types of friction

Group member Name:-1) Ram bhavesh (150210119085)

2) Vaja akhil (150210119121)3) Vala vivek (150210119123)

Subject:-mechanics of solids

Topic:-friction

Government Engineering college Bhavnagar-(021)

• Friction is a force between two surfaces that are sliding, or trying to slide across one another, for example when you try to push a toy car along the floor.

• Friction always works in the direction opposite from the direction the object is moving, or trying to move. It always slows a moving object down.

Moving

Friction

Free Body DiagramNormal Force FN

Friction Force ff

Applied Force F

Gravity Force Fg

Fg = mg FN = Fg

ff = F

Angle of repose 

When granular material is heaped, there exists a limit for the inclination of the surface. Beyond that angle, the grains start rolling down. This limiting angle upto which the grains repose (sleep) is called the angle of repose of the granular material.Significance of Angle of repose: The angle that an inclined plane makes with the horizontal, when the body supported on the plane is on the verge of motion due to its self -weight is equal to the angle of repose. Angle of repose is numerically equal to Angle of limiting friction

Five Types of FrictionRolling FrictionStatic friction Kinetic friction Sliding FrictionFluid Friction

Rolling FrictionRolling friction is

friction that occurs between surfaces in motion in which one of the surfaces is a wheel, roller, or ball.

Examples: Riding a bike – tires and

ground Bowling – ball and lane

Static FrictionStatic friction is friction

that occurs when the surfaces in contact are at rest (not in motion).

Examples: A book resting on a

desk. A potted plant sitting on

a sidewalk.

Static Friction

frictionstaticoftcoefficienFf

s

sNs

FN

fs

F

Fg

The Force of Static Friction keeps a stationary object at rest!

Kinetic Friction

frictionkineticoftcoefficienFf

k

kNk

FN

fk

F

Fg

Once the Force of Static Friction is overcome, the Force of Kinetic Friction is what slows down a moving object!

Motion

Sliding FrictionSliding friction is

friction that occurs when solid surfaces slide over one another.

Examples: Writing – pencil

point and paper Combing your hair –

surface of comb and strands of hair

Fluid FrictionThe force that tries to slow objects down when

they move through a liquid or a gas. It's also known as "drag", or "air resistance".

All gases and liquids are fluids. An airplane and a swimmer both experience

fluid friction.

Law of friction

1. The limiting frictional force f is directly proportional to the normal reaction N exerted by the surface.

i.e. f ∝ N or f = N where is a constant called coefficient of limiting friction.

2. The kinetic frictional force f is directly proportional to the normal reaction N exerted by the surface.

i.e. f’ ∝ N or f’ = ’N where is a constant called coefficient of kinetic friction.

Frictional force f

Applied force FA

Normal reaction N

For simplicity, take f = f’ = N and = ’

18

If the surface is smooth, = 0 ⇒ f = 0 N

Coefficient of friction depends on the two contacting materials.

For simplicity, take f = f’ = N and = ’

Rubber Concrete (Dry) 0.6 – 0.85

Rubber Concrete (Wet) 0.45 – 0.75

Frictional force does not depend on the area of contact of the surfaces.

A world without friction is like this !!

A_World_Without_Friction.webm