Re: Does a triple beam balance measure mass or weight? Why?

The triple beam balance MEASURES MASS by USING WEIGHT!!!  The balance 
compares its reference mass and the mass being measured, and it does so by the 
force created on the masses by the gravitational field in which the balance 
resides.  What we call "weight" is a force: mass times acceleration (the 
acceleration of gravity).  So, by comparing forces on masses, we measure mass.

This seems like a meaningless detail, but it's not.  If the triple beam 
balance is experiencing ANY acceleration, whether it's from gravity or from 
being in an accelerating rocket (for instance), it can make a meaningful 
comparison (measurement) of the masses.  But if there is zero acceleration 
(let's say it's in space and the rocket is coasting) the balance can not make 
any measurement!  The masses still have mass, but you can't measure it using the 
triple beam balance.

I hope this helps!

John Link, MadSci Physicist