Municipal budgetary educational institution
“Bolsheyalchik secondary school named after. G.N.Volkova"
Physics lesson “Friction Force”
(7th grade)
The purpose of the lesson:
to form in students an understanding of the force of friction (reasons, patterns)
Lesson objectives:
Educational:
Formation of the ability to plan and conduct physical experiments, explain physical phenomena
Formation in students of skills and abilities that contribute to the independent discovery of new knowledge, the use of new ways of searching for information, and the development of problem thinking.
formation of the ability to systematize what has been learned, to reveal the relationship between the studied theoretical material and phenomena in life, to develop the ability to interact in a group form of work.
Developmental:
Development of logical thinking.
Development of communication skills when working in the classroom
Developing interest in problem solving.
Increasing interest in physics.
Educational:
Cultivating interest in the subject
Fostering a conscientious attitude to work
Lesson type: lesson in the formation of new knowledge.
During the classes:
1. Organizational moment.
Hello, dear guys!
So let's start our lesson,
May it benefit you all.
Today is a special lesson!
Today we have to discover another secret of nature. Today we will meet mysterious force - the force of friction!In the lesson we must find out: friction is an ally or an enemy of a person. But in First, you need to repeat the knowledge you have acquired on the topic.
2. Testing knowledge acquired in previous lessons
- A boy weighing 35 kg put a backpack weighing 5 kg on his shoulders. With what force does the boy press on the floor?
3. Setting the lesson goal:
The topic of today's lesson:"Friction force » (slide 1).Write down the date and topic of the lesson in your notebooks. Now we need to study, in my opinion, one of the most important forces - the force 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. Learning new material
We have been familiar with the phenomenon of friction and friction force since childhood. We've all had to go out in icy conditions: how much effort was required to keep ourselves from falling, how many funny movements we had to do to stand!
Experience 1: Observation of the phenomenon of friction.
There is a wooden block on the table. Push it and watch its movement.
What can you say about the speed of the body?
What force arises? (Friction force).
What causes it? ( When the surfaces of bodies touch).
Conclusions:
Friction force is a force that arises when the surfaces of bodies come into contact and impedes the movement of one body on the surface of another.
Designation of friction force F tr.(slide 2).
What are the causes of friction? We can answer these questions based on the results of experiments.
Experience 2 : Take 2 pieces of sandpaper. Fold them and try to move them relative to each other. Name the causes of friction(slide 3).
Experience 3: Take 2 glass plates, press them together, and then move one plate relative to the other. What are you observing? Why are the plates difficult to move? Name the causes of friction(slide 4).
Conclusions:
surface roughness.
molecular interaction (according to the basic laws of MKT)
Where is the friction force directed?
Conclusion : - the friction force is directed in the direction opposite to the movement(slide 5).
What does the force of friction depend on? Experience 4: The friction force depends on:
from the weight of a moving body;
from the type of rubbing surfaces;
The friction force does not depend on the area of contacting surfaces.(slide 6).
Three types of friction forces can be distinguished:(slide 7).
Experience 5. Static friction F tr.pok (in order to move any body, some force must be applied)(slide 8).
Experience 6. Sliding frictionF tr.slide (sled) (slide 9).
Experience 7. Rolling friction F tr.kach (wheels) (slide 10).
F tr.pok > F tr.sliding >> F tr.quality
Experience 8. The force of friction, which is stronger than storms, winds and bad weather (two books whose pages are intertwined cannot be pulled 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, there is a struggle: the rubbing surfaces of machines are ground, simple plain bearings are replaced with ball or roller bearings, abundant lubrication is applied, lubricants are created.(slide 12).
On the other hand, what if friction disappeared? Friction helps when walking; trains and cars would not be able to move without friction.(slides 13-14).
In the absence of friction, nails and screws would slip out of the walls, they could not hold a single thing in their hands, the whirlwind would never stop, the sounds would not stop.
Every nation encapsulates its wisdom and life experience in sayings. For example:
If you don’t grease, you won’t go;
things went like clockwork;
what is round rolls easily;
skis glide through the weather;
a rusty plow is cleaned only during plowing;
There is no person who has not slipped on ice at least once. ( slide 15).
How can you use the studied phenomenon in life? Give your own examples. The phenomenon of friction is used in technology:
to transmit motion;
when processing metals and other materials;
during friction welding;
when sharpening tools;
for fastening materials and structural parts;
when grinding, polishing materials, etc.
How can you assess the role of friction in life? Considering the negative role of friction, it is necessary to reduce it. To do this you need:
Select materials with a low coefficient of friction;
Improve the quality of processing of rubbing surfaces;
Replace sliding friction with rolling friction;
Use lubricant.
5. Physical break
Before we begin solving problems, let’s take a physical break.
Why are the paths sprinkled with sand in winter?
Why is oil poured into a car engine?
Why do ski athletes apply a special lubricant to their skis?
Why are the bearings of bicycle wheels and pedals lubricated with grease?
Why do athletes wear sports shoes with spikes? ( slide 16).
9. Consolidation of the studied material. (With lead 17)
Students complete a test task. Answers are shown using signal cards at the teacher’s command.
1. What force prevents a heavy cabinet from moving?
A. Sliding friction forces.
B. The force of static friction.
B. Gravity.
2. A parachutist whose mass is 70 kg descends uniformly. What is the force of air resistance?
A. 700 N.
B. 0 N.
V. 70 N.
3. When lubricating rubbing surfaces, the friction force...
A. does not change.
B. increases.
V. decreases.
4. What is the direction of the friction force when the block moves across the table to the right?
A. To the right.
B. To the left.
B. Vertically down.
5. When there is ice, the sidewalks are sprinkled with sand. At the same time, the friction of the soles of the shoes on the ice...
A. does not change.
B. decreases.
V. increases.
10. Conclusions. (we draw a conclusion from the student) (5 min) (slides 21-22)
11. Lesson summary:
HOMEWORK. § 32-34 (slide 23)
Thank you, children, for the lesson!
Ubasev Sergey Vitalievich
Children love physics!
She is always, everywhere
Helps you with your skills
Both in life and in work!?
Lesson on the topic: " Friction force".
Objectives: To form an idea of the types, characteristics and causes of friction; show the role of friction force in the occurrence of natural phenomena.
Tasks:
Educational: explain the physical meaning and characteristics of each type of friction force.
Developmental: contribute to the creation of students’ skills to listen and hear each other, analyze the results of the experiment, argue their own and the group’s points of view.
Educational: to continue the formation of the scientific worldview of students by familiarizing themselves with the physical quantity “friction force”, to promote the inculcation of mental work, to create conditions for increasing interest in the subject being studied.
Lesson type: explanation of new material.
Equipment: laboratory rollers, wooden blocks, dynamometers, laboratory equipment for studying friction force, laboratory cups with water, string, sand, a set of weights.
Lesson steps:
Organizing time
Updating knowledge
Motivational stage
Learning new knowledge
Primary consolidation
Lesson summary
Homework
During the classes:
Organizing time. (Teacher's opening speech).
Updating and monitoring acquired knowledge. Guys, guess the riddle “What will be three, three, three” (Hole) What phenomenon are we talking about? Of course, about friction.
Guys, the topic of today's lesson is “Friction Force”. You encounter this physical phenomenon in everyday life, so we must find out the nature of these forces and learn to apply knowledge about them in practice.
Why do you think motorists change summer and winter tires? Why does the “studded tires” sign have to hang on the rear window of a car? We get answers to these questions and many others when studying the topic “Friction Force”
Slide No. 1 on screen
Children, love physics
She is always, everywhere
Helps you with your skills
Both in life and in work!
Working with handouts (in groups)
Frontal survey:
- What is called the interaction of bodies?
- What physical quantity characterizes the interaction of bodies?
What do you need to know to determine strength?
What does the action of force lead to?
What powers do you know?
How is force designated and measured?
What is the name of the device for measuring force?
What does the value of force depend on?
What force holds bodies on the surface of the Earth?
What force of gravity depends on body mass?
What is your body weight?
What force of gravity acts on you?
Work in groups is carried out using cards. For example, one of the options:
What force causes the formation of rockfalls in the mountains?
A) Heaviness
B) Friction
B) Elasticity
2 . What is the force of gravity acting on a body of mass 3 kg?
3. What is the approximate mass of a 20 kg body?
4. The force with which a body, due to attraction to the Earth, acts on a support or suspension is called...
A) Elasticity
B) Gravity
Mutual verification (Slide No. 2)
Checking the correctness of the completed task.
Every day we go somewhere
But at the same time we don’t slide,
Because our feet
Caught on the roads
Are we or are we slowing down?
Why don't we slip when we walk?
What helps us move?
The reason is friction force.
Guys, from your life experience, you know that a silk lace unties faster than a woolen one. And why?
Why is it easier to roll a log than to drag it?
Why doesn't a nail driven into a wall pop out?
Therefore, the purpose of the lesson is to understand all these why?
We come into contact with friction at every step. More precisely, we will not be able to take a single step without friction. The two most important inventions of man - the wheel and making fire - are associated precisely with the desire to reduce or increase friction.
People reflected the importance of friction in life in various Sami proverbs and sayings.
Things went like clockwork.
Rolls around like a dumpling in butter, etc.
Like a cow on ice.
Demo #1
Move a heavy object using a dynamometer and pull it evenly along a wooden horizontal surface, record the readings of the dynamometer.
Questions for the class
What forces act on the block during motion?
What type of friction is the frictional force that acts on the block?
What can be said about the resultant force in this experiment and why?
The experiment is repeated gradually loading the block, i.e. increasing the force of normal pressure, as well as the force of normal support reaction (N)
Move the block evenly on the wooden board.
Question for the class:
What force balances the external force? (Sliding friction force)
Demo #2
We place the block on two round pencils and move it using a dynamometer.
Question for the class:
What counteracts the external force? (Rolling friction force)
This method can even be used to move a house during reconstruction.
Teacher's explanation
Causes of friction:
Roughness of contacting surfaces;
Interaction of molecules in contact with the surface;
The friction force is electromagnetic in nature.
Depending on this, friction can be harmful or beneficial; it is either reduced or increased.
Ways to reduce friction:
Polishing contact surfaces
Application of oils
Application of ball or roller bearings.
Ways to increase friction:
Primary consolidation of the studied material.
Group work of students according to the plan for the study of friction forces.
Group 1. Study of the dependence of friction force on the type of rubbing surfaces.
Determine the price of dividing the dynamometer
Write the result in the table
| Type of working surfaces | Sliding friction force |
| Wood by wood | |
| Wood on smooth paper | |
| Wood on sandpaper |
Conclusion: The friction force depends on the type of rubbing surfaces.
Group 2. Study of the dependence of sliding friction force on pressure
Fill out the table
| F tr. Slip |
|
| 2 weights | |
| 3 weights |
Conclusion: the greater the pressing force, the greater the sliding friction force.
Group 3. Comparison of frictional forces of sliding, rolling and scratching of the body.
Determine the price of the dynamometer scale division
Fill out the table
| Friction force, rest force, N | Friction, sliding force, N | Friction, rolling force, N |
|
Conclusion: rolling friction is less than sliding friction.
6 . Lesson summary.
Guys, today we looked at the force of friction - a familiar, but mysterious force that is stronger than storms, winds and weather. Our life is unthinkable without friction.
Poem
If there was no friction
Our life is unthinkable without friction
What would happen if there were no friction?
I'll tell it in a poem
All cars
Let's get up now
And the pedestrians fell to the ground.
If the pen had not written, the house would have collapsed.
And there would be complete destruction on Earth!
The picture fell down
And we would dump
So easy to plug in
They couldn't stick it in.
And there would be a lot of terrible things
If there is no friction force,
Here on Earth.
In all the chaos I forgot to say,
That friction cannot be removed from the Earth so easily,
It was, is and will always be,
Long live friction!
Trenu - hooray!
7 . Reflection.
What did we do and what results did we get?
What problems remain?
What would you like to learn in future lessons?
8 . Homework.
Learn paragraph 11 of the textbook. Answer the questions.
Fill out the table
Class: 7
Presentation for the lesson
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Lesson type: combined.
Lesson type: Traditional with elements of laboratory work.
Lesson objectives: reveal the concept of friction force, explain the reasons for the occurrence of friction force, get acquainted with the different types of friction force, find out on what factors the friction force depends.
Tasks:
- Educational:
- consolidate existing knowledge on the topic “Forces in Nature”;
- become familiar with the force of friction;
- explain the causes of friction;
- continue to develop the ability to explain processes from the point of view of the structure of matter.
- Educational:
- formation of communicative qualities, communication culture;
- developing interest in the subject being studied;
- stimulating curiosity and activity in the classroom;
- development of performance.
- Developmental:
- development of cognitive interest;
- development of intellectual abilities;
- development of skills to highlight the main thing in the material being studied;
- development of skills to generalize the facts and concepts being studied.
Forms of work: frontal, work in small groups, individual.
Means of education:
- Textbook “Physics 7” by A.V. Peryshkin § 30, 32.
- Collection of problems in physics for grades 7-9, A.V. Peryshkin, chapter 15.
- Handouts (test sheets, practical tasks).
- Dynamometers.
- Wooden bars.
- Strips of different types of surfaces.
- Presentation "Friction Force".
- Computer.
- Illustrations on the topic.
Lesson plan:
- Organizing time.
- Repetition of learned material.
- Testing.
- Checking the test.
- Determining the topic of the lesson.
- The force of friction in life and in nature.
- Write down the topic of the lesson in your notebook.
- Setting goals and objectives for 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 friction force on the type of contacting surfaces.
- The dependence of the friction force on the force pressing the body to the surface.
- The difference between sliding friction force and rolling friction force.
- The friction force does not depend on the area of contacting surfaces.
- Consolidation of the studied material.
- Summarizing.
- Homework.
During the classes
| Stage number | Teacher's work. | Student work | Notebook entries | Used slides, manuals, equipment, literature | Time |
| 1. | Greetings. | 1 min. | |||
| 2. | Draws students' attention to the test handouts and reminds them of the rules for filling them out. | Fill out the handout sheets for the test. Annex 1 | Handout sheets. | 1 min. | |
| 2.1. | Reads the test questions and comments on them if necessary. Collects handouts. |
Answer the test questions. Hand out handout sheets. | Slides 2-7 | 5 minutes. | |
| 2.2. | Asks students to comment on their answer and then states the correct answer and explains it if necessary. | Once again, the students think through the answers named by the teacher and comment on their answers. | Slides 8-14 | 5 minutes. | |
| 3. | Asks to name the forces that were studied in previous lessons. He says that the lesson will talk about another force. | They remember what forces they have already studied. Gravity, elastic force, body weight. | 2 minutes. | ||
| 3.1. | Shows slides on the screen demonstrating the importance of friction in nature and life. Asks students to name the force in question. | They look at the slides, draw conclusions, name the strength. (As experience shows in the name, they are not wrong). | Slides 15-16 | 2 minutes. | |
| 3.2. | Dictates the topic “Friction Force” and writes it on the board. | Write down the topic of the lesson in your notebook. | Topic: “Friction force” – |
Slide 17 | 1 min. |
| 3.3. | Gives the definition of friction force and asks to write it down in a notebook. Defines the goals and objectives of the lesson. Distributes sheets with group assignments. | Keep notes in notebooks. The teachers listen attentively. | - this is the force that arises when one body moves along the surface of another, applied to the moving body and preventing movement.  |
Slide 17 | 3 min. |
| 4. | Asks students to help him explain new material. | They are getting ready to help. | |||
| 4.1. | Based on life experience, he shows that one of the reasons is surface unevenness, and demonstrates that in this case the friction force can be reduced by using lubricant. The other is the interaction forces between molecules. Dictates the main provisions into a notebook. | They remember where in life they encountered the force of friction and keep notes in their notebooks. | Causes of friction force: 1. unevenness of contacting surfaces. (Using lubrication, unevenness can be reduced.) |
Slides 18, 19, 20 | 5 minutes. |
| 2. mutual attraction of molecules of contacting 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 if the block moves uniformly. | Students are divided into groups (the division into groups and lists of groups were presented to the teacher before the lesson). Each group completes tasks that are written on the handout sheet. Appendix 2 They record 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 practical work, asks the groups to prepare to voice their results. | They 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 min. | |
| 4.3.1. | Listens to the answer, asks leading questions if necessary. Supplements the student’s answer with examples from life ( corrugated 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, and make the necessary notes in a notebook. | 1. Type of contacting surfaces. | Slide 23 | 2 minutes. |
| 4.3.2. | (the wheels of trams and trains, as well as the rails, have a smooth surface, but the friction force is high due to the large weight of the trams and trains). | They find out that the friction force depends on the force pressing the body to the surface, and 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. Supplements the answer with examples from life (the use of drags in some tribes, the invention of the wheel, dragging ships on dry land using logs in ancient times, the use of special horizontal baskets made of intertwined rods during the construction of Stonehenge, the use of bearings to reduce friction). | They find out that under equal loads the sliding friction force is always greater than the rolling friction force, and make the necessary notes in a notebook. | 3. Under 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. Supplements the answer with examples from life (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 their butt.” The French were the first to become interested in this phenomenon scientist Guillaume Amonton at the end of the 17th century (1699). His work was continued a century later by Charles Coulomb, and now the law on the independence of the friction force from the surface area is called the Amonton-Coulomb law.) | They 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 contacting surfaces. | Slides 31 | 2 minutes. |
| 5. | Questions: | Answers on questions. | Slide 32 | 3 min. | |
| 1. What force is called friction force? | this is the force that arises when one body moves along the surface of another, applied to the moving body and preventing movement. |
||||
| 2. What causes friction? | 1. Irregularities of contacting surfaces. 2. Mutual attraction of molecules of contacting bodies. |
||||
| 3. How can you reduce the force of friction? | Lubricate the contacting surfaces or replace the sliding friction force with rolling friction force. | ||||
| 4. What factors does friction force depend on? | 1. depending on the type of contacting surfaces 2. from the force pressing the body to the surface 3. under equal loads, the sliding friction force is always greater than the rolling friction force. |
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| 5. What factors does friction force not depend on? | From the area of contacting surfaces. | ||||
| 6. | Determining the importance of friction in life: What would happen if the friction force disappeared? Comments on the completion of lesson objectives, grading, gratitude to distinguished students. | If there were 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, car, or motorcycle (the wheels would spin in place), we would have nothing to wear (threads in fabric held together by friction forces). If there were no friction, all the furniture in the room would be crowded into one corner, plates, glasses and saucers would slide off the table, nails and screws would not stay in the wall, not a single thing would be able to be held in one’s hands, etc. and so on. To this we can add that if there had been no friction, it is unknown how the development of civilization on Earth would have proceeded - after all, our ancestors produced fire by friction. | Slide 33 | 2 minutes. | |
| 7. | Homework, necessary comments. | Recording homework in diaries. Textbook Peryshkin A.V. – § 30, 32 Collection of problems Peryshkin A.V. – Chapter 15. |
§ 30, 32 chapter 15 |
Slide 34 | 1 min. |
Used Books:
- Peryshkin A.V. textbook "Physics 7".
- Peryshkin A.V. “Collection of problems in physics grades 7–9”, Moscow, “Exam”, 2006.
- V.A. Orlov “Thematic tests in physics grades 7–8”, Moscow, “Verbum - M”, 2001.
- G.N. Stepanova, A.P. Stepanov “Collection of questions and problems in physics grades 5–9”, St. Petersburg, “Valeria SPD”, 2001.
- IN AND. Grigoriev, G.Ya. Myakishev “Forces in Nature”, Moscow, “Science”, 1988.
- kak-i-pochemu.ru
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Attention! Slide previews are for informational purposes only and may not represent all the features of the presentation. If you are interested in this work, please download the full version.
Target: consolidate acquired knowledge about forces in nature; introduce students to the force of friction; experimentally find out what the friction force depends on; consider the types of “dry” friction; compare rolling, sliding, and static friction; teach students to identify the type of friction; enter the calculation formula for finding the friction force (slide 2).
Necessary 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. Sayings about the force of friction are written (or printed) on the folding halves.
Equipment: a wooden block with edges of different areas, but the same surface roughness; set of weights of 100 g; wooden, poorly polished 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 class 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 will use experiments to confirm or refute the possibility of the events described. But first, let's remember what we learned in previous lessons and what we will 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 direction of the force).(Slides 4, 5)
B) The teacher prepares assignments at the blackboard in advance. While the student is working at the interactive whiteboard, the whole class is working independently in notebooks, the answers will be discussed when checking using a presentation.(Slide 6)
1. Where is the force of gravity greater? Where is the most weight?
2. Where is the elastic force greater (k 1 =k 2)? What can be said about the force of gravity if the bars are at rest? (Slide 7)
3. Where is the stiffness greater (m 1 =m 2)? What can be said about the force of gravity if the bars are at rest? (Slide 8)
4. Determine and designate the resultant of 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) are given a task and equipment: “Construct a graph of body weight versus mass. Equipment: dynamometer, set of weights” Students present their work to the class and draw a conclusion after discussing all the issues.
The teacher observes how students do their 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 assignments.
3. New material
In previous lessons, we have repeatedly touched upon the issue that if no other bodies act on the body or the action of these bodies is compensated, the body is either at rest or moving straight and uniformly (slide 10). A physical quantity that characterizes the action of bodies on each other is called force. Let's conduct an experiment: use a dynamometer to pull a block with weights so that the movement is uniform. Why is this possible? Correct, 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 this is, where it arises, where it is directed and what it depends on.
The teacher and assistants provide equipment (see above) to each desk.
Conduct the same experiment yourself and think: where is the force unknown to us directed?
This force is called friction force. It is designated Ftr, measured in N. Why does it arise? In connection with the contact of the block and the desk, it means that it arises at the point of contact of two bodies. There are two reasons for the occurrence of friction force (slide 12). When one body slides over the surface of another, the bumps cling to each other, which creates some force that retards the movement. But if you take 2 well-polished objects, for example two glasses, then the friction force also turns out to be great, since in this case mutual attractive forces arise between the molecules of the contacting bodies, which are the cause of friction.
What do you think this power may depend on? Check your guesses. Possible assumptions. (Slide 13, 14)
(It is better to organize work in groups - each group tests one hypothesis and voices and comments on the result)
1. On speed (does not depend).
2. From the transported mass.
The more P, the more Ftr.
4. From surface roughness, etc.
The teacher helps to simulate the students' experiment in such a way as to test all the assumptions made. After this, all findings are recorded.
In notebooks we write down Ftr. (Slide 15)
- Directed in the direction opposite to movement.
- Occurs at the point of contact of two bodies
- Depends: on the weight (mass) of the body and surface roughness.
That. Ftr is calculated by the formula (slide 16): Ftr = 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 a definition of Ftr - this is the force that arises when the surface of one body interacts with the surface of another, when the bodies are stationary or moving relative to each other.
Now place rollers under the block with weights and measure the friction force. Compare it with the readings you performed for the same weight in the previous experiment. What conclusion can be drawn? That's right, 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 initially increases greatly, and when the block begins to move, it becomes equal to the frictional force obtained during sliding. Those. In nature, three types of “dry” friction are distinguished: sliding friction force, rolling friction force and static friction force.
Place signs between F.rolling tr._____F.sliding tr._____F.rest. (Slide 17)
4. Consolidation
(Slide 18) Arrange the type of friction force for each situation depicted. Give your own examples of each type of friction force.
How can you increase and decrease the friction force?
Explain the meaning of the sayings presented on the board. Do they have physical meaning? (Slide 19)
Additionally: Give examples of the manifestation of the friction force.
Is there any benefit to friction? What?
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 developments in physics: 7th grade. - 2nd edition. – M.: VAKO, 2009.
MBOU "Motyzleyskaya public school"
The lesson was developed by a physics teacher:
Leontyeva N. A.
2013
Lesson objectives:
Educational:
Formation of ideas about the force of friction,
Study the causes and types of friction,
Reveal the nature of friction force,
Determine experimentally what the friction force depends on.
Educational:
Develop observation, attention, ability to analyze, compare results, draw conclusions;
Develop practical work skills.
Develop creative activity using curiosity as a stimulus for cognitive activity.
Educators:
To promote the formation of a worldview idea of the knowability of phenomena and properties of the surrounding world.
Create a situation of success for each student.
Equipment:
dynamometers, planes, bars coated with different materials, a set of weights, a computer with a multimedia projector.
Expected results:
This lesson provides an opportunity to deepen knowledge of the subject for each student to understand the processes occurring around us.
DURING THE CLASSES
1. ORGANIZATIONAL STAGE. (Slide No. 1)
Teacher. Good afternoon dear friends! I'm glad to see you, let's welcome our guests and start working. On the way today I met the postman, he asked me to give you a letter from Santa Claus. I’m so curious, I’ve been dying to find out what this letter is about. And you? Will you let me read it?
2. PREPARING STUDENTS FOR WORK AT THE MAIN STAGE OF THE LESSON.
MOTIVATION
Teacher. (reads the letter). “ Dear Guys! I am writing you a letter in the hope that you will help me. New Year is coming soon, and I have to deliver New Year's gifts to everyone who behaved well during the year. But, unfortunately, now I can’t leave my house. Firstly, my new silk bag is constantly untied, and I am afraid of losing all the gifts along the way. Secondly, my sled cannot move on the ground without snow; December is not very snowy these days. Please, help me, give me advice on how to get out of this situation. I look forward to your answers. Father Frost”.
You know, we can help Santa Claus! We will give him the answer, but on one condition: if in today's lesson we reveal one very important secret, the name of which you will find yourself if you answer the crossword questions correctly.
3. ACTUALIZATION (Slide 2)
Teacher. Let's solve the crossword puzzle. 1. Unit of force. 2. The phenomenon of conservation of the speed of a body in the absence of the action of other bodies on it. 3. The force with which a body, due to attraction to the Earth, acts on a support or suspension. 4. Device for measuring force, 5. Physical quantity. Characterizing the action of bodies on each other, 6, The smallest particle of matter.
4. STUDYING NEW MATERIAL.
Teacher. So, you and I learned the name of the secret - friction. This phenomenon accompanies us literally at every step and therefore has become familiar and unnoticeable. And it is characterized by the force of friction. The force of friction will be discussed in today's lesson. So, let's write down the date and topic of the lesson(Slide 3): “Frictional force.”
Tell me, what forces do you already know?
Students . Gravity. The force of universal gravity. Elastic force. Body weight.
Teacher. What determines the result of a force?
Students.
- from direction
- numerical value
- application points.
Teacher. The result of the friction force also depends on which body this force is applied to, where it is directed and what its numerical value is. The purpose of today's lesson will be to prove this.(Slide 4).
Teacher. What happened to the speed of the car whose path the cat crossed?
Students. She has changed.
Teacher. What is the reason for the speed change?
Students. There is a force acting on him.
Teacher. How is this force directed?
Students. Against traffic.
Teacher. Why do you think so?
Students. If it were directed in the direction of travel, the speed of the car would increase. And since the speed decreases, it means that the force is directed against the movement.
Teacher. The force in question is called friction force. It is always directed against the movement of the body in question on the surface of another. Let's formulate a definition of friction force and write it down in a notebook.(Slide 5)
Force, that occurs when the surfaces of bodies come into contact and prevents their movement relative to each other is called friction force. And it is designated F tr. (Slide 6)
Teacher. Let's find out what is the reason for the friction force, and
The textbook will help you find out the cause of the friction force (p. 71)
- Surface roughness.(Slide 7)
- With ideally smooth surfaces, mutual attraction occurs between the molecules of contacting bodies. (Slide 8)
Teacher. Well done, yes, guys, with rough surfaces friction is mainly due to the first reason, and with very smooth surfaces the molecular nature of friction is affected. Let's write this down in our notebook.
Teacher. Let's conduct a small experiment, as a result of which we will find out what types of friction forces there are:
(Slides)
Teacher. Using the textbook, we will create an inclined plane and place the block on it. When a body is at rest on an inclined plane, it is held on it by the force of friction. Indeed, if not for friction, the body would slide down the inclined plane under the influence of gravity.
The frictional force that arises between bodies at rest relative to each other is calledstatic friction force.
The force of static friction holds a nail driven into a board, prevents the bow on the ribbon from coming undone, etc.
Teacher. Pull the thread attached to the bar. Try to pull evenly, parallel to the table surface. When one body slides over the surface of another, friction occurs, which is calledsliding friction. For example, the movement of a sleigh in the snow.
Teacher. Place pencils and pens under the block, and pull the thread.
If one body does not slide, but rolls on the surface of another, then the friction that arises in this case is calledrolling friction.For example, the movement of car wheels.
Teacher. Now let’s write down what types of friction forces we have learned.(Slide with types of friction forces)
Teacher. Which Of the friction forces, which is the greatest and which is the least?(Slide 19 with conclusion)
Demonstration (At the same angle of inclination of the plane, we consider the movement of the pencil by rolling friction and sliding friction)
Teacher . Which friction force is greater? F tr. slip . or F tr. rolling
Students. Rolling friction
5. EXERCISE FOR THE EYES.
- Guys, look how much we have already learned about the force of friction. Tired?
– warm up your palms;
how to fight the flu virus? – stimulate the immune system!
– rub the earlobes, which contain biologically active points that affect the immune system;
– to relax the back muscles, rub your fists along the spine to improve blood circulation in these muscles.
– let’s walk: 3 steps forward and three back.
– Thank you, have a seat.
6. FRONTAL EXPERIMENT
Teacher. Now guys, let’s divide into groups and carry out the proposed experiments in each group. At the end of the work, you need to conclude what the friction force depends on.. (Slide 20)
But before you start testing hypotheses, I want to ask you how you can measure the force of friction?
The experiment is carried out by the teacher:
– Move the block evenly using a dynamometer. What forces act on the block along the line of motion?(Traction force and friction force)
– If the speed of movement is constant, then what can be said about the resultant of these forces?(It is equal to zero).
– What is the sliding friction force?(It is equal in absolute value to the traction force, which is shown by the dynamometer)
The class is divided into groups of 4 people.
Group 1 – on the table there is a wooden ruler, a tribometer, a dynamometer.
(Students determine the dependence of friction force on surface area.)
Students. The friction force does not depend on the surface area.
Group 2 - on the table there is a dry ruler and a ruler covered with a layer of Vaseline, a tribometer and a tribometer with sandpaper attached, a dynamometer. (the dependence of friction force on lubrication is established.)
Students. When using lubricant, the friction force is less.
Group 3 – on the table there is a tribometer ruler and weights. (the dependence of the friction force on the force pressing the body to the surface is established.)
Group 4 – on the table is a tribometer, a ruler, a ruler with sandpaper, a tribometer with sandpaper, a dynamometer. (The dependence on the type of rubbing surfaces is established.)
(Slide 21 with a conclusion on what the friction force depends on)
Friction force:
Students. The friction force depends on the type of rubbing surfaces
Teacher. Guys, life experience tells us that friction is very important in our lives and plays both a positive and negative role.
1. Any people encloses wisdom and life experience in proverbs and sayings.
For example:
- If you don't butter it, you won't eat it
- Things went like clockwork
- What's round is easy to roll
- Skis glide according to the weather
- There is no such person who has not slipped on ice at least once.
(Slides 22, 23, 24, 25, 26, 27 with beneficial and harmful friction forces)
Teacher. Guys, at the end of our lesson, let's summarize what we learned today about the force of friction?(Slide 28).
Well, when we found out everything about a force that is very important for our lives - the force of friction, what would you advise our Santa Claus?
Students. Change the bag to a rougher one, such as plush or calico. If there is no snow, then transfer from the sleigh to a cart or carriage. Since the rolling friction force is less than the sliding friction force.
7. PINCHING (Slide 29)
Teacher. Now guys, let's answer the test questions that I gave you
prepared.
TEST
P. rolling friction force
U. sliding friction force
IN. static friction force
S. increases
D. does not change
E. decreases
A. by movement
P. against traffic
N. has no direction
I. does not change
E. decreases
U. increases
K. 15 kN
L. 300 kN
X. 150 kN
TABLE OF ANSWERS
Let's check the answers. Who received the code word “success”? Prepared .
8. HOMEWORK: (Slide 30)
Answer the question in writing in your notebook: if the friction force disappeared, would we shout “Hurray” or “Guard”?
Literature:
- School Student's Handbook. Physics. – M.: Philological Society “Word”, Peryshki A.V. Physics-7 Ed. – M.: Bustard, 2004.
- Zubkova L.A. Friction force. – Physics (PS), 1998, No. 2. Publishing house First of September – Physics No. 21 2007
Lesson-trip on the topic: "Friction Force"
Physics lesson plan
Grade: 7th grade
Program section:“Interaction of bodies.”
Lesson type: lesson in learning new knowledge.
View: combined lesson.
Technology: personality-oriented.
Lesson objectives:
- Didactic: create conditions for mastering new educational material using information technologies and elements of the “Collaboration” technology.
- Educational:familiarize students with the phenomenon of friction, form the concept friction force , consider the types of friction, experimentally establish what this force depends on, find out the causes of the friction force.
- Educational: develop a quality area of students; develop logical thinking; to form an idea of the process of scientific knowledge; development of skills to experiment; develop the ability to use equipment; analyze, compare experimental results; continue to develop the ability to construct a supporting outline.
- Educational: instill a culture of mental work.
- Motivational: stimulate interest in studying the subject.
Teacher equipment:computer, multimedia presentation “Friction Force”, toy car, sand, wooden block with thread, pen, dynamometer, glass plates - 2 pcs., reference note “Friction Force”.
Equipment for students:a dynamometer, a sheet of smooth and sandpaper, a wooden block with thread, 100 g mechanical weights (2 pcs.), supporting notes.
Preparation for the lesson:
- each student is given a sheet of reference notes, equipment, and sheets of test tasks;
- On the demonstration screen or on a large sheet of Whatman paper, you need to prepare a sheet of supporting notes.
Lesson Plan
Types and forms of activity |
|
1. Organizational moment | Greetings |
2. Motivational start of the lesson | Statement of educational problem |
3. Learning new material | Story - conversation, frontal experiment, filling out the supporting notes |
4. Stage of generalization, systematization of knowledge and consolidation of new material | Completing test tasks, practical work in groups |
5. Summing up, homework | Writing on the board and in the diary, reflection |
During the classes
I. Organizational moment.
II. Motivational start to the lesson.
Teacher: Hello guys, today in the lesson we will continue our journey through the Kingdom of Powers.
Look closely at the clouds
Listen to the birds
Touch the springs -
Nothing will happen again.
Moment by moment, hour by hour
Be amazed
Everything will be like this and everything will be wrong
In one moment
We will take luggage for the trip:
Textbook, pen, pencil,
Notebook and knowledge bag.
But before we go on a journey through the Kingdom of Powers, let's remember what countries of powers we have already visited? (GRAVITY, ELASTIC FORCE, BODY WEIGHT)
The path to the Kingdom of Powers is open before us, now we will find out which country we will go on a trip to today. And we will make our trip by car. Let's sit down and let's go.
(the teacher at the demonstration table sets the toy car in motion)
Teacher: What bodies interact when a car moves? What is the result of the interaction of bodies? What happened to the speed of the car? Why did the car stop? (friction force acts) I invite you on a journey through the country “The Force of Friction”!
III. So, we begin our journey with a visit to the country’s scientific center “Friction Force”. During the trip, we will keep travel notes, i.e. a supporting summary (students write down the topic of the lesson in their supporting notes).
BACKGROUND SUMMARY
Teacher: I am a Master of Exact Sciences and welcome you to the scientific center. Here you will get acquainted with the phenomenon of friction, find out what types of friction live in this country, determine the point of application and direction of this force, experimentally establish what the friction force depends on and why does it arise?
Question: Let's find out in which direction our car is moving? Do you think the friction force helps or hinders the movement of the car? ( prevents)
If physicists decided to issue passports to all forces, then this document would definitely have three columns: MODULE. DIRECTION. APPLICATION POINT. Let's determine in which direction the friction force is always directed? (in the opposite direction to body movement) Let us determine the point of application of the friction force (indicate the point of application and direction of the friction force in the supporting outline).
We introduce the definition of friction force:The force that arises when one body moves on the surface of another, applied to the moving body and directed against the movement, is called the friction force.
Teacher: The residents of this hospitable country are waiting for us to visit. Let's get to know them better. Let's find out what types of friction exist.
Demonstration experiment(book and pen, teacher demonstrates the forces of sliding, rolling and resting friction).
Teacher: So, we met the friction force family. This is rolling, sliding and static friction (students write in their supporting notes). And now I suggest you relax in the literary drawing room. Let's consider examples of the manifestation of friction forces in nature. In the examples given, determine what frictional force acts on the body.
In the winter twilight, nanny's tales
Sasha loved. In the morning in the sled
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 your bike
And he's lucky with jam
Everyone's welcome.(rolling friction force)
Here comes winter! The frosts are crackling
Snow sparkles in the sun
The convoys went with goods
Across Rus' along and across.
The oak runner creaks as it crawls.
Whether it’s a river or a steppe - there’s no need,
There will be footprints everywhere!
I. S. Nikitin (sliding friction force)
Though the burden is heavy at times,
The cart is light on the move;
Dashing coachman, gray time,
Lucky will not get off the irradiation machine.
A. S. Pushkin (rolling friction force)
Cat for Bug
Bug for granddaughter
Granddaughter for grandmother
Grandma for grandfather
Grandpa for the turnip
They pull and pull, but they cannot pull. (static friction force)
Teacher: Why does friction force arise? What are the causes of friction? Let's conduct an experiment (toy car, sand).
Conclusion: Surface roughness, irregularities (students are enrolled in OK).
Experiment with two glass plates.
Conclusion: Interaction of molecules of a substance (students are enrolled in OK).
Teacher: Strength is a physical quantity. What does it mean? (it can be measured) Now we will measure the frictional force that acts on a wooden block.
Frontal experiment: wooden block with thread, dynamometer.
The teacher explains to the class how to measure friction force. Two forces act on the block in the horizontal direction. One force is the elastic force of the dynamometer spring, directed in the direction of movement. The second force is the frictional force directed against the movement. Since the block moves uniformly, the resultant of these forces is equal to zero. Consequently, these forces are equal in magnitude and directed in opposite directions. The dynamometer shows the friction force (students measure friction force).
IV. Teacher: Let's continue our journey. Let's take a look at the creative workshop. I am an experimenter and so are you ( putting on a robe ). I suggest you compare the forces of static, sliding and rolling friction, and also study the force of sliding friction.
Students perform practical work in groups (Frontal experimental tasks in physics: A manual for teachers / V.A. Burov, V.I. Sviridov. - M.: Education, 1981. - 112 p.).
Teacher: Guys, do you know that in this mysterious country the force of friction is constantly changing. It is either reduced or increased. Let's try to find out more about this. You are invited to solve witty puzzles by G. Oster.
Task 1. Hooligans Sidorov and Ivanov sprinkled sand on the skating rink and watched with interest as Tanechka Petrova skated. What goal do Ivanov and Sidorov pursue? (increase in friction force)
Task 2. What are the cunning seventh graders up to who, sparing no expense of expensive motor oil, generously pour it into the brakes of the school principal’s car? (reduce friction force, lubrication)
Teacher: Each of you constantly solves everyday tests. Now you have to resolve some of the problems you are facing at home.
Students complete test tasks “Life Test”.
Life tests
1 group
- The closet doors in Vanya's room began to creak. Vanya lubricated the hinges with oil and the creaking stopped. What phenomenon did he use?
- While hiking, Vanya slipped on the wet grass, fell and realized that...
2nd group
- Vanya saw that his mother could not remove the ring from her finger, and advised her to soap her finger. Mom accepted the advice, and the ring came off easily. What is Vanino’s proposal based on?
- From the window Vanya saw that an ice path had formed in front of the door of their house. Vanya went outside and sprinkled sand on the ice. Why did he do this?
3 group
- Vanya is getting ready to go hiking on a bicycle. But the pedals did not spin well, so he lubricated them with machine oil. What phenomenon did he use?
- When the first snow fell, Vanya’s dad began to change his summer car tires to winter ones. Winter tires had a deeper tread pattern and also had studs. Vanya asked his father why they change the car’s tires?
4 group
- Vanya was going to go skiing with his friends. Before the walk, Vanya advised his friends to lubricate their skis with a special ointment. What is Vanin’s advice based on?
- Vanya noticed that in winter the highways are sprinkled with a special mixture (sand and salt). He decided to ask his father what role does this mixture play in the movement of cars?
Teacher: Dunno recently visited the country “Friction Force”. He left us his notes. Let's take a look at them. What mistakes did Dunno make? (overhead projector, film)
Teacher: Guys, I invite you to go to the cinema to watch the film “Friction Force”.
View the multimedia presentation “Friction Force” ( Annex 1).
Teacher: We are leaving the Kingdom of Powers, but a test awaits us at the exit. Take the knowledge control sheets and complete the tasks suggested in the test.
TEST
1. The sled is rolling down the mountain. What type of frictional force acts on the sled?
P. rolling friction force
U. sliding friction force
B. static friction force
2. During icy conditions, sidewalks are sprinkled with sand. At the same time, the friction force of the shoe soles on the ice...
S. increases
D. does not change
E. decreases
3. How is the friction force directed when a body moves?
A. by movement
P. against traffic
N. has no direction
4. When lubricating rubbing surfaces, the friction force...
I. does not change
E. decreases
U. increases
5. An electric locomotive, moving uniformly, pulls a train with a force of 150 kN. What is the friction force?
K. 15 kN
L. 300 kN
X. 150 kN
TABLE OF ANSWERS
Let's check the answers. Who received the code word “success”?
V. Teacher: Our journey through the country “Friction Force” is coming to an end. Let's summarize (grading).
Reflection: Guys, please analyze the “movement” of your thoughts, feelings, sensations that arose during the lesson. Write them down on pieces of paper and give them to me.
Preview:
Friction is a type of interaction between bodies. The force that arises when the surfaces of bodies come into contact and impedes their relative motion is called the friction force. F tr
Causes of friction: Roughness of the surfaces of contacting bodies Mutual attraction of molecules of contacting bodies
The force of static friction is the force that prevents a body from moving from its place.
Sliding friction force Sliding friction force is the resistance when one body slides over the surface of another.
Rolling friction is the resistance force when one body rolls over the surface of another.
Types of friction force Static friction Sliding friction Rolling friction
Comparison of rolling friction force and sliding friction force Conclusion: under equal loads, the rolling friction force is always less than the sliding friction force.
Let's find out what the friction force depends on 1 group 2 group 3 group 4 group Establish the dependence of the friction force on the surface area Establish the dependence of the friction force on the lubricant Establish the dependence of the friction force on the force pressing to the surface Establish the friction force on the type of rubbing surfaces
friction force The friction force does not depend on: the area of contacting surfaces.
friction force The friction force depends: when using a lubricant, the friction force is less
The friction force depends on: on the force pressing the body to the surface. friction force
friction force The friction force depends on: the type of contacting surfaces.
The friction force depends on: does not depend on: 1) the type of rubbing surfaces; 2) the force pressing the body to the surface 1) the area of contact of the body with the surface
"Useful" friction.
“Harmful” friction Ways to reduce friction: Replacing sliding friction with rolling friction. Introduction of lubricant between rubbing surfaces.
Conclusion: Frictional force occurs between contacting surfaces. The force of friction depends on the type of contacting surfaces. The friction force does not depend on the area of the rubbing surfaces. The friction force decreases when sliding friction is replaced by rolling friction and when rubbing surfaces are lubricated.
Answer table 1 2 3 4 5 success
Homework. Answer the question in writing in your notebooks: If the friction force suddenly disappeared, what would we shout: “Hurray” or “Guard”
Thanks for the lesson. Happy New Year!!!
