23 Jun
2004
23 Jun
'04
3:07 p.m.
A gallon (US) of water weighs *about* 8 pounds. There
are *about* 8
gallons in a cubic foot (to within 10%). So, a cubic foot of water
weighs *about* 60 pounds. And, that 8*20*30 foot swimming pool holds
*about* 350,000 pounds of water. (am I still within 10%?? <shrug>)
No, but within 20%. I fired up units and did the work to decent
precision (28.316847 litres in a cubic foot, 2.2046226 kilograms in a
pound[%]. Looking at my CRC, I see that the density of water varies
comparatively little with temperature, less than 5% difference between
the 4? and 100? figures; using the approximation that 1 litre weighs 1
kilogram[%], I get 8*20*30*28.316847*2.2046226 = 299654+ pounds. Given
that 5% variation and a few other errors (the density of water is not
quite 1 g/cc even at 3.98?), that figure looks more precise than it is,
but even putting all the errors together and assuming they all go in
the same direction, I can't get to within 10% of 350000lb.
[%] Strictly, this is a units clash; a kilogram is a mass unit, whereas
pounds and other weights are force. For the picky, read
kilogram-weight for kilogram throughout.
So, when the kid at the local grocery store rings up
your *two* $9.95
items and tells you the total is *$40*, you can just smile and say
"What's wrong with this picture?"
Uhhh...a recent sales tax increase? :)
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