Quantcast
  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Would a bullet travel farther in a vacuum?

Discussion in 'General Gun Discussions' started by ehanger, Jul 21, 2011.

Thread Status:
Not open for further replies.
  1. ehanger

    ehanger Member

    Joined:
    Nov 12, 2010
    Messages:
    21
    If you fired a rifle at a perfectly horizontal angle (zero degrees), would the bullet travel farther if there was a vacuum?

    On one hand you have air resistance slowing the bullets horizontal velocity, which would serve to decrease the total distance traveled, but then at the same time the air beneath the bullet would act as a cushion slowing its vertical descent, which would increase the total distance traveled.

    I'm guessing that the bullet would travel farther in a vacuum, because if you take an object moving at supersonic speeds in the X dir and only a small fraction of that speed in the Y dir (falling speed), the force of air resistance is doing much more to slow the bullet down horizontally than vertically. In other words air resistance is hindering the bullet more than it is helping.

    Any physicists here care to explain?
     
  2. gathert

    gathert Member

    Joined:
    Feb 18, 2011
    Messages:
    419
    Location:
    Clemson, SC, Good old USA
    I'm going with a yes on this one. Gravity is constant, but air resistance would seem to be the difference maker.
     
  3. ants

    ants Member

    Joined:
    Nov 24, 2007
    Messages:
    3,710
    No, the air above the bullet pushes down on the bullet, speeding up its vertical descent.




    Well, if everyone else can make up a dumb theory, so can I. :p
     
  4. ants

    ants Member

    Joined:
    Nov 24, 2007
    Messages:
    3,710
    Fired horizontally to the plane of the earth:

    The only thing decelerating the bullet is air drag, until the bullet hits its target.

    Gravity is actually accelerating the bullet downward, just as it accelerates all falling objects.
     
  5. THplanes

    THplanes Member

    Joined:
    Mar 12, 2010
    Messages:
    115
    Location:
    DFW
    Fire two bullets, one in a vacuum and the other in air. Discounting the curvature of the earth, the bullets would hit the ground at the same time. The bullet fired into air will have lost a great deal of velocity due to friction with the air, while the bullet in the vacuum will have lost no velocity. The the bullet in a vacuum goes much further.
     
  6. BeerSleeper

    BeerSleeper Member

    Joined:
    Mar 24, 2010
    Messages:
    688
    Farther. Assuming a bullet fired horizontally (at 90 degrees to your gravity vector), the effect of air resistance on the vertical component of the bullets velocity is insignificant in comparison to the effect of air resistance on the horizontal component of it's velocity.
     
  7. Geckgo

    Geckgo Member

    Joined:
    Dec 14, 2010
    Messages:
    784
    Location:
    Southern Louisiana
    Yes the bullet would travel farther, brace a gun in a vice on the salt flats, fire one shot, then suck all the air out of the atmosphere, fire another shot, the second will go farther. The reasoning is pretty simple, they both fall at the same speed, regardless of air, because the resistance due to air along the "down" axis is going to be small enough to ignor completely for a bullet. If we were talking feathers then there might be something to consider in that respect, but terminal velocity for a bullet is fairly high compared to that of a feather.

    The reason the second would go farther is because it will not bleed off velocity due to friction with the air, known as drag. If it takes off at 3000 ft/s, it will still be going that fast when it hits the dirt.

    I believe this is explained better by saying if you shoot a bullet horizontally and drop another next to the barrel, they both hit the ground (assuming it's flat) at the same time.
     
  8. 303tom

    303tom member

    Joined:
    Jul 16, 2011
    Messages:
    4,059
    Location:
    Missouri
    Sounds like a Myth Buster thing !
     
  9. JohnBiltz

    JohnBiltz Member

    Joined:
    Aug 17, 2010
    Messages:
    1,610
    Location:
    Phoenix, AZ
    Look to the 6.5 Grendel for the answer. It flies so well because the shape is so efficient. With no air every bullet would be like that only better, a lot better.
     
  10. Geckgo

    Geckgo Member

    Joined:
    Dec 14, 2010
    Messages:
    784
    Location:
    Southern Louisiana
    hmm, does make me wonder though, if you fired them off the edge of a cliff horizontally, giving time for air friction to take it effect,,,, *scribble scribble* I'll get back to you.
     
  11. Amb

    Amb Member

    Joined:
    May 11, 2011
    Messages:
    28
    Location:
    Parker, Colorado
    if it's all the same to you, I'd rather you did the second shot on the Moon. I'm rather fond of breathing.
     
  12. Geckgo

    Geckgo Member

    Joined:
    Dec 14, 2010
    Messages:
    784
    Location:
    Southern Louisiana
    ^--maybe you don't deserve air if can't see the need to sacrifice ourselves in the name of SCIENCE!!! hahaha j/k
     
  13. ehanger

    ehanger Member

    Joined:
    Nov 12, 2010
    Messages:
    21
    On earth, any object in free fall will be slowed by air resistance. If it falls for long enough it will stop accelerating due to the effect of terminal velocity. Bullets when fired from a gun are in free fall (accelerating downwards) despite the extremely high horizontal velocities. You could take two bullets held at the same height, drop one from your hand and fire the other from a gun at 1000's of ft/s and they would both hit the ground at the exact same time.

    If you take those same two bullets and drop one in a vacuum and the other in an atmosphere, the bullet in a vacuum will hit the ground first (assuming the same force of gravity). When you drop something there is the acceleration due to gravity but also the deceleration due to air resistance. As an object accelerates downwards the force of gravity remains constant but the force of air resistance rises exponentially. Eventually, the force of air resistance cancels out the force of gravity. When this happens the object stops accelerating and falls at a fixed speed (terminal velocity). Any changes in the shape or density of the object as it falls will affect its terminal velocity.

    What I'm saying is that air resistance doesn't only slow a bullet down horizontally, it also slows it down vertically. If there wasn't any air resistance, bullets would drop much faster than they currently do. But as most people know they would also retain their muzzle velocities even at long range.
     
  14. Iramo94

    Iramo94 Member

    Joined:
    Jul 16, 2011
    Messages:
    266
    Location:
    South Florida
    We actually could do an experiment about this. Using very accurate clocks, drop a bullet in air, then drop the bullet from the same height in a vacuum chamber. That accounts for the Y-axis drag. I would assume that is so small that it is within the inaccuracy of the clock. Then, on a small scale, shoot a gun at sea level, and again on a plateau a few hundred feet up. There's nature's vacuum for you! Do a few different shots at different altitude, then graph them and expand the line until air pressure = zero. If the line is anything but vertical (or horizontal if you ride that bus), the vacuum wins. I would guess the vacuum does win, because I play mountain golf courses one club shorter than sea level courses.
     
  15. Geckgo

    Geckgo Member

    Joined:
    Dec 14, 2010
    Messages:
    784
    Location:
    Southern Louisiana
    wow, this is tricky, I'm getting old and my differential equations is a little rusty, I think I'm onto something here though with the cliff analogy. Assuming a ~230gr bullet with a mussle velocity of ~990fps (staying away from supersonic problems if you don't mind).
     
  16. oerllikon

    oerllikon Member

    Joined:
    Dec 24, 2010
    Messages:
    141
    Location:
    Western Wisconsin
    If you watch videos with a vacuum chamber, a feather and hammer dropped at the same time, hit the same time. I think the drop rate on anything is 32 ft per second per second. So theoretically, one bullet fired in a chamber, and one bullet fired in the atmosphere: The vacuum chamber one would hit the ground at the same velocity it started, and the one in atmosphere would hit the ground at a lower velocity.
     
  17. Iramo94

    Iramo94 Member

    Joined:
    Jul 16, 2011
    Messages:
    266
    Location:
    South Florida
    with a feather, the answer is easy. The problem is that bullets are more like hammers than feathers. They are aerodynamic and have a good mass-to-surface area ratio. Has anyone ever done a vacuum to nonvacuum hammer drop comparison on video?
     
  18. shiftyer1

    shiftyer1 Member

    Joined:
    Jun 26, 2008
    Messages:
    1,649
    Location:
    central texas
    nope an old kirby stopped a weak 38 round dead ;)
     
  19. Geckgo

    Geckgo Member

    Joined:
    Dec 14, 2010
    Messages:
    784
    Location:
    Southern Louisiana
    the difference in bullet drop with or without air is negligable unless it drops far enough where friction will take an effect.
     
  20. Sheepdog1968

    Sheepdog1968 Member

    Joined:
    Jul 20, 2009
    Messages:
    3,518
    Location:
    CA
    in the ballpark for the Colorado Rockies, the air is thinner (mile high stadium). Basebals definately travel further and lots written about it. Read a book a decade ago called Physics of Baseball. Same stuff would apply to bullets.
     
  21. Geckgo

    Geckgo Member

    Joined:
    Dec 14, 2010
    Messages:
    784
    Location:
    Southern Louisiana
    guys, let's stay focused, your baseballs and atheletes are preforming better primarily do to a different gravitation force rather than the miniscule difference in air pressure. If you go high enough you get into what is called geosynchronous orbit, which is another matter entirely.. back to the regular programming.

    I want to congradulate ehanger. Though the question seems benign in nature, when fired from normal benches, the vaccum will always carry the bullet further (and I thought this thread was going to be about space guns :D ) . You, ehanger, have however given me a mathematical puzzle that is going to keep me up this morning. All conventional means of solving this problem are trash, and I have to resort now to specific cases and whatnot to figure out which would go further if fired from atop a tall cliff or the top of a building. It seemed like such an innocent question, but the math to figure it out is chipping away at the physics part of my soul. I applaud your question, and if I do manage to scratch out an answer this morning I will be sure to post it. If I ever teach a physics class, I'm putting this question on the final. hehehe :D
     
  22. Oathkeeper1775

    Oathkeeper1775 Member

    Joined:
    Jun 3, 2011
    Messages:
    138
    Location:
    Oregon Coast Range
    Relativity

    Relatively speaking...there is no such occurrence where there isn't a vacuum of some level or degree in any environment, relative to the object(s) moving through or within them.

    Zero pressure or negative vacuum? There are different degrees of vacuum. If a bullet is in an environment where there is enough vacuum; it could explode.

    I can't back that up :D
     
  23. gamestalker

    gamestalker member

    Joined:
    Sep 10, 2008
    Messages:
    9,832
    Location:
    SW Arizona
    Deffinitely not a myth buster thing, it is based on physical facts. If fired in a total vacume, in other words zero atmosphere, it will maintain the same velocity at the muzzle up until gravity has brought it to the ground. So trajectory is going to very different due to the absolute absence of drag. The bullet is going to get from point A being the muzzle, to point B in the same time frame. For the sake of all things being equal, the bullet is going to travel much farther without any atmosphere to drag on it, but that doesn't change the amount of time they take to contact the ground if both are released at the same time and from the same hight.
    This kind of reminds me of an old bench rest shooter friend that engaged me in an argument about bullet rise. He was insistent that a bullet rises after leaving the muzzle and would hit the ground at a different time, than a bullet being dropped from the same exact hight from the ground. In all the years of loading and shooting with him I never was successful in educating him about trajectory, or the fact that the air pressures is equal on all sides of the spinning bullet because there is nothing about the shape of a bullet that provides any lift. To attain lift it requires higher air pressure on the under side of the bullet and lower air pressure on the top side of the bullet to create what is refered to as lift, which is accomplished by air foil. Very simple fact of the physics involved if one gives it just a minimal degree of thought.
     
  24. Geckgo

    Geckgo Member

    Joined:
    Dec 14, 2010
    Messages:
    784
    Location:
    Southern Louisiana
    okay, this is what I've got,, I can't do the math, but the time elapsed differentials are pointing to something clever. Over the first second, the bullets will both drop 4.9 meters, the one in air is a tad less but nothing to worry about without looking at a lot of decimal places. The one in air has slowed considerably, whilst the one in vaccume is still cruising at it's higher velocity. This first second gives the vaccum bullet enough of a lead that falling in a perfect parabola, the air bullet should never be able to catch it. In certain cases (oddly shapped bullets, something like a flying pin), the air bullet may catch it at some time after reaching terminal velocity, where it's curve will straighten a bit, but it will still be slowing down. In other words...

    Look at time alone, at any time the one in vaccume will have a lead on the air bullet, but for enormous drops, the vaccum bullet will hit the ground sooner, but go out to infinity, and the air bullet hits a vertical asymtope, which means it has a maximum range, no matter how long you let it drop, and will at some point reach a vertical slope where it is just in free fall. The vaccum bullet doesn't have this threshold and will continue forward forever. So while the line comes closer around terminal velocity time, I don't think that the airborne bullet ever has a chance of outperforming the vaccum bullet. The equations are giving me a headache, but this is what I'm seeing. If you ever need a physicist, gimme a call ;)
     
  25. Geckgo

    Geckgo Member

    Joined:
    Dec 14, 2010
    Messages:
    784
    Location:
    Southern Louisiana
    and there is no such thing as negative vaccum, oathkeeper, just fyi. Though creating a perfect vaccume poses a problem, even in space. Unless there is a hollow center filled with compressed air, I think the bullet is safe from explodies ;)
     
Thread Status:
Not open for further replies.

Share This Page