2.1 INTRODUCTION
R
N
G
Force of
friction
f
W
f
W
P Direction of
impending motion
N
Fig. 2.1
2.1.1 Engineering Applications of Friction
­
f
Impending motion
Static
fricton
fm
Dynamic friction
P
It is the angle made by the resultant () of the normal reaction () and
limiting force of friction ( ) and made with the direction of normal reaction.
is the resultant of normal reaction and force of friction .
=
2 2
is the angle of friction
tan =
or
= tan 1
N
R
P
f
W
It is ratio of limiting frictional force and the normal reaction.
The coefficient of friction,
=
= tan =
N
f = N
Y
X
W cos Motion
W sin W
­
­
­ ­
20 N
N
P sin 25°
25°
f
W
­
­
­
­ ­
­
N
P
P sin P cos f
W
­­ n
N si
N
f
N cos Y
X
W
P
N
Y
X
W cos f
W sin W
s
N
P
co
Y
P sin X
P
W cos f
W sin W
P
P sin Y
N
P cos X
W cos f
W sin W
P f
N
Y
X
W cos W sin W
P
Y
N
X
W cos f
W sin W
­
­­
P
N
Y
X
W cos f
W sin W
­
s
co
N
P
in
Ps
Y
P
X
W cos f
W sin W
­
5m
0.2
RR
fR
X
RF
fF
mg cos mg sin W = mg
m
0.5
0.5
m
Y
­
­ ­
fB
B
B
L/2
L
W
fA
A
O
RA
RB
­­­
B
RB
300 N
fA
A
60°
RA
­
­
B
RB
10 m
5m
6m
20 N
fA
A
RA
O
8m
­
fB
B
RB
l
x
1.5W
W
l/2
fA
45°
A
O
RA
­
­
B
RB
3.5
m
3m
7m
800 N
600 N
fA
60°
A
O
RA
­
­
­
­
­
­
­
­
Y
R1
f1
N1
W
X
R2
N2
R2 cos ( + )
f2
R2 sin ( + )
R2 sin ( + )
f2
Y
R2 cos ( + )
R2
N2
P
X
R3
N3
Motion
f3
­
­
­
­
Driver
Slack side
Follower
T2
r2
r1
Tight side
T1
­
­
­­ ­
­
d
r
T1
T2
­ ­ ­
­
­
­
0.9155 N-m
Ans.
Example 2.14:
­
Solution:
25 kW Ans.
Example 2.15:
Solution:
1.054 kN.m
Ans.
Example 2.17:
­
­
­
0.5
m
T2
T1
Solution:
1562.2 N
Ans.
Example 2.18: ­
­
­
­
­
­ ­ ­
R
W
P
p
dm
­ ­ ­
­ ­
­
0
