most common in mathematics. There are two supple-
mentary units: the radian used for
ANGLE
measure and
the steradian for measuring a
SOLID ANGLE
. By multi-
plying and/or dividing these base and supplementary
units, other derived units are obtained. For instance,
the unit of area is “square meter” (meter times meter),
and the unit of velocity is “meter per second” (meter
divided by second). There are 18 specific derived units
that have their own names, such as a Newton (N) for a
measure of force (given as kilograms times meter per
second squared). The following table lists the basic and
supplementary units and their symbols.
Multiples and fractions of units are defined in multiples
of 1,000 and are denoted by special prefixes or sym-
bols. These are shown in the table below. For example,
1 mega-amp equals 106ampere, and 1 millimeter equals
10–3 meters.
The following additional prefixes are also often used:
The metric system, a system of quantifying units of
measure in terms of powers of 10, was first established
in 1790 by a special Committee of Weights and Mea-
sures of the French Academy of Sciences. Surprisingly,
bases other than 10 were seriously considered at the
time. (There were arguments for using the duodecimal
system of base 12, as well as consideration of a base
11 system, hoping to take advantage of
PRIME
base.)
As scientific progress was made over the centuries, the
metric system was extended to include measurements
of electric current, light intensity, temperature, and
molecular quantities. This expanded system of SI units
described was adopted at the 11th International Gen-
eral Conference on Weights and Measures in 1960.
Minor adjustments to the system were made in subse-
quent meetings.
skew lines Two nonparallel straight lines in three-
dimensional space are skew if they do not intersect. No
pair of skew lines lie in a common plane.
skewness A measure of the degree of asymmetry of a
DISTRIBUTION
is called its skewness. If a distribution
has a short tail to the left and a long one to the right,
then it is called positively skewed, and negatively
skewed if the situation is reversed.
See also
STATISTICS
:
DESCRIPTIVE
.
slide 15 puzzle (Boss puzzle, fifteen puzzle) In 1878
famous American puzzlist Sam Loyd (1841–1911)
introduced his “Boss puzzle,” today called the slide 15
puzzle. The game consists of 15 tiles, numbered one
through 15, held within a 4 ×4 frame with one space
left free. Tiles may slide horizontally or vertically into
the blank cell, but all moves are confined to the plane
of the frame. The challenge is to convert the given
arrangement of tiles shown top left to the one shown
102hecto- (h) Greek: hekatón: hundred
10 deka- (da) Greek: déka: ten
10–1 deci- (d) Latin: decim: ten
10–2 centi- (c) Latin: centum: hundred
1024 yotta- (Y) Greek: okákis: eight times (24 = 8 ×3)
1021 zetta- (Z) Greek: heptákis: seven times (21 = 7 ×3)
1018 exa- (E) Greek: hexákis: six times (18 = 6 ×3)
1015 peta- (P) Greek: pentákis: five times (15 = 5 ×3)
1012 tera- (T) Greek: téras: monster
109giga- (G) Greek: gíg–
as: giant
106mega- (M) Greek: mégas: big
103kilo- (k) Greek: chílioi: thousand
10–3 milli- (m) Latin: mille: thousand
10–6 micro- (µ) Greek: m–
ıkrós: small
10–9 nano- (n) Greek: n–
anos: dwarf
10–12 pico- (p) Italian: piccolo: small
10–15 femto- (f) Danish: femten: 15
10–18 atto- (a) Danish: atten: 18
10–21 zepto- (z) Greek: heptákis: seven times
10–24 yocto- (y) Greek: oktákis: eight times
Quantity Name Symbol
length meter m
mass kilogram kg
time second s
temperature Kelvin K
amount of a substance mole mol
electric current ampere A
light intensity candela cd
angle (supplementary) radian rad
solid angle (supplementary) steradian sr
slide 15 puzzle 465