Which hits the floor first – a dropped bullet or a fired bullet?

A good question, talked about in pubs everywhere we think. Well the Discovery Channel’s ‘Mythbusters’ tested the theory that they both hit the floor at the same time. See above for their findings and click here for the math behind the theory. – Deskarati

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6 Responses to Which hits the floor first – a dropped bullet or a fired bullet?

  1. alfy says:

    This gets the Alfy Bum Clip Award (ABCA) of the week. It has a perfectly simple concept and yet the clip is totally and utterly confusing. It is never clear as to what has actually been established by experiment.
    One of the commentators on the main blogsite made a very simple and sensible contribution. “So, one other reason a fired bullet won’t hit the same time a dropped bullet will. It has vertical, upword movement; a dropped bullet does not.” Does this not depend on whether the bullet is fired from the exactly horizontal or not?

    • Deskarati says:

      This clip is from the Mythbusters series on the Discovery channel. I have watched the show many times and can advise that they are usually unbiased and very thorough. So I would expect that they would have checked that the bullet left the barrel horizontally.

  2. alfy says:

    Were you not confused by the clip, Jim?

  3. Deskarati says:

    My impression is that, because the experiment is over a relatively short distance the only measurable effect is due to the air and the bullets flight through it. With the shape of the bullet offering some ‘flight’ or vertical upward movement (even a plane can fly upside down) it takes slightly longer before it hits the ground than the dropped bullet, even if the bullet leaves the barrel exactly horizontally.
    In my opinion this has no bearing on the ‘thought experiment’ that both bullets are equally effected by gravity. This is beyond my comprehension, so I’ll do my usual guess work. If you extrapolate from one extreme to the other, at its slowest speed the bullet leaving a gun will hit the floor at the same time as the dropped bullet (excluding air resistance) and at its fastest speed the bullet could actually escape the earth’s gravitation pull and not land at all. So as always the truth of the argument is probably in how the question is phrased.
    Whether a bullet can actually be fired that fast, I have no idea, but would guess not.

  4. Steve B says:

    I promised myself that I would not comment on this subject, but hey ho …

    Let’s assume that the force of the gun propels the fired bullet strictly horizontally. Thus, the only downward force in play is gravity, which acts equally on both bullets. Therefore they both hit the ground at the same time. (Assuming a vacuum)

    However, If the fired bullet travels only a short distance, then yes, both bullets hit the ground at the same time. However, if the fired bullet travels far enough, the earth, being round, curves away from it. (Remember Newton’s first law of motion: moving objects tend to travel in a straight line.) Since the fired bullet has farther to fall, it takes longer to hit the earth, so the dropped bullet hits the ground first.

    What’s more, if the fired bullet travels fast enough (roughly five miles per second — a practical impossibility given atmospheric friction, but never mind), it goes into orbit around the earth and never hits the ground at all.

  5. Deskarati says:

    You should have kept your promise Steve, now your stuck in the loop.

    So if the starting data is (‘a short distance’ = both hit at the same time) and the end data is (the fired bullet ‘never hits the ground at all’) then the problem seems to be describing ‘a short distance’ as the curvature of the earth must apply throughout.

    As the force of gravity is radial, doesn’t it apply equally along the route of the bullet being fired. If so, at what speed would the bullet start having an effect against gravity? (I’m thinking at any speed above zero). And if that’s correct (and I’m sure I probably missed something) the dropped bullet always hits the ground first.

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