in3
ft3
m3
Specific weight
lb/in3
lb/ft3
N/m3
Mass density
bl/in3
sl/ft3
kg/m3
tion written for a problem solution, whether in school or in professional practice. If properly written, an equation should cancel all units across the equal sign. If it does not, then you can be absolutely sure it is incorrect. Unfortunately, a unit balance in an equation does not guarantee that it is correct, as many other errors are possible. Always double-check your results. You might save a life.
E X A M P L E 1 - 1
Units Conversion
Problem
The weight of an automobile is known in lbf. Convert it to mass units in the SI, cgs, fps, and ips systems. Also convert it to lbm.
Given
The weight = 4 500 lbf.
Assumptions The automobile is on earth at sea level.
24
MACHINE DESIGN -
An Integrated Approach
1
Table 1-5
Selected Units Conversion Factors
These conversion factors (and others) are built into the files UNITMAST and STUDENT
Multiply this
by
this
to get
this
Multiply this
by
this
to get
this
acceleration
mass moment of inertia
in/sec2
x
0.0254
=
m/sec2
lb-in-sec2
x
0.1138
=
N-m-sec2
ft/sec2
x
12
=
in/sec2
moments and energy
in-lb
x
0.1138
=
N-m
angles
ft-lb
x
12
=
in-lb
radian
x
57.2958
=
deg
N-m
x
8.7873
=
in-lb
area
N-m
x
0.7323
=
ft-lb
in2
x
645.16
=
mm2
power
ft2
x
144
=
in2
hp
x
550
=
ft-lb/sec
area moment of inertia
hp
x
33 000
=
ft-lb/min
in4
x
416 231
=
mm4
hp
x
6 600
=
in-lb/sec
in4
x
4.162 E–07 =
m4
hp
x
745.7
=
watts
m4
x
1.0 E+12
=
mm4
N-m/sec
x
8.7873
=
in-lb/sec
m4
x
1.0 E+08
=
cm4
pressure and stress
ft4
x
20 736
=
in4
psi
x
6 894.8
=
Pa
density
psi
x
6.895 E-3
=
MPa
lb/in3
x
27.6805
=
g/cc
psi
x
144
=
psf
lb/in3
x
1 728
=
lb/ft3
kpsi
x
1 000
=
psi
g/cc
x
0.001
=
g/mm3
N/m2
x
1
=
Pa
kg/m3
x
1.0E–06
=
g/mm3
N/mm2
x
1
=
MPa
force
spring rate
lb
x
4.448
=
N
lb/in
x
175.126
=
N/m
N
x
1.0 E+05
=
dyne
lb/ft
x
0.08333
=
lb/in
ton (short)
x
2 000
=
lb
stress intensity
length
MPa-m0.5
x
0.909
=
kpsi-in0.5
in
x
25.4
=
mm
velocity
ft
x
12
=
in
in/sec
x
0.0254
=
m/sec
mass
ft/sec
x
12
=
in/sec
blob
x
386
=
lb
rad/sec
x
9.5493
=
rpm
slug
x
32.17
=
lb