of students in such a way as to check all the suggested assumptions. After that, all conclusions are recorded.
In notebooks write the FTR. (Slide 15)
- Directed to the side opposite to movement.
- Occurs in the place of contact of two bodies
- Depends: on the weight (mass) of the body and roughness of the surface.
So The FTR is calculated by the formula (slide 16): FTR \u003d μN, where μ is a friction coefficient depending on the kind of rubber surfaces, N is the reaction force of the support, i.e. The strength of elasticity arising in the support under the influence of body weight.
Let the definition of the FTR - it is the force arising from the interaction of the surface of one body with the surface of another when the bodies are fixed, or move relative to each other.
And now put under the bar with weights of the rollers and measure the friction force. Compare it with the testimony that you have completed for the same weight in the previous experiment. What conclusion can be done? True, this friction force is less. Now put a bar with weights on a rough plane and try to move it. What is observed? The force first increases greatly, and when the bar comes in motion - it becomes equal to the force of friction obtained by sliding. Those. In nature, there are three kinds of "dry" friction: the strength of friction of sliding, rolling friction force and the strength of friction of rest.
Arrange the signs between the FTR. Issue _____ FTR. Pokoy. (Slide 17)
4. Fastening
(Slide 18) Arrange the type of friction force for each depicted situation. Give your examples of each type of friction force.
How can I increase and reduce friction force?
Explain the meaning of the sayings presented on the board. Do they have a physical meaning? (Slide 19)
Additionally: Give examples of manifestation of friction force.
Is there a benefit from the friction force? What?
What harm brings the power of friction? Is it possible to deal with it? How?
Homework: §30, 31, tasks 1 and 2, home experiment, get acquainted with an additional material. (Appendix 2). ( Issued either in printed or in electronic form). (Slide 20).
Bibliography
1. PRIRRYKIN A.V. Physics. 7 CL: student. For general education. Institutions / A.V. Pereyshkin. - 12th ed., - M.: Drop, 2008.
2. Volkov V.A., Polyansky S.E. Pounding development in physics: grade 7. - 2nd edition. - M.: Vako, 2009
