文档介绍：Chapter 8 - Friction
Characteristics of dry friction
Friction - a resistive force that prevents or retards the slippins25 - 吃蚣=Pcos25「
=Pcos25
P
N =78?.4oN25 Psin25
Same as a). only use
N
FBD
ZFx =0
800sin 25 —F -PX =0
-」XN 二 Pcos25
2Fy =0
N -800cos25' -Py =0
N =800cos25 Psin 25
-(800cos25 Psin 25 ) = P cos25
-280cos25〉P(cos25 . sin 25 )
P =80 N
. Give n: = ^^ = between all surfaces.
ABC
100 kg
D
150 kg P ■
Find: Determi ne the smallest TorceP required to start blockD movi ng. FBD Block C
Wc = 981 N
y
X
F1
N1
Tab -_T~ 二
ZFy -0
N1 _Wc =0
N1 =981 N
F1 二訥=(981)
F^ N
FBD Block D
N1
F1
P
F2
N2
WD
ZF^0 F2 = 2N2 =() ZF^0
N2 -弘-WD =0 F1 ^ N
N2 =981
P - F1 - F2 = 0
P =
P=1030N >
N2 = N
. Give n: Three 4 kg packagesA, B, and C are placed on a conv eyor belt which is at rest.
Betwee n the belt and both packageA and C, = a nd」k =. Betwee n packages
and the belt,」s 二 a nd」k 二 . The packages are placed on the belt so that they are
in con tact with each other and at rest. 十'" Fi nd: Determ ine which, if any, of the package^will each package.
Con sider C by itself
15o
and the friction force acting on
匸Fy =0
NC -Wcos15 =0
NC =4()cos15
NC 二 N
ZF^0
FC -Wsin15 =0
Fc =4()si n15
FC = N
-assumeC is