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January 7, 2008, 12:07 PM   #26
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Quote:
 Originally Posted by JohnKSa Axion is correct, this is only true in the absence of drag (air resistance). This is a common misconception due to the fact that people remember basic physics problems but forget the assumptions and conditions specified in them.
I don't think I forgot the assumptions, but isn't drag relatively negligible (relative to mass between a bullet and similarly-sized/reasonably spherical hailstone), up until you start getting near the hailstone's terminal velocity? I don't remember the details very well, but I think it's quite small next to the mass difference.

Once your hailstone hits terminal velocity, the bullet goes quite a bit faster, of course, but I'm not sure if the bullet gets there, starting from the ground and all.

It's too early to be doing physics problems. -.-

January 7, 2008, 11:36 PM   #27
JohnKSa
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Quote:
 ...isn't drag relatively negligible...
Air resistance is pretty significant. It's often neglected in problems given to students--not because it's negligible but because it can be quite difficult to calculate.

The more aerodynamic object will accelerate faster (since there's less force from air resistance fighting that acceleration) and will eventually reach a higher velocity before the air resistance balances the force of gravity.
Quote:
 I'm not sure if the bullet gets there, starting from the ground and all.
A bullet will travel upwards thousands of yards--experiments have shown a 30-06 rifle bullet will reach a height of around 9000 yards. That's enough time for the bullet to attain terminal velocity on the way down.

Interestingly enough, the person (Julian Hatcher) who did the experiment calculated that the bullet would have attained a height of over 21 MILES had there been no air resistance. Drag can not be neglected.
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 January 8, 2008, 04:12 AM #28 Adrian Senior Member   Join Date: November 7, 2007 Location: Free of California! Posts: 262 Oh... right. That comment about "9000 yards" reminded me: bullets go really fast and the faster you go, the more drag matters. I remember doing some simple drag problems and getting reasonably small answers (ideal non-tumbling cylinders and spheres, dropped from rest on a decent-height building), but... bullets go a lot faster than that. That's why they're useful. Sorry for the hijack, everyone; I'm an idiot.
 January 21, 2008, 02:06 AM #29 SMiller Member   Join Date: January 29, 2007 Posts: 71 Had a 9mm go off in my house, went through the carpet and foam padding, through the 2x10 hand cut floor and out of my basement wall that was concrete block, I wouldn't have wanted to be on the outside waiting for it!!! You would think it woundn't have made it through the floor. As for going through a wall, you know it's going to go through...
January 21, 2008, 12:12 PM   #30
Covert Mission
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Quote:
 These will definitely have enough "oomph" to be lethal and it's not that hard to find evidence to support that fact. I did an internet search looking for deaths from descending bullets some time ago and found enough documented instances to convince even the most skeptical.
Here's a first hand anecdotal example: I covered the first Gulf War as a photojournalist, with the 1st Marine Div, and ended up in Kuwait City the day it was liberated (SEALs and maybe CIA paras were there the day before, at least). The city was going totally wild with celebration for days, mainly along the seaside boulevard near the US Embassy. There were the usual wingnuts capping off their AKs into the air like firecrackers...hundreds of rounds. Here's the "joke": instead of aiming out over the sea just across the road, they were usually pointing their muzzles over the city. You guessed it...every day, people killed and wounded by falling projectiles. Pure genius!

On New Years, many LAPD patrol units working the late show pull into parking garages at midnight, because of falling lead.

 January 21, 2008, 06:22 PM #31 SamHouston Senior Member   Join Date: December 11, 2007 Location: DFW Posts: 247 A bit off subject but locally in a 3 story apartment complex where the 1st level offered attached garages. Several years back, Man decides to commit suicide by carbon monoxide poisioning in a closed garage. He was successful but also killed the guy asleep in the 2nd floor apartment above the garage. Actions have consequences.
 January 22, 2008, 10:24 PM #32 chopz Senior Member   Join Date: June 6, 2007 Posts: 184 all physics aside, i seem to remember massad ayoob writing about shooting at a downward angle to avoid doing something stupid when you're not sure of your backstop. i'd rather risk my life dodging some bg with a limp than risk shooting the little girl down the street. no matter how brave a bg might be, i'd think a weapon pointed at his family jewels would be more than enough deterrent.
 January 23, 2008, 01:57 AM #33 ShootemDown Junior member   Join Date: April 25, 2007 Posts: 254 I understand the bullet from the sky will fall at 9.8 meters per second max. thats like being hit with a bullet coming at you appx 30 FPS a reguarl bullet hitting you can be 1000 FPS. how is a bullet falling straight from the sky kill you ? at 30 FPS ?
January 23, 2008, 01:59 AM   #34
ShootemDown
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Quote:
 all physics aside, i seem to remember massad ayoob writing about shooting at a downward angle to avoid doing something stupid when you're not sure of your backstop. i'd rather risk my life dodging some bg with a limp than risk shooting the little girl down the street. no matter how brave a bg might be, i'd think a weapon pointed at his family jewels would be more than enough deterrent.
I think if your bullet makes it through the BG, you wont have to worry about the wall behind him and the little girl behind that...

January 23, 2008, 03:28 AM   #35
teeroux
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Quote:
 I think if your bullet makes it through the BG, you wont have to worry about the wall behind him and the little girl behind that...
yeah well if you have two BGs without body armor lined up one behind the other ill bet my 357 mag i can bag both of them with one shot from the same.

i think you should always be worried about whats behind the target

 January 23, 2008, 11:59 AM #36 ISC Junior member   Join Date: August 5, 2007 Location: Florida Posts: 1,982 inaccuracies OK, There is some good info here, but also some inaccuracies. 1) ACCELERATION due to gravity is 9.8 m/sÂ². That's an approximate value, it decreases as an object's distance from the center of the earth increases. There is a difference between speed and accelleration, and they are related by the formula v=at (velocity = accelleration x time) . That means that it is travelling at 9.8m/s after one second, 19.6 m/s after 2 seconds, 29.4 m/s after 3 seconds, etc. Even if the accelleration is constant, the velocity would change. 2)In the case of the bullet fired into the air, the accelleration isn't constant. The net vector accelleration is the sum of the alleration due to gravity (which changes slightly as elevation increases) and negative accelleration (decelleration) due to wind resistance (which is a function of the projectile's speed, ballistic coefficient, flight profile, and air desity) Last edited by ISC; January 23, 2008 at 01:34 PM. Reason: corrected brain fart
January 23, 2008, 01:00 PM   #37
DaveBeal
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Quote:
 they are related by the formula v=1/2at (velocity = 1/2 accelleration x time)
No, it's v = at. So, in the absence of drag, a dropped object is traveling approximately 9.8 m/sec after one second, 19.6 m/sec after two seconds, and so on.

You're thinking of d = (1/2)at^2, which describes distance traveled.

 January 23, 2008, 01:35 PM #38 ISC Junior member   Join Date: August 5, 2007 Location: Florida Posts: 1,982 yep dave you're right. I corrected my post.
 January 23, 2008, 10:28 PM #39 Hook686 Senior Member   Join Date: May 22, 2005 Location: USA The Great State of California Posts: 2,076 I really hope it does not injure anyone. That said, I will only draw and shoot if I preceive a serious, or lethal threat immenanent against me. That trumps any 'maybe', 'possible', or 'might happen' scenarios. It is real, immediate and of a serious/lethal level to me. __________________ Hook686 When the number of people in institutions reaches 51%, we change sides.
 January 26, 2008, 09:26 PM #40 allenomics Senior Member   Join Date: January 20, 2007 Posts: 1,505 Obviously it does matter. Who's on the other side of the wall? What about the welfare of people who reside in townhomes, condominiums and work in next door office/business suites? __________________ NRA Benefactor Life Member Knowledge is not power. Applied knowledge is power!
 January 26, 2008, 11:05 PM #41 Doberguy Member   Join Date: November 16, 2006 Location: Colorado Posts: 17 I have a keepsake of a shot going through one house and into another. A jewelry box and a pocket watch Neighbor cleaning his rifle (unsure of caliber need to ask parents) at night. Round goes out through exterior wall, travels approx. 60ft, goes through another exterior wall, travels about 10 ft passing over my crib (had I woke up like kids do in the middle of the night and stood up=headshot), enters a jewelry box, and stops hitting a pocket watch inside making a good dent breaking the watch. Both homes stick framed with wood siding. __________________ Steve Springfield XD-40 Sub Compact Browning Buckmark .22 Mossberg 500A
 January 26, 2008, 11:19 PM #42 chopz Senior Member   Join Date: June 6, 2007 Posts: 184 being a parent i don't have the luxury of worrying about imminent lethal threat to myself. god forbid i'll ever need to face someone down in my own home. but every scenario i've ever imagined always begins with me thinking where i would need to maneuver to to keep my son's room out of the line of my own fire, as well as any wild shots in my direction.
February 4, 2008, 07:32 PM   #44
Aqeous
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A question for SMiller

"Had a 9mm go off in my house, went through the carpet and foam padding, through the 2x10 hand cut floor and out of my basement wall that was concrete block . . ."

1.) Did you by any chance see the actual exit of this round or did you assume that it permeated all the way through?

2.) Do you by any chance recall its brand and loading? I would like to know.

To be honest the carpet and floor I understand but it would be highly unusual for a 9mm to completely permeate a concrete block. Don't get me wrong, I'm not doubting you, it is only that most of the time you might expect a bullet of this type to either embed into the concrete or even more typically ricochet off of it after making a small crater. Could you explain this happening in greater detail for me I would very much like to know more about it?

The picture link below is what is more typical expected from of a 9mm impacting concrete.
Attached Images
 9mm Vs concrete.jpg (32.2 KB, 41 views)

 February 4, 2008, 07:47 PM #45 warrior poet Senior Member   Join Date: December 13, 2007 Location: Whereever Uncle Sam wants to put me Posts: 415 Oy vay. Calculus... again... Okay. You asked for it. For something fired straight up, the bullet slows according to: Distance = initial (muzzle) velocity * time - 9.8 meters per second PER second * time. (This is the simplest one, not including wind resistance.) To include that.... You would also subtract the Area under the curve defined by the integral for the force of friction with respect to instantenous velocity. Leaving a system of equations with respect to three related variables- time, coefficient of friction and velocity. YUCK! All of that will yield the max height of the bullet, which gives the gravitational potential energy. From that you again subtract the wind resistance, giving the kinetic energy on impact with the Earth. All of this is moot, because it is IMPOSSIBLE to predict the bullet's coefficient of friction on the return trip b/c it is no longer stabilized by its spin. Net result... a statistical window in which three standard deviations will fall- roughly 99% of all bullets fired thusly. Would it kill when it hits... statistically no, but that only accounts for 99%.... there is always that slim chance that it might self-stabilize on the return trip, and be lethal. That is the mathematical answer... period. It isn't a physics problem, but one of statistics, b/c there is NO definitive way to predict wind resistance on the return trip. Okay? Now, I'm going to enjoy some scotch... and kill off those offending brain cells I just used. __________________ Trigger control: The skillful manipulation of the trigger, which causes the weapon to fire, while maintaining sight alignment and sight picture.
 February 4, 2008, 08:15 PM #46 Aqeous Senior Member   Join Date: December 24, 2007 Posts: 646 Response to Warrior Poet Mathematics is defiantly not my strength Let alone calculus, but I think you are expressing mathematically why a bullet will keyhole (impact sideways) after permeating and object or after bleeding off excessive speed am I right? If I am right than you are right (I think ) and so their is far too many variables to calculate. Such as how many people per cubic mile inhabit a given area of space of which a falling rouge bullet may have a chance to impact. (am I right?) And just because mathematically their are too many variables, that does not follow that bullets falling on ballistic trajectories have not proved themselves quite deadly time and time again.
February 5, 2008, 03:01 AM   #47
JohnKSa
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Quote:
 All of this is moot, because it is IMPOSSIBLE to predict the bullet's coefficient of friction on the return trip b/c it is no longer stabilized by its spin. ... Okay?
Sounds good except that Hatcher's tests proved conclusively that a bullet can remain stabilized by spin on the return trip. In his 30-06 tests, the 150gr bullets remained stabilized and fell base first while the 175gr bullets tumbled on the return trip. The falling 150gr bullets were traveling around 300-400fps which is fast enough to penetrate the skull.

A tumbling bullet is going to have a much reduced terminal velocity, testing I've seen indicates that a typical, tumbling pistol bullet will fall at somewhere around 150fps, give or take. That's not likely to be terribly dangerous although I think it would make an impression on someone if it hit them.

The more dangerous case than either tumbling or falling base first is a steeply elevated trajectory (when the bullet is fired steeply upward but not STRAIGHT upward). In that case the bullet will tend to remain stabilized and come down nose first with not only terminal velocity but also the remainder of the horizontal component of it's velocity left after drag. The resulting velocity is the vector sum of the terminal velocity plus the remaining horizontal velocity after drag loss. Definitely lethal potential.
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 February 5, 2008, 04:58 AM #48 nobody_special Senior Member   Join Date: November 20, 2006 Location: Southwest US Posts: 277 Jumping in here since I'm a physicist... JohnKSa pretty much has it right. Warrior Poet: You really can't ignore air resistance and expect to get a solution that is anywhere near correct. Air resistance is very significant in ballistics. Also, the bullet will remain spin-stabilized until something stops the spin; reaching the apex of a ballistic trajectory does not cause the spin to cease. One thing about spin-stabilized objects is that you can get interesting behavior, such as precession (like the wobbling of a spinning top). Precession should increase drag somewhat, but some degree of axial stability remains; you won't get actual tumbling until the rotation of the bullet is mostly gone.
 February 5, 2008, 10:30 AM #49 Aqeous Senior Member   Join Date: December 24, 2007 Posts: 646 "bullet will tend to remain stabilized and come down nose first with not only terminal velocity but also the remainder of the horizontal component of it's velocity left after drag. The resulting velocity is the vector sum of the terminal velocity plus the remaining horizontal velocity after drag loss. Definitely lethal potential." This is whats called a ballistic trajectory. And yes they are very dangerous, everyone should be aware of this fact.
 February 5, 2008, 12:44 PM #50 tegemu Senior Member   Join Date: October 14, 2005 Location: Orange Park, Fla Posts: 1,019 I once had a negligent discharge of a 1911. The .45 ACP bullet went through my wall and murdered my neighbors air conditioner. A \$1360.00 negligence. The frightening part was that had it gone at a slightly different angle, it would have gone through his wlls with enough force to seriously wound someone in his house, if not kill them. __________________ People sleep peaceably in their beds at night only because rough men stand ready to do violence in their behalf. - George Orwell

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