Which bullet hits ground 1st: Dropped or shot w/o obstacle?

[surprise_i'm_armed]

Let me credit the source of this question and answer:
Parade Magazine (Sunday supplement to other newspapers)
10/17/2010. The column is "Ask Marilyn", who is Marilyn
vos Savant, self-appointed smarty pants. :-)

Q. Say you shoot a bullet straight across an open, perfectly level plain.
Simultaneously, you drop a bullet from the height of the gun barrel.
Which one will hit the ground first?
Cheryl Smith, Anaheim, CA

A. In theory, both will strike the ground at the same time.
Contrary to intuition, the sideward force doesn't interfere
with the downward force.
The gunshot sends the bullet across the plain while gravity
takes it down.

[gigag04]

If you assume a vacuum, yes.

[Dragonfighter]

If you assume a vacuum, yes.

Exactly, the air that the bullet travels through generates lift. Thus in the course of the trajectory the bullet can actually rise (30.06 comes to mind as an exceptional example) gaining altitude. Only until the velocity degrades to where the bullet no longer can equalize the forces of drag and gravity does it arc into the ground.

[gigag04]

I don't think a a bullet generates net lift. The "lift" generated by the sloped nose acts in all directions equally, unless I'm missing something.

[Bullwhip]

If you assume a vacuum, yes.

Exactly, the air that the bullet travels through generates lift. Thus in the course of the trajectory the bullet can actually rise (30.06 comes to mind as an exceptional example) gaining altitude. Only until the velocity degrades to where the bullet no longer can equalize the forces of drag and gravity does it arc into the ground.

Nope, no such thing as bullet lift. Bullets "rise" because because they are fired on an upward trajectory. If a bullet leaves the gun "flat" with the earth, it falls to the ground and never reacheas the point of aim.

No such thing as "flat", either. The earth curves. "flat" = "tangential". Gravity curves with the surface, so "flat and straight" is a curve. Confused? Me too, I can't explain it, but I understand it.

[Bullwhip]

I don't think a a bullet generates net lift. The "lift" generated by the sloped nose acts in all directions equally, unless I'm missing something.

Yeah, what I tried to say.

[Teamless]

Mythbusters did a spot on this. The dropped bullet hit the ground first, but it was a microsecond difference whichever way it went.
http://www.youtube.com/watch?v=D9wQVIEdKh8" onclick="window.open(this.href);return false;

[Dragonfighter]

In discussing the Bernoulli Principle (increase in fluid velocity decreases pressure) you can fly a brick, given enough thrust to overcome the monstrous drag and gravitational effects. A perfect sphere at sufficient velocity generates disparate pressures in the upper and lower hemispheres due to a slight increase in the lower hemisphere by the sphere's "pressing down" on the lower stream, thus slowing the fluid (air) and increasing its pressure as it flows around the lower half. As long as sufficient velocity is maintained, the sphere will continue to fly.

A boat tailed projectile should experience the same effect, to a lesser degree admittedly, but still generating a nominal lift. There is also gyroscopic progression that will increase the effect on the lower half favoring the descending side of the rotation (Magnus effect IIRC). A perfectly smooth bullet will experience negligible effect but we know a round is grooved or faced coming from a rifled barrel. A round nose bullet has a disadvantage as it is also suffering from parasitic drag on the flat trailing edge due to low pressure.

Now firing in a vacuum on a mathematically "flat" plane would be interesting. There would be no air to act either positively or negatively on the projectile so there is just gravity vs. inertia. And forward velocity is supposed to be independant of gravity. I'd suspect a much shorter trajectory and possibly the "simultaneous" impact theorized.

Of course I could be wrong as she who must be obeyed oft reminds me.

BTW, Given a perfect sphere, if you double the velocity, you quadruple the drag.

[RPB]

Long answer:
In theory .......In a vacuum
if the fired bullet went far enough and had a perfectly flat trajectory,
due to the curvature of the Earth, once the bullet passed the horizon,
even without "rise" it would be farther up from the ground, relatively, than it was where it started,
because the Earth is farther down, relative to the straight line trajectory.

However, which would hit first then, would relate to the amount of mass, and diameter of the Earth, moon or object beneath it, as to how fast the fired one would "relatively rise" versus how fast gravity would make it "relatively fall" The dropped one of course, would have zero "relative rise"

Short answer:
I dunno, too early and too time consuming for me to figure it out, given the great importance of the results relative to my life.


But thanks for the mental exercise

(Admittedly, My IQ is 2 points lower than Einstein's, so HMMV, His Mileage May Vary)

What color is the bullet? I think I saw it continue out into space, was that a +++++P+++++ pressure? ...

[jimlongley]

Way to many factors involved to give an absolute answer to the original question.

Given a perfect vacuum and a perfectly plane surface, the bullet dropped precisely as the bullet fired leaves the muzzle will drop at the same rate of gravitational acceleration as the fired bullet and hit the plane surface at exactly the same moment.

Introduce absolutely still air with no pressure gradients, and conditions change, but no one knows for sure what the difference will be because that is a condition that is impossible to achieve, so the answer is theoretical.

And every answer beyond that is equally theoretical because not one of the many factors can be controlled for.

Wind speed, direction, and even the presence of turbulence in the air, all contribute to variations in trajectory. For very long shots, as in artillery or ballistic missles, fluctuations in local graviation even have an effect.

And whether the projectile is spinning or not, and which direction it is spinning relative to wind, and its shape, and, and, and . . .

[Ed4032]

I remember when they did this on the Moon. They dropped a Feather and a Hammer at the same time. They hit the ground together. Yeah, it was a vacuum.

[The Annoyed Man]

Bullet "rise" is primarily due to the fact that the line of sights or scope are not parallel to the bore axis. If they were parallel, it would be physically impossible to zero a scope or your iron sights.

That said, and atmospheric influences aside, bullets do exhibit "spin drift" caused by the rotational inertia of the bullet in flight. Spin drift will cause a bullet to tend to rise and drift left or right off its base trajectory according to the direction of its rotation. This effect becomes more pronounced the faster the bullet is spinning and the longer the distance to the target. So obviously, a 175 grain Matchking exiting the muzzle of a 1:10 twist .308 caliber barrel at 2800 fps is spinning at a much faster rate than a 230 grain RNFMJ exiting the muzzle of a 1:16 twist .45 caliber barrel at 850 fps, and the effect of that drift will be vastly more pronounced over a long range rifle shot than over a self defense distance pistol shot. As a practical matter, spin drift can be entirely discounted in pistol bullets; and whenever you have zeroed your rifle scope, you have unknowingly taken spin drift into account in achieving zero.

All good ballistic calculators - such as my "Shooter" application on my phone - take spin drift into account when generating a ballistics table over varied distances. If your rifle is zeroed at 100 yards for instance, then including spin drift as a variable for an 800 yard shot is absolutely necessary if maximum accuracy is desired.

[puma guy]

All good ballistic calculators - such as my "Shooter" application on my phone - take spin drift into account when generating a ballistics table over varied distances. If your rifle is zeroed at 100 yards for instance, then including spin drift as a variable for an 800 yard shot is absolutely necessary if maximum accuracy is desired.

What caliber is your phone? I want one.

[esxmarkc]

As mentioned earlier in the thread Mythbusters really did a good job on this one. Pretty much confirmed that dropped vs. shot was indescerneable.

If you want to argue the pyhsics of it there is no aerodynamic lift since the bullet is symmetrical and travels through the air with a neutral angle of attack. It remains neutral throughout it's flight since it is spin stabilized. Even if it was possible to present a spin-stabilized bullet from the barrel that was not neutral AOA the spinning of the bullet pretty much distorts any boundary layer effects and would play havoc on any possible lift properties - You would be shooting a curveball (The severe effects of spin drift as TAM explains)

If on the other hand, you were shooting tiny spinning Frisbees them little boogers would travel across the border.

IANAPBAACAYAGTG (I Am Not A Physicist But Am As Close As You Are Going To Get )

[surprise_i'm_armed]

Bravo to all the Junior Physicists on the board for the
englightening, and sometimes disparate, explanations
for their take on the "dropped vs. fired" bullets.

Maybe this is too simple a question but if the bullet
had "aerodynamic lift", wouldn't it have to have a power
source to keep it going as fast as when it left the barrel?

Aircraft taking off generate enough lift to leave the earth,
but then they need the jets to continue supply thrust to
keep the aircraft aloft, n'est ce pas?

What say you, forum? :-)

SIA