[meteorite-list] fall patterns

From: MexicoDoug <MexicoDoug_at_meteoritecentral.com>
Date: Sun, 8 Apr 2007 11:18:30 -0500
Message-ID: <012401c779f9$8e65c3c0$f7cf5ec8_at_0019110394>

Hello Robin

If there were only gravity to worry about and no atmosphere, all you would
need to know would be the masses to answer this. If all the masses of the
breakup came in at the same velocity you would get a line of stones with the
heaviest downfield.

If you add a stagnant atmosphere to see how this scenario changes, you now
need to consider the effect of atmospheric friction. Friction depends on
the area exposed into the "wind". If every stone were a sphere, then the
heavier ones would go downfield still, along a line since the bigger the
sphere the more mass:area you can fit in the spherical volume.

Next, you can add wind of a constant direction - call it at a right angle
for fun. This will sort the pieces (still assumed to be spheres) in the
residue stream with the smaller pieces getting diverted more for the same
reasons on exposed area given above. So no you get a right triangle shape
strewn field with the heaviest being at the downfield vertex.

No ellipse yet!

Next, we change the wind direction and consider it varies in different
places along the stream like the real world and notice pieces take a random
walk on the way to the ground and we get a classic elliptical shape in
meteoritics. This is not to be confused with a true geometric ellipse,
because the upfield end will be more disperse and the downfield will come
more to an arrow where the main mass falls.

OK. Now we stop idealizing this whole thing as spheres and make them every
shape and size imaginable, from dinner plate flat to marbles to baseballs
and hens' eggs. The dinner plate may be heavier than the baseball, but die
to the area exposed,if it orients flat against the wind is will fall much
quicker due to the friction (like putting your hand out the car window).
You can then have it cut through the air edge-on and even if it is half as
heavy as the baseball it still might go further downfield.

So we now have a total impossibility to generalize since the wind conditions
in the atmosphere were unknown and even cross sectional area changes as they
ablate and break apart high above.

When all this is put together, ellipses are about all we can generally
guess. And we haven't even mentioned that upon breakups, the velocities for
different pieces probably become different.

What we are left after all of this is that usually the heavier piece is
downfield at the head of in an ellipse dispersion pattern of the finds. But
there are plenty of cases in the minority where this is inverted and hands
are waved regarding what caused that, with the wind usually blamed.

How far would you need to look? -
- How steep was the incidence angle of the original mass?
- What were the wind conditions and latitude?
- At what altitude did it stop falling?
- At what altitude did it break up?
etc... you get the idea...

If you only have one piece, there is nothing you can say. You can only
start guessing as to the dynamics when many pieces are already recovered and
then work backwards on how this came about, instead of considering billions
and billions of situations.

That said - the best bet may be bigger falls further and go up to 5 miles in
minor falls:-)

Best luck and health - hope my opinion helped a little,
Doug




----- Original Message -----
From: "Robin Galyan" <robin_707a at ifiles.com>
To: <meteorite-list at meteoritecentral.com>
Sent: Sunday, April 08, 2007 12:18 PM
Subject: [meteorite-list] fall patterns


> So what I am now trying to logicate is fall patterns. In particular the
> relationship of smaller chunks vs larger ones.
>
> Perhaps you can assist me in my thinking.
>
> Say a breakup occurs and the debris is rushing in thru the atmosphere.
> The heavier ones would fly straighter and faster right? (further). Or
> would gravity make them fall faster hence sooner?
>
> If a 1 lb (say 500g) specimen was found on a hillside, I guess I am
> trying to figure where to look for the smaller ones that probably fell
with
> it. Further up the hill or down? or both? And how far would I
need
> to look?
>
>
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Received on Sun 08 Apr 2007 12:18:30 PM PDT