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7 Major Effects of Friction (with illustrations)

Compiled by Stanley Udegbunam ||updated Oct 13, 2020

In today’s article, we’ll be looking at the different effects of friction.

But before then, Let’s have a quick overview of friction.

Table of Content

1. Overview of Friction

Overview of Friction

Friction is the resistance between contacting bodies when one moves relative to another.

It’s applicable in every sphere of life and this makes it one of the fundamental topics in physics.

There are three major types of friction.

1. Static friction: friction force between an object at rest relative to a surface.
2. Kinetic friction: friction force between surfaces that moves or slides relative to each other.
3. Rolling friction: friction force that resists the rolling motion of an object against a surface.

Major Effects of friction

1. Friction causes wear and tear in mechanical parts.
2. We are able to walk because of friction
3. Vehicles rely on friction for accelerating and decelerating.
4. Friction produces heat for body warmth
5. Heat generated from friction can cause ignition or start up fire.
6. Friction is present in synovial joints.
7. Friction causes a loss in power.

Detailed Explanation of Friction Effects

1. Wear and tear in mechanical parts.

Friction is the major cause of wear and tear in mechanical parts of automobiles and engines.

If left unattended to, the end result can be disastrous.

Car components like clutches, brake pads, and brake disc often wear off due to continuous surface contact.

This the reason why lubricants and grease are often applied to moving parts.

Effective lubrication will lead to a prolonged machine life and reduced heat buildup.

2. Thankfully, we are able to walk as a result of friction.

When you walk, the backward movement of our feet exerts a force on the ground as the other foot moves forward.

When this force is exerted on the ground, then an equal and opposite force is exerted by the ground on our feet.

Downward push by our feet = Equivalent Upward push by the ground

This agrees with Newton’s 3rd law of motion which says that action and reaction are equal and opposite.

Without this friction, your feet would slip out from under you, making it difficult to walk.

Friction is also responsible for running, jogging and any human activity that requires motion.

image credit: @lexonart / instagram.com

A lady playfully chasing after her kid brother in the streets of Jamaica, Africa

3. Apart from human movement, vehicles rely on friction for accelerating, decelerating, and changing direction.

When you step on your car brake, the car comes to a stop immediately or gradually depending on the mode of application.

This is because kinetic friction exists between the car tires and the coal tar upon which you ride.

There are so many things that can go wrong if this friction isn’t present in the magnitude required.

A sudden reduction in traction can lead to loss of control and in most cases, accidents.

Without friction, a moving object will never come to stop.

The friction that exists between the contact surface of a rolling object is called rolling friction, as defined above in the friction overview.

See rolling friction examples here: Detailed Examples of Rolling Friction

4. Friction produces heat that helps in keeping the body warm.

During the winter period or cold seasons, we often rub our palms together.

This rubbing action generates minimal heat and helps keep the body warm.

5. Friction causes ignition

Can be seen as one of the major effects of friction.

In the absence of a lighter or matches, we can strike sticks and stones together to produce fire

The friction between the contacting surfaces converts the kinetic energy into thermal energy.

image credit: Paul Banton/ Shutterstock

These are warriors from the Masai tribe in Kenya, Africa. They produce fire for domestic purposes by rubbing two dry sticks together.

6. Friction is present in synovial joint

Static and kinetic friction are both present in joints.

The majority of joints in the body are synovial joints.

A synovial joint is the joint found between bones that move against each other, such as the joints of the limbs (e.g. shoulder, hip, elbow, and knee).

The body uses various methods to decrease friction in joints including synovial fluid.

Therefore, Synovial fluid serves as a body lubricant and it decreases the friction coefficient between bone surfaces in synovial joints.

Synovial joints allow for smooth movements between the adjacent bones.

7. Friction causes a loss of power.

The efficiency of machines is never 100 % because work must be done to overcome friction.

About 20% of a machine’s power is usually lost to friction.

Conclusion

Since friction is needed to maintain grip and responsible for motion and other things mentioned above;

We all can then agree that friction is important and the world will be highly unbalanced without it.

Nevertheless, they are some bad effects, like machine wear and power loss.

20% power loss is a very huge loss especially when you consider the monetary value and the man-hour.

That’s why it’s very important to reduce or mitigate friction loss to the lowest minimum.

Reduce heat buildup by lubricating components and changing worn-out parts.

This will not only lead to prolonged machine life but also a higher efficiency.

That’s it… our article on the 7 major effects of friction✨.

But I’m sure there are so many other friction effects in the world.

So I’ll like to hear from you…

What other effects of friction can you think of?

Share your thoughts and answers with us in the comment section below.

Detailed Examples of Rolling Friction (with pictures)

updated Oct 13, 2020

In today’s guide we’ll be looking at various examples of rolling friction.

But before then, Let’s have a quick recap on rolling friction.

Overview of Rolling Friction

Rolling friction is the friction force that resists the rolling motion of an object against a surface.

Also known as rolling resistance or rolling drag,

It is the friction that exists between the contact surface of rolling object.

Before an object can roll, the force applied on the object must first overcome the rolling friction.

Rolling friction possesses the least friction force when compared to other friction types which include:

Static friction: friction force between an object at rest relative to a surface.

Kinetic friction: friction force between surfaces that moves or slides relative to each other.

In a hurry and won’t be able to stick to the end?

See this quick summary below.

Examples of Rolling Friction

Whenever a rolling object is tossed against a surface, it’s bound to experience rolling friction.

Some examples of objects that experiences rolling friction includes:

1. Rolling paint brush
2. Ball bearing
3. Lawn tennis
4. Office chairs with base rollers
5. Bowling ball and Golf ball
6. Antiperspirant roller
7. Wheels
9. Car tires, bike tires, skateboard and trolley tires

Picture Slides of Rolling Friction examples

This section is added to enhance understanding and better retention..

Click the arrow symbols to toggle across slides.

Car Bearing

ROLLING FRICTION EXAMPLE

Rolling Paint Brush

Lawn Tennis

ROLLING FRICTION EXAMPLE

Office Chair with Base Rollers

Bowling Ball

Bowling Ball

Car Wheels

Car tires

Common Examples of Rolling Friction in Everyday life

• A ball rolling on a smooth surface will encounter lesser rolling resistance compared to a ball rolling on a rough surface.

Did you know that smooth surfaces also contain tiny traces of rough plane when viewed on the microscopic level?

This microscopic unevenness is called surface irregularities.

• Rolling friction is dependent on the shape of the rolling object, a cylindrical shaped object will experience a higher friction drag than a spherical shaped object.
• Riding a rubber-wheeled bicycle on sand will yield more rolling resistance than riding on concrete.
• It is easier to push an empty shopping cart than a loaded cart because of the lower rolling resistance in the former. (rolling friction is weight dependent).
• Smooth tires offer better traction in smooth roads and dry surfaces because of its high rolling friction in such surface conditions.
• Also, threaded tires offer better traction in muddy roads and wet surfaces because of its high rolling friction in such surface conditions.
• It is difficult to push a car with a flat or deformed tire compared to one with to tire defect because of the high friction drag.

Conclusion

If you wish to have an in-depth knowledge on rolling friction, check out our guide;

ROLLING FRICTION – The Complete Guide

Can you think of any other example of rolling friction?

Share your thoughts and answers with us in the comment section below.

50+ Detailed Examples of Static Friction (with pictures)

updated Oct 10, 2020

In today’s article we’ll be looking at various examples of static friction.

These examples will be categorized under different subheadings for better understanding.

But before then, Let’s have a quick overview on static friction.

Overview

Static friction is the friction force between two surfaces at rest relative to each other.

It exists between the contact surfaces of static objects.

For objects to move, the static friction must first be overcome by the applied force.

Static friction possesses the highest friction force when compared to other friction types.

The nature of the contact surface, the weight of the object, and the static friction coefficient are the three factors that determine the magnitude of static friction.

Other friction types include:

Kinetic friction: Friction force between moving or sliding surfaces.

Rolling friction: Friction force that resists the motion of rolling objects on a surface.

Fluid friction: Friction force that prevents different fluid layers from flowing against each other.

Let’s get started.

In a hurry and won’t be able to go through the various examples?

See this brief info-diagram.

Examples of Static Friction in Everyday life

Static friction is experienced everywhere around us.

Some common examples of static friction in everyday life include:

1. Ladder leaning on a wall
2. Car parked on a hill
3. Tightened bolt
4. Standing Lantern
5. Clothes hung on a cloth line
6. Towel hanging on a rack
7. Slippers on the floor
8. Piano stand
9. Hanging picture frame
10. Wall clock

Examples of Static Friction in Physics

Static friction is present in laboratory equipment’s by virtue of its stationary position.

Examples of objects that experience static friction in physics include:

2. Analytic balance
3. Test tube rack
4. Dry cell battery
5. Ring Stand
6. Prism blocks
7. Lens holder
8. Voltmeter
9. Stoppers and corks
10. Wooden Meter Rule

Examples of Static Friction in Science

Stationary equipment is not only found in physics but also dominant across various fields in the sciences.

Examples of objects that experience static friction in science include:

1. Transformers
2. Fixed telescope stand
3. Bunsen Burners
4. Gas cylinders
5. Laboratory sink
6. Microwave transmitter
7. Fume cupboard
8. Bomb Calorimeter
9. Bench-top sterilizers
10. Laboratory autoclaves

Examples of Static Friction in Sports

Various sporting equipment experiences static friction. They include:

Examples of Static friction in sports include:

1. Storage cabinets
2. Goalposts
3. Jersey lockers
7. Volleyball net and duffle bag
8. gym equipment
9. Rest Bench
10. Field Race hurdle

Examples of Static Friction in the Classroom

Examples of static friction in the classroom include:

1. Books kept in the bookshelves
2. Tables and Chairs
3. Floor mat
4. Standing fans
5. Hanging Board
6. Water Stand
7. Ringing bell kept on the shelve
8. Duster holder
9. Stationary Chalk and Marker casing
10. Water Dispenser
11. Waste bin
12. Files on a rack

Now, Over to You…

Can you think of any other example of static friction?

Either under a specific category or just any random example?

I bet you can ?…

Kindly share your thoughts and answers with us in the comment section below.

ROLLING FRICTION:

The Complete Guide

If you are surfing the web for in-depth knowledge on ROLLING friction, then you NEED this guide.

Why?

Well, It covers everything you need to know about rolling friction in one single article.

With simplified definitions and explanations, it is packed with illustrative diagrams to enhance understanding.

Bottom line:

If you want to get the most out of rolling friction, you’ll love this guide.

Contents

CHAPTER 2

Examples of Rolling Friction

CHAPTER 5

Rolling Friction in Action

CHAPTER 1

ROLLING FRICTION: Definition and Explanation

What is rolling friction?

Rolling friction is the friction force that resists the motion of a rolling object on a surface.

It is the friction that exists between the contact surface of rolling object.

Rolling friction is also called rolling resistance or rolling drag.

The force applied on an object must overcome the rolling friction before an object can roll.

When an object at rest is rolled against a surface, the friction force in action changes from static friction to rolling friction.

For instance;

Consider a ball rolling in the forward direction as shown below.

Rolling friction exists at the point of contact between the ball and the surface beneath.

This friction opposes the forward motion and tries to bring the ball to a complete stop.

To maintain this forward motion, the rolling force of the ball must be greater than the rolling resistance.

You should know that friction is a contact force and it always act in the opposite direction to motion.

By contact force, it means that friction only exists between surfaces that are physically in contact.

Since the point of contact between the rolling object and the surface beneath is small, rolling friction offers the least resistance to motion when compared to static and kinetic friction.

CHAPTER 2

Examples of Rolling Friction

Examples of Rolling Friction

All rolling object encounters rolling friction when tossed against a surface.

Some examples of objects that experiences rolling friction includes:

• Ball bearings
• Car tires
• bike tires
• Skateboard tires
• Rolling paint brush
• Lawn tennis
• Office chairs with rollers
• Bike wheels
• Trolley tires
• Bowling ball
• Golf ball
• Antiperspirant roller
• Soccer ball, basketball, or baseball

4 (four) examples of rolling friction

LEARN MORE: Still curious, see our article: Detailed Examples of Rolling Friction

CHAPTER 3

Factors affecting Rolling Friction

Factors affecting rolling friction

These are various factors that affect rolling friction.

They include:

1. Surface Irregularities
2. Nature of the surface on which the object is rolling.
3. The shape of the rolling object
4. Material type of the rolling object and the surface
5. The weight acting on the wheels
6. Roller or wheel diameter
8. Thickness, shape, and orientation of thread on tires
9. Deformation of the object or of the surface.
10. Coefficient of rolling friction

Let’s quickly look at how these different factors affect rolling friction.

SURFACE IRREGULARITIES

The surface upon which an object rolls and the object itself is perfectly not smooth.

No matter how smooth a surface might appear, it still contains traces of minute rough planes or unevenness.

This unevenness might not be visible to the human eyes due to its tiny proportion but can be detected with a microscopic lens.

Microscopic view of the contact surface between the ball and the table

The tiny rough planes are called surface irregularities.

The interlocking of surface irregularities hinders the motion of rolling objects and gives rise to rolling friction.

Nature of the surface upon which the object rolls

The degree of surface roughness or smoothness affects rolling friction.

On rough surfaces, there are a larger number of irregularities.

So the rolling frictional force is greater if the surface is rough.

A ball rolling on a smooth surface will encounter lesser rolling resistance compared to a ball rolling on a rocky surface.

Sticky surfaces also increase rolling resistance.

The shape of the rolling object

Compare these two objects below;

The first one is a milk tin which is cylindrically shaped and the other is a spherical ball.

Now,

Which of these two objects will travel lesser distance when rolled on a given surface under the same environmental condition and with the same applied force?

The tin will quickly come to a stop and won’t travel as much distance as the ball.

Reasons;

• Spherical shapes are perfectly streamlined to continue rolling after the motion is initiated.
• For the tin milk, there is a greater surface area in contact in contact with the ground.

This larger contact area increases the chances of asperity interlocking and adhesive bond which hinders motion.

Since the surface contact area of the ball is small, the rolling resistance or friction acting on the ball is minimal.

So we can boldly say that the shape of an object is one factor to be considered when discussing rolling friction.

While some object shape creates a lot of friction drag, others make it easier to maintain motion.

Material Typeof the rolling object and the surface

The material type also affects rolling friction.

Rubber tire on a paved road will have higher rolling resistance than a steel railroad wheel on a steel rail.

Riding a bicycle with rubber wheels on sand will give more rolling resistance than concrete.

Adding different filters and polymers in tire composition can improve traction while reducing energy loss.

The use of exotic materials including nano-clay has been shown to reduce rolling resistance in high-performance rubber tires.

The weight acting on the wheels

The weight of the object is directly proportional to rolling friction.

It determines the degree of the material deformation.

The normal force acting on the object depends on the weight of the object.

If the surface is flat, the normal force acts in opposite direction to the force of gravity.

A greater weight pushes the surfaces together, leading to an increase in contact surface and a greater friction resistance.

From the photo, the pressure on the tire is increased due to the weight of the calf.

This added weight increases the rolling resistance making it difficult for the boy to roll the tire.

Therefore, an increase in object weight will lead to a corresponding increase in rolling friction due to increased pressure.

And a reduced weight will cause a decrease in rolling friction.

Roller or Wheel Diameter

The roller or wheel diameter affects rolling friction and there are two rules to back up this statement.

The 1st rule proposed by Coulomb in 1785 says that “rolling resistance is inversely proportional to the diameter of the wheel”.

This rule is known as Coulomb’s law.

The 2nd rule proposed by Dupuit in 1837 says that “rolling resistance (of wheeled carriages with wooden wheels and iron tires) is approximately inversely proportional to the square root of wheel diameter”.

This rule opposes Coulomb’s law and has only been experimentally verified for some certain carriage wheels.

Regardless of the dispute between both laws, we can still clearly see a matching correlation between a wheel diameter and rolling friction

Adhesion is the force of attraction between molecules of different substances.

Adhesive force contributes in gripping rolling bodies to avert motion.

Rolling objects possess the least adhesive force when compared to static and kinetic friction.

This is because of the low contact area and reduced molecular interaction with the surface when the object is rolling.

Thickness and orientation of tread on tyre

In tires, tread thickness, shape, and orientation all affect rolling resistance.

The thicker and more contoured the tread, the higher the rolling resistance.

Regular tires are designed with tread to keep a car stable and safe in different road conditions.

Tread patterns also allow the tire to dig into the ground’s surface for better grip and offers better traction when driving on sand, dirt, or mud.

When you drive on tires for a while, the tread will start to wear away.

When the thread depth is worn below the critical level, you won’t be able to maintain effective road contact.

At this point, the brakes won’t function effectively since the rolling friction is reduced.

The question is:

Tread tires or smooth tires?.. Which is preferable in considering the rolling resistance?

Well, it depends on the surface condition.

Tread tire is far more suitable for wet surfaces.

They are designed to remove water from the contact area through the grooves, thereby maintaining road traction in wet conditions.

On the other hand, smooth tire also known as slick tires are suitable for dry condition.

They provide far more traction than grooved tires on dry roads, due to their greater contact area.

Slick tires provide the largest possible contact patch to the road which is required to maximize traction in smooth roads. They are used in auto racing.

The tires of common road vehicles are designed with tread to operate in different weather conditions.

The surface traction is directly proportional to rolling friction.

High surface traction yields high rolling friction and vice-versa.

Deformation of the object or the surface

Rolling friction is mainly caused by non-elastic effect which arises from material deformation.

Rolling objects experiences repeated cycles of deformation and recovery.

For deformable materials like rubber, the energy of deformation is greater than the energy of recovery.

This energy loss is dissipated as heat and gives rise to hysteresis.

A highly deformable material will encounter more rolling friction and more energy will be lost.

Coefficient of rolling friction

The coefficient of rolling friction denoted as µk.r is a system property.

Coefficient of friction is a numerical value that quantifies the intensity with which two sliding or contact surfaces grip each other.

The rolling friction coefficient is a measure of the rolling resistance of an object against a surface.

A high coefficient of rolling friction indicates high rolling resistance between the given contact surfaces.

Since the rolling friction force is smaller than kinetic and static friction force, the coefficient of rolling friction also possesses the least value.

Graph plotted with coefficient values from the three friction types.

The values were practically estimated under similar conditions. These conditions are denoted by the color transition in each column of the friction coefficient plot.

Friction Coefficient Comparison

Stanley Udegbunam (Afrilcate)

want to see a comprehensive list of rolling friction coefficient of different materials and surfaces?

Check out our article: The coefficient of rolling friction (fully explained)

CHAPTER 4

Calculations on Rolling Friction

Calculations on rolling friction

The formula for rolling friction is given as the product of the coefficient of rolling friction and normal force.

 Fk,r = µk,r  N

Where,

• Fk,r is the force of rolling friction
• µk,r is the coefficient of rolling friction
• N is the normal force, sometimes it’s denoted by η

Normal force has the same magnitude as the weight.

It’s represented by the equation; N = m x g

If the object or plane is inclined at an angle (∅), the normal force becomes:

N = m gcos∅

Where m = mass of the object.

And g = acceleration due to gravity.

F and N are measured in units of force (such as Newton or pound).

Since friction is a force, the unit of the frictional force is the newton (N).

The coefficient of rolling friction is unitless.

Example

A loaded trolley pushed on a wooden floor with μk,r = 0.2 has a mass of 40 kg.

What is the rolling resistance? Take g = 9.81m/s2

Solution

Fk,r​​k,r​ N

Normal force, N = mg

Coefficient of friction, μ k,r= 0.2

Fk,r​​k,r x mg

Fk,r​​= 0.2 x 40 x 9.81 = 78.48 N

Consider a car tire rolling on a smooth horizontal surface.

Given N = 806 N and

Fk,r = 1.38 N, the coefficient of the rolling friction is:

X wrong!!

✔ Correct

X wrong!!

d.) none of the above

X wrong!!

CHAPTER 5

Rolling Friction in Action

Let’s wrap this up by looking at some real-life case studies of rolling friction in action.

There are various examples of rolling friction in action in everyday life.

• A soccer ball kicked across a grassy field will travel lesser distance due to high rolling friction compared to one kicked across a smooth or less grassy field.
• A loaded shopping trolley will be much more difficult to push compared to an empty cart as a result of greater rolling friction.
• Bike wheels that are thicker will lessen the potential speed of the bike because there is a greater wheel surface to create friction against the surface and this will slow the bike.
• Rollerblades have lesser rolling friction than roller skates because there is lesser surface-to-wheel contact on rollerblades.
• A basketball rolled on the court will eventually come to a halt because of rolling friction caused by the surface traction.

Rolling friction in action

FRICTION FACT

Rolling friction and kinetic friction are quite similar.

Apart from the fact that rolling friction has a lower frictional force, another difference between rolling friction and kinetic friction stems from the fact that kinetic friction is much more difficult to measure.

Phew! I put A TON of work into this guide.

So I   hope you enjoyed it.

Now I’d like to hear what you have to say.

Are you conversant with other friction types or would you like to see more articles like this?

Can you think of any other example of rolling friction in action?

Let me know by leaving a comment below.

KINETIC FRICTION:

The Complete Guide

If you want in-depth knowledge on kinetic friction, then you NEED this guide.

Why?

Well, It covers everything you need to know about kinetic friction in one single article.

With simplified definitions and explanations, it is packed with illustrative diagrams to enhance understanding.

Bottom line:

If you want to get the most out of kinetic friction, you’ll love this guide.

Contents

CHAPTER 2

Examples of Kinetic Friction

CHAPTER 1

KINETIC FRICTION: Definition and Explanation

What is kinetic friction?

Kinetic friction is the friction between two surfaces that moves or slides relative to each other.

It is the friction that exists between the contact surface of moving objects.

Kinetic friction is also called sliding friction or dynamic friction.

When a body at rest is set in motion, the friction force in action changes from static friction to kinetic friction.

Let us buttress this point with two case studies.

CASE 1

Consider a lady riding a bicycle in the forward direction.

Kinetic friction exists between the tires of the bicycle and the surface upon which she rides.

This friction opposes the forward motion and tries to bring the bicycle to a complete stop.

To maintain this motion, the driving force of the bicycle must be greater than the kinetic friction.

The more force exerted on the bicycle pedals by her feet, the greater the driving force.

You should know that friction is a contact force and it always act in the opposite direction to motion.

By contact force, it means that friction only exists between surfaces that are physically in contact.

CASE 2

An object at rest weighing 200N is to be pushed across a surface with friction resistance of 100N.

Similar with the previous case, the applied force must be greater than the friction resistance before motion can be initiated. This means that the push exerted must be greater than 100 N.

The friction force acting on the object when at rest is the static frictional force.

The static frictional force is always greater than the kinetic frictional force because a stronger adhesive bond is formed between stationary surface compared to surfaces in relative motion.

Let’s take a quick look at the friction plot.

From the plot, you will observe that the object begins to move when the applied force exceeds the maximum static threshold.

The sharp downward drop from the plot shows a reduction in friction force once the applied force exceeds the threshold of motion.

Generally, the terms “kinetic”, “sliding” and “dynamic” all refer to objects in motion.

For friction, they all mean the same thing and are used interchangeably.

That’s why some text calls it sliding friction, others use dynamic friction.

But for this guide, let’s stick with the word kinetic friction.

Kinetic friction is slightly different from rolling friction.

While kinetic friction exists between surfaces that move or slides relative to each other, rolling friction resists the motion of a rolling body on a surface.

CHAPTER 2

Examples of Kinetic Friction

Examples of kinetic friction?

There are various examples of Kinetic friction in everyday life.

Out listed below are some common examples:

1. A book being slid across a table.
2. An ice skater skating on ice.
3. A car moving on a road.
4. A pressing iron being pushed across material.
5. Movement of door hinges when the door is opened or closed.

CHAPTER 3

Factors affecting Kinetic Friction

Factors affecting kinetic friction

There are three factors that affects kinetic friction. They include:

1. Nature of surfaces in contact
2. Weight of object
3. Coefficient of Kinetic friction

Apparently, the factors affecting kinetic friction is the same as that affecting friction generally.

The only difference is the specific reference given to the friction coefficient.

Let’s see how these three factors affect kinetic friction.

Nature of surfaces in contact

To a large extent, kinetic friction depends on the nature of the surfaces in contact.

No matter how smooth a surface might appear, it still contains traces of minute rough planes or unevenness.

This unevenness might not be visible to the human eyes due to its tiny proportion but can be detected with a microscopic lens.

Microscopic view of two surfaces in contact

These tiny rough planes are called surface irregularities.

The interlocking of surface irregularities hinders the relative motion of objects and gives rise to kinetic friction.

Generally, the roughness or smoothness of the contact surface affects kinetic friction.

They are larger number of irregularities on rough surfaces.

If two surfaces in contact are extremely rough, the surface irregularities will easily be locked together.

This will strengthen the intermolecular bond due to adhesion and further prevent the sliding action of the object.

The interlocking of surface irregularities and adhesive bond is strongest in static friction and weakest in rolling friction.

Smooth surfaces offer a lesser resistance to kinetic friction.

For practical purposes, try pushing a box along a tiled surface, then repeat the same action on a tarred road.

Which of these two surfaces do you think will require more push?

Since the tarred road rougher than the tiled floor, you will exert a greater force to cover the same distance with the tiled floor.

Therefore, the friction force is greater if the surface is rough.

Sticky surfaces also hinder motion and this enhances kinetic friction.

That’s why we expel more energy when walking on a muddy floor.

Weight of object

The normal force acting on an object depends on the weight of the object.

Normal forces are support forces that assist an object to stay at the surface of another object.

When a body is moving over a horizontal surface, it presses down against the surface with a force equal to its weight, the pull of gravity.

An increase in the weight of an object will cause an increase in the resistance offered to motion.

And a decrease in weight will offer lesser resistance and reduced kinetic friction.

Forcefully moving heavy objects over  rough surfaces can lead to the dislodging of the material particles, a process called surface abrasion.

Coefficient of Kinetic Friction

The coefficient of kinetic friction, denoted as µk is a system property.

Coefficient of friction is a numerical value that quantifies the intensity with which two sliding or contact surfaces grip each other.

The kinetic friction coefficient is a measure of the material grip between a moving object and its contact surface.

Since static friction force is greater than kinetic friction force, static friction coefficient has a greater value than kinetic friction coefficient.

Rolling friction coefficient possesses the least value due to the small contact area between the rolling object and the surface.

Graph plotted with coefficient values from the three friction types.

The values were practically estimated under similar conditions. These conditions are denoted by the color transition in each column of the friction coefficient plot.

Friction Coefficient Comparison

Stanley Udegbunam (Afrilcate)

The higher the coefficient of friction, the higher the frictional force.

Similarly,

The higher the kinetic coefficient of friction, the higher the kinetic friction force.

CHAPTER 4

Calculations on Kinetic Friction

Calculations on kinetic friction

The formula for kinetic friction is given as the product of the coefficient of kinetic friction and normal force.

 Fk = µk N

Where,

• Fk is the force of kinetic friction
• µk is the coefficient of kinetic friction
• N is the normal force, sometimes it’s denoted by η

Normal force has the same magnitude as the weight.

It’s represented by the equation; N = m x g

If the object or plane is inclined at an angle (∅), the normal force becomes:

N = m gcos∅

Where m = mass of the object.

And g = acceleration due to gravity.

F and N are measured in units of force (such as Newton or pound).

Since friction is a force, the unit of the frictional force is the newton (N).

The coefficient of kinetic friction is unitless.

Example

A 3kg  stainles cup is pushed accross a horizontal glass table with µk = 0.6

Calculate the kinetic friction force given that g = 9.81 m/s2.

Solution

Fk = µkN

but N = m x g

Fk = µk mg

Fk = 0.6 x 3 x 9.81

Fk = 17.66 N

A total force of 20N is required to move a 5 kg block along a horizontal wooden surface.

If the acceleration due to gravity is estimated to be 10 m/s2, calculate the coefficient of kinetic friction.

X wrong!!

✔ Correct

X wrong!!

d.) none of the above

X wrong!!

want to know more about kinetic friction coefficient?

See our article: Coefficient of Kinetic Friction (Fully Explained)

DO YOU KNOW?

Just like motion, there are basic laws that governs friction.

These laws were postulated by Guillaume Amontons, a French Physicists who was a major pioneer in studying the problem of friction.

These laws are known as laws of friction.

Now, Over to You…

There you have it: our guide on Kinetic Friction.

I hope you enjoyed it.

Now I’d like to hear what you have to say.

Are you know you conversant with outer friction types?

While reading this guide, were you in a static or kinetic position? ….or you transitioned across both positions?

Either way, Let me know by leaving a comment below.

STATIC FRICTION:

The Complete Guide

Imagine searching the web continuously for different articles on static friction.

What if there is one single article out there that’s well designed to clarify all your questions and doubt on static friction.

You will probably be pumped to read through it right?

Luckily for you, that’s exactly what I’m going to share with you in this post.

Everything you need to know about static friction in one single article.

At the end of this guide, I will show you some real-life applications of static friction.

Let’s get started.

Contents

CHAPTER 2

Causes of Static Friction

Calculations on

Static friction

cHAPTER 3

Examples of Static Friction

Static Friction

in Action

Contents

cHAPTER 3

Examples of Static Friction

Calculations on

Static friction

cHAPTER 6

Static Friction

in Action

CHAPTER 1

STATIC FRICTION: Definition and Explanation

What is static friction?

Static friction is the friction force between two surfaces at rest relative to each other.

It is the friction that exists between the contacting surfaces of static objects.

The static friction force must be overcome by the applied force before an object can move.

Once the object is set in motion, kinetic friction takes over.

For instance;

Consider pushing an object of weight 200N across a surface with friction resistance of 100N

For the object to move, the applied force exerted by the lady must be greater than the friction resistance. This means that the push exerted must be greater than 100 N.

Let’s take a quick look at the friction plot.

From the plot, you will observe that, the object begins to move when the applied force exceeds the maximum static threshold.

Friction acts opposite the direction of the net applied force.

µs represents the coefficient of static friction. We’ll talk more on this in subsequent chapter.

Generally, the word “static” refers to an object at rest or in a stationary position.

Can you think of any object in a stationary state?

Then, the object is said to be under the influence of static friction.

This is a desk lamp sitting undisturbed on the table.

There is static friction between the bottom hub of the lamp and the table top.

I guess you are also sited on a chair right now. If so, then static friction exists between your butt and chair surface.

Without this static friction, you might sink into the chair just like dropping a pebble in an ocean.

One major thing to note here is that, friction is a contact force.

This means that it can only exist between surfaces that are physically in contact.

CHAPTER 2

Causes of Static Friction

What causes static friction?

Static friction is caused by:

1. Interlocking of surface irregularities or asperities.
2. Material Deformation of static object.
3. Intermolecular bond due to surface adhesion.
4. Stickiness of contact surface.
5. Surface abrasion between contacting pairs.
6. Surface roughness or degree of smoothness.

INTERLOCKING OF SURFACE IRREGULARITIES

All objects have rough planes regardless of how smooth they may appear.

It might not be visible to the naked eyes but can be detected using microscopic lenses.

These minute rough planes are called surface irregularities.

The interlocking of these surface irregularities give rise to static friction.

Microscopic view of two surfaces in contact

Surface irregularity are also called Asperities; a common term in material science that defines the unevenness of surfaces.

Even if the surface is polished, it still contains tiny bits of unevenness.

Apparently, there is no known material surface that is completely devoid of surface irregularity.

Surface asperity consists of:

1. Surface Hills (mountains)
2. Surface Valleys (grooves)

The choice of term is left for you. You can say hills and valleys or mountains and grooves.

You can also cross-interchange the terms, still acceptable.

The question is,

what do these terms have to do with friction?

The informative diagrams below gives a clearer explanation.

Much like the geographic land form you are familiar with:

An Asperity valley is the lower points or depression. It’s either U-shaped or V-shaped.

The mountains of the asperity are the higher points of the irregularity or the elevations.

Since mountains are opposite of valleys, It’s the upside-down (U-shape or V-shape).

When we try to move one object over another object, these mountains and valleys gets entangled or locked with one another.

This opposes the motion of one object over the other and give rise to the force of friction.

From a detailed perspective, the interlocking of irregularities refers to the locking together of minute surface mountains and valleys of contact objects.

Due to this microscopic surface unevenness, the actual contact area is slightly less than what is expected when viewed with the naked eyes.

Deductive implication;

MATERIAL DEFORMATION OF STATIC OBJECT

Deformation is another cause of static friction.

The deformation can be elastic or plastic. The force of friction will increase if the two surfaces are pressed harder.

This means an increase in weight will lead to a corresponding increase in static friction.

You can experience it by dragging a mat when nobody is sitting on it, and when a child is sitting or lying on it.

The weight of an object directly affects the material deformation.

The deformation will continue until the contact area is great enough to support the load.

Excess weight acting on an object can lead to a permanent distortion of the object’s shape or orientation.

This non-reversible deformation is called plastic deformation and large deformation can leads to one object sinking into the other.

Generally, soft material deforms under pressure.

Although such deformations are elastic in nature, it still increases the resistance to motion.

Some common examples of elastic deformation due to friction includes:

• Slight inward depression of our feet when standing on a rug.
• Weight dip when we lie on the bed
• Sitting on an office leathered chair
• Cuddling a pillow
• Rubber tire flattens out at the area of contact with the road.

Deformation creates a ploughing effect. i.e. the slight “sinking “of the hard object when placed on a soft surface.

If the hard object is pushed across a soft surface, then the ploughing force must be greater than the resistive force to enable motion.

Hence, the resistive force comes into play whenever the tip of the hard object plough (move) through the surface.

Ploughing as a friction component arises due to material deformation.

Therefore, it is largely dependent on the penetration depth.

INTERMOLECULAR BOND DUE TO SURFACE ADHESION

Surface Adhesion is the driving force of static friction.

Adhesion is the force of attraction between molecules of different substances.

When two objects or surfaces are brought into contact, the adhesive or electromagnetic forces attracts the molecules of the two objects together.

Think of the rain droplets on your window after rainfalls or morning dew.

The force of adhesion between the liquid droplets and the glass surface prevents it from sliding down thereby maintaining a stationary position.

The static nature of the object makes it possible for stronger molecular bonding which in turn leads to a rigid conjoined surface asperity.

This is one major difference between static and kinetic friction. Since kinetic friction involves motion, the molecules in contact don’t get the chance or needed time to form such strong adhesive bonds.

That’s why static friction force is greater than both sliding (kinetic) friction force and rolling friction force.

Trying to slide one object across the other requires breaking these adhesive bonds.

STICKINESS OF CONTACT SURFACES

Sticky surfaces also give rise to static friction.

The composition of some solid materials greatly increases their adhesion and makes them even “sticky” to the touch.

For two objects to stick together their surfaces must come in contact as closely, and at as many points, as possible.

This stickiness greatly increases friction.

Rubber and adhesive tape are examples of sticky materials that have this type of friction.

A common example of sticky surface is the household mouse glue.

Since sticky surfaces enhance static friction, sticky materials like the sticky pad are used in automobiles to keep objects intact.

Sticky pad is a friction device used to prevent objects from sliding on a surface, by effectively increasing the friction between the object and the surface.

The pad has a large friction coefficient and a multifaced sticky property.

This means it maintains complete stickiness with the dashboard surface and also with the item laid on it.

Sticky pads are commonly used on car dashboards where forces caused by the acceleration of the vehicle would cause objects on dashboards to slip off.

DEGREE OF SURFACE ROUGHNESS OR SMOOTHNESS

We have said earlier that all solid materials have some degree of surface roughness irrespective of how smooth they may appear.

In many cases, rough surface is referred to as the primary cause of friction.

But this is not always true since adhesion, deformation and other friction causes listed above still have a role to play.

Nevertheless, the degree of the surface roughness greatly affects friction.

If two surfaces in contact are extremely rough, the surface irregularities will be easily locked together.

The increased contact points will strengthen the adhesive bond which will in turn lead to higher static friction.

On rough surfaces, there are a larger number of irregularities.

So the frictional force is greater if the surface is rough.

For practical purposes, try rolling a ball through a smooth surface.

Now, try rolling the same ball over a rough or coarse surface.

You will observe that the ball in the rough surface will quickly come to a stop compared to that of the smooth surface.

This means that surface roughness not only affects static friction but also rolling friction. Smoothening rough surface reduces the interlocking of asperities thus causing a decrease in static friction.

The smoother the surface the lower the friction force and vice versa.

To smoothen a rough surface, you can either use sandpaper or apply a coat of high coverage primer.

Lubricating contact surfaces is another common way of reducing friction.

SURFACE ABRASION BETWEEN CONTACTING PAIR

Abrasion is the process of scraping off or wearing away material surfaces by means of surface contact.

Surface abrasion hinders surface friction by reducing the material roughness.

When surface abrasion occurs, particles of the materials are dislodged from their surfaces. This reduces the chances needed for asperity interlocking and weakens static friction.

When we attempt to move any object, we have to apply a force to overcome interlocking.

For the object to slide over another surface, the adhesive force between the contact molecules must be broken. This process involves the abrasion of contact points.

This means that the interlocked areas must be broken apart or plastically deformed before the object can move.

Once movement is initiated, some abrasion continues to occur, but at a much-reduced level than the static position.

CHAPTER 3

Examples of Static Friction

Examples of Static Friction

There are various examples of Static friction.

Out listed below are some common examples:

• A standing lantern
• A car parked on a hill
• A standing fan
• A tightened bolt
• Clothes hung on a clothesline
• A ladder leaning against the wall
• Book kept on a surface
• Fruits hanging from a tree
• Static friction enables us to walk, run, jog etc.

ooh, I played the musical instrument this morning before preparing this article.

And I took some photos thereafter.

Since they are sitting undisturbed on the bed, permit me to add this as another example of static friction.

Can you think of any other example of static friction around you?

Reserve your answers for the comment session at the end of this guide.

Let’s continue…

CHAPTER 4

Factors affecting Static Friction

Factors affecting Static friction

Friction factors are different from friction causes although they are closely related.

The different friction causes listed above can be properly grouped into three major factors of static friction.

The factors affecting static friction are:

1. Nature of surfaces in contact
2. Weight of object
3. Coefficient of Static friction

Apparently, the factors affecting static friction is the same as that affecting friction generally.

The only difference is the specific reference given to the friction coefficient.

Let’s see how these different factors affect static friction.

Nature of surfaces in contact

Static friction greatly depends on the nature of the contact surfaces.

Majority of the friction causes centers around the surface nature of the objects at the point of contact.

This is in accordance with the Laws of friction.

To know if a given pair of contact surface will have high static friction, you need to ask yourself the following questions:

• Does the object material permit asperity interlocking?
• How strong is the adhesive force between the contact surfaces?
• Is the contact surface rough or smooth?
• Is the surface sticky?

The nature of the surface in contact will provide all the needed answers to these questions.

If the surface is polished, asperity interlocking will be minimal.

The adhesive force depends on the interactions of the surface molecules.

Rough and sticky surface increases static friction.

Weight of object

The weight of the object is directly proportional to static friction.

The object weight determines the degree of the material deformation and also responsible for surface abrasion.

The normal force acting on an object depends on the weight of the object.

Normal forces are support forces that assist an object to stay at the surface of another object.

Depending on the inclination of the surfaces, the normal force can act at an angle but if the surface is even or flat, the normal force equals the force of gravity.

A greater weight pushes the surfaces together, causes more of the asperities to come together, and increases the contact surface.

Therefore, an increase in object weight will lead to a corresponding increase in static friction and a decrease in weight will lead to a decrease in static friction.

Coefficient of static friction

The Coefficient of friction is a numerical value that quantifies the intensity with which two sliding or contact surfaces grip each other.

Also known as friction coefficient, it measures the degree of “stickiness” of surfaces in contact.

The static friction coefficient tells us the extent or degree with which static objects and contact surface grip each other.

The coefficient of static friction is typically larger than the coefficient of kinetic friction and the rolling friction coefficient.

This is expected because the static position allows more time for asperity locking and molecular bond formation unlike objects in the sliding or rolling state.

Graph plotted with coefficient values from the three friction types.

The values were practically estimated under similar conditions. These conditions are denoted by the color transition in each column of the friction coefficient plot.

Friction Coefficient Comparison

Stanley Udegbunam (Afrilcate)

Since the static friction coefficient is higher, more force will be required to initiate motion if an object is stationary.

Coefficient of friction is symbolized by the Greek letter µ, while the static coefficient of friction is denoted with µs.

The higher the coefficient of friction, the higher the frictional force.

Similarly,

The higher the static friction coefficient, the higher the static friction force.

CHAPTER 5

Calculations on Static Friction

Calculations on static friction

The formula for static friction is given as the product of the coefficient of static friction and normal force.

 Fs = µs N

Where,

• Fis the force of static friction
• µis the coefficient of static friction
• N is the normal force, sometimes it’s denoted by η

Normal force has the same magnitude as the weight.

It’s represented by the equation; N = m x g

If the object or plane is inclined at an angle (∅), the normal force becomes:

N = m gcos∅

Where m = mass of the object.

And g = acceleration due to gravity.

F and N are measured in units of force (such as Newton or pound).

Since friction is a force, the unit of the frictional force is the newton (N).

The coefficient of static friction is unitless.

For an object to be set in motion, the applied force must be greater than the force of static friction, Fs.

This is best thought of as a maximum value because it increases up to a certain max. point and when this point is exceeded through the addition of external force, the object begins to move.

At this point, the friction coefficient under consideration changes from static friction coefficient to kinetic friction coefficient.

From a deductive view,

 Fs​ ≤ μs​ N​

Example

A 50N force acts on a kerosene lamp that’s static on the floor. If the coefficient of friction is 0.3, determine the static friction.

Solution

Fs = µN

Normal force, N = 50 N

Coefficient of friction, µs = 0.3

Fs = 50 x 0.3 = 15N

Therefore, the static friction is 15N.

The force acting on a microwave at rest is 220N.

If the value of the static frictional force 506N, determine the friction coefficient.

X wrong!!

X wrong!!

✔ Correct

d.) none of the above

X wrong!!

want to know more about static friction coefficient?

See our article: Coefficient of Static Friction (Fully Explained)

CHAPTER 6

Static Friction in Action

Okay, Enough of the theories.

Let’s wrap this up by looking at some real-life case studies of static friction in action.

Case 1:

The photo below shows great warriors from Masai tribe in Kenya, Africa using the principle of static friction to solve common problems.

They produce fire for domestic purpose by rubbing two dry sticks together.

image credit: Paul Baton / shutterstock.com

Case 2:

Friction aids movement.

When we walk, the backward movement of our feet exerts a force on the ground as the other foot moves forward.

When this force is exerted on the ground, then an equal and opposite force is exerted by the ground on our feet.

Without static friction, your feet would slip out from under you, making it difficult to run or walk.

And if an object is moving, it would never stop if there were no friction.

The photo below shows a lady playfully chasing after her kid brother in the streets of Jamaica, Africa.

Static friction is ever present between the surface of their feet and the tar road.

image credit: @lexonart / instagram.com

Case 3:

Again, using friction to generate fire when going for long distance hiking or camping can stand as a survival skill.

Watch this short 2-mins video to see how Jack generated fire sparks to heat up his food by just smashing two pyrite stones together.

FRICTION FACT

The study of friction, wear and lubrication, bearing designs and relative motion of interacting surfaces is called tribology.

Phew! I put A TON of work into this guide.

So I   hope you enjoyed it.

Now I’d like to hear what you have to say.

Do you know any other common example of static friction?

While reading this guide, were you in a static or kinetic position? ….or you transitioned across both positions?

Either way, Let me know by leaving a comment below.