From: Eugene.Leitl@lrz.uni-muenchen.de
Date: Tue Dec 29 1998 - 11:34:08 MST
From: Nick Moffitt <nick@zork.net>
----- Forwarded message from glen mccready <glen@qnx.com> -----
Forwarded-by: Nev Dull <nev@bostic.com>
Forwarded-by: Lawrence Kesteloot <lk@pdi.com>
Forwarded-by: Grue <grue@pdi.com>
Forwarded-by: V for Vendetta <yerazunis@guess.enet.dec.com>
> There was still one aspect of the whole concept of a ravioli-loaded
> railgun type wepon which we, lolling about late on a weeknight, with
> only a few neurons randomly firing, could not resolve. Would a chunk
> of metal (can of ravioli) impacting another, larger, rest mass
> structure (star destroyer) produce an "explosion" effect, or simply
> punch an appropriately shaped hole as it passed through? Bill?
What am I, the neighborhood blast physicist??? Well, maybe... :-)
It all depends on speed of impact versus the speed of sound in the target
(what is called the Mach number, where Mach 1 means the speed of sound,
Mach 2 is twice the speed of sound, etc), and the speed of the ravioli
versus the speed of light in the target (which I'll call the Cerenkov
number, where Cerenkov 1 is the speed of light in anything; Cerenkov 1.3
is the speed of high-energy protons in a water-cooled reactor (that's why
you get that nifty blue glow), and you can get up to Cerenkov 2.4 using
diamonds and nuclear accellerators. In the late 40's people used to talk
about Cerenkov numbers, but they don't anymore. Pity.). Lastly, there's
the ravioli velocity expressed as a fraction of the speed of light in a
vacuum (that is, as a fraction of "c"). "C" velocities are always between
0 and 1.
At low speeds (REAL low) the ravioli will simply flow over the surface,
yielding a space-cruiser with a distinctly Italian paint job.
Faster (still well below speed-of-sound in the target) the metal of the
space-cruiser's skin will distort downward, making what we Boston drivers
call a "small dent".
Faster still, you may have a "big dent" or maybe even a "big dent with a
hole in the middle", caused by the ravioli having enough energy to push
the dent through, stretching and thinning the hull metal till the metal
finally tears in the middle of the dent.
Getting up past Mach 1 (say, 5000 feet/sec for steel), you start to get
punch-a-hole-shaped-like-the-object effects, because the metal is being
asked to move faster than the binding forces in the object can propagate
the "HEY! MOVE!" information. (After all, sound is just the binding
forces between atoms in a material moving the adjacent atoms -- and the
speed of sound is how fast the message to "move" can propagate.) From
this, we see that WileE Coyote often reached far-supersonic speeds because
he often punched silhouette-type holes in rocks, cliffs, trucks, etc.
Around Mach 4 or so, another phenomenon starts -- compressive heating.
This is where the leading edge of the ravioli actually starts being heated
by compression (remember PV=nRT, the ideal gas law?) Well, ravioli isn't
a gas, but under enough pressure, ravioli behaves as a gas. It is
compressed at the instant of impact and gets hot -- very hot. Likewise,
the impact point on the hull is compressed and gets hot. Both turn to
gasses -- real gasses, glowing-white-hot gasses. The gasses expand
spherically, causing crater-like effects, including a raised rim and a
basically parabolic shape. In the center of the crater, some material is
vaporized, then there's a melt zone, then a larger "bent" zone, and the
raised rim is caused because the gas expansion bubble center point (the
bending force) is actually *inside* the hull plate. If the hull plate
isn't thick enough, then the gas-expansion bubble pushes through to the
other side, and you get a structural breach event (technically speaking,
a "big hole") in the side of the space-cruiser.
Compressive heating really hits the stride up around 20,000 feet/sec (Mach
4 in steel, Mach 15 in air) and continues as a major factor all the way
up to the high fractional Cerenkov speeds, where nuclear forces begin to
take effect.
Aside: the "re-entry friction heating" that spacecraft endure when the
reenter the atmosphere is NOT friction. It's really compressive heating
of the air in the path. As long as the spacecraft is faster than Mach 1,
the air can't know to get out of the way, so it bunches up in front of
the spacecraft. When you squeeze any gas, it gets hot. So, the glowing
"reentry gas" is really just squeezed air, which heats the spacecraft heat
shield by conduction and infrared. The hypersonic ravioli can be expected
to behave similarly.
As we increase speed from the high Mach numbers (about 10 miles/sec) all
the way up to about 150,000 miles/sec, not much different happens except
that the amount of kinetic energy (which turns into compressive heat)
increases. This is a huge range of velocity, but it's uninteresting
velocity.
At high fractional Cerenkov speeds, the ravioli is now beginning to travel
at relativistic velocities. Among other things, this means that the
ravioli is aging more slowly than usual, and the ravioli can looks
compressed in the direction of travel. But that's really not important
right now.
As we pass Cerenkov 1.0 in the target, we get a new phenomenon -- Cerenkov
radiation. This is that distinctive blue glow seen around water-cooled
reactors. It's just (relatively) harmless light (harmless compared to
the other blast effects, that is). I mention it only because it's so
nifty...
At around .9 c (Cerenkov 1.1) , the ravioli starts to perceptibly weigh
more. It's just a relativistic mass increase -- all the additional weight
is actually energy, available to do compressive heating upon impact. The
extra weight is converted to heat energy according to the equation E=mc^2;
it looks like compressive heating but it's not.
[Here's where I'm a little hazy on the numbers; I'm at work and
don't have time to rederive the Lorentz transformations.]
At around .985 c (Cerenkov 1.2 or so), the ravioli now weighs twice what
it used to weigh. For a one pound can, that's two pounds... or about sixty
megatons of excess energy. All of it turns to heat on impact. Probably
very little is left of the space-cruiser.
At around .998 c, the impacting ravioli begins to behave less like ravioli
and more like an extremely intense radiation beam. Protons in the water
of the ravioli begin to successfully penetrate the nuclei of the hull
metal. Thermonuclear interactions, such as hydrogen fusion, may take
place in the tomato sauce.
At around .9998 c, the ravioli radiation beam is still wimpy as far as
nuclear accellerator energy is concerned, but because there is so much of
it, we can expect a truly powerful blast of mixed radiation coming out of
the impact site. Radiation, not mechanical blast, may become the largest
hazard to any surviving crew members.
At around .9999999 c, the ravioli radiation may begin to produce
"interesting" nuclear particles and events (heavy, short-lived particles).
At around .999999999999 c, the ravioli impact site may begin to resemble
conditions in the original "big bang"; equilibrium between matter and
energy; free pair production; antimatter and matter coexisting in
equilibrium with a very intense gamma-ray flux, etc.[1]
Past that, who knows? It may be possible to generate quantum black holes
given a sufficiently high velocity can of ravioli.
--Bill
[1]According to physicist W. Murray, we may also expect raining frogs,
plagues of locusts, cats and dogs living together, real Old Testament
destruction. You get the idea...
----- End forwarded message -----
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