2 – 1
Chapter 2
2.1.1.
V = 10 m
3
, W = 60 kN.
Specific weight,
J
= W/V = 60 kN/10 m
3
= 6 kN/m
3
= 6000 N/m
3
Density,
U
=
J
/g = 6000 N/m
3
/9.81 kN/m
3
= 611.62 kg/m
3
Specific gravity, s.g. =
J
/
J
w
= 6 kN/m
3
/9.81 kN/m
3
= 0.612.
2.1.2.
s.g. = 0.7.
In SI units:
U
oil
= s.g.
U
w
= 0.7(1000 kg/m
3
) = 700 kg/m
3
.
J
oil
= s.g.
J
w
= 0.7(9810 N/m
3
) = 6867 N/m
3
.
In English (FPS) units:
U
oil
= 0.7(1.94 slugs/ft
3
) = 1.36 slugs/ft
3
.
J
oil
= 0.7(62.4 lb/ft
3
) = 43.68 lb/ft
3
.
2.1.3.
From Newton’s second law,
F = ma. Thus, unit of force = unit of mass x unit of acceleration = kg x m/s
2
.
This is unit is called newton, denoted by N, and it is equivalent to kg x m/s
2
.
2.1.4.
In English units, unit of mass = the unit of Force divided by the unit of
acceleration due to gravity = lb/(ft/s
2
) = lbs
2
/ft.
This unit is called slug, and it is thus equivalent to lbs
2
/ft.
2.1.5.
W
earth
= 9810 N. g
moon
= (1/6)g
earth
= (1/6)(9.81 m/s
2
) = 1.635 m/s
2
.
M
earth
= M
moon
= W
earth
/g
earth
= 9810 N/9.81 m/s
2
= 100 kg.
W
moon
= M
moon
g
moon
= 100 kg (1.635 m/s
2
) = 163.5 N.
2.1.6.
T = 110
o
F. Using the relationship
o
C = (5/9)(
o
F – 32):
T in
o
C = (5/9)(110 – 32) = 43.33
o
C.
2.1.7.
At 20
o
C, 50
o
C and 80
o
C, the densities of water are 998.2 kg/m
3
, 988.1 kg/m
3
and 971.8 kg/m
3
, respectively (Table 2.1.2). Thus, from
(i) 20
o
C to 50
o
C, percent change in
U
= (998.2 – 988.1)(100)/998.2 = 1 %;
(ii) 20
o
C to 80
o
C percent change in
U
= (998.2 – 971.8)(100)/998.2 = 2.6%.
2.2.1.
Q
= 4 x 10
4
m
2
/s, s.g. = 1.5.
U
liquid
= s.g.
U
w
= 1.5(1000 kg/m
3
) = 1500 kg/m
3
.
P
=
QU
= 4 x 10
4
(1500 kg/m
3
) = 0.6 Ns/m
2
(Pas)
2.2.2.
P
= 2.09 x 10
5
lbs/ft
2
.
In Ns/m
2
, m = [2.09 x 10
5
lbs/ft
2
] x [4.448 N/lb] x [1 ft/0.3048 m]
2
= 1x 10
3
Ns/m
2
(kg/m.s)
1 poise = 1 g/cm.s, and 1 centipoise = 0.01 g/cm.s = 0.001 kg/m.s.
Thus, 2.09 x 10
5
lbs/ft
2
= 1 centipoise.
2.2.3.
1 stoke = 1 cm
2
/s = 10
4
m
2
/s.
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1 centistoke = 0.01 stoke = 10
6
m
2
/s.
Thus, 800 centistokes = 800 x 10
6
m
2
/s = 8 x 10
4
m
2
/s.
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 Surface tension, Kilogram, OC, Pabs

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