[meteorite-list] Terminal velocity of small falling objects

From: Mark Miconi <mam602_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:26 2004
Message-ID: <002501c25d8c$ffba4fc0$54b60344_at_ph.cox.net>

I was pretty sure....but I may have been mistaken. I will say I am wrong
until I can look it up. It was the name that stuck in my head...at 42 years
old it seems that somethings are not sticking in the right places.

Let me research it so I can be correct.

Sorry to all I will check my work and get back.

Mark
----- Original Message -----
From: magellon <magellon_at_earthlink.net>
To: Mark Miconi <mam602_at_cox.net>
Sent: Sunday, September 15, 2002 10:33 AM
Subject: Re: [meteorite-list] Terminal velocity of small falling objects


> Are you sure that was Megan's Law?
>
> http://www.parentsformeganslaw.com/html/questions.lasso
> http://www.meganslawnationwide.com/
>
> Best,
> ken newton
>
> Mark Miconi wrote:
>
> > By the way...I was the poster that said simple ballastics and that comes
> > from many years of competing in rifle and handgun events. Your math did
not
> > take into consideration or show the "Foot Pounds" of energy that the
object
> > would retain. At 200 meters through a pair of 7 power binoculars it is
> > possible to see a 240 grain 44 caliber pistol bullet fly in to and
strike a
> > mettalic ram target. The target weighs on the order of 30-40 pounds and
the
> > bullet will knock it over if hit properly.
> >
> > Here in Phoenix that young girl that was killed by a 240gr 44 caliber
slug
> > was a couple of miles from the shooter. In court the experts deduced
that
> > the bullet was fired at near vertical into the air, it reached apogee
and
> > began its decent. Even though it was tumbling and had reached whatever
> > terminal velocity you wish to calculate for it, it retained enough foot
> > pounds of energy to penetrate her skin, skull and brain with enough
retained
> > energy that when it stopped and that energy was dissipated in her brain
it
> > killed her instantly in mid conversation with her best friend on the
phone.
> > In her memory we named the law...."Megans Law" for her and it is now a
> > felony with a mandatory sentence for anyone convicted of discharging a
> > weapon into the air.
> >
> > I stand by my statement as do others on this list that even a piece of
> > meteorite travelling at the speeds you calculated would do enough
physical
> > damage to warrant a visit to a doctor, if not a hospital, expecially for
a
> > young child.
> >
> > Mark Miconi
> > Phoenix AZ
> > ----- Original Message -----
> > From: Piper R.W. Hollier <piper_at_xs4all.nl>
> > To: <meteorite-list_at_meteoritecentral.com>
> > Sent: Saturday, September 14, 2002 12:59 PM
> > Subject: [meteorite-list] Terminal velocity of small falling objects
> >
> > > Hello Tom, Tom, Shaun, Dave, Ron, and list,
> > >
> > > > As I said before, simple ballistics made it impossible, the girls
foot
> > would
> > > > have been damaged and in need of a hospital.
> > >
> > > Ron, I DON'T agree with this statement made by an unnamed contributor,
nor
> > > with several other similar statements. My disagreement is based not on
> > > "simple" ballistics, but on "mathematical" ballistics, that is, taking
> > > known formulas and plugging in reasonable input values and seeing what
> > > comes out.
> > >
> > > I will make an amateur attempt here to contribute something about the
> > > physics of small meteorite falls. Like many other phenomena where most
> > > humans have little or no first-hand experience, some people may
develop
> > > intuitive notions about the subject which are rather inconsistent with
the
> > > laws of physics. The sensationalist bent of the media doesn't help
much. I
> > > am a firm believer in "doing the math". Calculations based on known
> > > formulae are arguably not as good as making experimental measurements,
but
> > > are still considerably better than seat-of-the-pants guesswork.
Somebody
> > > please correct me if my logic or my math are off track in the
following
> > > analysis.
> > >
> > > An object dropped and allowed to fall through the lower atmosphere
does
> > not
> > > continue to accelerate indefinitely. There will instead be an upper
> > > boundary on the velocity at which it falls, called the "terminal
> > velocity".
> > > At the terminal velocity, the downward force cause by gravitational
> > > attraction between the object and the earth (the "weight" of the
object)
> > is
> > > exactly balanced by the upward force of the aerodynamic drag of the
> > > object's passage through the atmosphere. When these two forces are in
> > > balance there will be no further acceleration and the object will
maintain
> > > an essentially constant downward velocity.
> > >
> > > For a sky diver the terminal velocity is about 53 meters per second,
or
> > 120
> > > mph. There is only significant acceleration during the first 10
seconds or
> > > so of fall. After that, the onrushing air pushes the person up just as
> > hard
> > > as the earth pulls him or her down, and the fall velocity levels off.
> > > Animals smaller than sky divers have a lower terminal velocity -- in
the
> > > case of small insects it can be much less than 1 mph. This is part of
the
> > > reason why bugs, lizards, tree frogs, and even small mammals can fall
out
> > > of tall trees, hit the ground, and usually simply walk away unharmed,
> > while
> > > a human would be seriously injured by a fall from the same height.
> > Terminal
> > > velocity is also the reason that a small meteorite can fall "for
miles",
> > > hit a person, animal, car, or building and do little or no damage.
Small
> > > meteorites will in most cases have lost all of their cosmic velocity
at a
> > > considerable distance above the ground, and the fall velocity upon
> > reaching
> > > the ground is the aerodynamic terminal velocity.
> > >
> > > How small does a meteorite need to be to not be dangerous?
> > >
> > > The magnitude of the terminal velocity depends on a number of things:
> > >
> > > 1. The density and viscosity of air. The exact values of these at sea
> > level
> > > depend on barometric pressure, temperature, and humidity, but for the
> > > purposes of rough calculations can be assumed to be about 1.222 kg per
> > > cubic meter density and 1.73 x 10^-5 newton-seconds per square meter
> > > viscosity on a typical pleasant afternoon in Northallerton.
> > >
> > > 2. The density of the falling object. This is typically 3.25 to 3.90
grams
> > > per cubic centimeter for ordinary chondrites and about 8 grams per
cubic
> > > centimeter for irons.
> > >
> > > 3. The size of the falling object. Use a ruler or make an estimate
from a
> > > photo. The meteorite in the Northallerton photo looks like it is about
one
> > > inch (2.5 cm) in diameter.
> > >
> > > 4. The shape of the falling object.
> > >
> > > 5. The rigidity of the falling object.
> > >
> > > If one makes the simplifying assumptions that the object is spherical
and
> > > rigid, the calculation of terminal velocity is rather straightforward.
> > > These are not unreasonable approximations when making rough
calculations
> > > for falling meteorites.
> > >
> > > There is a convenient web page where one can simply plug in the
relevant
> > > values and have a computer do the calculation:
> > >
> > > http://www.processassociates.com/process/separate/termvel.htm
> > >
> > > If we assume a small meteorite with a typical chondritic density of
3.65
> > > grams per cubic centimeter and a diameter of 2.5 cm (roughly one
inch), we
> > > come up with a terminal velocity of about 46.8 meters per second, or
> > > roughly 105 mph. This meteorite would weigh about 29.8 grams, or
roughly
> > > one ounce. The question of how much damage a hard one-ounce object
> > > traveling at 105 mph might do upon striking a human being is left to
the
> > > reader's own judgment and intuition. Personally I think it would hurt
a
> > lot
> > > but would not necessarily require a trip to the emergency room, much
less
> > > the morgue. This is far from a "speeding bullet" velocity. It is not a
lot
> > > faster than a fast ball pitch and the object is a lot lighter than a
> > > baseball -- batters routinely survive getting hit with a fast ball.
> > >
> > > An iron meteorite of the same diameter with a density of 7.9 grams per
> > > cubic centimeter would weigh about 65 grams, or about 2.3 ounces. The
> > > terminal velocity would be about 69 meters per second, or roughly 155
mph.
> > > I would not want to be in the way, but getting hit by even this
falling
> > > object would probably cause a lot less damage than a gunshot at close
> > > range. Short of a hit on the top of the head, this is probably a
> > survivable
> > > encounter in most cases.
> > >
> > > Somewhat counter-intuitively, it doesn't really matter whether these
> > > meteorites had been falling through the air "from miles up" or only a
few
> > > hundred meters. Once the velocity approaches terminal velocity, which
> > > happens in just a few seconds for small objects, there is no
significant
> > > further acceleration.
> > >
> > > The 3 gram chondrite fragment which hit the boy at Mbale would have
been
> > > falling at approximately 33 meters per second, or about 73 mph. Once
> > again,
> > > I think it would have been painful if it had hit him directly, but
> > accounts
> > > stating that his life was saved because the meteorite was slowed down
by
> > > hitting a tree before striking him seem sensationalistic to me.
Falling
> > > stones that weigh only three grams are just not a big danger,
regardless
> > > of what height they fall from.
> > >
> > > The Sylacauga, Alabama stone which fell through a house in 1954,
hitting a
> > > woman and severely bruising her, weighed a very substantial 3.9 kg
(8.6
> > > pounds). This is another situation entirely compared to small stones
> > > weighing an ounce or less. Calculation of the fall velocity is left as
an
> > > exercise for the reader. If several layers of house construction
hadn't
> > > slowed the rock down, she would almost certainly have qualified for a
very
> > > unique epitaph on her gravestone.
> > >
> > > Best wishes to all,
> > >
> > > Piper
> > >
> > > PS -- BTW, I don't doubt in the least that it is dangerous,
irresponsible,
> > > and idiotic to amuse oneself by shooting a gun into the air in
populated
> > areas.
> > >
> > >
> > >
> > > ______________________________________________
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> >
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Received on Mon 16 Sep 2002 10:26:08 AM PDT