[meteorite-list] Suspected Meteorite GoesThroughWindowinIllinois

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Thu, 15 Mar 2007 16:52:54 -0700 (PDT)
Message-ID: <255406.90195.qm_at_web36912.mail.mud.yahoo.com>

Hi Chris -

I wonder if you could use strewn field data to
estimate the porosity of the different types of parent
asteroids?

good hunting,
Ed


--- Chris Peterson <clp at alumni.caltech.edu> wrote:

> 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
>
> *****************************************
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
>
>
> ----- 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
> GoesThroughWindowinIllinois
>
>
> > 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
>
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Received on Thu 15 Mar 2007 07:52:54 PM PDT