[meteorite-list] Terminal velocity of small falling objects

From: Rosemary Hackney <ltcrose_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:25 2004
Message-ID: <001001c25c71$7dc1ade0$6e74d6d1_at_default>

LOL.. reminds me of the time my sis demanded my bro to apologize to the cat
for stepping on her cat..she gave him a second opportunity and he declined
and laughed. On the third insistence, he declined and she shot him point
blank with a BB rifle.. he had a bruise at least 6 inches in diameter...Oh
the good old days... :-)

But in my old skydiving days.... I remember that terminal velocity was for
free fall was _at_ 180 mph while a delta track may get up to 200 mph.

Anywho .. my two cents worth...

Rosie


----- Original Message -----
From: "David Freeman" <dfreeman_at_fascination.com>
To: "James_TOM Knudson" <peregrineflier_at_hotmail.com>
Cc: <piper_at_xs4all.nl>; <meteorite-list@meteoritecentral.com>
Sent: Saturday, September 14, 2002 6:16 PM
Subject: Re: [meteorite-list] Terminal velocity of small falling objects


> Dear James, Piper, and List;
> I still think that the way that a pea sized stone hits my car windshield
> at 90 miles an hour and puts a very large star in that rather much
> harder than my skin windshield, would tend to probably imbed it self in
> my skin. Now if you want to talk about small very round objects and
> velocities of 600-800 feet per second, why not just shoot your foot with
> a bb gun. I have seen others do it and I choose to not do that. A bb
> will go into the skin and muscle an inch with good penetration and less
> with less.
> Do the math, yah, just shoot your foot, but don't put your eye out!
>
> Dave Freeman
>
> James_TOM Knudson wrote:
>
> >
> >
> >
> >
> > Hello, I don't know if this post is in regards to the post I posted
> > about the girl getting hit by the meteorite, but it sure sounds like
> > it. I do not think a small meteorite would necessarily hurt a person!
> > The hole weight X velocity thing! She stated that she noticed the
> > falling meteorite at about roof level. I know the velocity of a small
> > falling rock from "miles up" has to be to fast for some one to
> > "notice" it falling from roof level! It sounds to me that she noticed
> > it at the top of its apogee, about roof level after it was thrown at
> > her! You through a small rock at least 120mph and try to see it! I
> > don't agree with your terminal velocity thing ether : ) A 16 lb
> > bowling ball might reach terminal velocity and stay at that speed,
> > But, a 2 lb female Peregrine Falcon will reach terminal velocity with
> > out flapping and then keep accelerating as long as it's aerodynamics'
> > allow some where over 200mph.
> > Thanks, Tom
> >
> > From: "Piper R.W. Hollier" To: meteorite-list_at_meteoritecentral.com
> > Subject: [meteorite-list] Terminal velocity of small falling objects
> > Date: Sat, 14 Sep 2002 21:59:45 +0200 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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Received on Sun 15 Sep 2002 12:36:41 AM PDT