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Fundamental Physical Properties

I have a question that has been perplexing me for several years now. The
two physical science texts that I have used since beginning to teach this
course three years ago refer the the four fundamental physical properties,
length, mass, time, and electric charge, and state that all other physical
properties or quantites can be stated as combintations of these four. For
example in Physical Science, 3rd. Ed., by Bill W. tillery, p. 6, it states
that "There are four properties that cannot be described in simpler terms,
and all other properties are combinations of these four." In Physical
Science, by Jerry Schad, p. 10, it states that "It is remarkable that
every physical property you can imagine can in some way be expressed in
terms of one or more of only four fundamental properties: length, time,
mass, and charge. These properties are fundamental in that they cannot be
expressed in simpler terms." I took this as a revelation of some basic
insight into the nature of the Universe. And then I became aware that in
the SI system, there are seven base units. And so for the past few years,
I have been trying to figure out how to express the kelvin, the mole, and
the candela in terms of the meter, kilogram, and second. I have not
researched these units as thoroughly as I might, but I thought I might
be able to get some response as to whether I am headed in the right

The candela seems to be a unit of intensity, restricted to the visible
spcetrum, but measured in watts per steradian.

The mole seems to be a reflection of having defined the kilogram, and
hence the gram, and then finding that there are Avogadro's number of
carbon-12 atoms in 12 g of carbon-12 atom's. It is a fundamental constant
of nature, but related to the definition of the unit of mass.

But the kelvin has me stumped. The nearest I have come is the internal
energy of an ideal monatomic gas, U=(3/2)nRT, but this does not give a
definition of the kelvin in terms of the meter, kilometer, and second, and
is only true for ideal and monatomic gases. Real gases and molecular
gases contain different amounts of energy even while they are in thermal
equalibrium, i.e.; at the same temperature. Is not the kelvin as
fundamental as the other four units?

Joe D. Darling
Instructor of Physics and Physical Science
Ozarks Technical Community College
815 North Sherman Avenue Springfield, MO 65802
(417) 895- 7295 (417) 895-7249 FAX