Monday, August 13, 2007

Re: [papercreters] PSI -was- Insulation Value

"A pint is a pound the world around" may have originally been a Limey saying.  The English soon forgot about it but it was taken up by the Americans (who didn't know any better) and taught in grade school as a rough shortcut for the kids.
 
Actually  a pint is 16 ounces of volume, while a pound is 16 ounces of weight.   The popular rhyme can help you remember this, but keep in mind that they're not really equivalent.
The Handbook of Chemistry and Physics specifies the weight of 1 US gallon of water in air at 68 degrees F to be 8.32487 pounds.   One cubic foot of water contains 7.48 gallons of water, weighing in at 62.3 pounds, so Spaceman is approximately exactly correct at 1/2 PSI.
 
Neal
 
----- Original Message -----
From: slurryguy
Sent: Monday, August 13, 2007 12:33 PM
Subject: [papercreters] PSI -was- Insulation Value

WARNING! Geek talk follows: Read at your own risk!

The old timey axiom is:
"A pint is a pound the world around."

One pint of water weighs exactly one pound. So, Bob has it exactly
right. There are 8 pints in a gallon, so a gallon OF WATER weighs
exactly 8 pounds.

To get 1 psi, one would have to stack one pint of water inside a
column that has a cross sectional area of one square inch.

One LIQUID pint of water has a volume of 28.875 cubic inches.

Go 28.875 inches deep in water and you'll experience 1 psi
differential pressure compared to whatever pressure is at the surface
of the water. (usually atmospheric pressure)

28.875 is a little more than 2 feet. Spaceman's approximation of 1/2
psi per foot depth in water is reasonable when a rough guess is all
that's needed. That approximation makes for easy off-the-cuff math
done in your head.

If a more precise measurement is required, use the 28.875 in/psi.

This whole calculation demonstrates the beauty of the metric system.
It's a lot easier to use for calculating stuff like this.

Did I confuse or put everyone to sleep with the geek talk?

I am what I am. Accept me for who I am. Don't try to change me
baby! Isn't that a song?

Hope this helps,

geekguy

--- In papercreters@yahoogroups.com, <bob@...> wrote:
>
> Good thinking- I like the thought process. If your form has a
trough on top
> with a water repellent barrier- then you could use water to
compress the
> slurry-more water more compression. What is water about 8 pounds to
the
> gallon? Bob C
>

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at 2:54 PM