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hmmmm.. In a vacuum, Galileo proved that a feather
and a rock fell at the same rate. 32 ft per second per second. ( gravity )
The difference outside of a vacuum depends on the
density of air i.e sea level.. or airplane altitude.. Air currents.. temperature
and shape of the item.
Terminal velocity for a skydiver in vertical
position is @ 180 mph. Tracking ( delta position) maybe @ 200mph.
by the by.. My bro was a champion flour bomber from
his little Grummen.( Ruffles,
cuz she had ridges) :-).
Rosie
----- Original Message -----
Sent: Tuesday, March 02, 2004 9:50
PM
Subject: Re: [meteorite-list] A "Strike"
with a spare ball
Hola Rob,
You're right about the
terminal velocity of a chondrite, in the shape of a bowling ball being much
faster than a conventional bowling ball. This might still be a little
counter intuitive, but, here are some 9 inch diameter bowling ball terminal
velocities (there's a lot of algebra behind all the numbers that
follow):
Doug's really heavy 14 pounder (6.35 kg): 153 mph (69
m/s)
Rob's super duper heavy 16 pounder (7.26 kg): 164 mph (73 m/s)
A
bowling ball with a density of 2g/mL = 12.51 kg = 27.6 pounds: 215 mph (96
m/s)
Typical chondrite ball @ 3.65 g/mL (50.3 pounds or 22.83 kg):
291 mph (130 m/s)
Iron meteorite ball @ 8.0 g/mL (110.3 pounds or 50.0
kg): 431 mph (192 m/s)
Shield shaped Iron (Cabin Creek AR): 300
mph (134 m/s)
Oriented fat beer can shaped Iron at 50 kg (length = 3 times
diameter): 700 mph (312 m/s)
Cabin Creek shaped Chrondrite: 202 mph (90
m/s)
Oriented fat beer can chrondrite as above: 473 mph (211 m/s)
So
for a bowling ball shape, it would actually take an iron to achieve the 140
m/s, an ordinary chondrite falls somewhat slower, in the shape of a bowling
ball.
Could an ordinary Doug's bowling ball fall at the rate of a
chondrite? Maybe, at the limits. We have focused more on mass for
the given cross sectional area. But to fall at the same terminal rate,
all that is required is the same ratio of sqrt(mass)/sqrt(X-area) or really
just mass divided by area being the same. So, if it is twice the
density, it needs to be cut in half. Could an Iron fall at the same rate
of the ordinary bowling ball? Probably not, but for illustration, let's
consider Cabin Creek, which is quite close to the 50 kg - the same size as our
bowling ball - and a wonderful oriented shield shape I'd say around the
dimension ratio 33 X 33 X 10. That actually gives around double the
surface area as the spherical solid bowling ball shape, so it probably fell at
about "only" 300 mph (134 m/s), close to a bowling ball chondrite. In
the other hand a cylindrical shape (I arbitrarily set the length three times
the diameter.
Of course there are other considerations like the
frictional ablation shaping, which is why cylinders turn into nosecones and
bullets, and it is no wonder that the Cabin Creek sample was know to be hot
upon fall. All the acceleration due to gravity holding back a 50 kg mass
of iron several hundred miles per hour is dissapated into heat.
Alternately nosecones are more likely to be cool and also with less
thumbprinting.
The table above summarizes all my calculations, maybe
there is an error, but I hope not. This should clear up free fall of
stones that lose their "cosmic velocity" as well as for bowling balls, and how
it fits in. A person typically free falls at 110 mph or so thought they
can double that by playing with orientation. Ha. The calculations
also showe this doubling effect for likely masses. Keep in mind non iron
meteorites are practically never going to stand the shear frictional forces of
shield shapes and "explode" into pieces. Also for fun, an oriented
bowling ball that fractures in exactly two hemispherical pieces traveling
terminally at 150 mph will leave the two fragments at a terminal rate of ...
106 mph a piece. That's probably why "explosions" seem to brighten
fireballs. Suddenly the greater surface area for the same total mass
steps up the overal frictional energy released and the meteors slow down from
an instantly greater potential.
I get into this stuff. That's why
I liked the bowling ball expt. which really sounds like an excuse for some
fun.
Saludos
Doug Dawn
Mexico
En un
mensaje con fecha 03/02/2004 7:26:12 PM Mexico Standard Time,
[EMAIL PROTECTED] escribe:
Hi Doug,
Good point on the density of a
bowling ball. Intuitively, I would have guessed
the density was around 2
g/cm^3, when in fact it is barely above 1 g/cm^3 --
about 1.15 for a 16-lb ball
(the mass I was assuming). An ordinary chondrite
of the same size would weigh
close to 50 lbs! So yes, air friction is going to
be a serious factor, and a
bowling ball isn't going to have a chance of reaching
the terminal velocity of a
chondrite (let alone that of an iron).
To do this experiment
properly, then, they're going to need to drop an object
of the proper density.
--Rob
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