Re: Mass

[cliff parker <cparker@CHARTER.NET>]

From: "Michael Edmiston"

> As I mentioned in another thread a long time ago... a beam balance
> compares two masses that are displaced in space whereas a single-pan
> electronic balance compares two masses that are displaced in time.  For
> the beam balance to work properly the gravity has to be the same in the
> two locations during the comparison.  For the electronic balance to work
> properly the gravity has to remain constant over the duration of the
> comparison.
>
> Today you simply cannot state that a beam balance measures mass whereas
> an electronic balance measures weight.  Both balances make a mass
> comparison.  They are both equally good as measuring mass.

I am confused.  The way I have explained this to my students is that neither
makes a mass comparison.  A comparison is made of the force of gravity
between the Earth and the two bodies.  When we find the two weights to be
the same we make the assumption that the masses are the same.  The same goes
for inertial balances except this time we are comparing inertia.  When we
find equal inertia we assume equal mass.  At no time did we measure mass
directly.  Where am I going wrong?

Cliff Parker

Never express yourself more clearly than you can think.
Niels Bohr