## PSN-L Email List Message

From: "James Hannon" jmhannon@.........
Date: Mon, 10 Apr 2006 10:19:29 -0500

```There are actually two types of "weighing machines" scales. One uses springs and actually measures force. The other is a balance which compares one mass against another. This type of scale will be accurate in measuring mass as long as there is any gravity at all.

---------- Original Message ----------------------------------
From: ian
Date:  Mon, 10 Apr 2006 16:11:58 +0100

>yes, mass is a constant which is the nice thing about it.
>
>Sorry to bring this discussion here, apologies in advance.
>
>The problem is that mass and weight are different concepts.  When we buy
>a quantity of goods, like flour for instance, we put the flour on a
>weighing machine, which measures the weight but, under the metric
>system, we quote the weight in units of mass (Kg).
>
>Now if we buy 10 Kg of flour in Reykjavik then take it and the measuring
>machine to Panama and measure out another 10 Kg, we will find that the
>two 10 Kg bags of flour are different (by a tiny amount).  This takes us
>back to the original (correct) premise that mass does not vary and so
>there is something wrong with our experiment.
>
>The something wrong is that we used a weighing machine (instead of a
>"massing" machine) and implicitly applied a constant to convert the
>weight into mass.  The constant is the thing that varies with where you
>are on the Earth and mainly consists of the acceleration due to the
>Earth's gravity, minus the centrifugal force caused by the Earth's
>spin.  Both contributions vary around the globe.
>
>Again, apologies for the non-quaky topic.
>
>Ian
>
>Barry Lotz wrote:
>
>> Hi All
>>  If I remember my physics, mass does not vary with location (unless
>> you are traveling very fast) but force does ( f=m*a) . the earths
>> acceleration does vary with location.
>> regards
>> Barry
>>
>>
>> ian  wrote:
>>
>>     at the risk of religious wars(!), the "kilo" is subject to
>>     variation from place to place because we use a weighing machine to
>>     measure it!
>>
>>     Sigh.
>>
>>     :-)
>>
>>     Ian
>>
>>
>>     ChrisAtUpw@....... wrote:
>>
>>>     In a message dated 04/04/2006, ian@........... writes:
>>>
>>>         the comparrison is deeply flawed.  A metric tonne is a unit
>>>         of mass, a ton is a unit of force. Someone screwed up
>>>         significantly when we went metric. It should have been
>>>         Newtons or Kilo-Newtons for measuring weight.
>>>
>>>         Ian.
>>>
>>>     Hi Ian,
>>>
>>>         No, it should not be defined as the force. If it were, the
>>>     actual quantity (mass) would vary from place to place. The ton in
>>>     commerce is also mass. Going metric wasn't a 'screw up'?
>>>
>>>         Regards,
>>>
>>>         Chris Chapman
>>
>>
>
>

--
Jim Hannon
http://www.fmtcs.com/web/jmhannon/
42,11.90N,91,39.26W
WB0TXL
--
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