## PSN-L Email List Message

From: ian 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
>
>

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 <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

```