From: Ronald Wong (ronwong@inreach.com)
Date: Sat Nov 22 2003 - 17:19:13 PST
Message-Id: <l03102800bbe4647c1518@[209.209.18.101]> Date: Sat, 22 Nov 2003 17:19:13 -0800 From: Ronald Wong <ronwong@inreach.com> Subject: Re: pounds
In response to the original query by Jessica regarding whether pounds
measured weight or mass, ROY MAYEDA said:
>And it gets worse... Actually, a pound is not necessarily a pound.
>The old trick question, "Which weighs more: a pound of feathers or
>a pound of gold?"...
I brought this question up as the first part of an addendum to a message I
posted on Pinhole not too long ago.
Once the students were told that it was the feathers that weighed more
because, despite the similarity in terminolgy, the standards used depended
on whether it was a commodity or a precious metal being weighed, I then
asked my students, "Which weighs more: an ounce of feathers or an ounce of
gold?" (this was the second part of the addendum).
Based on their newly found knowledge, almost all responded by saying that
an ounce of feathers weighed more than an ounce of gold. A few held back -
having just learned that a "pound" was not always a "pound", they began to
wonder whether an "ounce" was always an "ounce".
When I pointed out that, in fact, a troy ounce was heavier than an
avoidupois ounce, the more attentive students asked, "How could this be, if
a pound of feathers weighed more than a pound of gold?". This was when I
pointed out that there are less troy ounces to a troy pound than there are
avoidupois ounces to...
So, not only are there different sets of pounds and ounces depending on
what was being measured but the conversion factors differed as well.
Both the troy ounce and the avoidupois ounce are based on
the unit called the "grain". There are more grains in a troy
ounce than there are in an avoidupois ounce (480 grains vs.
437.5 grains). So, whereas a pound of feathers is heavier than
a pound of gold (16 ounces of the former vs. 12 ounces of the
latter), an ounce of feathers is lighter than an ounce of gold.
Fortunately, when it comes to grains, a grain is a grain no
matter what you are measuring.
Now, when it comes to "tons", there are at least 5 types that
I know of (6, if you include "tun") depending on what is being
measured.
The British Poundal System is SO creative....
I used these two questions not only to review what the students had already
learned regarding a fundamental property of measurement (the need for
standards which are themselves arbitrarily chosen) but to begin a theme
that ran throughout my physics course - the role that frames of references
play in how we interpret the world around us. It's probably the most
important thing they ever learned in my course and it came up again and
again.
Cheers.
ron
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