Spehro Pefhany wrote:

> Liquids are a subset of fluids. Gases are also fluids.

In any case, it seems to me that the general distinction between solids and
liquids is pretty arbitrary, depending more on a "more or less" (viscose)
than a difference in quality.

When you look at the pitch drop experiment
http://www.physics.uq.edu.au/pitchdrop/mainstone.html and compare that to
this phrase from
http://dwb.unl.edu/Teacher/NSF/C01/C01Links/www.ualberta.ca/~bderksen/florin.html:

"The prolonged survival of this legend, chiefly among English speakers (and
particularly among North Americans) is puzzling -- especially when one
considers that glass and glassy materials are readily available, and one
can easily verify if one can pour a gallon of glass, or drain a pint of
obsidian."

I can't but wonder... you can't "pour a gallon" of pitch, but it still
drops. Is a material that drops a solid? :)


Then, on that same page, you see this definition by the ASTM: 

"A material that flows a total of 2 in (50 mm) or less within 3 min is
considered a solid. Otherwise it is considered a liquid."

Key is here "a material that flows ... is considered a solid." That's not
the everyday, common definition of "solid" :)  50 mm in 3 min is not too
slow, either -- with some patience you can /see/ it flowing. I'm pretty
sure that not many outside the ASTM would consider such a material "solid". 

Whether one puts the dividing line between solids and liquids at 50 mm in 3
min or at 10 mm in 1 year or pretty much anywhere else seems only
arbitrary.

Gerhard

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