[meteorite-list] Strewn fields

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From: MexicoDoug_at_aol.com <MexicoDoug_at_meteoritecentral.com>
Date: Thu Apr 22 10:17:49 2004
Message-ID: <38.40264698.2d1148ad_at_aol.com>

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En un mensaje con fecha 12/16/2003 11:19:06 PM Mexico Standard Time,
mikewm_at_ctaz.com escribe:

> The second part of my question is are there other types of "strewnfields"?
> More to the point, explosions that occurred closer to the surface and that
> might be described as a shotgun pattern?

Hello Mike,

The physics of the frictional forces according to common wisdom seems to
dictate that the explosion is a result of meteorites with relative velocities on
the order of say, 10,000 to 100,000 km per hour upon slamming into the levels
of the atmosphere higher than 6 miles to typically say 15 miles. The Space
Shuttle Columbia sadly demonstrated this at even a higher altitude, where the
atmospheric skipping and resistance begins to get serious, over Texas...on the
way to Florida.

In order for the meteoric material to explode and produce a "shotgun pattern"
it would need to have the shear forces necessary to tear it apart acting.
However, by the time you get near ground level, the atmosphere is so dense, and
viscous, from the point of view of the meteorite, most masses have slowed down
to what is called "free fall" velocity. For a person skydiving, for example,
free fall terminal velocity is in the neighborhood of 120 miles per hour.
The is when the momentum has been dampened in the case of the meteorite. At
that point, the meteorite is not experiencing drastic sheer, not much more than
some of the good baseballs thrown in the major leagues, or tennis serves. So
it won't "blow up", though pieces might fragment away with no particular rush.

Terminal velocity is influenced by two factors only: Mass and exposed surface
area. The denser, the less surface area and the faster it falls against
friction. So to reach near the surface of the planet, where pressure
exponentially increases (and I believe friction goes up exponentially too, you need a huge
mass (the surface area shear forces become negligable across the whole
object). Then the atmosphere does not significantly slow it down. But the result
is more of a "Shot put" than a shot gun, and you are left with a crater hole
and impactites all over, in a symmetrical form like at the Arizona Meteorite
Crater.

So the ellipse is pretty much the rule, as it is a moving circle; though if
you push it you could make arguments for special cases, say, if an oriented
stone suddenly loses it near Mount Everest you might get a "shotgun pattern".
Check out the Chines iron shrapnel that is always being hocked from there. Not
exactly what you asked, but somewhat explosive...

The closest I can imagine would be a coincidental stone which somehow managed
to assume huge velocity perfectly downward, would create more of a circular
(=shot gun) pattern since there is no horizontal displacement. Remember an
circle is just an ellipse with eccentricity = 0. And if a shotgun produces a
circular pattern, that is a special case of an elliptical pattern, just like a
square is a special case of a rectangle. But if you don't shoot the shotgun at
point blank range into a wall, but rather over a field somewhat parallel, it
will also produce an elliptical impact field.

SaludosDoug Dawn
Mexico

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<HTML><HTML>En un mensaje con fecha 12/16/2003=20=
11:19:06 PM Mexico Standard Time, mikewm_at_ctaz.com escribe: 
 
<BLOCKQUOTE TYPE=3DCITE style=3D"BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT=
: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px">The second part of my question=20=
is are there other types of "strewnfields"? More to the point, explosions th=
at occurred closer to the surface and that might be described as a shotgun p=
attern?</BLOCKQUOTE> 
 
Hello Mike, 
 
The physics of the frictional forces according to common wisdom seems to dic=
tate that the explosion is a result of meteorites with relative velocities o=
n the order of say, 10,000 to 100,000 km per hour upon slamming into the lev=
els of the atmosphere higher than 6 miles to typically say 15 miles.  T=
he Space Shuttle Columbia sadly demonstrated this at even a higher altitude,=
where the atmospheric skipping and resistance begins to get serious, over T=
exas...on the way to Florida. 
 
In order for the meteoric material to explode and produce a "shotgun pattern=
" it would need to have the shear forces necessary to tear it apart acting.&=
nbsp; However, by the time you get near ground level, the atmosphere is so d=
ense, and viscous, from the point of view of the meteorite, most masses have=
slowed down to what is called "free fall" velocity.  For a person skyd=
iving, for example, free fall terminal velocity is in the neighborhood of 12=
0 miles per hour.  The is when the momentum has been dampened in the ca=
se of the meteorite.  At that point, the meteorite is not experiencing=20=
drastic sheer, not much more than some of the good baseballs thrown in the m=
ajor leagues, or tennis serves.  So it won't "blow up", though pieces m=
ight fragment away with no particular rush. 
 
Terminal velocity is influenced by two factors only: Mass and exposed surfac=
e area.  The denser, the less surface area and the faster it falls agai=
nst friction.  So to reach near the surface of the planet, where pressu=
re exponentially increases (and I believe friction goes up exponentially too=
, you need a huge mass (the surface area shear forces become negligable acro=
ss the whole object).  Then the atmosphere does not significantly slow=20=
it down.  But the result is more of a "Shot put" than a shot gun, and y=
ou are left with a crater hole and impactites all over, in a symmetrical for=
m like at the Arizona Meteorite Crater. 
 
So the ellipse is pretty much the rule, as it is a moving circle; though if=20=
you push it you could make arguments for special cases, say, if an oriented=20=
stone suddenly loses it near Mount Everest you might get a "shotgun pattern"=
.  Check out the Chines iron shrapnel that is always being hocked from=20=
there.  Not exactly what you asked, but somewhat explosive... 
 
The closest I can imagine would be a coincidental stone which somehow manage=
d to assume huge velocity perfectly downward, would create more of a circula=
r (=3Dshot gun) pattern since there is no horizontal displacement.  Rem=
ember an circle is just an ellipse with eccentricity =3D 0.  And if a s=
hotgun produces a circular pattern, that is a special case of an elliptical=20=
pattern, just like a square is a special case of a rectangle.  But if y=
ou don't shoot the shotgun at point blank range into a wall, but rather over=
a field somewhat parallel, it will also produce an elliptical impact field.=
 
 
SaludosDoug Dawn 
Mexico</HTML>

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Received on Wed 17 Dec 2003 12:50:37 AM PST

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