Page 79 - CITS - WCS - Mechanical

WORKSHOP SCIENCE - CITS

Limiting Friction
Friction created when two static surfaces come into contact with each other. The limiting frictional force is
independent of the area of contact and is proportional to the reasonable reaction between the contacting surfaces.

When the frictional force is at its maximum possible value, friction is said to be limiting. If friction is limiting, yet
the book is still stationary, it is said to be in limiting equilibrium. If you push ever so slightly harder, the book will
start to move.

Limiting friction is important in many everyday applications. For example, the limiting friction between your shoes
and the floor keeps you from slipping when you walk on the floor. Similar, the limiting friction between your car’s
tires and the road prevents your car from skidding.
The maximum or limiting value of friction between two surfaces is FMAX=µR F MAX = µR where μ is the coefficient
of friction and R is the normal reaction between the two surfaces.

Coefficient of Friction
The coefficient of friction, µ, is a measure of the amount of friction existing between two surfaces. A low value of
coefficient of friction indicates that the force required for sliding to occur is less than the force required when the
coefficient of friction is high. Ratio of the frictional force (F) to the normal force applied.

F
m =
N
F = Friction force

N = Normal force

It is usually symbolized by the Greek letter mu (μ). Mathematically, µ = F/N, We know that,
where F is the frictional force and N is the normal force. F mN (1)
The value of the coefficient of static friction depends on the objects that are m = coefficient of friction
causing friction. Considers D OBC,
OPP

It’s value is generally between 0 and 1 but it can be greater than 1. The value Tanq = adj

equal to 0 means there is no friction between two objects. All objects will have BC
some friction when they come in contact with each other. =
OB
BC = OA
OA
=
OB
F
=
N
mN
= [From (1)]
N
tanq = m
q = tan (m)
-1

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CITS : WCS - Mechanical - Exercise 6