Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site ut-dillo.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!gamma!epsilon!zeta!sabre!petrus!bellcore!decvax!decwrl!pyramid!ut-sally!ut-ngp!ut-dillo!darin
From: darin@ut-dillo.UUCP (Darin Adler)
Newsgroups: net.puzzle
Subject: Re: feathers vs. gold (really mass vs. force vs. weight)
Message-ID: <259@ut-dillo.UUCP>
Date: Wed, 18-Dec-85 15:45:51 EST
Article-I.D.: ut-dillo.259
Posted: Wed Dec 18 15:45:51 1985
Date-Received: Fri, 20-Dec-85 04:47:38 EST
References: <846@ecsvax.UUCP> <902@ecsvax.UUCP> <456@eneevax.UUCP> <1671@cae780.UUCP>
Distribution: net
Organization: UTexas Computation Center, Austin, Texas
Lines: 33

<>
> Have I missed something?  Grams and pounds are both units of the same thing -
> feel free to call it FORCE if you wish.  The "puzzle" makes use of the wild
> inconsistencies of "English measures", with different sized ounces and a
> different number of those ounces in the corresponding pounds.  So what's the
> problem?
 
You most assuredly have missed something.  Grams are a unit of *mass*.  This
is a measure of the amount of "stuff".  Porunds are a unit of *force*.  This
is a measure of how hard something is "pushed" or "pulled". When we talk about
the *weight* of an object, (measured in pounds, or the metric unit, newtons) we
talk about the amount of force that gravity exerts on it (due to the proximity
of the object with a very large mass, usually the earth).  Mass is a constant
(ignoring relativity for the moment), while "weight" is dependent on the
mass of the object with respect to which you are measuring weight.
 
My favorite example, from when I originally learned these ideas, is that of
a space traveller on the Moon.  Due to the fact that the Moon has a much
smaller mass than the Earth, the traveller would find that objects have a
*weight* of about 1/6 of what he is used to.  But the *mass* would not change.
Thus, even though it would be easier to pick up objects (because there is
less force pushing them down), it would be just as hard to push them around
(ignoring reduced friction, of course).

By the way, the *slug* is a unit of mass in the English system.  I am not sure
what relationship it has to a quantity of matter which weighs a pound on Earth.

(The reason this is posted to net.puzzle and not net.physics is that I think
 the folks in net.physics probably know all this already.)
-- 
Darin Adler	{gatech,harvard,ihnp4,seismo}!ut-sally!ut-dillo!darin

"Such a mass of motion -- do not know where it goes"	P. Gabriel