Volume

V

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.

Image 40

 

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