n F1 F2 Fi Fn
A1 A2 Ai An
W
i=n
W = Fi
i=1
Fi W Fi W
F1 Fi Fn
C
W
C
 W Oy
My = W xc
F Ai
Miy = Fixi
i=n
W xc = Fixi
i=1
xc
i=n
Fixi
i=1
xc =
i=n
Fi
i=1
i=n
Fiyi
i=1
yc =
i=n
Fi
i=1
i=n
Fizi
i=1
zc =
i=n
Fi
i=1
C
Fi Gi = Vi " Å‚ Vi
Å‚
i=n
Gixi i=n Viłxi i=n Vixi
i=1 i=1 i=1
xc = = =
i=n i=n
Gi i=n Vił Vi
i=1 i=1 i=1
i=n
Giyi i=n Viłyi i=n Viyi
i=1 i=1 i=1
yc = = =
i=n i=n
Gi i=n Vił Vi
i=1 i=1 i=1
i=n
Gizi i=n Viłzi i=n Vizi
i=1 i=1 i=1
zc = = =
i=n i=n
Gi i=n Vił Vi
i=1 i=1 i=1
Áxdv
xc =
m
Áydv
yc =
m
Ázdv
zc =
m
kg
Á m
m3
m = Ádv
Áxdv Oyz
Áydv Oxz
Ázdv Oxy
q Gi = liq
i=n
qlixi i=n lixi
i=1 i=1
xc = =
i=n
qli i=n li
i=1 i=1
i=n
qliyi i=n liyi
i=1 i=1
yc = =
i=n
qli i=n li
i=1 i=1
i=n
qlizi i=n lizi
i=1 i=1
zc = =
i=n
qli i=n li
i=1 i=1
xdl ydl zdl
l l l
xc = , yc = , zc =
l l l
l
 l1 l2
l3
l1 l2 l3
i=3
lixi l1x1 + l2x2 + l3x3 20 " 0 + 30 " 15 + 10 " 30
i=1
xc = = = = 12, 5cm
i=3
20 + 30 + 10
li l1 + l2 + l3
i=1
i=3
liyi l1y1 + l2y2 + l3y3 20 " 10 + 30 " 0 + 10 " 5
i=1
yc = = = = 4, 25cm
i=3
20 + 30 + 10
li l1 + l2 + l3
i=1
 r
Ox
xdl
l
xc =
l
l = 2rÄ…
dl = r " dĆ
x = r cos Ć
r2 ą cosĆ dĆ
rsinÄ…
-Ä…
xc = =
2rÄ… Ä…
Ä„
Ä… =
2
xc
2r
xc =
Ä„
 vi = Ai´ Ai
´
i=n i=n
Aixi Aiyi
i=1 i=1
xc = , yc =
i=n i=n
Ai Ai
i=1 i=1
Aixi A Aiyi
A
xc = , yc =
A A
Sy = x dA y
A
Sx = y dA x
A
a b h
1 1 1 2
A1 = ah x1 = h A2 = bh x2 = h
2 3 2 3
ah h + bh h
A1x1 + A2x2 1 1 1 2 h a + 2b
2 3 2 3
xc = = =
1 1
A1 + A2 ah + bh 3 a + b
2 2
 C r
2Ä…
rdĆ
2
r
3
2
r
3
2 rsinÄ…
xc =
3 Ä…
Ä„
Ä… =
2
4 r
xc =
3 Ä„
Áxdv
xc =
m
Áydv
yc =
m
Ázdv
zc =
m
C Oz
 dz z
z
Á = r
h
z
dV = Ä„Á2dz = Ä„( r)2dz
h
h
zdV 1 z Ä„r2 h 3
zc = = zĄ( r)2dz = z3dz = h
V V h V h2 0 4
V 0
1
V = Ä„r2h
3
1
h
4