Ballistics Question

Discussion in 'Shooting, Hunting and Fishing' started by Tartan_Terrier, Jan 24, 2009.

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  1. I bought a book on hunting yesterday (Jagt I Norden) and while flicking through it found a statement that seemed odd.

    It said that if you fired a horizontal shot along a pefectly flat field, and at exactlythe same moment dropped a bullet from the same height as the muzzle both bullets would hit the ground at the same time.

    Is this correct? Surely the bullet fired would be in the air for longer due to it's horizontal momentum.... Or am I mistaken?

  2. Assuming no aerodynamic effects, it is absolutely true.

    Horizontal momentum acts, by definition, in the horizontal and has no effect whatsoever in the vertical.

    It assumes that the barrel is absolutely horizontal, which is rarely the case in the real world.
  3. Sympathetic_Reaction

    Sympathetic_Reaction LE Book Reviewer

    It is true, assuming a whole load of 'ideal' conditions. It's the initial method of aerodynamic assessment that they teach at uni...the real world is different due to lots of non-ideal conditions that exist.

    The one that took me a bit of time to absorb was curvature of the earth and earth spin effects on ballistics.

  4. The book is correct. Aerodynamic effects may make a tiny difference but nothing from a practical point of view.

    You can test it yourself with a couple of marbles etc.
  5. The other one that messed with my head for a while was the penny and the feather in the vacuum tube - both fell at the same velocity.
  6. There has been a lot in ballistics that has messed with my head. Coriolis effect, the magnus effect, the idiot effect..................
  7. Biped

    Biped LE Book Reviewer

    It is right. What we are talking about is the rate of acceleration on a free-moving body caused by gravity.

    Thus, a feather, in a vacuum will accelerate towards the deck at the same rate as, say, a bullet. The density of air is what slows the feather down, not a reduction of the effect of gravity.

    The horizontal momentum matters not . . . . up to a point. If the bullet is travelling at relativistic velocities, it will actually get further away from the ground because of the curvature of the Earth.

    If you drop a 1 tonne steel block off the top of the Eiffel tower, at the same time as a marble, they will both hit the deck at the same time.
  8. As long as its in a vacuum :p
  9. Whether I put a bullet OR a marble in the vacuum between my ears, I would hit the ground at the same (relative) time
  10. Biped

    Biped LE Book Reviewer

    Does it take into account the deceleration of the objects on hitting the girders though?

    I would suggest that the marble may actually bounce back up a ways before falling again, whereas the 1 tonne steel block will actually only slow somewhat as it crashes through some of the girders, which would accelerate said girders, along with most of the ones above the POI in a downward direction, at ever-increasing speed through the remaining structure. Depending on which way the wreckage (and the 1 tonne steel block) falls, the marble may, in actual fact keep bouncing off the various bits all the way down and actually arrive on the ground after both the 1 tonne steel block AND the Eiffel Tower. It may be that the marble arrives at ground level a full ten seconds after the steel block, in bits.
  11. Isn't he talking about the bullet drop there, rather than your Eiffel Tower analogy?
  12. Biped

    Biped LE Book Reviewer

    mmmm, could be. I'd rather visualise the process than wrk it out mathematically - I'm cr@p at maths.
  13. Biped

    Biped LE Book Reviewer

    Thanks for the informative update.

    Are you suggesting that, on facing a force accelerating toward it, the French concrete may, rather than stop the mass, crumble and disappear, allowing the mass to continue through, only to be be stopped by another country's concrete - one made of sterner stuff perhaps?

  14. (My highlight)

    Good grief, Biped — what kind of guns do you sell?? I think this one goes beyond your local civpol: expect a visit from the Men in Black. :eek: