On 21 Dec 2003 07:54:12 -0800, jim rozen wrote:
In article , Gary Coffman says...

Ok, the feathers and lead are hanging from the opposite arms
of a balance. Which side goes down? Better?

OK the balance that has both is in air, right?

But how did you determine the original 1 metric ton
number? If you put each of the items on a scale,
in air, and added or subtracted lead/feathers until
the number said "one" each time, then the
balance will stay zeroed when you compare the
two directly.

Right. The balance is only comparing moments,
ie torques, ie force times distance. In air (or water)
the force is dependent on other things besides
mass. So you can't accurately measure mass that
way.

Remember that mass is a measure of inertia, so to
measure it properly, you have to make some sort
of measurement which depends solely on the inertial
properties of the body you're measuring.

Gary