http://www.jumptown.com/events/speedskydiving.shtml
Saludos Doug
En un mensaje con fecha 03/03/2004 12:09:37 AM Mexico Standard Time, [EMAIL PROTECTED] escribe:
Asunto: Re: [meteorite-list] A "Strike" with a spare ball
Fecha: 03/03/2004 12:09:37 AM Mexico Standard Time
De: [EMAIL PROTECTED]
Para: [EMAIL PROTECTED], [EMAIL PROTECTED]
CC: [EMAIL PROTECTED]
Enviado por Internet
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 -----Hi Doug,
From: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED]
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:
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
