Mythbusters: bullet fired vs. bullet dropped video...

Discussion in 'Rifle Country' started by saturno_v, Aug 20, 2015.

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  1. saturno_v

    saturno_v Member

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    I did watch this interesting video by the Mythbusters gang.

    I believe it is in 4 or 5 parts, first segment is here:

    https://www.youtube.com/watch?v=2tiOmp1BE8Y


    I did not expect dramatically different results but I was a bit surprised that the fired bullet did not generate any kind of lift whatsoever....the two bullets touched the ground at the almost exactly same time.

    Granted, because of space concerns they performed the test on a 1911 45 ACP pistol, low speed cartridge, not particularly aerodynamic bullets (round nose FMJ) inside an empty and long San Francisco warehouse.

    Do you think the test performed with a FMJ spitzer bullet fired from a 308 or a 30-06 would have yielded exactly the same results or these very aerodynamic bullets would generate a bit of lift??


    So bullets drop indeed, they do not fly.....
     
  2. taliv

    taliv Moderator Staff Member

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    why did you expect lift?


    i'm not saying anybody really understands gravity, but it does seem fairly predictable.
     
  3. MrBorland

    MrBorland Member

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    Of course. The only vertical force on a dropped bullet and a bullet fired from a level barrel is the force of gravity. The same force on the same mass equals same acceleration downward.
     
  4. rcmodel

    rcmodel Member in memoriam

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    Of course bullets don't 'fly'.
    How could they?

    They are round, and spinning rapidly.

    So any aerodynamic lift would be as likely toward the ground as toward the sky.

    They start falling as soon as they leave the barrel (which was all that was holding them up.)

    Remember Sir Isic Newton and the apple from grade school science?

    https://www.york.ac.uk/physics/about/newtonsappletree/

    rc
     
  5. JSH1

    JSH1 Member

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    As they said in the intro, this is a textbook physics problem. The vertical force of gravity in the Y axis is the same no matter how fast an object is travelling horizontally in the X axis.
     
  6. 10mm Mike

    10mm Mike Member

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    Not to be nit picky, but the mass is irrelevant. They will accelerate towards the ground at the same rate. One could have been a 115gr 9mm and the other a 230gr .45, and they still would have hit the ground at the same time regardless of which one was dropped and which one was shot.
     
  7. Slamfire

    Slamfire Member

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    I am going to say, had they shot a 22lr into a headwind, the dropped bullet would have hit the ground before the inflight bullet.

    This is based on my experience shooting 22LR match bullets in small bore prone competition. I have seen the bullet impact go up with 12 0'C puffs of wind. These 22 LR bullets are ballistically inefficient, I think on a par with spit balls and tissue paper. Every puff of wind causes the things to float with the wind, which is why wind separates the men from the boys in Smallbore prone.

    Gravity of course is real, and in a vacuum, it is simple to model drop speed. However there are media, such as air, (planes anyone) and water (surfboards), that will effect the drop rate of an ballistically inefficient object.
     
  8. MrBorland

    MrBorland Member

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    I said as much, though I agree my explanation was confusing. The force of gravity is the same, so, yes, objects of any mass accelerate down equally.
     
  9. redneck2

    redneck2 Member

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    Uhhhh....no.

    Now, I believe that your bullet hit high, but it's because the barrel of the rifle is angled upward and the wind is pushing against the bottom side of the bullet nose
     
  10. saturno_v

    saturno_v Member

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    In a vacuum yes, in the real world atmosphere not, you have to take into account aerodynamic drag.
     
  11. 10mm Mike

    10mm Mike Member

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    True, real world atmosphere does play a role, but in this particular case it is so insignificant it can be disregarded. Now, at a higher drop distance with different test subjects it will make a world of difference.
     
  12. DanTheFarmer

    DanTheFarmer Member

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    The only difference I can see in the atmosphere vs. vacuum situation is the slightly different drag coefficients caused by the change in profile of the bullets.

    The only motion that is relevant is the vertical motion.

    In the atmoshpere:

    For the dropped bullet, dropped nose down, the ballistic coefficient is well known. It is the "published number".
    For the fired bullet, travelling nose first in a horizontal direction and "sideways" in the vertical direction, the ballistic coefficient will be different and larger.

    For the relatively low vertical speeds this difference should be absolutely minimal.

    In a vacuum, the orientation of the bullet will not matter since there is no aerodynamic drag.

    Dan
     
  13. Scooter22

    Scooter22 Member

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    No bullets won't "lift" like a wing of a plane or a aircraft built with a lifting body. But if your real good you can curve them. Just be careful you don't curve it so much you shoot your own butt.:rolleyes:
    https://www.youtube.com/watch?v=lGZQi3ODB-U
     
  14. H&R Glock

    H&R Glock Member

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    Mythbusters: Proof that a 10 minute show can be made to last an hour.
     
  15. MachIVshooter
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    MachIVshooter Contributing Member

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    As DanTheFarmer pointed out, if you were timing in microseconds, yes, you might see slightly different impact times in real-world testing due to the different drag coefficients caused by bullet orientation. Of course, dropped from shoulder height, it may not matter, as the distance is insufficient for either bullet to reach it''s terminal velocity.

    All things falling at earth gravity accelerate at 32 FPS per second, up to their terminal velocity, which is gravitational force vs. density and aerodynamic drag. A feather and a piece of iridium accelerate to their terminal velocities at the same rate; the Ir ball just has a much, much higher terminal velocity.
     
  16. rcmodel

    rcmodel Member in memoriam

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    But, a higher BC will not change the acceleration of gravity.

    A bullet with a high BC will go further, faster, before it hits the ground.

    But, fired level with the ground, it will in fact hit the ground at the same exact time as one dropped from the same height at zero forward velocity at the muzzle.

    rc
     
  17. Aragon

    Aragon member

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    Absolutely true. An exaggerated situation -- a lead slug and a large feather weighing the same won't hit the ground at the same time if they are dropped from the Empire State Building at the same time.

    They would though if they were dropped in a vacuum however.

    Given the high rotational velocity of a fired projectile (~250K RPM or so?), I could definitely see how geometric differences in the projectiles could cause enough of a difference in drag to cause differing "drop times" -- if one had sophisticated enough instrumentation to record the differences.
     
    Last edited: Aug 20, 2015
  18. Aragon

    Aragon member

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    But the vertical aerodynamic drag of two projectiles flying (or "dropping" if you prefer) through the atmosphere could be different enough to determine where they ultimately land. The difference might be tiny and the MB's may have not had the instrumentation to accurately measure the difference, but it exists.

    32 feet/second/second is in a vacuum...
     
  19. MachIVshooter
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    MachIVshooter Contributing Member

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    No, it's absolute. What changes in a vacuum is that the terminal velocity becomes infinite with no resistance; the object will continue to accelerate until it hits something.
     
  20. Aragon

    Aragon member

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    I'm not talking about a falling projectile with respect to the ground. I'm talking about two projectile dropping to Earth compared to one another.

    The feather with the same mass as the slug isn't going to hit the ground at the same time -- unless both bodies are under a vacuum.
     
  21. DeepSouth
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    DeepSouth Contributing Member

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    I didn't even take high school physics and even I can figure this out without much thought at all.

    The force of horizontal acceleration has nothing to with the force of vertical acceleration, so, yes they'll both hit the ground at the same time. Obviously their are a ton of variables, but if they're all the same then they'd definitely fall at the same rate therefore hitting the ground at the same time.


    This isn't rocket science, at best it's middle school physics.

    Or possibly, I'm an uneducated idiot that just thinks I'm right. Lol
    Just doesn't seem complicated to me at all.


    I'd love to see Mythbusters take on building a light bulb with 1889 technology, they'd concluded it couldn't be done....and yet, it was.
     
  22. Aragon

    Aragon member

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    Sorta sad how people keep trying to conflate the X and Y axis here.

    Like it or not, different things don't fall to the Earth at the same rate unless they are in a vacuum. A lead bullet projectile with a mass of 1 slug (pun intended) will hit the ground before a large feather also with a mass of 1S. The projectile is cleaner aerodynamically and accelerates faster. The feather would float to some degree.

    Now the difference between two geometrically different lead projectiles of the same mass over say 5' of vertical drop would be infinitesimally smaller but there would still be a difference.

    Odd some cannot grasp that and continue to attempt to pull the horizontal component into into play to muddy things up.
     
  23. MachIVshooter
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    MachIVshooter Contributing Member

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    No. They both accelerate at 32 ft/sec squared. The reason they won't hit the ground at the same time is that the object with lower density and/or higher drag attains a lower terminal velocity. Both accelerate to their respective terminal velocities at the same rate, vacuum or not. It's the disparity in terminal velocities that results in different times of descent.
     
  24. JohnKSa

    JohnKSa Administrator Staff Member

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    Acceleration is the result of force.

    Each object (as soon as it starts falling) will have two forces acting on it in the vertical direction. The downward force due to gravity and the upward force due to drag.

    Each will accelerate at a rate based on the magnitude and direction of the net force.

    The object with the high drag, at any given downward velocity greater than zero, will have a much larger force in the upward direction generated by drag and that will result in a much lower net force in the downward direction. It will accelerate slower due to the smaller net force in the downward direction and will reach a lower terminal velocity. At terminal velocity, the drag force will equal the force of gravity and there will no longer be any net force. At that point the balanced forces will mean no acceleration and the object will continue to fall at terminal velocity.

    The object with low drag will have very little force generated by drag which will mean that there will be a larger net force in the downward direction. It will accelerate at a higher rate and reach a higher terminal velocity.
     
  25. JDGray

    JDGray Member

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    Bullet lift.....:D
     
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