Hi Bill et al:
Points well-taken Bill.
I use one liter of water as one kilogram as a benchmark to help guide people in
their every day thinking, understanding and estimating. I did not mean to
indicate that one liter of everything weighs one kilogram; I think most people
understand this when they are in grocery stores and they buy a bag of sugar, a
jar of marshmallow fluff or something else. The mass of a liter of soda is
another good estimate as Bill points out.
Familiarization is important. When people begin to understand the mass of air
in a kL is about a kg and the mass of water in a kL is a metric ton or a kg/L,
then they will be able to use these to understand force for safety purposes
when water and air are moving. Also, they should be able to estimate carrying
capacities and volumes needed to catch rain in a barrel for later use. The use
of gm/L of air is difficult to relate to real life situations.
Regards, Stan Doore
----- Original Message -----
From: Bill Hooper
To: U.S. Metric Association
Sent: Sunday, May 06, 2007 2:08 PM
Subject: [USMA:38603] Re: People oriented metric use
On 2007 May 6 , at 12:09 PM, Mike Millet wrote:
... useful ... (for people to) know that the one liter bottles of soda or
water ... are one kilo. ... it at least helps them equate mass and volume ...
The first point is a good one but I'd be careful of the second one.
Yes, it is true that one litre of water has a mass of one kilogram, one litre
of soda has a mass of one kilogram only because soda is mostly water.* It is
not true for most other materials.
And we need to be careful NOT to "equate" mass and volume as Mike wrote. I'm
sure Mike didn't mean it that way, but in presenting such information to less
informed people, it is necessary to make sure that they aren't led to think
that volume and mass are the same thing. We may say that volume and mass are
"related" but I think "equated" gives a false impression. It is most certainly
NOT true that "1 L = 1 kg".
While it IS true that one litre of WATER will HAVE A MASS of one kilogram:
1. it is NOT true that 1 L of anything else will have a mass of 1 kg
(unless that something else is composed mostly of water or is some other
material that coincidentally has the same density as water);
and
2. it is NOT true that 1 kg is EQUAL to 1 L in general (for water or
anything else).
Regards,
Bill Hooper
Fernandina Beach, Florida, USA
* The litre bottle of soda (or water) will have a mass of 1 kg only if we can
also ignore the mass of the bottle, but that is probably OK for the plastic
bottles usually used.
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SImplification Begins With SI.
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