liter or litre (L or l)
the common metric unit of volume. The liter was originally defined to be the
volume occupied by a kilogram of water, and the gram as the mass of a cubic
centimeter of water. This would make the liter equal to exactly one cubic
decimeter, that is, to the volume of a cube 0.1 meter (or 10 centimeters) on a
side. Unfortunately, the physical objects constructed to represent the meter and
kilogram disagreed slightly. As measured by the standard meter and standard
kilogram, the standard liter turned out to be about 1.000 028 cubic decimeters.
This discrepancy plagued the metric system for a long time. In 1901 an
international congress accepted the discrepancy and formally defined the liter
to be exactly 1.000 028 dm3. No one was particularly happy with such
an awkward definition, so in 1964 the CGPM repealed the definition. In the SI, volumes are to be
measured in cubic meters or power-of-ten multiples thereof, not in liters.
However, the SI states
that the liter "may be employed as a special name for the cubic decimeter."
Throughout this dictionary, the liter is used as a name for exactly 1 cubic
decimeter, 1000 cubic centimeters, or 0.001 cubic meter. In its new guise as the
cubic decimeter, the liter is approximately 61.023 744 cubic inches. Compared to
the customary volume units, the liter is a little more than a U. S. liquid quart
(1.056 688 qt or 33.814 fluid
ounces) but a little less than a U. S. dry quart (0.908 08 qt) or a British
imperial quart (0.879 89 qt or 35.195 fluid ounces). Its name comes from a
French volume unit, the litron, which was in turn derived from the Latin
litra. Both the lower case letter l and the upper case L are accepted as
symbols for the liter, but the U.S. Department of Commerce specifies that L be
used, at least by businesses, to avoid confusion with the numeral 1. The unit is
spelled liter in the U.S. and litre in Britain; there are many
other spellings in various languages (see Spelling of Metric
Units).
----- Original Message -----
Sent: Friday, 2004-02-20 22:08
Subject: [USMA:28829] Re: litre and hectar are not SI
units
> Clarify why you say the litre is not part of SI. Has
it been replaced with the
> cubic decimeter because of the slight
difference between the two (as detected
> by precise modern equipment),
or is it because cubic decimeters and cubic
> meters meters make the
liter (litre) unneeded?
The litre and the cubic decimetre are one and the same
since 1964 when the CGPM made the litre the "special name" for the cubic
decimetre.
Likewise why is the hectare not to be used. Are we
supposed to say 10,000 square meters or 100 ares instead of
hectare?
>
The hectare is the same as the square hectometre.
Even though the name is not SI, it is equivalent to the SI derived unit the
sqaure metre with the SI prefix hecto attached. Just like the millibar is
numerically eqal to the hectopascal.
In true SI we can use square dekametres, square
hectometres, square kilometres, etc. Each step varies by a factor of
100. Thus any thing greater then 100 hm2 (ha) can and should be
expressed in square kilometres as anything below 1 hm2 can and should
be expressed in square deka metres, etc.
Euric
