abdul.ahad

I don't know much about this topic so I'm not going to pretend...
Generally, during detonation of an atom bomb, mass is converted into
energy in accordance with the famous equation of E=MC^2 and I believe
the highest efficiency of conversion of mass into energy in such a
reaction has been observed to be less than 10% (is it 8%?). I have 2
questions in relation to this:-

1. Is there an example of a reverse, 'energy' back into 'mass' type
reaction in every day life and what is the highest efficiency (%)
observed in that kind of a reaction? Are there many more examples of
energy back into mass?

2. What is the % efficiency of mass into energy conversion inside a
typical living cell? I know we are talking here an entirely different
ball game to the nuclear fission inside an atom bomb, but I see bumble
bees buzzing around with tons of energy... having consumed only a few
milligrams of pollen from a flower in my garden. So they must have a
very high mass ==> energy conversion efficiency. Is this something
that has been measured in a few test cases and is there any research
papers accessible on the net?

Cheers
Abdul Ahad
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john larkin

On 10 Aug 2004 05:24:42 -0700, abdul.ahad@ntlworld.com (AA Institute)


Nukes don't turn *real* mass (ie, whole particles) into energy, they
just shuffle nuclear binding energy around, so efficiency of apparent
mass to energy conversion a tiny fraction of a percent. To truly turn
mass to energy you should destroy some genuine mass in a
matter-antimatter reaction, which is 100% efficient at the emm-cee-squared thing.

Antimatter from cosmic rays is very efficient at conversion, but just
barely "every day life."

Photosynthesis is energy-to-mass on a tiny scale. The mass is
expressed as chemical energy, not the creation of new particles.


Living things use chemical energy, involving electron energy levels.
You could say that *any* mass-to-energy conversion is 100% efficient
for the mass that is used, but the mass equivalent of stored chemical
energy is incredibly small compared to the Mc^2 potential of the
entire hunk of stuff involved. Bees consume a lot of nectar (sugar)
and react it with a lot of oxygen. A hummingbird will consume
multiples of its own body weight per day. Lots of work has been done
on insect energetics.

John

r. h. allen

Just to reinforce what John is saying, living creatures use the energy
released by the breaking and formation of chemical bonds. Changes in
energy state *are* reflected in the masses of the chemicals before and
after the reactions, but these changes are so small as to be
imperceptible (or at least very nearly so) by even the most sensitive
measurement equipment. If the bumblebee were to convert a milligram of
honey to pure energy -- destroying all of the nectar's mass -- it would
release 90 trillion joules of energy.

To put that in perspective, let's assume that milligram of honey
releases enough energy in a mass-to-energy conversion (i.e., E = mc^2)
to sustain the bee for 24 hours. Then on average, the bee will release
energy at the rate of about a billion joules per second, or 1 gigawatt
-- about the same amount of power generated by a large power plant. I
think it's safe to say that if that were truly the case, the bee would
instantly disappear in a rather large fireball!

In reality, honeybees burn energy at the rate of about 0.1 nutritional
calories per minute, which works out to about 7 watts -- a bit more than
I expected. (Remember that a nutritional calorie is equal to 1000
thermochemical calories.) So if you insist on counting the mass changes
from the chemical reactions to calculate an efficiency for E = mc^2 in
bees, I suppose you can divide 7 watts by 1 gigawatt, which gives you an
efficiency of 0.7 millionths of a percent. Of course, that assumes that
bees really do live on a milligram of honey per day -- I don't know
whether that's accurate, but the efficiency is so small that it really
doesn't matter anyway.

thoovler

There is really no physical conversion of matter to energy or vice
versa. The equation simply states that mass and energy are the same
thing. They have different units, hence the mathematical conversion
factor of c^2. In nuclear fission, the energy that is liberated is a
portion of the binding energy that holds the nucleus together. Thus,
the nucleus splits, other elements are formed, and energy is available
for doing work.

What we are talking about here are chemical processes, which are much
much less energetic than nuclear processes. No mystery here. Bees
tend to powered by sugars (the nectar that they imbibe at the flowers
they visit), which tend to be a large source of chemical energy. Same
is true of hummingbirds. In fact, I've heard it said that
hummingbirds must injest a certain high level of sugars each day just
to keep their wings beating that rapidly. Interesting stuff, but no
mass to energy conversion is necessary.

gs

Where are these changes? AIUI the breaking and formation of bonds involves
exchanges of electrons, and changes in the energy levels of the electrons -
there is no mass <> energy conversion by any of the particles involved in a
chemical reaction. Did I miss something while I was out?

GS

hhc314

John, the result of all nuclear energy liberating reaction is a
product whose collective net mass is less that the mass of the
components used to create the reaction. This is where E=MC^2 enters
the scene.

The loss in mass will alway EXACTLY equal the amount of energy
released.

Actually, it's a pretty simple concept, once you understand it, and it
has been experimentally tested at many scales.

Forget your matter-antimatter reactions, and focus your future
attention on a good, university level, introductory, nuclear physics
text and less on the coffee-table/sci-fi crap.

Harry C.

hhc314

Compress a spring. In theory is has more mass than the same spring in an uncompressed condition.

It's 100%, because mass-energy is required to be conserved. Still,
there is no nuclear reaction present, simply chemistry.


Insects' energy puzzle me as well, but I suspect that your question is
more in the domain of biology and organic chemistry than in physics.
At any rate, I believe I can confidently assure you that nuclear
fission is not involved in the process.

Harry C.

n10

An estimate of electron mass has been given as 9.10956 x 10-28 gram.

Biological Electron donators loose mass to this degree but only at none
relatvistic speeds of course

N10

dan bloomquist

Or, 511 Mev. Which brings this full circle.


Best, Dan.

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http://Reserve****yst.com
No EXTRA stuff for email.

john larkin

I recall saying that fairly recently, only somebody snipped it.


Geez, Harry, I know all that stuff... I'm working on a 1.5 megajoule
UV laser to do fusion right now, and some amount of Physics is
involved.

There's nothing sci-fi about antimatter, and it's the only mechanism I
know of for 100% matter-to-energy conversion. Even nuclear fission
converts a fraction of a percent of the fuel mass into energy; as I
said, it's the mass equivalent of nuclear binding energy that gets
converted in a nuclear reactor or a bomb, and that's very small
compared to the MC^2 potential of all the available mass.

John