Very Interesting Ben
My GCE Ordinary level engineering science (which differed only from physics
in using random units rather than a consistant SI set of units) had it the
other way round. The pound mass was the standard and we had to be very
careful about using the term pound weight should we want to use it for a
force. The standard unit of force we used was the poundal (the force
required to accelerate one pound (mass) at 1 ft/s/s) so 1 pound weight is g
poundals. The slug refered to by "Eric" as a unit of mass was described
as an archaic American usage but its use would define the pound (weight) as
that force required to accellerate a slug at 1 foot/s/s and I guess gives
an opportunity for a slug force of g pounds. Now if I do that to one of our
slugs I get a real flat slug which reduces the toll on the lettuces :-)
By the way the multiplicity of units (we used FPS, CGS, MKS and other
systems some of which had to be described as part of the set problem in
order that the student could solve the problem) merely served to obscure
the underlying principles. That said we were real good at converting
units. Thank god the Advanced Level and Degree all used SI and sorted out
the confusion.
It still doesn't explain why an ounce of water should weigh anything other
than an ounce. As a pint (20 ounces) of my water weighs a pound and a
quarter and a gallon weighs 10 pounds.
Where a pint (16 ounces) of your water weighs a pound and presumably a
gallon of your water weighs 8 pounds.
Moreover a pound (mass) of anything weighs a pound weight under standard
gravitational conditions and presumably under those same gravitational
conditions a pound weight is the weight of a pound(mass) unless it has a
slug crawling on it.
Or are we talking about different pounds here? Who was that Helen of Troy
anyway and what a way to launch ships!!!
Appologies to those people not fascinated by unitary confusion. Just think
all this started with a legitimate query about the oil capacity of a
Salisbury Axle, goes to show how careful you have to be!! Have you heard
the one about the aliens visiting Earth?
Dave
Ben Palmer <palsy@bellatlantic.net> on 22/04/99 08:59:49
Please respond to palsy@bellatlantic.net
To: Dave Vodden/Basingstoke/ECI Telecom@ECI Telecom
cc: morgans@autox.team.net
Subject: Re: Specs. please?
Dear Dave:
There is a difference between fluid ounces (volume) and ounces of
weight.
There are 12 troy ounces in a pound of gold. Although a troy ounce is
heavier (in grams) than an avoirdupois ounce, a pound of water still
weighs more than a pound of gold. One close relationship that is easy
to remember is, "A pint's a pound -- the world around!" Except in
England.
Ben Palmer
>From Eric's Treasure Troves:
=Pound=
A unit of Weight defined as the basic unit (instead of Mass) in the
Imperial system. It corresponds to a Mass of 453.592 g, and a Weight of
1 lb = (0.453592 kg)(9.80665 m/s2) = 4.448
N.
See also Bag, Pound-Mass, Pound-Volume, Slug ,Stone
at http://www.astro.virginia.edu/~eww6n/physics/physics.html
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