State two advantages and disadvantages of friction.

Advantages of friction: \\(1.\\) Friction enables us to walk freely.\\(2.\\) It helps to support ladder against wall.\\(3.\\) It becomes possible to transfer one form of energy to another.\\(4.\\) Objects can be piled up without slipping.\\(5.\\) Breaks of vehicles work due to friction.Disadvantages of friction:\\(1.\\)It always resists the motion, so extra energy is required to overcome it.\\(2.\\)It causes wear and tear of machines.\\(3.\\)It decreases the life expectancy of moving parts of vehicles.\\(4.\\)Since friction is very useful in some cases while harmful in some cases, friction is called a necessary evil.

Mention the methods used to decrease friction

\\(\textbf{Cause of Friction: }\\)To Identify methods of reducing friction, we first have to understand what is the cause of friction. There are two reasons behind friction:Whenever two surfaces come in contact, then the temporary bond's start forming between them, which resist the movement between the surfaces. Higher the area of contact, larger the number of bonds, higher the value of friction force.The abnormality/Roughness of the surface, more rough the surface is, higher the friction.Value of friction force is proportional to the Normal contact force. Higher the Normal force, larger is the friction\\(\textbf{Methods for Reduction friction: }\\)Make the surfaces little more smoother. Rough surfaces produce more friction and smooth surfaces reduce friction. Note: Making surface highly smooth will also increase the friction, as large number of bonds will form then.Lubrication is another way to make a surface smoother. A lubricant is a slippery substance designed to reduce the friction between surfaces. Make the object more streamlined. A streamline shape is one that allows air or water to flow around it easily, offering the least resistance.Reduce the Normal force acting between the surfaces in contact. The stronger the Normal force acting on the surfaces, the higher the friction.Reduce the contact between the surfaces, so that less number of bonds will be formed. Spheres are the best shape for reducing friction because very little of a spherical object is in contact with the other surface.

Starting from rest ,a body slides down a 45\\(^{o}\\) inclined plane in twice the time takes to slide down the same distance in the absence of friction .The coefficient of friction between the body and inclined plane is

Case (1) When there is no friction, From newton's second law, F=ma \\(\Rightarrow mg\sin { \theta }= m{ a }_{ 1 }\\) \\(\Rightarrow {a }_{ 1}= g\sin { \theta } \\)Now, as body starts from rest so initial velocity (u)=0 m/s.Let, body travels 'x' distance in \\({t}_{1}\\) time,So from equation of motion, \\(x=ut+\frac { 1 }{ 2 } a{ t }^{ 2 }\\) \\(\Rightarrow x=\frac { 1 }{ 2 } { a }_{ 1 }{ { t }_{ 1 } }^{ 2 }\\) \\(\Rightarrow { t }_{ 1 }=\sqrt { \frac { 2x }{ { a }_{ 1 } } } =\sqrt { \frac { 2x }{ g\sin { \theta } } } \\)Case (2) When there is friction, From newton's second law, F=ma \\(\Rightarrow mg\sin { \theta } -\mu mg\cos { \theta } =m{ a }_{ 2 }\\) \\(\Rightarrow { a }_{ 2 }=g\sin { \theta } -\mu g\cos { \theta } \\)Now, as body starts from rest so initial velocity (u)=0 m/s.Let, body travels 'x' distance in \\({t}_{2}\\) time,So from equation of motion, \\(x=ut+\frac { 1 }{ 2 } a{ t }^{ 2 }\\) \\(\Rightarrow x=\frac { 1 }{ 2 } { a }_{ 2 }{ { t }_{ 2 } }^{ 2 }\\) \\(\Rightarrow { t }_{ 2 }=\sqrt { \frac { 2x }{ { a }_{ 1 } } } =\sqrt { \frac { 2x }{ g\sin { \theta } -\mu g\cos { \theta } } } \\)It is given that \\({t}_{2}=2{t}_{1}\\)So, \\(\sqrt { \frac { 2x }{ g\sin { \theta } -\mu g\cos { \theta } } } =2\sqrt { \frac { 2x }{ g\sin { \theta } } } \\)Now, substituting \\(\theta=45\\) and solving above equation we get, \\(\sqrt { \frac { 1 }{ 1-\mu } } =2\\) \\(\mu =\frac { 3 }{ 4 } =0.75\\)

A marble block of mass 2kg lying on ice when given a velocity of \\(6m{s}^{-1}\\) is stopped by friction in 10s. Then the coefficient of friction is ( Take \\(g=10ms^{-2}\\))

\\(a=\mu g = \dfrac{6}{10}\\) [using v=u+at]\\(\Rightarrow \mu = \dfrac{6}{10 \times g}= \dfrac{6}{10 \times 10}=0.06\\)

A block of mass \\(1\ kg\\) lies on a horizontal surface in a truck, the coefficient of static friction between the block and the surface is \\(0.6\\). What is the force of friction on the block if the acceleration of the truck is \\(5\ m/s^{2}\\) ?(Take \\(g=10\ m/s^{2}\\))

Maximum frictional force acting \\(= \mu mg = 0.6 \times 1 \times 10 = 6 \; N\\)Pseudo force acting on the body \\(= ma = 1 \times 5 = 5 \; N\\)\\(\because\\) pseudo force \\(<\\) frictional forceThe frictional force acting is only \\(5 \; N\\).

Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below.Choose the correct arrangement.

Sliding friction is the force of friction, below two objects, when one of them is sliding over the surface of the other. The force of sliding friction between them is a little smaller than static friction between them. Between the same two surfaces, once motion is started the friction becomes slightly less than maximum static force rolling friction - force of friction that comes into play when one body rolls over the surface of another body.It is more convenient to roll then to slide an object once the surface of other Hence, static friction > sliding friction > Rolling friction.

It is easier to pull a lawn roller then to push it because pulling:

When we push a lawn roller , the normal component of force applied by us increases the effective weight of roller , on the other hand , in pulling normal component of our force decreases the effective weight of roller . Therefore it is easier to pull a roller than pushing it .

A 50 kg crate is being pushed across a horizontal floor by a horizontal force of 575 N. If the coefficient of sliding friction is 0.25, what is the acceleration of the crate ?

We know frictional force \\(f=\mu N\\) where N=normal force=mgGiven sliding friction\\(\mu=0.25\\) Thus, \\(f=0.25\times 50\times 10=125 N\\)Hence \\({F}_{net}={F}_{app}-f=575-125=450 N\\)Also we know Force\\(F=ma\\)\\(a=\dfrac{450}{50}=9 m/{s}^{2}\\)

A block of weight \\(100\\) \\(N\\) is lying on a rough horizontal surface. If coefficient of friction \\(\cfrac{1}{\sqrt{3}}\\). The least possible force that can move the block is

We have formula\\(F_{min}-\mu N\\)Here \\(\mu=\\) coefficient of function \\(=\dfrac {1}{\sqrt 3}\\)and \\(N=100\ N\\)So \\(F_{min}=\dfrac {100}{\sqrt 3}\\) ans

A block of mass \\(5 \,kg\\) is (i) pushed in case (A) and (ii) pulled in case (B), by force \\(F = 20 \,N\\), making an angle of \\(30^o\\) with the horizontal, as shown in the figures. The coefficient of friction between the block and floor is \\(\mu = 0.2\\). The difference between the accelerations of the block, in case (B) and case (A) will be:\\((g = 10 \,ms^{-2})\\)

\\(N_1 = 60\\) \\(N_2 = 40\\)\\(a_1 = \dfrac{10\sqrt{3} - 0.2 \times 60}{5}\\) =1.064 \\(a_2 = \dfrac{10\sqrt{3} - 0.2 \times 40}{5}\\) =1.86\\(a_2 - a_1 = 0.8\\)

What is Rolling Friction? | Definition, Examples, Diagrams

Q: Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below.Choose the correct arrangement.

Sliding friction is the force of friction, below two objects, when one of them is sliding over the surface of the other. The force of sliding friction between them is a little smaller than static friction between them. Between the same two surfaces, once motion is started the friction becomes slightly less than maximum static force rolling friction - force of friction that comes into play when one body rolls over the surface of another body.It is more convenient to roll then to slide an object once the surface of other Hence, static friction > sliding friction > Rolling friction.

definition

Types of Friction

There are 2 types of coefficients of friction.
1. Static
2. Kinetic
The static coefficient of friction is more than or equal to Kinetic coefficient of friction.

definition

Rolling and sliding friction

When a body slides (moves with all its surface area in contact) over another body, the resistance faced is due to sliding friction. On the other hand, if a body rolls (moves with just a single point of its surface in contact) over another body, the resistance offered is a case of rolling friction.

Rolling friction is generally lesser than sliding friction. In rolling, the surfaces in contact don't rub against each other as they do in sliding friction. An example is the case of tires in vehicles. When they are moving on the road, some rolling friction acts on them. When the brakes are applied, rolling motion is reduced and sliding friction takes over to slow down the vehicle.

example

Rolling Friction

A solid sphere of mass

m

is placed on a rough inclined plane as shown in the figure. The coefficient

μ

is insufficient to start pure rolling. The sphere slides a length

ℓ

on the incline from rest and its kinetic energy becomes

K

. Then, the work done by friction will be given by:
Work done by friction + Work done by gravity + work done by normal force = Kinetic energy

K

(Work energy theorem)
work done by normal force=0
Work done by gravity is mglsin

θ

Work done by friction =

- m g l s i n θ + K

What is Rolling Friction?

definition

Types of Friction

definition

Rolling and sliding friction

example

Rolling Friction

Quick Summary With Stories

Rolling friction

State two advantages and disadvantages of friction.

Mention the methods used to decrease friction

Starting from rest ,a body slides down a 45 $^{o}$ inclined plane in twice the time takes to slide down the same distance in the absence of friction .The coefficient of friction between the body and inclined plane is

A marble block of mass 2kg lying on ice when given a velocity of $6 m s^{- 1}$ is stopped by friction in 10s. Then the coefficient of friction is ( Take $g = 10 m s^{- 2}$ )

A block of mass $1 k g$ lies on a horizontal surface in a truck, the coefficient of static friction between the block and the surface is $0.6$ . What is the force of friction on the block if the acceleration of the truck is $5 m / s^{2}$ ?
(Take $g = 10 m / s^{2}$ )

Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below.
Choose the correct arrangement.

It is easier to pull a lawn roller then to push it because pulling:

A 50 kg crate is being pushed across a horizontal floor by a horizontal force of 575 N. If the coefficient of sliding friction is 0.25, what is the acceleration of the crate ?

A block of weight $100$ $N$ is lying on a rough horizontal surface. If coefficient of friction $\frac{1}{3}$ . The least possible force that can move the block is

definition

Types of Friction

definition

Rolling and sliding friction

example

Rolling Friction

Quick Summary With Stories

Rolling friction

State two advantages and disadvantages of friction.

Mention the methods used to decrease friction

Starting from rest ,a body slides down a 45o inclined plane in twice the time takes to slide down the same distance in the absence of friction .The coefficient of friction between the body and inclined plane is

A marble block of mass 2kg lying on ice when given a velocity of 6ms−1 is stopped by friction in 10s. Then the coefficient of friction is ( Take g=10ms−2)

A block of mass 1 kg lies on a horizontal surface in a truck, the coefficient of static friction between the block and the surface is 0.6. What is the force of friction on the block if the acceleration of the truck is 5 m/s2 ? (Take g=10 m/s2)

Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Choose the correct arrangement.

It is easier to pull a lawn roller then to push it because pulling:

A 50 kg crate is being pushed across a horizontal floor by a horizontal force of 575 N. If the coefficient of sliding friction is 0.25, what is the acceleration of the crate ?

A block of weight 100 N is lying on a rough horizontal surface. If coefficient of friction 3​1​. The least possible force that can move the block is

Starting from rest ,a body slides down a 45 $^{o}$ inclined plane in twice the time takes to slide down the same distance in the absence of friction .The coefficient of friction between the body and inclined plane is

A marble block of mass 2kg lying on ice when given a velocity of $6 m s^{- 1}$ is stopped by friction in 10s. Then the coefficient of friction is ( Take $g = 10 m s^{- 2}$ )

A block of mass $1 k g$ lies on a horizontal surface in a truck, the coefficient of static friction between the block and the surface is $0.6$ . What is the force of friction on the block if the acceleration of the truck is $5 m / s^{2}$ ?
(Take $g = 10 m / s^{2}$ )

Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below.
Choose the correct arrangement.

A block of weight $100$ $N$ is lying on a rough horizontal surface. If coefficient of friction $\frac{1}{3}$ . The least possible force that can move the block is