What is friction force. “Friction is useful and harmful. Ways to increase and decrease the force of friction
Abstract of an open lesson in grade 7 on the topic“Friction is useful and harmful. Ways to increase and decrease the force of friction.
Within the framework of the regional seminar
Introduction of the course "Elements of physics in everyday life and at work" as an innovative technology in the system of teaching students of correctional schools of the VIII type
04.12.2013
Teacher BRYKSINA E.S.
Target: continue acquaintance with the force of friction, learn ways to increase and decrease the force of friction.
Lesson type: combined.
Lesson objectives:
Educational
: the formation of skills in working with physical devices,
the ability to draw their own conclusions.
Developing: learn to see the relationship between the studied
theoretical material and phenomena in life.
Educational: development of the desire for knowledge.
Equipment:
A bar, a set of weights, rulers, dynamometers, round sticks, sandpaper strips, cards for individual work, a laptop, a multimedia projector, a screen.
Lesson structure:
Organizational moment and preparation for the lesson.
Repetition of previously learned material.
Learning new material.
Correction in the process of obtaining new knowledge.
Consolidation of new material.
Summarizing.
Homework announcement.
Conclusion from the lesson.
1. Organizational moment
Greeting guests. Message about the topic and purpose of the lesson.
Today we have a lot of guests at the lesson. Let's welcome them. They sat down quietly. They looked at each other, smiled, wished good luck. We start to work.
What is the name of the general topic we are studying? (Force)
What power did we meet in the previous lesson? (with friction force).
Today we continue our acquaintance with the force of friction. The topic of our today's lesson is “Friction is useful and harmful. Ways to increase and decrease the force of friction.
2. Repetition of previously studied material.
When does friction force occur? In which direction is it directed? (when one body moves on the surface of another, it is directed against the movement).
Name the causes of friction force.
a) surface roughness
b) mutual attraction of molecules.
What types of friction do you know? (sliding friction, rolling friction, static friction).
So, There is a force of friction in the world,
She matters a lot!
There are three types of friction: sliding, resting, rolling.
Everyone is very important
And in this world, of course needed!
-
When does the sliding friction force arise? (when one body slides over the surface of another), give examples.
When does the rolling friction force arise? (when one body rolls on the surface of another, give examples.
What does the static friction force mean? (This is the force that prevents an object from moving), give an example.
Prepared signal cards (they are in your notebooks)
They took card number 1. Task: label the types of friction under the pictures.
Types of friction
static friction
rolling friction
sliding friction
(frontal survey on pictures: give examples for each type of friction, pasting cards into a notebook).
Get your fingers ready. Let's break them down and rub them. What type of friction are we currently seeing? (sliding friction). (paste the card in the notebook).
Friction is a familiar yet mysterious force.
Friction can be beneficial and harmful.
Tell me when does friction help us? (useful friction)
When walking
Hold items
Stopping the car
Machine start
When writing
Brush your teeth
Apply a bandage
Wear clothes
Light a fire, etc.
When does friction stop us? (harmful friction)
Moving parts get hot and wear out
Creaking doors, floors
Calluses on feet and hands
Joint pain
They took card number 2. Look carefully at your drawings and say: where do you see useful friction, where is it harmful? (they answer in a chain) Under the drawings they signed harmful or useful friction. (frontal survey on pictures). Paste the card into the notebook.
Friction good and bad
____________ ________________________
mechanism wear __________________ _____________________
__________________ _____________________
Preparation for the perception of new material.
Today we will get acquainted with ways to increase and decrease friction.
After all, the two most important inventions of man are
The wheel and making fire are connected precisely
With the desire to increase or decrease friction.
You know that friction is a physical quantity.
What are the units in which force is measured? (in Newtons)
Who is the unit of force named after?
What letter stands for force (F)
What is the name of the device for measuring force? (dynamometer).
What is the division value of the dynamometer? (1 \ 10 N) (repeat the rule for determining the division value of the dynamometer)
Now we will empirically compare sliding friction and rolling friction.
They took card number 3
Demonstration of experience: a trolley (inverted) with a load with a dynamometer attached moves along the table. What type of friction are you seeing? (sliding friction). What is the force of sliding friction? (Using a dynamometer, we determine the force of sliding friction).
If the body is difficult to move
Friction can be reduced.
Mankind invented the wheel a long time ago.
There is friction, rolling friction.
We turn the trolley over, put it on wheels along with the load. What type of friction are you seeing? ( There is friction, rolling friction).
Using a dynamometer, we determine the force of rolling friction.
Which is easier: rolling or sliding?
The output is written on the card below:………..
By replacing sliding friction with rolling friction, do we thereby increase or decrease the friction force?
Practical work#1
Comparison of sliding and rolling friction
Conclusion: rolling frictionmore less
sliding friction.
Now you will establish the dependence of the friction force on the surface material.
They took card number 4
Practical work №2
The dependence of the friction force on the surface material.
Conclusion: the higher the surface roughness, the more less friction force.
What physical body will you move? (bar)
On what surfaces will you move the block?
We put a wooden ruler in front of us, put a bar on it, hooked the dynamometer and move the bar. Write down the value of the force in the table.
Now measure the friction force as the bar moves across the sandpaper.
Compare the friction forces and draw a conclusion. (Paste the tables in a notebook).
Fizminutka
So that we don't get tired
You need to give your body a rest.
Let's hang out with you quickly
And we will return to the place again.
We will rub the muscles of the thighs
We will remember the friction
The benefit here is friction
from sliding friction.
We stretch the muscles of the shoulders
Friction is remembered again
Let's clasp our hands together
There will be friction of rest.
Quietly sat down, we continue to get acquainted with ways to increase and decrease friction.
if friction is useful, then it is increased:
Sprinkle the paths with sand during ice
The soles of winter shoes are made ribbed (sports shoes)
Wheel tires (summer tires and winter)
Gymnasts, weightlifters rub their hands with talc before performances
Rubber mats, tool handles, ribbed hitch, pliers, etc.
if friction is harmful, then it is reduced:
- grind the surfaces of sewing needles, medical needles, tools
Add lubricants, oils
Bearings (ball and roller) are used (where?) (in cars, lathes, electric motors, bicycles, etc.)
Eye Charging:
Don't waste your time
And repeat the movements
The heat from friction will help us to see.
Card number 5 ways to reduce and increase the force of friction (paste in a notebook)
Reducing surface roughness.
Lubricant application.
Replacing the force of sliding friction with the force of rolling friction.
Application of bearings.
Increase in surface roughness.
Increasing the force of pressure on the surface.
TEST(card number 6)
Test
1) What force does not allow you to budge a heavy cabinet?
A. Force of sliding friction B.static friction force. B. Gravity
2) When lubricating rubbing surfaces, the friction force ....
AT . Decreases
3) In ice, 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 . is increasing B. Decreases
4) The surface of the shoe is made ribbed while the friction force ... ..
A. Does not change B. is increasing B. Decreases
5) Sometimes, before driving a nail into the board, it is lubricated with oil, while the friction force ......
A. Does not change B. Increases AT. Decreases
Poem "Friction":
Tired of this friction! I just don't have the patience!
I'm learning about him! How long to? I do not want!
I'm closing the textbook. I go to sleep and I forget about everything.
I foresee peace. Only a strange dream I see:
I suddenly observe a picture - there is no friction even in half.
The world without friction friends has changed.
I see how a passer-by is sliding on the ice,
And any car knew inertia, it seems
And never slowed down.
The threads in the fabrics slipped, in an instant the clothes parted.
Miracles surprised you. Apparently, trouble has struck.
I shout that without a doubt, it’s bad for everyone without the power of friction.
All the knots are untied, objects are falling.
I cling to corners - everything slides. "Where are you?
Only I marveled at the dream - lo and behold, the textbook opened itself,
It would be useful for me to know everything about the force of friction.
So, guys, let's sum up, attention to the screen !!
5. Summing up (presentation)
- What new did you learn at the lesson today?
How will you apply what you learned in class to your life?
6. Homework
Write a mini essay on friction using the words: sliding friction, static friction, rolling friction.
Friction plays an important role in everyday life. This force has to be taken into account when designing a wide variety of technical systems, the principle of operation of which is based on the direct contact of moving parts. Friction is not always a harmful factor, but nevertheless, in most cases, developers are trying to reduce in a variety of ways.
Instruction
In the simplest case, try to change the degree of roughness of the surfaces of the objects in contact. This can be achieved by grinding. Bodies whose interacting surfaces are smooth and polished will move relative to each other much more easily.
If possible, replace one of the mating surfaces with one that has a lower coefficient of friction. It can be an artificial coating - for example, Teflon has one of the lowest coefficients of friction, equal to 0.02. It is easier to change the element of the system that plays the role of a tool.
Use lubricants by introducing them between the rubbing surfaces. This method is used, for example, in skiing, when a special paraffin lubricant is applied to the working surface of the skis, corresponding to the temperature of the snow. Lubricants used in other technical systems can be liquid (oil) or dry (graphite powder).
Consider using "gaseous lubrication". This is the so-called "air cushion". The friction force is reduced in this case by creating an air flow between previously contacting surfaces. The method is used in the design of all-terrain vehicles designed to overcome difficult terrain.
If the system in question uses sliding friction, replace it with rolling friction. Do a simple experiment. Place an ordinary glass on a flat table surface and try to move it with your hand. Now put the glass on its side and do the same. In the second case, it will be much easier to move the object from its place, since the type of friction has changed.
Use bearings where friction occurs. These elements allow you to transform the type of movement, thereby significantly reducing friction losses, reducing its strength. This method is the most widely used in technology.
At first glance, excessive friction is harmful. It reduces the efficiency of mechanisms, wears out parts. But there are cases when the friction force needs to be increased. For example, when rolling wheels, it is necessary to improve their grip on the road. See how this can be done.
Instruction
To understand how to increase the force of friction, remember what it depends on. Consider the formula: Ftr \u003d mN, where m is the friction coefficient, N is the support reaction force, N. The support reaction force, in turn, depends on the mass: N \u003d G \u003d mg, where G is the body weight, H-m is the mass bodies, kg - g - free fall acceleration, m/s2.
From the formula, we can conclude that the friction force depends on the coefficient of friction. The coefficient of friction is determined for each pair of interacting materials and depends on the nature of the material and the quality of the surface.
Thus, the first way to increase friction is to change the material of the sliding surface. You have probably noticed that in one shoe it is almost impossible to move on a wet tiled floor, and in the other you do not feel any inconvenience. This is because the soles of the shoes are made from different materials. Slippery shoes have a low coefficient of sliding friction of the sole relative to wet tiles.
The second way is to increase the surface roughness. Example - winter tires for a car have a more embossed tread than summer tires. Due to this, on a slippery winter road, the car can move confidently.
The third way is to increase the mass. As can be seen from the formula, the friction force directly depends on the mass. This explains why it is sometimes easier for a loaded car to get out of the mud than one that is light. This rule works with a certain quality of the soil - in viscous, swampy soil, a heavy machine will sink more than a light one.
The fourth way is to remove the lubricant. Imagine a production line conveyor consisting of rotating rollers on which a belt is stretched. The conveyor rollers begin to slip on the belt if they are dirty. In this case, the dirt acts as a lubricant. By cleaning the parts of the mechanism, you will increase the friction force and increase the efficiency of the equipment.
The fifth way is polishing. By polishing the surface, you can increase the friction force. This is due to the fact that when the polished surfaces come into contact, the forces of intermolecular attraction are switched on. For example, it is very difficult to move apart two sheets of glass stacked together.
Any movement of bodies, one way or another, is accompanied by friction. With any mechanical movement, bodies come into contact with each other. This phenomenon also occurs in a liquid or gaseous medium. In this case, the question arises, what is the force of friction? It occurs at any degree of interaction of bodies with each other and is directed in the direction opposite to the movement. This force has a direct influence on the movement itself.
Types of friction force
The force of friction exists in several forms. First of all, it is dry friction, which is divided into rolling and sliding. It is formed when solid bodies moving relative to each other come into contact with each other.
If solid bodies move through a liquid or gaseous medium, then viscous or liquid friction appears. The same phenomenon occurs when solids are stationary and liquids or gases flow past them. In the case when, when trying to move a motionless body, a certain force is applied to it, static friction occurs.
The main reason, as a result of which the friction force appears, is the roughness of the surfaces that are in contact with each other. In addition, the magnitude is largely affected by the mutual attraction of molecules that occurs between the bodies.
How to reduce the force of friction
In order to reduce the friction force, the mating surfaces can be ground. In addition, friction points are lubricated and sliding friction is replaced by more efficient rolling friction.
The protrusions on one of the surfaces never coincide with the same protrusions on the other. However, when compression is applied, these projections deform, resulting in an increase in contact area in proportion to the applied load. It is these places of irregularities that resist shear, which are the cause of the friction force. At the same time, one should not forget that even on ideally smooth surfaces, the friction force will appear due to molecular attraction.
In addition, you need to know that this is a value that can be measured with a special device - a dynamometer. If the body moves uniformly, then in this case the traction force reflected on the dynamometer is equal to the friction force.
The unit of measurement for the force of friction, like any other force, is one newton.
Often the question arises which is more effective - rolling or sliding friction. It all depends on the specific conditions. For example, for wheels to roll normally, the surface must be firm, smooth and non-slippery. And, conversely, it is best to slide on a slippery surface. It is the right choice that can give the maximum effect.
§ 1 What causes the force of friction and what is it?
Each of us went sledding or skiing, and who asked himself the question: “Why didn’t I push off as much as I would, anyway, I’ll stop sooner or later”?
Imagine such a picture - a textbook lying on a desk. If you push him, that is, apply force to him, then he will change the speed from zero to a certain value. However, the tutorial will stop after a while.
We already know that a change in the speed of a body is the result of the application of a force. What force is at work in this case?
The force of friction helped the textbook to stop. The friction force arises when some bodies move along the surface of others, and when they try to move the body.
What is the force of friction?
To answer this question, you can do a simple experiment. Let's try to draw a line with a simple pencil, first on paper and then on glass. We can do this on paper, but not on glass. This is because the surface of the paper and pencil lead is rough when viewed under a microscope. The particles of the stylus, as it were, cling to the roughness of the paper and remain there. The surface of the glass is smooth and we do not observe this.
From this we can conclude that the magnitude of the friction force depends on the presence of roughness of the contacting surfaces.
And will the friction force disappear when both surfaces are smoothly polished? To answer this question, we can conduct the following experiment: we will try to tear off glass or a mirror from the surface of the water. This is quite difficult to do. In this case, the friction force will also arise, but the reason for its existence is different - the mutual attraction of the molecules of the contacting surfaces. And in the last example, the magnitude of the friction force will be many times greater.
In addition to magnitude, the force must have a direction. The force of friction is always directed in the direction opposite to the motion of the body.
§ 2 Types of friction
Friction is of three types:
1. Friction of rest. All bodies rest in place only due to rest friction. Otherwise, everything would fall.
2. Sliding friction. An example of this type of friction is sledding downhill.
3. Rolling friction. An example would be driving and stopping a car.
Of all three types, static friction has the largest value, and rolling friction has the smallest. Rolling is easier than dragging. That is why in all engineering structures and technology, where possible, sliding is replaced by rolling.
So for the construction of a monument to Peter I in St. Petersburg, a huge stone block weighing about 1000 tons was delivered to the city on skating rinks, since it would be impossible to drag the pedestal for the monument to the founder of the city.
The magnitude of the friction force can be measured with a dynamometer, and it is measured in Newtons.
§ 3 The importance of friction in human life
From the point of view of benefits to humans, friction can be harmful and beneficial. For example, when a door begins to creak and open poorly, friction is considered harmful. Useful friction is the friction at which a cyclist can stop at a traffic light. If it weren't for him, he would continue to move uncontrollably. In some cases, various lubricants are used to reduce friction. Not a single bearing without technical oil will be able to work.
Therefore, friction is extremely important in our lives. Friction not only allows you to control movement, it also contributes to the stability of bodies.
Without it, everything will roll and slide until it is on the same level. Nails and screws will slip out of the walls, fabrics will spread, not a single button will be sewn on, the threads simply will not stick to either the needles or the fabrics.
Without the friction of rest, we would not be able to walk or ride. Remember how difficult it is to move in ice. The cause of the friction force can be either the presence of roughness on the contacting surfaces, or the mutual attraction of the molecules of the interacting bodies. The force of friction is measured in Newtons and is directed in the direction opposite to the movement of the body.
List of used literature:
- Physics. Chemistry. 5-6 classes. Gurevich A.E., Isaev D.A., Pontak L.S. – M.: Bustard, 2011.
- Physics. Grade 7: Textbook for educational institutions / A.V. Peryshkin. – M.: Bustard, 2006.
- Physics. Grade 8: Textbook for educational institutions / A.V. Peryshkin. – M.: Bustard, 2010.
- Entertaining physics. Y. Perelman
- Physics. 7th grade. Textbook. Gurevich A. E.
"The nature of the friction force" - Using the figure, determine the friction force acting on the car. In technology, the force of friction is of great importance. Solution: Scale: 1 bar = 100 H Fpull = 600 H Ftr = 600 N. Without friction, objects would slip out of your hands. The simplest bearing consists of an outer ring and an inner ring. Friction in nature and technology.
"Friction Physics" - History of the study of friction. The direction of the friction force. Teflon is a child of 20th century chemistry. It is easier to move a book on a smoothly polished table than on a rough one. What does the force of static friction depend on? On Mars, gravity is half that of Earth, and the atmosphere is very rarefied. The first "Swedish matches" of Lundstrem, which have survived almost to this day.
"Friction" - What kind of friction are there? Friction of rest. The friction of movement. Friction at rest Sliding friction Rolling friction Designed by Gabdrakhmanova Z.K. Tyulyachinskiy district Saush secondary school. The concept of friction. Friction force. Physics grade 7. Sliding friction.
"Body friction" - The purpose of the lesson: Answer: walking, rolling and rest. Lesson Objectives: Replace the block with a cylinder and do the same. II (2) When lubricating rubbing surfaces, the friction force ... 1. does not change. 2. increases. 3. decreases. Is friction good or bad? V (2) The tractor, while plowing the land, moving evenly, developed a traction force of 15 kN.
"Friction force" - Tasks of the 1st group: Project objectives: Result of the 2nd group. Ways to increase the force of friction. To reduce the resistance force of water, air, a streamlined shape is used. 1. Comparison of sliding friction force and rolling friction force. The result of the 3rd group. Learn the types of friction force. Result of group 1. All forces act differently on the body.
"Friction Force" - Examples. Friction force. Moving an object out of place. But in other cases, friction is harmful. Screw driving. Making fire in a modern way. Friction is a familiar yet mysterious force. Vehicle movement (wheel friction on the road). Friction is one of the types of interaction between bodies. Handwriting on paper. Skating.
In total there are 19 presentations in the topic