Chemistry Reference
In-Depth Information
The advantages of SI will seem obvious to any student of science. Let's
compare the SI units of length to the English units of length:
Comparing English Units of Length to SI Units of Length
English Conversions
12 inches = 1 foot
SI Conversions
10 centimeters = 1 decimeter
3 feet = 1 yard
10 decimeters = 1 meter
1760 yards = 1 mile
10 meters = 1 dekameter
Figure 2-1a
Do you notice the difference? With the English units, there doesn't
appear to be any logic behind the conversions, whereas, with the SI con-
versions, you are always working with multiples of ten. Need another ex-
ample? Let's compare some U.S. (United States) units for volume to SI
units of volume:
Comparing U.S. Units of Volume to SI Units of Volume
U.S. Conversions
8 ounces = 1 cup
SI Conversions
1000 cubic millimeters = 1 cubic centimeter
2 cups = 1 pint
1000 cubic centimeters = 1 cubic decimeter
2 pints = 1 quart
4 quarts = 1 gallon
1000 cubic decimeters = 1 cubic meter
1000 cubic meters = 1 cubic dekameter
Figure 2-1b
Again, the SI conversions are more uniform and easier to remember.
The older system is even more confusing than it appears here when you
consider the fact that English cups, pints, ounces, and quarts are different
than the U.S. units with the same names. For example, there are 1.2 U.S.
gallons in 1.0 English gallon! For this reason alone, American students can
probably see the need for a common system.
Another thing that American students might find interesting is that the
units “liter” and “milliliter” are absent. When the General Conference on
Weights and Measures updated the metric system in 1960, they eliminated
the liter! This means that the only “metric” unit that we have really em-
braced in this country is the one that was declared “outdated” more than
40 years ago!
