As you can see, as engineering students, and later as practicing engineers, when perform-
ing analysis, you will find a need to convert from one system of units to another. It is very
important for you at this stage in your education to learn to convert information from one sys-
tem of units to another correctly. It is also important for you to understand and to remember
to show all your calculations with proper units. This point cannot be emphasized enough!
Always show the appropriate units that go with your calculations. Example 6.1 shows the
steps that you need to take to convert from one system of units to another.Example 6.1 A person who is 6 feet and 1 inch tall and weighs 185 pound force (lbf) is driving a car at a speed
of 65 miles per hour over a distance of 25 miles. The outside air temperature is 80F and has
a density of 0.0735 pound mass per cubic foot (lbm/ft
3
). Convert all of the values given in
this example from U.S. Customary Units to SI units. Conversion tables are given on the back
endpapers of this book.Person’s height,H
or
Person’s weight,W
Speed of the car,S
or
Distance traveled,D
Temperature of air,T
T 1 °C 2
5
9
180 322 26.7°C
T 1 °C 2
5
9
3 T 1 °F 2 324
D 1 25 miles2a
5280 ft
1 mile
ba
0.3048 m
1 ft
ba
1 km
1000 m
b40.233 km
Sa104,607
m
h
ba
1 h
3600 s
b29.057 m/s
Sa 65
miles
h
ba
5280 ft
1 mile
ba
0.3048 m
1 ft
b104,607 m/h104.607 km/h
W 1 185 lbf2a
4.448 N
1 lbf
b822.88 N
H 1 1.854 m2a
100 cm
1 m
b185.4 cm
Ha6 ft 1 1 in.2a
1 ft
12 in.
bba
0.3048 m
1 ft
b1.854 m
140 Chapter 6 Fundamental Dimensions and Units
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