Friction definition for kids: friction — Kids | Britannica Kids

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Friction for Kids | Friction | Types of Forces Examples

Friction is a force produced between two surfaces when one object rubs against the other. Friction always works against the motion. The lesson below, friction for kids, teaches about the science behind the force of friction.

 

 

(Click ‘Forces and Motion’ to learn about different types of forces around us.)

 

What is friction?

Friction is the force produced between two surfaces when they are rubbing or sliding against each other.

How friction applies when pushing something

 

Let’s learn more about this now, with Friction for Kids.

 

The force of friction always works in the opposite direction to the movement.

 

So, friction occurs when two surfaces stick to each other a little.

 

 

Friction always slows a moving object down, because it tries to stop the surfaces from sliding over one another.

 

For example;

  • The surface of the wheels sticks to the road, when car wheels roll along the ground.  The force of friction acts between the surface of the wheels and the surface of the road and slows the car down.

 

How friction applies when driving

 

  • You might have noticed that it is difficult to push a box along a cement floor. This is because; friction acts between the surface of the box and the surface of the floor and makes it difficult to push the box along the floor.

 

How friction applies when pushing something

 

Let’s now see how more and less friction apply in our daily life, with Friction for Kids.

 

More Friction and Less Friction

 

Where do you think, you can walk easily? On a rough surface or a smooth surface?

 

If you are unsure about your answer, let’s ask the question in a different way.

 

Where do you think you can walk easily? On the road or on ice?

 

The answer will obviously be on the road. Now if you think about these two surfaces; the surface of the road is rough whereas the surface of ice is smooth.

 

How more or less friction affects us when walking

 

When the surfaces that are touching each other are rough, more friction is produced.

 

When the surfaces that are touching each other are smooth, less friction is produced.

 

This is why walking on the road is easier than walking on ice.

 

The rougher the surface, the more friction is produced.

E.g. glass, ice

 

The smoother the surface, the less friction is produced.

E.g. sand paper, concrete

 

Therefore, more or less friction depends on the materials from which the two surfaces are made.

 

Another example;

Of the two tasks mentioned below, what is difficult to do?

Sliding along an unpolished cement floor in your socks or sliding along a tile floor in your socks.

 

You would have definitely experienced this!

 

There’s no way you could easily slide along an unpolished cement floor in your socks, but you could easily do this on a tile floor.

 

The smoother the floor, the faster you can slide. It is really hard to slide on a very rough surface.

 

How can you walk on some highly polished surfaces which seem to have less or no friction and perfectly smooth?

 

If you look at these highly polished surfaces with a microscope, you can see that even they have rough edges. The rubbing of these rough edges causes friction making you walk on the smooth surfaces.

 

Examples of useful friction

 
Both more friction and less friction can be useful.
 

Examples of more friction and examples of less friction

 

Uses of Friction

More Friction

Less Friction

Walking

Sledging

Writing

Skating

Driving

Sliding

Riding

Skiing

Climbing

For moving parts of machines

 

Examples of more friction

 

How can more friction be useful?

 

Walking

You couldn’t walk without friction. Friction prevents the soles of your shoes from slipping over the ground.

 

Examples of useful friction: We need more friction to walk easily

 

Writing

 

How is it possible to write with a pencil?

When you write with a pencil, friction rubs millions of carbon atoms off the end of the pencil, leaving the black mark on the paper.

 

Examples of useful friction: We need more friction to write easily

 

Climbing

If you do a sport like climbing, it’s often useful to make friction as large as possible. That’s why climbers use rubber soled boots for a better grip as they produce more friction.

 

Examples of useful friction: We need more friction to climb easily

 

Driving or Riding

 

Friction on the roads

 

Driving a motor car or riding a bike would be impossible without friction.

 

Tyres grip the road by friction and that’s what allows a driver or rider to control his car or bike. There has to be a larger amount of friction between the tyres and the roads so that the tyres can grip the road well. Then in a car:

 

  • when the engine turns the wheels, the car can go forward
  • when the driver turns the steering wheel, the car can turn a corner
  • when the driver puts the brakes on, the car can stop

 

Brakes work by friction too.

 

Next the lesson, Friction for Kids, shows you how brakes work by friction.

 

Remember the brake blocks on your bicycle? You need these to slow the bicycle down when riding. To do this bicycle brakes use friction. The rubber pads press against the wheel rims and cause friction that stops the wheels from going round.

 

Similarly, there is a set of brake pads on each of the car’s wheels. The brake pads press on metal discs fitted behind the wheels, when the driver presses on the brake pedal. This produces friction between the pads and the discs, making the wheels slow down.

 

 

Driving with less friction

 

Imagine walking on a slab of ice! It is really hard as there is less friction between your shoes and the slab of ice. So, definitely you need extra care when walking on slippery surfaces.

 

 

Similarly, driving becomes dangerous, if the friction between the tyres and the road is reduced. Driving on wet and icy roads needs extra care as water or ice acts as a lubricant between the tyres and the road and makes braking more difficult.

 

 

Treads

 

Shoe treads

 

Have you ever noticed the carved patterns underneath your shoes?

Your answer should be yes.
 

So, why are soles of shoes designed with these carved patterns?

 

We call these carved patterns underneath your shoes treads. Treads help you walk without slipping or sliding. Treads make the bottom of the shoes rougher, so that friction acts to grip the ground preventing you slipping or sliding.

 

Ballet dancers need to slide their feet a lot. This is why ballet shoes don’t have treads.

 

 

Tyre treads

Tyres of the wheels have treads too. Treads on tyres prevent skidding when driving. Vehicles like tractors have tyres with deep treads because they have to drive through muddy fields. This is why tractor wheels are large and their tyres are rough in order to give them extra grip in the mud. But an ordinary car tyre would get stuck in the mud, or spin round without gripping the ground as its wheels are not large and the tyres have no deep treads.

 

 

So remember;

The deeper the treads, the more they stick to the ground.

 

These are a few examples of the uses of more friction.

 

It is illegal to drive a car with a tyre tread less than 1.6 mm deep.

 

The pattern of grooves on a tyre is designed to let water escapes from underneath it.

 

Frictional Heat

 

How would you feel when you rub your hands together faster?

 

If you have not done it yet, here’s the chance! Rub your hands together faster and see how you would feel.

 

Yes, you definitely feel your hands get warmer. This is because of the heat energy produced by friction. We call this frictional heat.

 

 

Frictional heat is sometimes a good thing. When your hands are cold, you can rub them together and make them warm.

 

The friction between moving parts can create too much heat in machinery. This causes the parts to wear out quickly. Also, in some cases it could start a fire.

 

This is an example of problems caused by friction.

 

Reducing Friction

 

Examples of less friction

 

How can less friction be useful?

 

So, what is the solution to reduce the friction on moving parts of machines?

 

As you know, when the moving parts of machines rub on each other, they are worn away quickly by friction. The machine is slowed down too. As a solution, machines have to be lubricated with oil or grease. Lubricating cuts down friction. A well-oiled machine runs more smoothly, and lasts longer.

 

 

This is why oil is put in a car engine to reduce the amount of friction between the moving parts.

 

Also, wheels are often used to cut down friction.

 

Other uses of reducing friction

 

  • Skiers wax their skis to cut down friction.  Also, skis are designed smooth and narrow to reduce friction. This allows skiers to slide easily across the snow.

 

Examples of less friction – We need less friction for skiing

 

Examples of less friction – We need less friction for skating

 

Examples of less friction – We need less friction for sledging

 

  • Teflon, which is used to coat non-stick frying pans, produces less friction than any other solid.

 

Examples of less friction – Non-stick frying pans

 

Did you know?

A space rocket can keep flying at a steady speed with its engines off. This is because there is no friction in space to slow it down. The rockets speed can gradually change since they are affected by the pull of gravity from the nearest planet.

 

Hope you’ve learned a great deal of facts about friction by reading this lesson, Friction for Kids.

Written By : K8School 9:13 am

Force and Motion for Kids — Force and Motion Information for Kids

Everything in the entire universe is controlled by force. Planets are moving around in space, the sea is rolling in and out, planes can fly, trains can go, and people can live a comfortable life. But how is it possible? Let’s dive into the mysterious nature of force and motion and find out how the strengths work.

What is a force?

Force is a push and pulls in a specific direction. Even though force acts in every area of life, we rarely realize how it works. Fortunately, we can see the result of its impact. The force can:

  • make something move;
  • speed up;
  • change direction;
  • vary shape and size.

Force is pushing or pulling the object in the whole universe. You are participating in the interaction of different types of forces even when you read this article!

Combination of force

Force rarely works alone. There are combinations of different types of forces that affect the universe. First of all, start with an example to show how it works.

Imagine that you are sitting on the football pitch, and one of the footballers is kicking the ball. The ball is flying into the gate, and the fans go wild. Of course, at that moment, we are marveling at the player’s masterpiece. However, we all owe it to a combination of forces. Without various strengths, football wouldn’t even exist.

Three forces make the flying and falling of the ball:

  1. When a footballer kicks a ball — the force of his throw works;
  2. Then the ball is falling thanks to the force of gravity which is pulling it down;
  3. But the ball is not occurring on the ground at a glance. It is slowly falling thanks to the force of air resistance.

Takeaway: there are several types of forces. They are very mysterious and thrilling. See them yourself below!

Contact forces and field forces

Generally, there are contact and field forces. Contact strengths are made when objects touch each other. For example, a leg kicks a ball, or the wind blows against a moving car. All things in contact can exert various forces. Depending on the types of objects in interaction, we give them different names.

Interaction of objects without touching creates field forces. They can make a force at a distance. Such kinds of strengths are natural and very mysterious.

Gravity

It is an invisible force that pulls objects toward the ground. Thus, an apple falls from a tree, thanks to gravity. Gravity is a natural force, which controls everything in the universe — even revolving Earth around the Sun! Each thing has its gravity. The harder an object will pull, the stronger it will fall to the ground. We can feel the force of gravity on roller-coasters. When roller-cars get to the top, gravity pulls it down.

Takeaway: when you throw something, gravity will pull it to the ground. If things had no gravity, they would fly into space.

Tip to note: Newton was the first scientist to write about gravity.

Do you know? Earth is the nearest object to us, which has gravitation, but not the one! The Moon has gravitation, but less than Earth. The gravity of our Sun is the heaviest in our solar system.

Magnetic force

It is another invisible force that can pull and stick some objects to a magnet. Magnets are objects and materials which can produce a magnetic field. They pull on some metals such as iron and nickel. They don’t pull on wood, plastic, copper, or gold. The things which can pull objects are named magnetic. Other things are called non-magnetic.

Do you know? Magnetism is applied in different areas of life. For example, magnets are used in fridges, the doors of refrigerators close and stick tightly with them.

A maglev train can reach 360 mph without an engine, but thanks to magnets! Magnets under the train and on the track push against each other. It is the reason why the train always hovers up to nearly ½ inches above the track. Thus, sets of magnets push the train forward.

Normal force

Sometimes several forces can affect the object, but it remains its characteristics. That happens due to the equilibrium of forces. In that case, a book on the table stays still. It doesn’t move because the gravity that pulls the object down is equal to the force on the table pushing up. The force that keeps the book still is named normal.

Applied force

This is a force that is used to a subject. For example, when you push buttons on your smartphone or close the door.

Frictional force

When two surfaces slide against each other, they stick very slightly together with the help of friction. Some outsides create very little friction, for example, ice and glass. It is easy to move things when a little friction weakly sticks them. By contrast, the more contact between things is, the harder it is to push them.

For example, we can walk across the ground without sliding.

The friction between the ground and wheels of the skateboard helps to do tricks!

Tip to note: A person can not pull a train because there is a more intense force between a train and the ground.

Research on how friction works helps people make scientific breakthroughs. Thus, adding oil between rough surfaces helps slide an iron weight. Oil makes rough surfaces slippery and reduces friction. Oils also save iron from wearing away and reduce friction between moving parts.

Tension force

Tension is a force that is directed on another object. A string or a cable creates this force, for example, when we climb a mountain thanks to the rope.

Spring force

This kind of reactional force is produced when spring is stretched or compressed. Spring is a metal elastic device that can return to its original form after pulling or stretching. Spring force is repulsive when a spring is pressed. And it is attractive when spring is stretched. An example is a trampoline or a diving board.

Resisting force

It helps change, stop or slow a motion. For example, thanks to air resistance, the leaf can float in the wind. When you go swimming, you can notice the water pushing back against your arms and legs as you move forward. It is how water resistance works.

Nuclear force

It is a kind of force that keeps atoms and particles together.

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Balanced and unbalanced forces

The other characteristic of force is vital for our comfortable life. We have already told one of the general properties of force: the bigger force, the more reactions will be, but not always. What happens with the subject after forces affect depend on two things:

  1. How strong are the forces?
  2. What direction of forces?

Balanced forces are two or more forces that affect one object. If the forces act in opposite directions and have equal strength, their effects cancel each other, and the object will remain still. Planes can fly thanks to balanced forces: air resistance, thrust, lift, and gravity.

If one force is stronger than another, the object will change in motion. Such kinds of forces are called unbalanced. They make objects change in direction, speed, and motion.

How is the force measured?

The main but not the one measure of force is the newton. The one newton equals a force that can accelerate one gram of mass by one centimeter per second squared.

Vector

As we’ve mentioned above, the force is an energy in a certain direction. The force always has a direction. This is very important knowledge, which helps people to predict and control the force’s impact.

Tip to mention: vector is a line with an arrow.

If we dive into physics science, we find out that force has both magnitude and direction. The first one is measured in newtons, and the second one makes force a vector. The direction of force, or vector, is shown as an arrow. Vectors identify the direction of the force, and newtons identify magnitude.

You may also be interested in other “Physics for kids” topics :

  • States of matter: what are solids, liquids and gases?
  • What is gravity? — Simple explanation for kids 
  • What is electricity and how does it work?
  • Magnets and magnetism: simple introduction for kids

Inertia

Inertia is a property of objects with mass to resist a change in motion or rest. All things have inertia; they resist motion or rest when an outer force affects them. For example, you can feel inertia traveling by train: when the vehicle stops, it continues to move forward sometimes. This is because of inertia. Inertia is often masked by other forces such as friction, resistance, gravity. The more mass a subject has, the more inertia it has.

Force and motion

Motion is movement from one place to another. The force causes motion as force affects objects which start moving but not only. Forces affect the motion in several ways:

  1. Objects can start moving.
  2. They can move faster or slower.
  3. Objects can stop moving.
  4. They also can change direction or even shape.

When objects start moving faster, they accelerate. This property is called acceleration, which means an increase in speed.

Fun fact: The invisible forces make us giggle or scream. For example, when you ride a roller coaster, the forces lift you and go you downhill. At this time, your stomach lifts upwards and downwards, making you scream and giggle at the same time.

Laws of motion

Physicist Isaac Newton is the first scientist who writes about motion. He formulated three main laws describing the motion of things:

  1. Nothing moves unless a force acts on it.
  2. Forces accelerate things. This happens when you ride a bike: the harder you push on pedals, the faster the bike moves.
  3. When a force acts, there will always be an opposite force. Any directed force creates an equal one in the opposite direction. When you are sitting on the chair, your weight pushes down on it. But the chair also pushes you back. This is an example of balanced forces. When the old chair can’t push you back, it crashes, and then forces are unbalanced.

Summary

  1. Newtons (N) is the main measure of force.
  2. Forces rarely work alone; there are combinations of two or more strengths in nature.
  3. They affect subjects in a certain direction.
  4. Strengths are invisible, but we can see their effects.
  5. Strengths cause accelerations of subjects.
  6. Friction is an energy that is produced by several rubbing objects.
  7. The Sun has the strongest gravitation in our solar system.
  8. Forces cause not only motion but also changing of shape and size. For example, when we kick a ball, it will be compressed.
  9. A parachute can make an object slow down because of air resistance.
  10. Each object has a property named inertia — the tendency to resist a change in motion or rest.

Vocabulary

  • Force is a term in physics for pushing and pulling.
  • Balanced forces are forces that cancel each other in certain terms — they act in the opposite direction and have equal strength.
  • Unbalanced forces are forces that affect the subject, making it move or change its shape and size.
  • Gravity is a force pulling objects to the ground
  • Magnetism is a force pulling and sticking objects to a magnet.
  • Vector is an arrow with a dot that shows a director of force.
  • Inertia is a property of objects to stay rest or resist in motion until the outer force acts on them.
  • Motion is a movement from one place to another caused by force.

Questions

  1. In which units is force measured?
  2. What does Newton’s first law of motion explain?
  3. When are forces balanced?
  4. How does the second law of Newton help ride your bike?
  5. Define the motion law: a force acts in one direction and creates an equal force in the opposite direction.
  6. Who first wrote about gravity?
  7. Which things have magnetic properties, and which haven’t?

Answers

  1. In Newtons.
  2. Nothing moves unless a force acts on it.
  3. Balanced forces act in opposite directions and have equal strength if they cancel each other, and the object will remain still.
  4. As forces accelerate speed, the harder I push the pedal, the faster the bike rides.
  5. The third Newton’s law.
  6. Newton is the first scientist who wrote about gravity.
  7. Iron and nickel are magnetic; copper, gold, or wood are non-magnetic.

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What It Is in Simple Terms

The term sliding friction refers to the resistance created by two objects sliding against each other. This can also be called kinetic friction. Sliding friction is intended to stop an object from moving. Review some sliding friction examples and discover some key facts about this phenomenon.

sliding friction example sled on incline

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Basic Understanding: What Is Sliding Friction?

Friction is the resistance that occurs when two objects rub together. Sliding friction is one type of friction. Any time two surfaces that are solid slide across one another, sliding friction is created.

Factors that can affect the level of friction created include:

  • surface deformation (wrinkles, cracks, etc.) of the objects
  • roughness or smoothness of the surfaces of the objects
  • speed at which the objects are moving when they make contact
  • size of the objects
  • amount of pressure on either object
  • how adhesive the surfaces of the objects are

The amount of sliding friction created by objects is expressed as a coefficient, which takes into consideration the various factors described above.

Everyday Examples of Sliding Friction

Many examples of sliding friction can commonly be observed in daily life. Sliding friction can occur in objects of all sizes. Consider these sliding friction examples to help you better understand this concept.

Sliding Friction in Everyday Chores

As people go about their daily activities, they often create sliding friction without even realizing it. Any time you slide two solid objects across one another, you are creating sliding friction.

  • a beverage coaster sliding across a table
  • pushing an iron across material
  • the frame and the edge of doors sliding against one another
  • sliding a block across the floor
  • pushing the bottom of a drinking glass across a table
  • the sliding of the rope and pulley when opening or closing a set of blinds or curtains
  • the friction between two books when sliding one into place on a bookshelf
  • the friction between the bottom of a book and the shelf when sliding the book into place
  • a vegetable drawer sliding against the holder in the fridge
  • a paper sliding against the paper holder once emitted from a copy machine
  • sliding a chair out from under the dining room table so you can sit in it
  • rubbing a rag across the counter it is being used to clean
  • sliding a glass door against the track along which it is moving
  • pulling snug jeans up over your legs when putting them on
  • sliding a check across the counter at the bank to give it to the teller

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Sliding Friction With Heavy Objects

Some objects are so heavy that people often slide them when they need to be relocated rather than picking them up and carrying them. This creates sliding friction.

  • pushing a washing machine or dryer into place against the wall
  • sliding a stove out of its space so you can clean behind it
  • pushing a couch across the floor to move it
  • pushing a dresser on the carpet as you slide it to another part of the room
  • sliding cement or concrete blocks across the ground
  • pulling a heavy trash can down the driveway
  • sliding a heavy box that was delivered to your home across the floor

Activity-Related Sliding Friction Examples

Not all sliding friction results from household activities or pushing heavy objects. Sometimes the physics concept of sliding friction is all about fun and games.

  • rubbing both hands together to create heat
  • rolling a bowling ball down a lane at the bowling alley
  • sliding across home plate to score a run in baseball
  • sliding a sled across snow or ice
  • skis sliding against snow
  • a person sliding down a sliding board
  • two playing cards in a deck sliding against each other
  • sliding a birthday card out of its envelope

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Learn More About Friction

As these examples show, there are many different situations where sliding friction exists and where sliding friction creates resistance as objects rub against each other. There is a good chance you have encountered sliding friction examples in the real world. Now you will be able to recognize sliding friction examples when you come upon them since you have a better understanding of what sliding friction means. Ready to learn more? Explore some examples of rolling friction, which is the type of friction that occurs when a round object rolls over a solid surface, with friction slowing the rate of movement.

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Friction force — definition, formula, types, how to find?

Friction: magnitude, direction

Friction is something you encounter every second. Every time you interact with any surface — walking on asphalt, sitting on a chair, drinking tea from a cup — you are affected by the force of friction.

Friction is the interaction in the plane of contact between two surfaces.

To translate friction into the language of physics, the concept friction force is introduced.

Friction force is a value that characterizes the friction process in magnitude and direction.

Friction force is measured, like any force — in Newtons.

Friction force arises for two reasons:

  • Various roughness, scratches and other «imperfections» of surfaces. These defects touch each other upon contact and a force is created that slows down the movement.
  • When the contacting surfaces are practically smooth (it is impossible to bring to the ideal, but to strive for it means to tend the friction force to zero), then the distance between them becomes minimal. In this case, there is a mutual attraction of the molecules of the substance of these surfaces. Attraction is due to the interaction between the electric charges of atoms. In this regard, you can often hear the wording «The force of friction is a force of electromagnetic nature»

The friction force is always directed against the speed of the body. In this regard, everything is simple, but there is always a question:

In problems, they often write something like: “Assume the surface is ideally smooth. ” This means that there is no friction force in this problem. Yes, in real life this is impossible, but in the name of a beautiful mathematical model, friction is often neglected.

Do not worry about this injustice, but just solve problems without friction if you see the phrase «smooth surface».

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Dry and viscous friction

There is a very big difference between your contact with the water in the pool while swimming and the contact between the asphalt and the wheels of your bike.

In the case of swimming, we are dealing with viscous friction — the phenomenon of resistance when a solid body moves in a liquid or air. The plane is also subjected to viscous friction and that impudent pigeon from your yard.

But dry friction is a phenomenon of resistance when two solid bodies come into contact. For example, if a student fidgets in a chair or a villain from a movie rubs his hands, it will be dry friction.

What if the villain is clean and rubs his hands, dropping an antiseptic on them?

Then this is viscous friction, despite the fact that the hands are solid bodies. In this case, there is a wet layer.

Viscous friction is not considered in detail in the school physics course, but dry friction is analyzed up and down. Dry friction also has varieties, let’s talk about them.

Static friction

If you decide to move the truck, you are unlikely to succeed. It’s not that we don’t believe in you — it’s just impossible to do this because the mass of a person is many times less than the mass of a truck, and even the friction force prevents this from being done. The world is cruel, what can you do.

In the case when there is a friction force, but the body does not move, we are dealing with rest friction force.

The static friction force is equal to the traction force. For example, if you are trying to move a sled with a pull force of 10 N, then the friction force will be 10 N.

static friction force

F tr = F rod

F tr — static friction force [N]

F traction — traction force [N]

Let’s practice a little!

Problem

Find the static friction force for a body subjected to a traction force of 4 N.

Decision:

The body rests, which means

F TR = Fty = 4 H

Answer: Fright Strength is 4 N.

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Sliding friction

Now let’s skate on ice. The skating rink is quite smooth, but, as we have already found out, the friction force will still be present and will be calculated according to the formula:

Sliding friction force

F tr = μN

F tr — sliding friction force [N]

μ — coefficient of friction [—]

N — reaction force of the support [N]

The friction force that we get from this formula will be the maximum possible — that is, there is nowhere else.

Support reaction force is the force with which the support acts on the body. It is numerically equal to the force of normal pressure and opposite in direction.

Is normal pressure force the same as body weight?

Not really. The force of normal pressure is always directed perpendicular to the surface (the normal is perpendicular to the surface). The weight is not necessarily directed perpendicular to the surface.

In the school course, the weight is always perpendicular to the surface , so the reaction force of the support can be numerically equated to the weight.

Read more about body weight in our article😇

Also, if the body is on a horizontal surface, the support reaction force will be equal to gravity: N = mg.

Friction coefficient is a characteristic of the surface. It is determined experimentally, has no dimension and shows how smooth the surface is — the larger the coefficient, the more rough the surface. The coefficient of friction is positive and most often less than unity.

Let’s be vigilant!

The dependence of the friction force on the area of ​​contact does not follow from the formula. For example, if you put a bar on one side and drag it across the table, and then turn it over to another one that is not equal in area and do the same, the friction force will not change.

Problem 1

The mass of a cat lying on a table is 5 kg. Friction coefficient µ = 0.2. An external force equal to 2.5 N is applied to the cat. What friction force arises in this case?

Solution:

According to the condition of this problem, it is impossible to understand whether our cat is moving or not. The decision on whether we equate the force of friction with the force of thrust cannot be taken immediately. In such cases, you still need to calculate according to the formula:

F = μN

Since the cat lies on a horizontal surface, the support reaction force in this case is equal to gravity: N = mg.

F = μmg = 0.2 5 10 = 10N

We have obtained the maximum possible friction force. The external force, according to the condition of the problem, is less than the maximum. This means that the cat is at rest. The friction force balances the external force. Therefore, it is equal to 2.5 N.

Answer: there is a friction force of 2.5 N

Problem 2

A badger slides along a horizontal plane. Find the coefficient of friction if the friction force is 5 N and the pressure force of the body on the plane is 20 N.

Solution:

In this problem, we know that the badger is sliding. So you need to use the formula:

F tr = μN

F TR = μF D

We express the coefficient of friction:

μ = F TR / F D = 0.25

Reply: Ship coefficient is 0.25

Problem 3

Your grandmother’s 5 kg poodle slides on a horizontal surface. The sliding friction force is 20 N. Find the friction force if the poodle loses a lot of weight, and its mass is halved, and the coefficient of friction remains unchanged.

Solution:

In this problem, we know that the poodle is sliding. So, you need to use the formula:

F tr = μN

Since the poodle is on a horizontal surface, the support reaction force in this case is equal to gravity: N = mg.

F tr = μmg

0005

Answer: the friction force will be equal to 10 N.

Problem 4

The student conducted an experiment to study the sliding friction force, moving a bar with loads evenly over horizontal surfaces using a dynamometer.

The results of experimental measurements of the mass of the bar with weights m, the area of ​​contact between the bar and the surface S and the applied force F are presented in the table.

AMAZING FRICTION

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Introduction

Winter is a favorite time for many kids in the Kama region! After all, you can slide down a hill with a breeze, drive quietly through a fabulous winter forest and have fun skating with friends. I love winter fun too!

Once, my dad and I were skating down an ice slide. At first I moved out without ice. And I managed to get only to the end of the ice slope. Then I decided to get out on a plastic ice rink, and my distance almost doubled!

Problem: to understand what prevented me from going so far without ice.

The purpose of this project is to solve the mystery of the force of friction.

Tasks:

  • trace the historical experience of mankind in the use and application of this phenomenon;

  • find out the nature of the friction force;

  • conduct experiments confirming the regularities and dependences of the friction force;

  • to understand where a student of the 2nd grade can meet with the force of friction;

  • develop recommendations for classmates «Smart winter vacation».

To achieve our goals, we worked on this project in the following areas:

1) Research of public opinion;

2) The study of theory;

3) Experiment;

4) Design.

Hypothesis: the force of friction is necessary in people’s lives.

Scientific interest lies in the fact that in the process of studying this issue, some information was obtained on the practical application of the phenomenon of friction.

1 . What is friction (a bit of theory)

Objectives: to study the nature of friction forces.

Friction force

Why is it better to ride an ice rink from a snowy hill? How does the car accelerate, and what force slows it down when braking? How are plants held in the soil? Why is a live fish difficult to hold in your hand? How to explain the danger of ice in the winter? It turns out that all these questions are about the same thing!

The laws of friction provide answers to these and many other questions related to the motion of bodies. From the above questions it follows that friction is both a harmful and beneficial phenomenon.

Any body, moving along the surface, catches on its irregularities and experiences resistance. This resistance is called friction force . Friction is determined by the properties of the surface of solids, and they are very complex and have not yet been fully explored.

If we try to move the closet, we will immediately see that it is not so easy to do it. His movement will be hindered by the interaction of the legs with the floor on which he stands. What determines the amount of friction force? Everyday experience shows that the more strongly the surfaces of bodies are pressed against each other, the more difficult it is to cause their mutual sliding and to maintain it. We will try to prove this experimentally.

1.1. The role of friction forces

Let’s imagine that one day something strange happened on Earth! Let’s turn to a thought experiment, imagine that in the world some wizard managed to turn off friction . What would it lead to?

Firstly, we would not be able to walk, the wheels of cars would spin in place to no avail, clothespins would not be able to hold anything …

Secondly, the causes that generate friction would disappear. During the sliding of one object over another, it is as if the microscopic tubercles are meshing with each other. But if these tubercles did not exist, this would not mean that it would be easier to move an object or drag it. There would be a so-called STICKING effect, which is easy to detect when trying to move a stack of books in a glossy cover along the surface of a polished table.

This means that if there were no friction, there would not be these tiny attempts of each particle of matter to keep its neighbors around. But then how would these particles stick together? That is, inside the various bodies the desire to “live in a company” would disappear, and the substance would fall apart to the smallest detail, like a LEGO house.

Here are some unexpected conclusions that can be reached if we assume the absence of friction. As with everything that hinders us, we must fight it, but it will not be possible to completely get rid of it, and it is not necessary!

In technology and in everyday life, friction forces play a huge role. In some cases, friction forces are beneficial, in others they are harmful. The force of friction holds driven nails, screws, nuts; holds threads in matter, tied knots, etc. In the absence of friction, it would be impossible to sew clothes, assemble a loom, put together a box.

Friction increases the strength of structures; without friction, neither the laying of the walls of a building, nor the fixing of telegraph poles, nor the fastening of parts of machines and structures with bolts, nails, screws can be carried out. Without friction, plants could not be held in the soil. The presence of static friction allows a person to move on the surface of the Earth. Walking, a person pushes the Earth back from himself, and the Earth pushes the person forward with the same force. The force that propels a person forward is equal to the static friction force between the sole of the foot and the Earth.

The more a person pushes the Earth back, the greater the friction force applied to the leg, and the faster the person moves.

It is very difficult to walk and drive in icy conditions because there is very little friction. In these cases, sand is sprinkled on the sidewalks and chains are put on the wheels of cars to increase the rest friction.

The force of friction is also used to keep bodies at rest or to stop them if they are moving. The rotation of the wheels is stopped by the brakes. The most common are air brakes that are powered by compressed air.

2. Design work and findings

Goals: create a demonstration experiment; explain the results of the observed phenomena.

After studying the literature, my dad and I made several experiments. We thought through the experiments, and tried to explain their results.

Experience No. 1

Let’s go back to the story of my downhill ride.

Once, my dad and I were skating down an ice slide. At first I moved out without ice. And I managed to get only to the end of the ice slope. Then I decided to get out on a plastic ice rink, and my distance almost doubled!

Now, I understand that the force of friction the first time I rolled was greater, it made my body slow down faster. But even in this experiment, the hardness of the bodies matters. My winter suit is much softer than a plastic ice cap. This means that the suit interacts more with the slide and produces a greater friction force. Rigid ice is less “gripping” with the slide, and friction is less!

Experience No. 2

On a piece of cardboard one toothpick wide, and two toothpicks long, with plasticine, attach a toothpick across the cardboard in the middle. Then fold the edges of the cardboard. Draw a spider on colored paper. We draw a spider so that its body is larger than a rectangle. Glue a piece of cardboard to the back of the spider. Cut the thread to the length of your hand. We will thread the needle and stretch it through the cardboard. Pull the thread with the spider and hold it vertically. Then loosen the thread a little. How will the spider behave?

When the thread is pulled tight, it touches the toothpick and FRICTION occurs between them. Friction keeps the spider from sliding down.

Experience No. 3

This experiment shows what the friction force depends on.

Let’s take a sheet of paper. Let’s put it between the pages of a thick book lying on the table. Let’s try to pull out the sheet. Let’s do the experiment again. Now let’s put the sheet almost at the very end of the book. Let’s try to pull it out again. Experience shows that it is easier to pull a sheet from the top of a book than from the bottom. This means that the stronger the surfaces of bodies are pressed against each other, the greater their interaction, that is, the greater the friction force.

Experience No. 4

With repeated unbending and bending of the wire, the bending point heats up. This is due to friction between the individual layers of metal. Also, when rubbing a coin against a surface, the coin heats up.

Experiment No. 5

This simple experiment shows the application of the force of friction.

Sharpening knives in workshops. When a knife becomes dull, it can be sharpened with a special device. The phenomenon is based on the smoothing of the notches between the contacting surfaces.

The results of these experiments can explain many phenomena in nature and human life. Now that the secret of the force of friction has become known to me, I understand that it is also described in many fairy tales! This was another discovery for me!

I really want to give examples of fairy tales. In the fairy tale «Gingerbread Man» — the force of friction helps the protagonist to get out of difficult situations («Gingerbread Man lay down, lay down, took it and rolled — from the window to the bench, from the bench to the floor, along the floor to the door, jumped over the threshold — and into the canopy and rolled…”). In the fairy tale «Ryaba the Hen» — the lack of friction force led to trouble («The mouse ran, wagged its tail, the testicle rolled, fell and broke). In the fairy tale «Turnip» — the friction of the turnip on the surface of the earth made the whole family rally. The Snow Queen easily overcame the force of friction with her magic (“The sleigh drove around the square twice. Kai quickly tied his sledge to it and drove”).

It is interesting to look at famous works differently!

3. Public opinion survey

Objectives: to show what role the phenomenon of friction or its absence plays in our life; answer the question: “What do we know about this phenomenon?”

Proverbs and sayings were studied, in which the friction force of rest, rolling, sliding is manifested, human experience was studied in the application of friction, ways to combat friction.

Proverbs and sayings

— There will be no snow, there will be no trace.

— The quieter you go, the further you’ll get.

— A quiet cart will be on the mountain.

— It’s hard to swim against the water.

— You like to ride, love to carry sleds.

— Patience and work will grind everything.

— That’s why the cart sang that it hadn’t eaten tar for a long time.

— And scribbles, and rolls, and strokes, and rides. And all with language.

— He’s lying that he sews with silk.

All these proverbs indicate that people have noticed the existence of friction forces for a long time. The people reflect in proverbs and sayings the efforts that must be made to overcome the forces of friction.

Take a coin and rub it on a rough surface. We will feel resistance — this is the force of friction. If you rub faster, the coin will begin to heat up, reminding us that heat is released during friction — a fact known to man of the Stone Age, because it was in this way that people first learned to make fire.

Friction enables us to walk, sit, work without fear that books and notebooks will fall off the table, that the table will slide until it hits a corner, and the pen slips out of our fingers.

Friction is not only a brake on movement. This is also the main reason for the wear and tear of technical devices, a problem that man also faced at the very dawn of civilization. During excavations of one of the most ancient Sumerian cities — Uruk — the remains of massive wooden wheels, which are 4.5 thousand years old, were found. The wheels are studded with copper nails for the obvious purpose of protecting the wagon train from wear and tear.

And in our era, the fight against wear of technical devices is the most important engineering problem, the successful solution of which would save tens of millions of tons of steel, non-ferrous metals, and drastically reduce the production of many machines and spare parts for them.

Already in antiquity, engineers had at their disposal such important means to reduce friction in the mechanisms themselves as a replaceable metal bearing lubricated with grease or olive oil.

Of course, friction plays a positive role in our life. No body, whether it be the size of a stone block or a grain of sand, will ever rest on one another, everything will slide and roll. If there were no friction, the Earth would be without irregularities, like liquids.

4. Recommendations to classmates

I learned so many interesting and new things about the secrets of the force of friction. You need to fight it wisely in order to develop unprecedented speed. I decided to tell my classmates about how to ride the slides correctly and safely.

Winter is a time of fun and fun games. Slides are everyone’s favorite winter pastime. Speed, the whistle of a fresh wind, a storm of overflowing emotions — in order for your vacation to be not only pleasant, but also safe, you should think about choosing both slides and sleds.

1. With a baby under 3 years old, you should not go to a busy hill with which children 7-10 years old and older ride.

2. If the slide causes you concern, first let an adult ride it, without a child — experience the descent.

3. If a child is already riding a “busy” slide of different ages, an adult must be sure to follow him. It is best if one of the adults watches the descent from above, and someone from below helps the children quickly clear the way.

4. Under no circumstances should railway embankments and hills near the carriageway of motorways be used as slides.

Busy Mountain Rules:

  • Climbing a snow or ice slide should only be done at a climbing point equipped with steps; it is forbidden to climb a hill where others slide down towards you.

  • Do not move out until the previous descender has moved aside.

  • Do not linger below when you have moved out, but quickly crawl away or roll to the side.

  • Do not cross the icy path.

  • To avoid injury, you can not ride while standing on your feet and squatting.

  • Try not to slide backwards or head forward (on your stomach), but always look ahead, both when descending and when ascending.

  • If a passer-by walks past the hill, wait until he passes, and only then make the descent.

  • If it is impossible to get away from a collision (a tree, a person, etc.) on the way, then you should try to fall on your side on the snow or roll away from the ice surface.

  • Avoid skiing hills with uneven ice.

  • In case of injury, immediately provide first aid to the victim, report this to the emergency call service 01.

  • At the first sign of frostbite, or if you feel unwell, stop riding immediately.

  • There are a huge number of different slides now available, so you can find the right one to enjoy riding on any slide: from steep icy to gently sloping, covered with fresh snow.

Comfortable Ice Slide Vehicles:

Ice cube . The simplest and cheapest device for skiing in winter. They are intended for single skiing on icy and rolled snow slopes. The ice rinks are designed for children from 3 years old, because. It’s hard for kids to manage. A saucer-shaped ice cube becomes uncontrollable if you sit in it with your feet.

Ice-trough is very unstable, at the slightest unevenness it strives to fall on its side — thus, having flown up on a springboard, you can land upside down. Ledyanki are not designed for springboards or any other obstacles, because. any sharp jump on the hill is fraught with unpleasant consequences for the coccyx and spine of the rider!

Ordinary «Soviet» sleds are great for any snowy slopes. You can steer and brake with your feet. Falling sideways to avoid a dangerous collision is also quite easy and safe.

Snow scooter . For family skiing, you should not choose a snow scooter — it is designed for one or two kids aged 5 to 10 years. More than once, cases were noticed when snow scooters clung to an obstacle (tree root, snow mound) with the front skid and turned over. It is difficult to get off a snow scooter at high speed, and this vehicle develops a considerable speed on any slope and accelerates quickly. The brakes are located at the front, which increases the risk of rolling over your head when trying to brake hard. If an adult rides from a high mountain with a child, putting the baby on a snow scooter in front, it will be very difficult for them to steer, brake and evacuate in case of danger.

Cheesecakes . Recently, inflatable sleds are increasingly found on our slides. The most common inflatable circles are “sled-cheesecakes”. The cheesecake is light and rides well even in fresh snow on a completely unrolled hill. It is best to ride cheesecakes from gentle snowy slopes without obstacles in the form of trees or other people. As soon as the movement speed increases, the cheesecake becomes quite dangerous. Cheesecakes accelerate with lightning speed, and the speed is higher than a sled or a snow scooter on a similar slope, and it is impossible to jump off the cheesecake at speed. Cheesecakes cannot be ridden from slides with springboards — when landing, the cheesecake is very springy. Even if you don’t fall off, you can get severe injuries to your back and cervical spine. A good version of the «cheesecake» is a small inflatable ice rink (about 50 cm in diameter) — it’s easy to fall on your side (get off).

Carefully consider the choice of slides and means for skiing!

The hill is a place of increased danger, and not just another entertainment on a winter walk along with building snowmen and feeding birds! When riding children with adults, it is important not to forget that speed depends on mass. That is, the steeper and «icier» the hill or the larger the mass («dad is big and strong, it’s not scary with him»), the more deadly the force of the collision. That is why even in cars children are required to be carried fastened in car seats, and not in the hands of adults and not fastened together with an adult with one belt. The force of friction is not a magical force, it will not allow you to stop instantly!

Conclusion

  • We found out that a person has long been using knowledge about the phenomenon of friction, obtained empirically.

  • Now we know exactly when the friction force occurs.

  • We have created a series of experiments that help to understand and explain some of the «difficult» natural phenomena.

  • We have identified literary works that talk about the force of friction.

  • Most importantly, we realized how great it is to acquire knowledge ourselves, and then share it with others.

References

1. Elementary textbook of physics: Study guide. At 3 pm / Under the editorship of G.S. Landsberg. T.1 Mechanics.Molecular physics.M.: Nauka, 1985.

2. Ivanov A.S., Prokaza A.T. World of mechanics and technology: Book for students. – M.: Enlightenment, 1993.

3. Encyclopedia for children. Volume 16. Physics Part 1 Biography of physics. Journey into the depths of matter. Mechanical picture of the world / Chapter. Ed. V.A.Volodin. – M.: Avanta+, 2010

4. Children’s encyclopedia. I know the world: Physics / comp. A.A. Leonovich, ed. O.G. Hinn. — M .: LLC «Firm» AST Publishing House «.2010.-480s.

  • http://demo.home.nov.ru/favorite.htm

  • http://gannalv.narod.ru/tr/

  • http://en.wikipedia.org/wiki/%D0%A2%D1%80%D0%B5%D0%BD%D0%B8%D0%B5

  • http://class-fizika.narod.ru/7_tren.htm

  • http://www.physel.ru/component/option,com_frontpage/Itemid,1/

  • http://62.mchs.gov.ru/document/1968180

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«The force of friction»

Purpose of the lesson: to introduce students to the power
friction.

Tasks:

Educational: introduce the concept of friction force

Developmental: continue to develop in students
ability to compare, reason, logically
think, choose the main thing

Educational: education of students
goodwill towards each other, respect for
the opinion of others, the ability to listen.

Teacher’s equipment: tripod, ruler,
a machine, a piece of cloth and fur, a dynamometer,
a wooden block, a set of weights, a projector for
showing a presentation.

Students’ equipment: dynamometer,
wooden block, two weights, two pencils
(sticks), 5-6 pictures with different types of friction,
practice sheet.

Lesson progress

Introductory conversation:

you studied the physical quantity, which
called strength.

Questions to students:

1) What is strength? What do you know about her?

2) What kinds of forces have you already studied?

Today at the lesson we will get acquainted with another
strength, and now I invite you along with Vini
rest in peace and Piglet to make a small
travel.

Journey of Piglet and Winnie the Pooh.

Once Winnie the Pooh and Piglet went to visit
to the owl. The path was long, with obstacles, but they walked,
talking, and not even noticing fatigue.

Suddenly Winnie the Pooh asked: “Why are we moving
forward?»

— The legs themselves cross like this, — answered Piglet.

— Right. Why forward and not backward?

— I don’t know, maybe faster?

Seemingly stupid questions, stupid answers, but they
it was fun to walk on smooth asphalt
track. Nothing interfered, it was easy to go, although
damp. Suddenly Winnie the Pooh lost his balance, his legs
slipped, he loudly shouted: “Save,
Help». It turns out that the asphalt is over, and
there was wet clay underfoot. suddenly got up
a strong wind, snowflakes flew in, it became very
cold, the ground was covered with snow, it became slippery,
as ice formed on the puddles, it became more to go
more difficult. In order not to fall, travelers
held each other and walked small funny
step by step. They have very little to go. small house
the owl was already visible.

It is clear that for normal walking it is necessary, first
everything so that the legs firmly rest on the road and not
slipped. But why do they suddenly start
slide? How wet clay is inferior to asphalt, and
ice — even worse? To understand these
such simple questions, let’s see
several experiences.

Note: pre-write on the board
questions posed at the beginning of the lesson

Why are we moving? Why walk on asphalt
easily? How are ice and clay inferior to asphalt?

Experiment 1: slides down an inclined plane
machine and reaches the edge of the table

Experiment 2: spread a piece of cloth on the table,
now the car stops before reaching
table edges.

Experiment 3: spread fur or foam rubber on the table,
the machine, having driven into them, immediately stops.

Questions:

What causes the change in body speed
(machines)?

What force made the machine stop during
all three cases and why the car passed
different distances?

Next, the topic of the lesson is announced “Power
friction” (students write down the topic
lesson) — slide 1

Explanation of new material

Question: From what word did the word come
«friction»?

Friction occurs when one
body with another and preventing their relative
movement (the word “friction” comes from the word
rub).

Definition: Friction is the force
which occurs when a body moves along
surface of another body and directed against
their relative motion (recorded in
notebook). С slide 2.

To find out the causes of friction, students
recall the experiments shown at the beginning of the lesson.

Question: Why is the machine when driving on
mehu immediately stopped? ( fleecy fur,
pile catches on the wheels of the machine and
stops it).

Even the table looks flat and smooth at first glance
has many irregularities (open textbook p.
71, figure 79a).

1 cause of friction: roughness
bodies in contact.

Question: How will the friction force change if
reduce irregularities, for example, grind the body
very good and polished?

Practice shows that as the
irregularities, the friction force will be first
decrease, but when the surfaces are very
well polished, then the force of friction again
increases. Why? (remember the structure
substances)

2 cause of friction: the mutual attraction of molecules
bodies in contact. С slide 3

Consider the types of friction. С slide 4.

If a body slides on the surface of another body,
then there is sliding friction (examples).

If a body rolls on the surface of another body,
then there is rolling friction (examples).

If a body lies on the surface of another body, then
arises static friction (examples).

(write down the types of friction in a notebook, draw up in
block diagram form). C slide 5

Types of friction: 1 sliding friction

2 rolling friction

3 static friction

Question: In the picture, find the different types
friction and indicate between which bodies they
arise. С layd 6

And now let’s find out, how to measure the friction force?

Question: What device is used to measure
strength? (using a dynamometer).

Any measuring device has a scale,
so let’s remember how the price is found
division of the device (find the division price
dynamometer).

To measure the force of sliding friction
wooden bar on the table, must be attached to
him a dynamometer, then evenly move the bar
on the table, holding the dynamometer horizontally.

Question: What force will the dynamometer show?
(elastic force, as the spring is deformed).

But since the block moves uniformly, then
there are two forces at once, directed
horizontally, one is the spring force
(it is also the traction force) directed to
direction of motion, and the other — the force of friction,
directed against the movement. Since the bar
moving uniformly, this means that
the resultant of these two forces is zero, and
so these forces are equal in magnitude and opposite
towards. Dynamometer shows strength
elasticity, equal in modulus to the force of friction (students
measure the force of sliding friction).

Practical part

(the students have a sheet with the progress of work and
tables to fill in).

Practical work No. 1.

The goal is to find out how the friction force depends on
force pressing the body to the surface.

Equipment: wooden block,
dynamometer, two weights

Progress

  1. Attach a dynamometer to the bar and evenly
    pull it along the surface of the table (indications
    dynamometer, write in the table — in the column «force
    friction”)
  2. Measure the weight of the bar with a dynamometer
    (write to table)
  3. Place a weight on the block and measure the force again
    friction (write the readings in the table — experiment No. 2)
  4. Place two weights on the bar and measure again
    friction force (write in the table — experience No. 3)
    Determine and record in the table the weight of the bar and
    cargo.

Note: in order to save time, the weight
the load can be considered 1N, and the bar — 0.8 N (you can
check with a dynamometer)

Experience no. Body weight, N Friction force, N
1 (unloaded bar) 0.8
2 (bar with weight) 1.8
3 (bar with two weights) 2.8

Output : the greater the pressing force
body to the surface, the greater the friction force. C layd
7

Practical work No. 2

Purpose: to compare the force of sliding friction,
rolling and resting under the same loads (experiment
better to do with one load)

Equipment: block, dynamometer, weight, two
pencil (not cut)

Progress

  1. Put a weight on the bar, attach to the bar
    dynamometer and evenly start pulling it.
    Notice the dynamometer reading at the moment
    when the bar moves from its place — this will be the force
    static friction (record readings in table)
  2. Bar with a load using a dynamometer
    move evenly across the surface of the table and
    measure the force of sliding friction (write in
    table)
  3. Place two pencils under the block and measure
    rolling friction force (write in table)

    4. Type of friction Force, N
    1

    2

    3

    		Friction at rest

    Sliding friction

    Rolling friction

    Conclusion: the static friction force is always greater than the force
    sliding friction, and the sliding friction force
    more rolling friction — slide 8

    Question: Why is it difficult to move a heavy cabinet
    places, but it is easier to drag it, and even easier to roll,
    using rollers?

    In ancient times, people for dragging heavy
    cargo was first used by rollers, and later
    wheels were used.

By alexxlab

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