[meteorite-list] Suspected Meteorite GoesThroughWindowinIllinois

From: Chris Peterson <clp_at_meteoritecentral.com>
Date: Thu, 8 Mar 2007 16:14:54 -0700
Message-ID: <022801c761d7$9a961b20$2721500a_at_bellatrix>

Well shoot, Doug, it sounds like you've got more time than I to analyze
this thing. I do have a modeling tool that calculates the vertical
deviation for spherical objects falling in wind, but I haven't tried to
apply it here. I don't know how accurate it would be given that this
object is far from spherical. I use this tool to estimate strewn field
locations following high altitude fragmentations.

Just to clarify a point of apparent confusion: I was proposing two
completely different mechanisms that could impart a degree of horizontal
motion to a falling object. One is largely non-aerodynamic (except in a
trivial sense), and involves the object reaching a horizontal zero
airspeed (which in a wind means there is a non-zero ground speed). The
second is purely aerodynamic, and involves what happens when the object
is oriented and possibly tumbling. The first situation isn't too
difficult to analyze (we've both touched on parts of that); the second
is pretty much impossible to deal with.

The test case I alluded to was something I tried at the Roan Cliffs in
western Colorado, above Rifle (famous for a meteoritic non-crater that
the locals like to show off). There's an interesting spot up top where
winds are diverted upward. If you throw a stick over, it drops down and
then gets picked up, and can be carried many feet above the cliff top.
There's even a waterfall there that goes up when it reaches the edge,
and the water just evaporates overhead. But if you drop a flat rock,
like the sort you'd skim on a lake, it drops down, and will tumble
violently. It may literally look like a leaf falling, and can veer out
10 feet or more, or back into the side of the cliff hard enough to hear
when it's hundreds of feet down. A spherical rock just drops straight. I
tried this with dozens of different rocks. There's no doubt at all in my
mind that something shaped like the Illinois object, traveling at ~50
m/s, could execute some pretty impressive aerial maneuvers.

BTW, I'm not particularly arguing that this thing did fall, only
considering that it seems plausible.


Chris L Peterson
Cloudbait Observatory

----- Original Message -----
From: "MexicoDoug" <MexicoDoug at aim.com>
To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
Sent: Wednesday, March 07, 2007 6:03 PM
Subject: Re: [meteorite-list] Suspected Meteorite

> Chris wrote:
> "In a steady 18 mph wind [which would give the metal a fall angle of
> 20
> degrees], that equates to a horizontal ground speed of 18 mph. The
> heavier
> the object, the longer it will take to reach that zero airspeed. So if
> this
> thing was falling vertically, and then experienced a brief gust, it
> would
> hardly be affected. On the other hand, if fell a mile in that wind,
> I'd
> expect its ground speed to be close to the wind speed: it wouldn't be
> falling vertically. This has little to do with aerodynamics."
> OK Chris, I think I understand your assumptions and note your
> departure from
> reliance on aerodynamics which it originally sounded like you were
> depending
> upon for your assumptions. Now we are in the upstream/downstream
> textbook
> canoe problem. Whether you originally depended on aerodynamics is
> debatable
> though while my intuition had a problem with that, I think that is a
> harder
> argument for me to critique. Just one comment and I will put some
> 'hard'
> numbers to this which I invite you to pick apart if you can (or if
> not,
> perhaps use them for your own thoughts).
> "It is also why there can be no apparent relationship between the
> orientation of a strewn field and the path of the meteor that produced
> it."
> I think this is as poor an example as it is an interesting meteorite
> aside.
> But I agree that the physics of the wind are at work for this case.
> My
> objection: You are comparing the integrated effect of all winds in all
> directions at all altitudes (for a significant distance) with local
> atmospheric effects of a relatively unidirectional ''steady wind'.
> Now for the numbers I promised:
> This meteorthing has the following characteristics assuming it really
> is in
> free fall as you believe (compared to the 60 mph suggested somewhere
> else,
> that did not specify it was vt though that had to be the professor's
> assumption):
> Let me make a meteorthing terminal speed table showing how long it
> takes to
> fall a mile:
> Shield orientation: 38 m/s (86mph) 42 sec
> "Average orientation" 47 m/s (105mph) 34 sec
> Edge first orientation: 55 m/s (124mph) 29 sec
> note: terminal speed is bound by 38 < vt < 55 m/s (86 < vt < 124 mph)
> You mentioned: "On the other hand, if fell a mile in that wind, I'd
> expect
> its ground speed to be close to the wind speed: it wouldn't be falling
> vertically."
> How long is a gust? Better yet, let's put some momentum 'flux'
> constraints
> that the air imparts on the 'iron' given your 18 mph breeze that you
> believe
> can alter the fall angle to 20 degrees from vertical. I am using the
> average terminal velocity above, which you will see turns out actually
> to be
> generous, I think.
> The air imparts 1/103 (about one percent) of the momentum the
> meteorthing
> has per second as it starts whittling the angle upward. To get the 20
> degrees you claim, in the time frame you suggest, we theoretically
> need
> 34.2% (=sin(20)) of the momentum of the thing at minimum. So, in 36
> seconds
> will it be there? No. It will have just about traveled your mile,
> though.
> Theoretically this is because as soon as it starts gaining angle, the
> relative horizontal windspeed begins to equilibrate, and the momentum
> transfer rate will actually go down by the inverse square of the ratio
> of
> the relative windspeed to the 18 mph absolute windspeed. In other
> words,
> you get the meteorthing half way up to the speed and the momentum flux
> is
> already down to 25% of what it originally was. Now we're starting to
> fall a
> couple miles and it gets harder.
> However, it's worse: as this relative speed slows down and the
> momentum is
> being added with all of the corresponding aerodynamic effects of thing
> orientation frustrating attempts to increase the angle by doing a
> random
> walk. Additionally, there will be the practical world problem that
> windspeed is rarely steady even when we call it steady. A lull is an
> easy
> push downhill to a smaller angle, while getting back is uphill again.
> Cross
> drafts and anything outside of say a 60 degree cone are the same
> story. The
> atmosphere is complex enough to make just a concept out of the words
> steady
> wind.
> What I think, is you will need a much stronger wind to keep this thing
> in
> horizontal motion. I'll meet you half way and say we might get 10
> degrees
> out of the 18 mph wind. Or conversly a 36 mph 'steady' wind might
> work for
> getting 20 degrees.
> You mentioned:
> "I've dropped similarly shaped rocks off of cliffs, and watched them
> fall.
> They definitely don't and watched them fall. They definitely don't
> drop
> straight, but look a lot like falling leaves."
> I would love to do this on one of your nice Colorado cliffs, pay close
> attention to you and compare notes and surely learning a great deal.
> Though
> dropping rocks off a cliff bounded by a mountain is not all I would
> want to
> do. I would bring a kite and a fishing rod and reel with high tech
> high
> tensile low drag MICROfilament line. The kite,I would use to
> demonstrate
> in the nice steady wind (helped perhaps by steadying mountain
> geography),
> and how often it tugs, relaxes, and cross gusts and changes
> directions -
> even though on the ground it feels pretty much the same. (and you are
> talking about a 1609 meters fall, not less than my 100 meter kite
> line).
> Then I would find a cliff with an 18mph appropriately directioned wind
> and
> swap the kite for a sinker weight of nearly 1 pound (actually 402
> gram)
> meteorite shaped like a deck of cards. I would let it down 3 meters
> (10
> feet) of line and see if it deflected one meter from vertical (=the 20
> degree angle), which is over three feet. The I would toss the
> meteorite off
> the cliff to land 100 meters below, and put a rare earth magnet on the
> end
> of of my line and go fish for it starting vertically. I would then
> pick it
> off the ground and see if during 30 seconds to one minute,the iron
> slowly
> but surely creeped along a pendulum arc reasonably near the 34.2
> meters to
> one side - slowly, gracefully; and, surely? The is the small angle
> approximation here, so I understand it would fall a little short.
> Then I
> would like to interpret the results with you, and again compare notes.
> Back to this:
> "The object in question is quite small, and quite flat. It doesn't
> have to
> be a very good wing to still generate some lift and produce an angled
> descent (you'd probably use the term "crash" if an airplane landed at
> the
> same angle as this chunk of metal). I've dropped similarly shaped
> rocks off
> of cliffs, and watched them fall. They definitely don't drop
> straight, but look a lot like falling leaves."
> Now you are back to aerodynamics. So I am not sure if you are arguing
> case
> one of air movement, or case two of aerodynamics. You did say
> aerodynamics
> were negligible before so I must assume you mean this is another
> scenario
> that could result in the same effect independently or in concert.
> In addition to not buying the wing theory, I don't know if they can
> really
> be independent. Let me draw your attention to the pantagraph video
> posted.
> Look at the shape in the desk that was removed during the collision.
> It has
> every indication of looking like the 'deck of cards' iron was not only
> not a
> wing, but rather it went through edge on slicing in the wind direction
> just
> like a weather vane. Not much lift generated by weather vanes. Itis
> worth
> noting here that the comic book (whatever, atlas as you called it?)
> may have
> just gotten stuck in the hole in the desk in an inelastic collision
> and was
> simply torn through like tissue paper.
> I said:
> "What seems much more likely to me is that the object was hurled
> horizontally in which case it goes through the window and through the
> breaking glass is altered down at the desk which is plausible for an
> object
> hurled horizontally AFTER passing the maximum height (vertex) in its
> parabolic arc."
> You replied:
> "I would be more likely to believe this if it had just punctured the
> cheap
> particle board desk. But the damage to the atlas is more impressive. A
> stack
> of paper like that can absorb a lot of energy. It looks to me like the
> object had considerably more velocity than I'd expect from something
> tossed
> by hand. Maybe somebody a few blocks away built a potato cannon?"
> Heh. I don't have the answer, but we both have the same problem. I
> do have
> more suspicions now. While I previously mentioned I was very
> impressed by
> the book damage like yourself, I have since reconsidered (see above).
> Let's
> look at the collision and get a feel for how much force was applied
> for how
> long. Such a collision, usuing the speed of sound in wood, not to
> mention
> steel I estimate would last 0.1 milliseconds. That is quite an
> impulse with
> 400,000+ Newtons. The momentum of the thing, neglecting the window
> and
> shade, was 18.9 kg-m/s at the average terminal velocity of 47 m/s
> (105mph).
> A strong troublemaker who has access to slag could probably hurl the
> piece
> at a measly 18.5 m/s (42mph), exactly 40% of that number, say 160,000
> N over
> the same instant. My conclusion is that while your logic is sound, it
> doesn't fit the observations as well as a horizontal hurl. I have
> failed to
> take into consideration rotational inertia from a thrower, too. I
> don't
> think this changes the story as both cases can claim it. What I do
> see in
> the numbers is that any piece of iron that lands on an edge can do
> great
> damage by playing all that inertia against a tiny spot. There is one
> more
> comment. There was no other damage mentioned. I suspect the nealy
> one
> pound piece of iron (whoa, how much more lethal than stone) had a
> comparatively soft (non-damaging) landing on the chair, or perhaps the
> floor, after squeezing through the thin hole it made by hitting edge
> on.
> Just to be comfortable with this, I just undid the small base of my
> big
> tripod (metal from MMC :-)). It is 8cm x 8cm x 1cm and weighs 25%
> more than
> the meteorthing but is much smoother and nearly double the flat area
> on each
> side. It is a dangerous weapon. I have no doubt I could easily make
> a
> clean break in a major bone with it with a angry throw. And a bone
> has much
> greater strength than what the meteorthing did.
> Finally, all of this speaks nothing about the sheer coincidence that
> the
> hole in the shade, desk and up&down orientation of the thing is
> exactly at
> right angles to the wall. I followed the lines of perspective in a
> still
> from the video.
> Again, not dening your hypothesis is possible, just much more
> improbable.
> The one irreconcilable problem I see is the loss of height from the
> hole in
> the window to the shade. It seems lined up with the desk but way too
> much
> to have contunued on to the far corner of the desk, which puts all
> interior
> angular measurements suspect in my current view.
> Best wishes and Good Health,
> Doug
Received on Thu 08 Mar 2007 06:14:54 PM PST

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