Re: Effect of Moon on balance -- electronic balances

[John Clement <clement@HAL-PC.ORG>]

> I disagree with John Clement's assertion that an electronic balance is
> not a balance.
>
> The electronic balance and the equal-arm balance are almost the same
> thing.  The difference is the electronic balance has a temporal
> displacement and the equal-arm balance has a spatial displacement.

Please carefully consider the argument before you jump.  Nowhere did I
assert that it is not a balance.  The term balance is appropriate but
misleading to students as I pointed out.  The electronic balance is usually
a type of spring scale and as such it measures weight rather than mass and
does it by balancing forces.  An electronic balance will be inaccurate on
the Moon, but a conventional pan balance will be perfectly accurate
(assuming the vibrations do not knock it out of calibration).  Of course one
can as was pointed out calibrate the electronic balance for the Moon.
Neither one will work in the space station, and there they use an "inertial
balance".  This is actually used to see if the astronauts have lost mass
("weight???").

You are free to use the terminology as you see fit, but I submit that using
balance for both spring scales and pan balances will be misleading to
students.  By distinguishing between them in the terminology, you are
setting them up to be more able to understand the difference between these
different measuring devices.  I do not know of any research results that
show the advantage of one terminology over the other, so I can not prove my
assertion.

There is also a very interesting variant on the pan balance that requires no
mass sets or sliders.  These typically use weights arranged so that the
angle of the lever arm provides varying balancing forces.  This type of
scale must be installed properly vertical or else they will not give
accurate answers for the mass.  You can see these sometimes in older drug
stores where you put in a coin to get your "weight" and sometimes your
fortune.  Often you can see the masses through a glass window.  To
understand how these work consider attaching a mass on a lever to a pulley
or gear.  The pulley can then be geared to lift the person on the pan.

John M. Clement
Houston, TX