PSN-L Email List Message
Subject: Re: Man Made Quake
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 ----------------------------------
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.
>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.
>> 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!
>> 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.
>>> 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'?
>>> Chris Chapman
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