Depending on just exactly how it falls (nose first and stable, base first, or yawing/tumbling) its terminal velocity will be significantly less than its muzzle velocity (assuming a normally fast muzzle velocity). I'm guessing that something with the density of 75% lead and roughly 25% copper will max out at a few hundred FPS. I'm sure some of the physicist/engineer-types around here will have a table with an approximation. Of course, if the Earth had no atmosphere, its return velocity would be equal to its departure velocity (provided it didn't depart at escape velocity and leave the Earth completely, or alternatively go into orbit ).
Posts: 13274 | Location: Henly, TX, USA | Registered: 04 April 2001
No. When it returns, it starts at zero fps and travels the same distance, and even though gravity has no effect, air drag still does. I'm not sure what the maximum speed of return is, but its very, very slow in comparison.
I suggest the answer is "Enough". Not planning any parties, are we? Sorry for no link.
quote:From : THE CHICAGO SUN TIMES , tuesday , November 25 , 2003
Johnson City , Tenn. - A bullet fired in the air during a Ku Klux Klan initiation ceremony came down and struck a participant in the head , critically injuring him , authorities said.
Gregory Allen Freeman , 45 , was charged with aggrevated assault and reckless endangerment in the Saturday night incident that wounded Jeffery S. Murr , 24 . About 10 people , including two children , had gathered for the ceremony . The man who was being initiated was blindfolded , tied with a noose to a tree and shot with paintball guns as Freeman fired a pistol in the air to provide the sound of real gunfire , Sheriff Ed Graybeal said. A bullet struck Murr on the top of the head and exited at the bottom of his skull , authorities said. Freeman fled the ceremony but was arrested near his home , authorities said. He was released on $7,500 bail. AP
Posts: 588 | Location: Maryland | Registered: 08 April 2003
An object which is falling through the atmosphere is subjected to two external forces. One force is the gravitational force, expressed as the weight of the object. The other force is the air resistance, or drag of the object. The motion of a falling object can be described by Newton's second law of motion (Force equals mass times acceleration -- F = m a) which can be solved for the acceleration of the object in terms of the net external force and the mass of the object.
a = F / m
The net external force (F) is equal to the difference between the weight and the drag forces (W - D). When drag is equal to weight, there is no net external force on the object and the object will fall at a constant velocity as described by Newton's first law of motion. The constant velocity is called the terminal velocity .
We can determine the value of the terminal velocity by doing a little algebra and using the drag equation. Drag (D) depends on a drag coefficient, (Cd) the air density, (r) the square of the air velocity (V) and some reference area (A) of the object.
D = Cd * r * V ^2 * A / 2
At terminal velocity, D = W. Solving for the velocity, we obtain the equation
V = sqrt ( (2 * W) / (Cd * r * A) )
The terminal velocity equation tells us that an object with a large cross-sectional area or a high drag coefficient will fall slower than an object with a small area or low drag coefficient. (A large flat plate will fall slower than an a small ball with the same weight.) And if we had two objects with the same area and drag coefficient (two identically sized spheres), the lighter object would fall slower. This seems to contradict the findings of Galileo that all free falling objects would fall at the same rate with equal air resistance. But Galileo's principle only applies in a vacuum, where there is NO air resistance and drag is equal to zero.
Now you have the formula...
Posts: 3282 | Location: Saint Marie, Montana | Registered: 22 May 2002
Hatchers Notebook has a chapter on this subject titled "Bullets From The Sky". Every serious shooter should have a copy of this book. It's a classic and a very interesting read.
Posts: 8169 | Location: humboldt | Registered: 10 April 2002
So if you want assume about 100 m/s, a bullet will max out around 300-350 fps. At 180 grains, it's packing 42 foot-pounds of energy, about half the energy of a .22 at the muzzle. If it is coming down, you do not want to be under it.
Posts: 2281 | Location: Layton, UT USA | Registered: 09 February 2001
If there was not atmosphere or mountains in the way then if you had a rifle that did about 25,000 feet per second and you fired parallel to the ground then about 90 minutes later the bullet would hit you in the arse
Mike
Posts: 7206 | Location: Sydney, Australia | Registered: 22 May 2002
I've actually found quite a few bullets that were fired into the air, and came down on the concrete where I work. We found 13 on New Year's Day last year. (Yep, bad part of town.... and large expanse of concrete).
Most of the time, they hit nose-first. There is relatively little damage to them. A 7.62x39 bullet has the tip bent over, pistol bullets mostly show an imprint of the concrete surface. Still, I'd hate to take one to the top of my cranium!
I have them in a desk drawer at work. I can grab them later this week & take some pics if anyone is interested, but I'll need someone else to post them. (I can email them to somebody...).
The NRA Firearms Fact Book has a chart that was built on a mathematical model that shows a 180 gr 30-06 PSP as having a vel of 180 fps if tumbling during return, 323 fps if falling base down, and 457 fps if it falls point forward. The height of the bullet at turn over is figured at 10120ft assuming it was fired at 90 deg to the earth @2700 fps. The book states a bullet fired at 90* to the earth will normally fall base first or tumbling and one fired at a angle to the ground will fall point first and have more impact vel. The BC of the bullet comes into play just as it does when figuring trajectory. The bullet also hits a point when the drag of the air and the BC equal out and the bullet stops gaining vel no matter how much farther it falls.
quote: A bullet struck Murr on the top of the head and exited at the bottom of his skull
If the bullets path was as stated above I`d question where that bullet came from.........That sounds like a lot of penitration for a "falling" handgun bullet.
Posts: 2535 | Location: Michigan | Registered: 20 January 2001
I'll bet you were a pure delight in Science class. Actually it's a good question. I certainly didn't know the answer, then again I was an Arts major. Do you have anymore like this? Best wishes.
G'day Mike 375, you are right, if and only if, you are shootin due east, or due west! And then only if you are leaning over your bench in such a way that your butt is at the same elevation as the muzzle - I don't want to go there!!!! If shooting north, you will have a very sore left butt, south, your right butt will feel the pain! Remind me NOT to develop your cartridge.
Posts: 1275 | Location: Sydney, New South Wales, Australia | Registered: 02 May 2002
Sorry Mike, couldn't resist it LOL - on a more serious note, when a projectile leaves a barrel, it's spinning. My (rough calcs) suggest that a 270 at 3000 fps is going to be rotating at something in the order of 180,000 rpm. There ain't NO WAY that that projectile is going to slow down enough to tumble and come down point first!! Am I right? Or wrong - don't be shy, I can deal with correction!
Posts: 1275 | Location: Sydney, New South Wales, Australia | Registered: 02 May 2002
You have to remember that the bullet that was stable and spinning at 180,000 rpm at 3000 fps is no longer stable when spinning at 180,000 at 0 fps. Remember how a bullet is unstable and will tumble when the spin rate is not optimumal for the bullet's velocity and weight? Same thing here, and also, you must remember that the spin will not remain 180,000, it will be affected by the force of drag also and will be slowed considerably. I would be very surprised to see the bullet not tumble on the way back down when shot at 90 degrees. However, when shot at angles much less than 90 degrees, the bullet will not reach a velocity of zero but will form an arc. Depending on the angle of the arc, it may or may not keep the bullet pointed nose first. The more shallow the angle, the more of its initial velocity the bullet will retain and the more likely it will be to travel point first.
Regarding the bullet tumbling at the top of the arc, I believe the applicable term for this situation is tractability. The rotational velocity of the projectile does not slow that much in flight, certainly not in comparison to linear velocity. Tractibility is the simple act of the bullet nosing over as it proceeds over its course, and is inversely proportional to Gyroscopic Stability(GS). GS increases as velocity decays due to reduced aerodynamic forces on the projectile and is capable of forcing 'alpha' beyond 5 degrees which may lead to tumbling. In the vertical path there are no aero forces other than drag and the projectile remains gyroscopically stable. Remember that gravity is a force, and when momemtum is lost it accelerates the bullet downward causing precession to occur.
Robert McCoy's book "Modern Exterior Ballistics" details many of the results of tests done concerning tractibility and GS, and reports that most projectiles will in fact tip over at or shortly after the top of their arc in this scenario. My recollection is that most will have a terminal velocity below 750 fps, in some cases much lower, it becomes a matter of coeficient of drag at that point.
I may not have explained this as clearly as he did, but then I'm not a rocket scientist. Toodle..
Just to correct something stated above. If two equally sized and shaped objects with differnt densities (weights) are released from the same level at the same time they will also impact at the same time.
The acceleration is caused by gravity and is the same for each object.
What we call weight is the function of mass x gravity (acceleration). In free fall(zero gravity) you have the same mass as you do on the earth but no weight. On the moon you have the same mass but 1/6 the weight. I weight 180 on earth and would weigh 30 lbs on the moon.
Posts: 226 | Location: New Mexico | Registered: 10 October 2003
I skimmed most of this post thread but in regards to Brents post, max velocity for any object falling through the atmosphere is approx. 180 mph. Maxiumum for a skydiver is approx. 120 mph. but usually isn't that fast because they're falling spread eagle.
Anyway, the maximum speed a bullet can attain on the way back down (unpropelled) is going to be right about 180 mph. This is the maximum. That equates to approx. 264 fps. Keep in mind the speed references above are approximations, but they're close.
Posts: 852 | Location: Austin | Registered: 24 October 2003
quote:Originally posted by NMwater: Just to correct something stated above. If two equally sized and shaped objects with differnt densities (weights) are released from the same level at the same time they will also impact at the same time.
I respectfully disagree....
Compare a balloon, blown up (with air) to the same size as a bowling ball, and a bowling ball. Do you really think they are going to hit the ground at the same time?
Regards, Bill
Posts: 1169 | Location: USA | Registered: 23 January 2002
I should have added this to my post. Maximum velocity at higher altitudes will be higher, but will slow as the object approaches sea level due to the change in air density. I believe that 180 mph and 120 mph numbers are for that density.
I do know that Kittinger got up to something like 600 mph on his decent from over 100,000 ft. Now that's crazy. There was supposed to be a lady that was going to try to break his record this last year, but I don't know if anyone ever did.
Posts: 852 | Location: Austin | Registered: 24 October 2003
Even at 1000 yards a 168 grain .308 bullet from a 308 Win. rifle will become unstable and sometimes hit sideways. Most bullets become upset as they pass though the sound barrier so most rifle bullets should tumble on the way down. A pistol bullet starts at below the speed of sound in most cases and would not undergo this phenomena perhaps? I wonder if the bullet in the article about the morons was a 230 gr FMJ from a .45ACP? That would sure do some damage at low velocity
Posts: 1554 | Location: NC | Registered: 10 June 2002
quote:Originally posted by Kingfisher: I skimmed most of this post thread but in regards to Brents post, max velocity for any object falling through the atmosphere is approx. 180 mph. Maxiumum for a skydiver is approx. 120 mph. but usually isn't that fast because they're falling spread eagle.
Anyway, the maximum speed a bullet can attain on the way back down (unpropelled) is going to be right about 180 mph. This is the maximum. That equates to approx. 264 fps. Keep in mind the speed references above are approximations, but they're close.
density and shape come into play.
a aerodynamic shape (like a bullet nose down) will reach a MUCH higher velocity. 180 might be for a round object (quite a bit of drag).
I once saw a glider do a pass at an airshow after a straight dive. 300+ mph. THAT was impressive.
Posts: 201 | Location: NJ, USA | Registered: 22 August 2003
im with o'le joe. if that bullet went thru the top of his head all the way out the bottom.than lets see u all say it comes down at 350/400 fps thats as fast as my cheapo pellet gun. have to tell those pesky wabbits [cottontails] who laugh at me when i hit them with it to look out.i would say there was someone in a tree at this meeting that didnt like this guy. festus psle'joe u got that right
Posts: 85 | Location: West Fargo, ND, 58078 | Registered: 01 December 2002
rugeruser....It is true that bullets rotate at about 180,000 rpm. I was always impressed with that and thought that a bullet actually "drilled" its way through flesh. But rpm is missleading when thinking about bullets. Don't think about the rotation over time, but distance. Bullet rotation is determined by the rifle twist rate, so your .270 is one turn in 10 inches. It will continue to rotate about it's axis at a rate of ounce every 10 inches as it moves down range, until it stops moving forward. When it hits an animal it will only turn two times (if that)as it penatrates 20 inches into the animal. Not drilling to me, maybe augering at best. But when the bullet is shot into the air 90 degrees to the ground and it stops it's upward travel at say 11,000 ft.; it also stops to rotate and will not rotate about it axis as it falls. This falling bullet would be the same as you dropping the bullet from your fingers while standing on a 11,000 ft ladder. Gavity will excellerate it until it reaches it's terminal velocity, as others have said, about 300 ft/sec and it will not rotate about it's axis. So it will have no stability.
Also, Bill M is correct; objects with different densities and the same size and shape will fall at differant rates in air. Density is mass per unit volume. So if you drop a 2" lead ball, a 2" magnesium ball, a 2" Tungsten ball, and a 2" balloon from the same height at the same time in air....the tungsten ball (19.3 g/cc)will hit the ground first, lead (11.4 g/cc)second, magnesium (1.74 g/cc)third and the ballon a distant last. We get confused when we are taught in school that objects fall at the same rate in a vaccum, but we don't live in vacuums. Thats interesting but impractical.
Johnny B: You're on the right track on rotational speed of a projectile fired from a rifled barrel, but not quite.
The rotational speed does not slow nearly as quickly as the forward speed. Let's assume with a bullet fired vertically, for purposes of illustration, that while the forward velocity slows to zero (due to gravity and air resistance)at the apex of its flight, that rotational speed has only slowed 10% (since gravity has no effect on rotational speed and air resistance has only minimal effect). This would mean that the bullet is traveling at zero FPS, but it is spinning at 162,000 RPM (assuming an initial RPM of 180,000). This may not be the right figure, but the rotational speed is certainly more than zero.
Similarly, with a bullet fired horizontally at a target several hundred yards downrange, the bullet's forward velocity may be only half of its muzzle velocity, but its rotational speed may be very nearly the same as when it left the muzzle. Assuming a rifling twist of 1/10, then the bullet would be spinning at the rate of 1 turn in 5 inches at the hypothetical downrange distance.
Posts: 13274 | Location: Henly, TX, USA | Registered: 04 April 2001
The firearm used in this "initiation" was a 9mm pistol. Haven't seen the type of ammo specified in any news report. But IMO that guy was directly shot, not wounded by a falling bullet. I don't think it's possible that a falling 9mm bullet could enter the top of a man's skull and come out the bottom.
Posts: 424 | Location: Bristol, Tennessee, USA | Registered: 28 September 2003
For anyone who hasn't read the whole story, the young KKK initiate was blindfolded, tied to a tree, and shot with paintballs while one of the Klannies fired a 9mm pistol in the air, apparently so the guy would think he was really being shot. Sounds like maybe they got it mixed up: "Lessee, paintballs at the guy. Bullets in the sky. Or was that the other way around? D'uh..." Else, maybe somebody really seriously wanted to "blackball" the pledge.
Posts: 424 | Location: Bristol, Tennessee, USA | Registered: 28 September 2003
The next question. Remember when we all were kids, and play'in cowboys&indians? How 'bout shooting an ARROW straight up?
Lucky to still be alive.......close, but no cigar! Kevin Gullette
Been there, done that.
When I was about ten or eleven, I invented a great game with my recurve bow: Shoot an arrow as straight into the air as possible, then run to get as close as possible to its impact point. I finally succeeded in getting right under it. Fortunately, I was only using semi-blunt target points and the arrow caught me on meaty part of the forearm. It just bounced off after slightly penetrating the skin (but I could see the scar for many years). I would say that the terminal velocity was significantly less than the launch velocity, or the arrow would have surely penetrated deeper.
Isn't it a miracle that such a high percentage of children actually survive to adulthood?
(P.S. I fabricated a great story for my mother about the wound being the result of accidentally banging my arm into a mesquite tree. She actually bought it, and the bow and arrows remained unconfiscated.)
Posts: 13274 | Location: Henly, TX, USA | Registered: 04 April 2001
Kingfisher, that is not correct. Free fall objects broke the sound barrier at least as early as WWII in the form of certain bomb types. Kittinger broke the barrier as well, but slowed as the air density increased. Terminal velocity is determined in free fall by gravity vs. drag. Objects with low Cd and high mass can surpass 180 mph handily.
Stonecreek.....you are not on the right track with regard to rotation of a bullet. If your twist rate is 1 in 10 inch that twist rate will not change downrange to say 1 in 5 inch. The RPM will change as the bullet slows the RPM will slow (i.e. 140,000 RPM). But regardless of the bullet speed, the bullet rotation will continue to be 1 in 10" two miles down range. The bullet can only rotate if it has forward motion. If forward motion stops, so will rotation. The rifleing has set the rotation to it's twist rate of 1 in 10". If the bullet stopped in the barrel, it would not continue to rotate, nor in air; the rotation is driven by the forward motion only.
Robert Rinker says in his book "Understanding Firearms Ballistics" that typical downhill(as opposed to straight up) velocities will run 450-500 fps with a "typical" spitzer bullet(pointy end down). I am searching McCoy's book for his info.
JohnnyB, I may have taken your last post wrong but just in case: Bullet RPM decays more slowly than forward velocity. MUCH more slowly. The spin imparted by rifling does NOT maintain a constant radial speed per foot traveled down range, but rather increases relative to velocity over the bullets flight. IF a bullet is fired vertically, it does NOT stop spinning at the apex of its flight and for that brief instant of time it resembles a top suspended in space. Stonecreek is 100% correct.
quote:Originally posted by Johnny B: Stonecreek.....you are not on the right track with regard to rotation of a bullet. If your twist rate is 1 in 10 inch that twist rate will not change downrange to say 1 in 5 inch. The RPM will change as the bullet slows the RPM will slow (i.e. 140,000 RPM). But regardless of the bullet speed, the bullet rotation will continue to be 1 in 10" two miles down range. The bullet can only rotate if it has forward motion. If forward motion stops, so will rotation. The rifleing has set the rotation to it's twist rate of 1 in 10". If the bullet stopped in the barrel, it would not continue to rotate, nor in air; the rotation is driven by the forward motion only.
Actually Stonecreek is EXACTLY right. During the Aberdeen testing 50 BMGs were fired "straight up" to verify their behaviour. Some of these rounds did land close enough to the protected barricades to be observed. After traveling up AND back down they continued to spin in the sand for a short time even after impact - indicating a great deal of retained rotational inertia.
Exatly what mechanism were you attributing the rotational braking to? It took steel to make it spin at that rate. With out the steel rifleing what could possibly drag on the bullet in the direction required to slow it down THAT rapidly? Physics and observed behaviour say that there is nothing to do that.
Thanks, Vibe, but I think we're arguing with a stump.
JohnnyB is convinced that somehow the same forces which act on the forward motion of the bullet act equally and proportionally on its rotational motion. By his rationale, if you take a toy hand-thrown top (the kind you throw at the floor while you hold onto the string wound around it), when it hits the concrete sidewalk and its forward motion stops then its rotation will also stop. Millions of children the world over will be disappointed to learn that their tops don't really spin on the concrete.
(BTW, I'm not a mechanical engineer, but I did stay in a Holiday Inn Express once. )
Posts: 13274 | Location: Henly, TX, USA | Registered: 04 April 2001
Q: How fast does a bullet lose its spin velocity? A:This question cannot be answered in general. As a rule, spin is much less reduced than velocity: An estimate for the M80 bullet (7.62 x 51 Nato) fired vertically up gives the following values: all of the velocity has been lost at the summit only approx. 36% of the angular velocity has been lost at the summit.
Posts: 13274 | Location: Henly, TX, USA | Registered: 04 April 2001
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There was supposed to be a lady that was going to try to break his record this last year, but I don't know if anyone ever did.
le'joe u got that right 
