"mass

 "A measure of the total amount of material in a body, defined either by the
 inertial properties of the body or by its gravitational influence on other
 bodies."

 http://imagine.gsfc.nasa.gov/docs/dict_jp.html#M


 "Gravitational mass is measured by comparing the force of gravity of an unknown
 mass to the force of gravity of a known mass. This is typically done with some
 sort of balance scale. The beauty of this method is that no matter where, or
 what planet, you are, the masses will always balance out because the gravitational
 acceleration on each object will be the same.

 Inertial mass is found by applying a known force to an unknown mass, measuring
 the acceleration, and applying Newton's 2nd Law, m = F/a.

 This gives as accurate a value for mass as the accuracy of your measurements.
 When the astronauts need to be weighed in outer space, they actually find
 their inertial mass in a special chair."

 http://classicalmechanics.net/Facts.htm


 "The remarkable experimental fact that all objects fall with the same
 acceleration was known to the ancients. In the fifth century, a Byzantine
 philosopher, Iohannes Philiponus, recorded and possibly performed a
 Galileo-style experiment, as part of his commentary on Aristotle's Physics.
 The fact of the uniqueness of free fall is even more remarkable in the light
 of modern physics, because it requires that two fundamentally different
 quantities, inertia and passive gravitational mass, always be exactly
 proportional to one another. This is usually interpreted as implying that
 the two quantities are equivalent measures for a single physical property,
 the quantity of mass of an object; hence, the term Equivalence Principle.
 There is no similar principle for any of the other fundamental forces"

 http://einstein.stanford.edu/STEP/information/data/gravityhist2.html

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 Discussion URL

 "Your student is very perceptive and is to be congratulated for recognizing
 the circularity of the terms mass and matter, in most texts and references
 the two definitions ARE CIRCULAR."
 ...

 "What is glossed over in physics is that there are certain terms in the
 theory that cannot be defined within the system itself."

 http://www.newton.dep.anl.gov/askasci/phy00/phy00860.htm

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 `Perceptions' note -

 Here's a friendly set of cameos, illustrated intro's; starting with
 a space-encounter -

 www.perceptions.couk.com/uef/inertmass.html

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              FURTHER REFERENCES

 GO - "search perceptions" - in SEARCH-ENGINE


file-ID www.perceptions.couk.com/uef/massdefs.txt