Re: Weight and Mass

[cliff parker <cparker@CHARTER.NET>]

> Physical principle:  the triple-beam balance measures mass.  It does so by
> comparing the unknown to some known masses.

Does it really?  Not the way I look at things.  See below.

> 1) You can use a balance-beam to make a mass-to-mass comparison in a way
> that is independent of gravity.  Firmly attach a massive object to one end
> of a sturdy stick and a less-massive object to the other.  Drive a pin
> through the stick at the balance point.  Grab it by the pin.  Show that it
> balances.  Turn it upside down.  It still balances.  This is -1 Gee.
Shake
> it up and down.  It balances no matter what the local gravitational and/or
> other acceleration is.  It would work just fine on the moon.  It compares
> mass to mass under all conditions (although its sensitivity goes to zero
> under conditions of weightlessness).

If a balance as you have discribed measures mass then its sensitivity would
not go to zero under conditions of weightlessness.   Mass certinly does not
go to zero under these conditions.  A balance measures and compairs
gravitational force as it is typically used and inertia (perhaps along with
gravitational force) when used in the inventive manner you discribed by
shacking in up and down.  The equilivance of mass between objects on a
balence in equlibrium is assumed not measured.

By the way.  I enjoyed the examples of your early experimental endeavors.
Any ideas on how one could convince students that the resistance one feels
when pushing a car is largely because of inertia and not friction, short of
repeating the experiment on the moon?