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decimal, thanks to the same eminently logical people who brought about
the French Revolution. In deference to France, the system’s official name is
the Système International, or SI, meaning International System. (The
phrase “SI system” is therefore redundant.)
The wonderful thing about the SI is that people who live in countries
more modern than ours do not need to memorize how many ounces there
are in a pound, how many cups in a pint, how many feet in a mile, etc. The
whole system works with a single, consistent set of prefixes (derived from
Greek) that modify the basic units. Each prefix stands for a power of ten,
and has an abbreviation that can be combined with the symbol for the unit.
For instance, the meter is a unit of distance. The prefix kilo- stands for 10
3
,
so a kilometer, 1 km, is a thousand meters.
The basic units of the metric system are the meter for distance, the
second for time, and the gram for mass.
The following are the most common metric prefixes. You should
memorize them.
prefixmeaningexample
kilo-k10
3
60 kg= a person’s mass
centi-c10
-2
28 cm= height of a piece of paper
milli-m10
-3
1 ms= time for one vibration of a
guitar string playing the
note D
The prefix centi-, meaning 10
-2
, is only used in the centimeter; a
hundredth of a gram would not be written as 1 cg but as 10 mg. The centi-
prefix can be easily remembered because a cent is 10
-2
dollars. The official SI
abbreviation for seconds is “s” (not “sec”) and grams are “g” (not “gm”).
The second
The sun stood still and the moon halted until the nation had taken ven-
geance on its enemies...
Joshua 10:12-14
Absolute, true, and mathematical time, of itself, and from its own nature,
flows equably without relation to anything external...
Isaac Newton
When I stated briefly above that the second was a unit of time, it may
not have occurred to you that this was not really much of a definition. The
two quotes above are meant to demonstrate how much room for confusion
exists among people who seem to mean the same thing by a word such as
“time.” The first quote has been interpreted by some biblical scholars as
indicating an ancient belief that the motion of the sun across the sky was
not just something that occurred with the passage of time but that the sun
actually caused time to pass by its motion, so that freezing it in the sky
Section 0.5Basic of the Metric System