I thought that 10 of something used the prefix deka, not deca. Or are
both permissible?
David King
Bill Hooper wrote:
On 2007 Jan 21 , at 9:48 AM, [EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]> wrote:
I might be mistaken with my views of proper metric usage yet I fell
the need to share the embarrassment of asking if there is a place
held in the proper Si metric system that includes Decimeter.
Tim,
Yes, SI does include the decimetre.
The SI metric system has a basic unit for every type of measurement
and a series of prefixes used to form larger and smaller units. The
officially recognized and sanctioned prefixes DO include "deci-" which
may be appended to any basic unit to form a unit which is one tenth as
big as the basic unit. Thus, for example, it can be used with "metre"
to make "decimetre" where:
one decimetre = one tenth of a metre, or 1 dm = 0.1 m
Of course these relations can be reversed. So, we can write:
one metre = ten decimetres, or 1 m = 10 dm
It is often easier to discuss these things in this second form since
it does not involve fractions.
However, most of the prefixes in the SI metric system are used to make
new units that are 1000 times as big as the next smaller unit, not
just 10 times. To illustrate some of the more common prefixes, and
using "metre" as the base unit for example, we have:
1 gigametre = 1000 megametres
1 megametre = 1000 kilometres
1 kilometre = 1000 metres
1 metre = 1000 millimetres
1 millimetre = 1000 micrometres
1 micrometre = 1000 nanometres
etc.
In the earliest forms of the metric system, there were also prefixes
for every step-of-ten. There were only six at that time. Using "metre"
as the base again:
1 kilometre = 10 hectometres
1 hectometre = 10 decametres
1 decametre = 10 metres
1 metre = 10 decimetres
1 decimetre = 10 centimetres
1 centimetre= 10 millimetres
However, having a new prefix for EVERY factor of ten soon proved to be
too cumbersome. As the metric system was used for larger and larger
things (distances to stars) and smaller and smaller things (masses of
protons and electrons) there would need to be too many prefixes for
convenience. At some point the decision was made that, when adopting
additional new prefixes, only powers of 1000 would be used.
Since that time, one finds that in most areas, ONLY the powers of 1000
are used. However, hecto-, deca-, deci- and centi- ARE STILL A PART of
SI and there are a number of areas in which some of them are in quite
common use.
The prefix "centi-" is in very prevalently use as the "centimetre", of
course, although there are efforts in some parts of the world
(Australia, for example) to eliminate it and use millimetres
instead. In Europe it is not uncommon to find wine and beer served by
the centilitre or the decilitre.
The land area unit, "hectare", while not itself an SI unit, is defined
as 1 square hectometre and the liquid volume unit, "litre" (also not
an SI unit itself) is defined as 1 cubic decimetre. There are other
examples.
However, generally, there is a tendency to gradually eliminate the use
of the old power-of-ten prefixes in favor of using just power-of-1000
prefixes. Many people would agree, at least, not to introduce the
power-of-ten prefixes into situations where they are not already
traditionally used. Others would like to see them phased out even in
those traditional uses. While some people vehemently protest any
effort to eliminate those power-of-ten prefixes, others are ardently
in favor of doing just that. Time will tell.
I hope this answers your question and gives you some context for
understanding how the decimetre is (or is not) used.
Bill Hooper
1810 mm tall
Fernandina Beach, Florida, USA
