It was years ago on this list: - an interesting thread on demonstrating
the weight of an airmass by weighing a soda bottle before and after
compressing the air inside.
It probably stuck in mind because I tried it at modest pressure, and
another contributor took it to bursting point.
So now, it sticks in mind that a cubic meter of air is 1.3 kg!
These days, we buy water in plastic bottles because the local water is
close to a sulfite seam, useful for wall boards.
And I was tickled to learn that plastic memory is not just peculiar to
irradiated polyolefin tubing. It turns out that enthusiasts are
reclaiming plastic soda bottles (which are a triumph of the ChemEng's
craft - both light and strong, yet collapsible from cap to base with
moderate hand force.) It appears that cutting a band out of a used soda
bottle provides a very usable connector on (for example) broken chair
legs. Once in place, the band is heated by a hot air gun ($12 HF!) and
shrinks to a sturdy support. I suppose I should have grasped that an
object formed by heating and impressing plastic into bottle form, leaves
a thermal shape memory of some kind.
Echoes of the builder's art of testing concrete with a diamond coring
drill, used by geophysicists to core a rock and identify its magnetic
orientation - a key component in supporting the theory of buoyant plates
on Earth's surface last century.