Brian Greene: That Famous Equation and You

[David Farber <dave () farber net>]

Begin forwarded message:

From: "Lin, Herb" <HLin () nas edu>
Date: September 30, 2005 4:45:15 PM EDT
To: dave () farber net, Ip Ip <ip () v2 listbox com>
Cc: brett () lariat org
Subject: RE: [IP] Brian Greene: That Famous Equation and You


I suggest that both conceptions are not quite accurate.   When one burns
gasoline, one doesn't convert any of its mass into energy- Brett is
certainly correct about that.  But the total system IS lighter (though
by an infinitesmal amount), where "total system" is all of the atoms in
the original gasoline.  A system with a high potential energy does
"weigh" more than one with a low potential energy. But when chemical
potential energy is involved, the difference is very very very small.

Herb Lin


-----Original Message-----
From: David Farber [mailto:dave () farber net]
Sent: Friday, September 30, 2005 1:54 PM
To: Ip Ip
Subject: [IP] Brian Greene: That Famous Equation and You



Begin forwarded message:

From: Brett Glass <brett () lariat org>
Date: September 30, 2005 1:44:03 PM EDT
To: dave () farber net, Ip Ip <ip () v2 listbox com>
Subject: Re: [IP] Brian Greene: That Famous Equation and You


At 10:50 AM 9/30/2005, Brian Greene wrote:



> The standard illustrations of Einstein's equation - bombs and power
> stations - have perpetuated a belief that E = mc has a special
> association with nuclear reactions and is thus removed from ordinary
> activity.
>
> This isn't true. When you drive your car, E = mc is at work. As the
> engine burns gasoline to produce energy in the form of motion, it does


> so by converting some of the gasoline's mass into energy, in accord
> with Einstein's formula. When you use your MP3 player, E =
> mc2 is at work. As the player drains the battery to produce energy in
> the form of sound waves, it does so by converting some of the
> battery's mass into energy, as dictated by Einstein's formula.

Dave:

Alas, the above are common misconceptions that bear correcting. When one
burns gasoline, one doesn't convert any of its mass into energy.
One is merely allowing the chemical bonds in the gasoline (and the air
used to burn it) to rearrange themselves so that the resulting atoms and
molecules have less chemical potential energy. It's the equivalent of
allowing an anvil to descend from the top of a building to the bottom,
and using a rope attached to the anvil to turn a shaft or do other work
as it falls. The anvil has precisely the same mass at the bottom as it
did at the top; it merely has less gravitational potential energy
because it is closer to the center of the Earth. A similar process
occurs on a molecular level when a battery is discharged or gasoline is
burned.

Right now, the only known processes in which matter is actually
converted to energy are ones that involve the transmutation of elements
into other elements or isotopes. Such processes aren't uncommon in the
universe -- stars, such as our sun, are constantly carrying them out
-- but
they do not occur when one burns gasoline or discharges a battery.
Which is
sort of a shame. If it were really so clean and easy to convert matter
to energy, all of the geopolitical,economic, and environmental problems
surrounding fossil fuels and similar energy sources would be instantly
solved.

--Brett Glass




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