Re: Hey Mr. Hyde!

From: Alex McDonald (alex_mcd_at_btopenworld.com)
Date: 03/29/04 

Date: Mon, 29 Mar 2004 20:39:12 +0000 (UTC)

"Evenbit" <nbaker2328@charter.net> wrote in message
news:ecdc73cc.0403291109.28e4e966@posting.google.com...

> We DO NOT point to the _force of gravity_
> and say that it is the source of energy because we see that the _force
> of gravity_ is the SAME as it was before -- 9.8 meters per squared
> second -- and hasn't been reduced one iota. Likewise, we DO NOT point
> to the _force of magnetism_ and say that it is the source of energy
> because we see that the _force of magnetism_ of this particular magnet
> is the SAME as it was before -- say a flux density of 2.6 webers per
> squared meter -- and hasn't been reduced one iota.

[ Please don't do a Beth on me; this post is meant to be stimulating, not
confrontational. ]

That's a tricky one; perhaps it does change, even if by only an iota.
There's potential energy in the gravity well (as you note). Imagine a mass
the size of the Earth spread over the area of, say, the solar system. As all
the pieces accrete together, they fall down the gravitational well and loose
potential energy; so the Earth as a ball has less energy (hence mass) than
the pieces spread out. IIRC, the mass reduction is in fractional parts per
billion for an Earth sized object. It is, however, still a prodigious amount
of energy. (Imagine it in reverse; spreading the earth out over an area of
the solar system would cost energy, or mass equivalent.)

The magnet is very, very small compared with the Earth, but the energy lost
by dropping the magnet down the gravitational well increased the
gravitational force and decreased the mass of the whole system (by the mass
equivalent of the potential energy). The numbers are incredibly small, true;
but try a thought experiment (Gedankenexperiment) with a planet sized
magnet... 

-- 
Regards
Alex McDonald

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