The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading Velocity of a bullet in free fall?Go | New | Find | Notify | Tools | Reply | |
| Velocity of a bullet in free fall? | Login/Join |
| one of us |
Hi everybody! I was discussing this with a friend who said it was extremely dangerous to shoot straight up in the air. He had calculated that if you drop a penny from the tower of Eifel it would have such a speed that it would crush your head. I informed him about the friction of air and promised him that if he paid the trip to Paris I would gladly stand beneath the Tower of Eifel with only my ordinary cap on  .Now, my question to all of you, which speed does an ordinary "160gr" bullet get before it reach the state of equilibrium between gravitation and air friction? My guess (from ballistics tables) would give a speed at about 15m/s(50fps). Am I way off or? PerN | ||
|
| <Don G> |
At a guess, I'd say it would be closer to 500 fps. A human being (sky diver) has a terminal velocity of about 120 mph or 176 ft/sec. A bullet is a lot more dense. Don | ||
|
one of us |
Depends on if it is falling flat, base down or point down. But here are a few examples of terminal velocity for common objects. Terminal Velocity Examples | |||
|
| <Bill> |
the constant rate of gravity is -9.8ms^s^2 | ||
|
| <rolf> |
From what I�ve heard, getting smacked on the head with a 160 grainer freefalling is simular of being hit with a 22LR from a distance of 80 meters, app 90 yards. In my book that�s leathel. Wouldn�t want to stand in the way. Rolf | ||
|
| one of us |
I am shocked!!! You could explain the Magnus force and not such a simple thing as the speed of a falling bullet!!  I was impressed by Don G and Ricciardelli how a least gave me something to compare with, and that within minutes  That golfball has a speed I think could be comparable??? Since it is made to have minimum friction , while a bullet although denser, would probably go into spin (as jsirm informed) or do as boat in the wind, show it widest side to the wind? A speed of 35m/s (115fps) would give a energy of less then 6,5Joule, I think my cap would stand that PerN | |||
|
| <LReynolds> |
I remember a few years back reading a newspaper article of a 6 yr old child getting killed from a falling bullet which had come from a handgun fired up in the air. They estimated the velocity at 500 to 600 fps......LR | ||
|
| <Loren> |
Fired "up in the air" could mean anything over the roof of the house next door. There is a critical angle for maximum distance for cartridges. That angle is around 40 degrees. Firing anywhere close to this angle (+ or -) and the bullet is still far faster than terminal velocity at impact. Going the critical angle will result in less distance AND less impact velocity but slowly. So, for most "up" angles the impact velocity is far greater than that of a "dropping" bullet. Most people "shooting into the air" are not careful enough to ensure that they are shooting vertically or even close to vertical. The reporter that coverd the event probably had very little to go on other than 30 seconds from the investigating officer, and likely had no clue about what actual angle the shot was fired at. [This message has been edited by Loren (edited 12-07-2001).] | ||
|
| one of us |
Theres a lot of variables that go into figuring this out. You have to keep in mind not only how dense but the shape of the bullet. If anything drag is what causes a bullet to slow down the most, not air resistance. With this said it does matter what shape, length and wieght. You also need to figure how high its fired. If you look at a 80 grain .224 target bullet it would come down a lot faster with a lot more energy that a 165 grain .45. With this said its also not including freak accidents and comeplete coincidence. Ive seen deer shot with a .177 air rifle drop on the spot, and deer shot with a .30/06 run for hours. Either way im not going to make a guess at what the speed may be and im not planning on going out and try to catch my own bullets either. But if i were to take a "shot in the dark", if it were a flat base and full metal jacket i would guess around 250 fps. | |||
|
| <Don G> |
Hatcher says (p. 514) that the return velocity of the 150 grain service 30-06 was estimated at 300 fps. They took roughly a minute to return to the ground. He gives a theoretical answer of 320 fps, which agrees with the experimental data. He estimates that a 50 cal BMG round would fall at 500 fps. Don | ||
|
| <Don Martin29> |
The answer is in Hatchers Notebook. I am not positive but I think the testing showed it could be lethal. If your wondering. Don't do it. | ||
|
| <Antonio> |
They call them "Balas Perdidas" (lost bullets)over here... Years ago Mexicans used to like firing all sorts of guns into the air at New Years Eve and many people got hit by falling bullets. I know a girl who got hit on one leg while dancing and had to go to hospital to get the bullet removed. Antonio | ||
|
one of us |
quote: Actually, that's the figure for acceleration, not any constant velocity...that's why it's squared. | |||
|
| one of us |
Hmm... Maybee I should stay home and not try to convince him to test this at the Eifel tower PerN | |||
|
| one of us |
I remember an article in the Shotgun news, about Billy Dixon who supposedly shot an indian off the top of his horse at 1500+yds with his sharps...I recall that the physicists and other testers who did the math that the bullet would have to have 330 or so fps to be considered lethal...now that's with a .50cal projectile...and it turned out that the bullet would have had the velocity to kill the target at that distance and some to spare. So there is a relative number to compare with (.50cal @ 330+fps to be lethal) and I hope this helps straighten something out, otherwise I just added a post for nothing :P ------------------ [This message has been edited by the444shooter (edited 12-08-2001).] | |||
|
| <nated> |
according to that military test with the 30 cal returning spinning... supposedly one of the rounds came down on a piece of wood, leaving both spin marks (as stated above, very little resistance to spin)& a 1/32 inch dent, from the base, in the wood. according to calculations a 160 gr at 300 fps has about 32 ft/lbs energy. at the same time a 7.4 gr pellet at 900 fps has about 13 fps of energy. i wonder what a ballbearing has out of a slingshot? could be an interesting comparison, projectile, speed... a 45 gr. penny (average, use a newer one, they are about 40, old ones are 50), at 175 fps (generous) has a whopping 3.05 ft/lbs. now maybe if all the planets were in the right (wrong for you) order, and you pissed off the great shooter in the sky, that could kill you. 150 fps is about 101 mph. so if you get a pitcher throw a penny that fast, you don't get to go to paris. this also assumes that a penny will reach terminal velocity in the height of the eifel tower. | ||
|
| one of us |
This can be easily calculated...or impossible to calculate....  The easy way: Assssume the bullet is falling point down. All you need to know is its Cd (coefficient of drag). Unfortunately there is no direct conversion factor from a BC but it could be measured or calculated/estimated reasonably accurately. Then, the force of drag on the bullet by the air is f = Cd*A*.5*ro*V^2 where A is the frontal area in square feet, ro is the density of the air for the given conditions in slugs/cubic foot and V is of course, velocity in FPS. The force accelerating the bullet is simply equal to the acceleration of gravity 32.2 (depending upon where you are, in FPS) times its mass (in slugs). If you want to accept an estimate of the acceleration of gravity, it's already included in the english force unit (not mass) lbs--simply divide the bullet's weight in grains by 7000. The velocity at which those two forces are equal is the terminal velocity. It's that simple.
| |||
|
| <ppk1911> |
i remember a physics class i had in college where they asked the same question. the "answer" was that a bullet would have the same velocity/energy when it returned to it point of launch as it did "when it was fired".... i guessed that meant at the muzzle. i answered NO WAY is it possible and was marked incorrect-- i was told that even though the explosion of the powder puts a tremendous force on the bullet when it is fired, as soon as it leaves the barrel that force is removed and the only forces acting are friction (air resistance) and gravity-- both opposing the direction of motion. the professor went on to explain that on the way back down, the driving force acting on the bullet was much smaller but it acts over a much longer period of time (he neglected to mention anything about which direction it was pointing when it was falling-- nose up or down-- or say anything about spin stabilization or terminal velocity) another one of his questions always bothered me too: he conjectured, why in the movies do the bad guys always fly backwards when they're shot and the good guy just stands there one handing his/her .44Mag dirty harry style? (even worse are the number of movies where women are one handing .50 desert eagles and doing fast double/triple taps! yea right! ever see Mean Guns?) anyway he said that the ammount of energy dumped into the target must be equal to the ft/lbs the shooter absorbs-- yea right i said! i guess he'd never seen a reloading manual where there are separate columns for ENERGY and RECOIL ENERGY. these things always bothered me and i just didn't believe him. but since he was a professor at an ivy league school and i was just a lowly freshman i guess i eventually took his word for it. at the time i had never shot a gun before let alone ever seen a reloading manual. but the explanations he gave us just didn't make sense! had i known what a 577 Tyrannosaur was i would have said, "so professor, if what you say is true about target and shooter absorbing equal energy, and i shoot an elephant with my T-Rex and dump 10,000+ ft/lbs into the poor sucker, how come my shoulder is still in one piece?" hehe btw, this is my first post to the site and i just wanted to say what a great resource it is and how much i enjoyed watching all the videos! keep up the great work! | ||
|
| <Infidel> |
ppk1911, your professor was dead wrong on the first part. Jon A was exactly right. The only thing preventing us from calculating the terminal velocity of a falling bullet right here is that we do not know the pro0jectile's coefficient of drag. On the second, he was also wrong. The amount of momentum transferred to the target and to the shooter are equal in magnitude and opposite in direction. Energy is the product of momentum and velocity, so the bullet has a higher kinetic enrgy than the gun. It's a general principle in mechanics that momentum is always conserved, and is the thing of interest in analyzing the dynamics of an interaction. What school? | ||
|
| one of us |
ppk911 Infidel is exactly right. I am currently in college and had a very similar problem to the one you describe in some homework and on a test. The answer that the bullet will have the same velocity as when fired is correct IF you neglect air resistance. In my class we usually did. ------------------ | |||
|
| one of us |
Yeah, what those two guys said...in any physics class, it's almost ALWAYS a perfect scenario, (vacuum, no air resistance) and that's when the question in question would hold true, thus your professor would be right. Adding REAL WORLD factors into the problem, it's just plain common sense that the bullet's velocity final wouldn't equal velocity initial, thus making you right. ------------------ | |||
|
| Powered by Social Strata |
 | Please Wait. Your request is being processed... |
|
The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading Velocity of a bullet in free fall?
Visit our on-line store for AR Memorabilia
| View $GS_USERNAME's Public Profile |
| Add $GS_USERNAME to my Buddies |
| Add $GS_USERNAME to my Ignore List |
| Invite $GS_USERNAME to a Private Topic |
| View Recent Posts by $GS_USERNAME |
| Notify me of New Posts by $GS_USERNAME |