Scribd
Upload
39 views2 pages

Friction

Friction is the opposing force that comes into play when one body moves or tends to move over the surface of another body. There are two main types of friction: static and kinetic. Static friction is the maximum opposing force when an object first begins to move, while kinetic friction opposes the motion of objects that are already moving. Friction arises due to interatomic/intermolecular forces between surfaces in contact and depends on factors like the nature and roughness of the surfaces as well as the normal force pressing them together. While friction can cause wear and tear and a waste of energy, it also serves important purposes like enabling walking and the function of brakes. Methods to reduce friction include lubrication, polishing surfaces, and

Uploaded by

Danisha mathur
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
39 views2 pages

Friction

Friction is the opposing force that comes into play when one body moves or tends to move over the surface of another body. There are two main types of friction: static and kinetic. Static friction is the maximum opposing force when an object first begins to move, while kinetic friction opposes the motion of objects that are already moving. Friction arises due to interatomic/intermolecular forces between surfaces in contact and depends on factors like the nature and roughness of the surfaces as well as the normal force pressing them together. While friction can cause wear and tear and a waste of energy, it also serves important purposes like enabling walking and the function of brakes. Methods to reduce friction include lubrication, polishing surfaces, and

Uploaded by

Danisha mathur
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 2

Friction: Friction is opposing force that comes into play when one body moves (slides or rolls) or tends

to move over
surface of another body.

Origin of friction:

Old View: Roughness is cause of friction. A surface which appears very smooth to naked eye is found to have
irregularities (roughness) when seen through a powerful microscope.

Modern View: Force of friction arises on account of strong interatomic or intermolecular force of attraction
(adhesive) between two surfaces at points of actual contact.

Friction depend upon

(i) Nature of surface i.e. (a) Adhesive force between molecules of surfaces (b) Interlocking of surfaces which depend
upon smoothness of surfaces.
(ii) Actual area of contact which further depends upon normal reaction

Note: Friction is independent of apparent area of contact.

Types of Friction: 1. Static friction 2. Kinetic friction

1. Static friction: It is the opposing force that comes into play when one tends to move over surface of another.

Suppose we apply a force As we increases the applied force, a stage comes when
the body just starts moving. The static friction at this stage is maximum called
limiting value of static friction or limiting frictional force.
The direction of force of limiting friction is opposite to the direction in which the
body tends to move with respect to other surface.
The limiting value of static friction is directional proportional to normal reaction
i.e. (𝒇𝒔 )𝒎𝒂𝒙 ∝ 𝑵 or (𝒇𝒔 )𝒎𝒂𝒙 = 𝒖𝒔 𝑵

where 𝒖𝒔 is constant called coefficient of static friction which depends on surface.

So 𝒇𝒔 ≤ 𝒖𝒔 𝑵

2. Kinetic friction/dynamic friction: It is the opposing force that comes into play when one body moves over surface
of another body and its direction is opposite to relative velocity.

Force of kinetic friction is directional proportional to normal reaction

i.e. 𝒇𝒌 ∝ 𝑵 or 𝒇𝒌 = 𝒖𝒌 𝑵

𝒖𝒌 is coefficient of kinetic friction which depends on nature of surfaces.

Note: 𝒖𝒌 is always less than 𝒖𝒔 .

Further kinetic friction can be divided into two types:

(a) Sliding friction: The opposing force which comes into play when one body is actually sliding over the surface of
other body. E.g. a block moving over the flat surface of table.
(b) Rolling friction: The opposing force which comes into play when one body is actually rolling over the surface of
other body. e.g. a wheel or disc rolling over a surface.

Laws of friction/ laws of limiting friction:

1. Force of friction/ force of limiting friction is depend upon nature of surfaces in contact.

2. The Force of friction/ force of limiting friction is directly proportional to the magnitude of normal reaction, N

i.e. 𝒇 ∝ 𝑵 or 𝒇 = 𝝁𝑵 (𝒇𝒔 )𝒎𝒂𝒙 ∝ 𝑵 or (𝒇𝑠 )𝒎𝒂𝒙 = 𝝁𝒔 𝑵

Where 𝝁 is constant called coefficient of friction.

3. Force of friction/ force of limiting friction is independent of the apparent area of contact.

4. The direction of Force of friction/ force of limiting friction is opposite to the direction in which the body moves or
tends to move with respect to other surface.

5. The coefficient of static friction is greater than the coefficient of kinetic friction. Kinetic friction is independent of
velocity.

Friction is necessary evil: Friction involves wastage of energy but it is required at some instances like walking.

Friction is evil (disadvantage)

1. It cause unnecessary wear & tear of machinery

2. A part of useful energy is dissipated in overcoming it.

Friction is necessity (advantage)


1. Friction helps us to walk.
2. Brakes of vehicles will not work without friction.
3. Writing on black board.
That’s why friction is necessary evil.
Methods to reduce friction:
1. By polishing.
2. By lubrication (using oil, grease)
3. By streamlining (sharp in front of fast moving jets, plane)

4. By converting sliding friction into rolling by using ball bearing in bicycles, bikes etc.

You might also like