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I appreciated the various ways of viewing mass that John D. itemized.
was less thrilled with his comment that he is not comfortable definingamount of material in place of all the other things in John's list. I'm
mass in terms of amount of material. I'm not saying to substitute
(1) It's the way students learned it in chemistry. And at most places
they still teach chemistry before physics. So students are going to
come into physics class thinking of mass as how you measure the quantity
of something.
(2) If we are ever successful at getting US households to have balances
in their kitchens, that will really cement the idea that mass is a
measure of how much stuff you have.
(3) I believe it is the way Newton viewed it, and that is why he was
talking about volume and density. He knew mass had something to do with
size (volume) but he also knew the need to include density. Had he
known about protons and neutrons and what atoms are, I suspect he would
have been able to better describe what he probably had in mind.
(5) Depending on how the NIST experiments turn out, we may end up
defining the standard kilogram as a certain number of atoms (probably of
silicon).