Re: [Phys-l] definitions ... purely operational, or not

[Hugh Haskell <haskellh@verizon.net>]

At 12:30 -0500 11/08/2010, Anthony Lapinski wrote:
> True weight is mg, while apparent weight is given by a bathroom scale,
> which shows the upward support force. Jump off a cliff, and that scale
> reads zero. You have no apparent weight, just like those floating
> astronauts in the orbiting shuttle. Plenty of true weight. You can also
> hang a wood block with a spring scale. Release the block and it falls due
> to its true weight. But the scale reads zero while the block falls.
While I believe that trying to achieve a uniform definition of weight 
in this world is truly tilting a windmill, I can't help getting 
involved. To my way of thinking, the only useful definition of weight 
is that which the bathroom scale reads when you stand on it (assuming 
it is an accurate bathroom scale). This is not inconsistent with Al 
Bartlett's definition, only a little homier.

This, then is consistent with what we say from orbit, from the bottom 
of a swing and while standing on the earth. And everyone understands 
what you are talking about. It also enables us to banish the silly 
concept of "zero gravity." If we remove gravity from the definition 
of weight, then wherever you are, you never have to reconnect the 
two. Weightless is weightless, heaivier is heavier, and lighter is 
lighter. And we don't have to worry about gravity.

Then what to we do with mg? Just leave it as is. g is simply the 
(corrected for local effects like the rotation of the earth) 
gravitational field strength, so mg is then completely analogous to 
qE (the force of gravity on an object of mass m and the force of 
electricity on a charge q), and there is no magical turning on or off 
of gravity. And we don't have to worry about differentiating between 
"true" weight and "apparent" (i.e., "liar's") weight. Weight is just 
weight, and as we all, including little kids, know, it varies with 
the circumstances--you're heavier at the bottom of the Ferris wheel 
and lighter at the top, and all that stuff.

So let me add my voice to the hopeless cause of getting the ambiguity 
out of our understanding of gravity and weight.

Hugh
--

Hugh Haskell
mailto:hugh@ieer.org
mailto:haskellh@verizon.net

It isn't easy being green.

		--Kermit Lagrenouille