Bullet physics, confirmed.

[TCS]

Remember that if you drop an unfired round from barrel height at the exact moment that a round exited the muzzle of that rifle, the two rounds would hit the ground at the same time (assuming a flat plane with unlimited length). The only difference between the two is that one would travel really, really far in that time.

: How's this?

Sounds unlikely to me... not saying it's not possible in the amazing world of physics, but just one of those things I'd have to "see to believe"... got a link to something that proves this? Just curious, not trying to call you out.

[Wolfmaster]

well it makes sense. the bullet you drop is affected by one force. gravity. it falls to the ground at a speed determined by the mass of the bullet and the ammount of gravity. (falls less fast on the moon because of less gravity). the bullet fired from the barrel is affected by two forces. gravity and a pushing force. the mass and gravity are still the same so the bullet drops at the same speed. however, meanwhile the pushing force has pushed it over a long distance.

picture:


saved it as jpeg instead of bmp while i made it with paint. made it vaguer. should have known.

edit: christ, it looks even worse on the internet. but you'll know what i mean.

[TCS]

Sounds like you probably know what you are talking about... but still it doesn't convince me.

I'm just speaking from personal experience... I know about how long it takes to drop a .50 cal bullet to the ground from "muzzle height" (I happen to have one right here, and I just dropped it... seriously.) I've also fired many .50 cal rounds downrange and watched the tracers as they take their sweet time hitting a berm and ricochet skyward. From my fuzzy memories, I recall it taking a lot longer for the bullet to reach the berm, which is by no means it maximum range. Talk about comparing a 40mm grenade being launched vs. dropped, and it seems like it would be much bigger distance.

Maybe I'm just overlooking something obvious... it's early and I'm hungry!

[Psycho_Sam]

It is correct that a bullet will hit the ground at the same time as one fired from a gun.

http://hyperphysics.phy-astr.gsu.edu/hb ... v.html#bul

[TCS]

Thanks for that link Pshycho_Sam. I can't even begin to understand the math involved... but I guess what's happening here is that they are calculating a bullet fired from a gun with the barrel aligned perfectly horizontally across perfectly flat ground.

I can't say for sure, but any range I've fired on was probably not following these conditions. Anything I've ever seen in real life would have been very different from this situation, because you normally fire from on top of a berm, and the range is sloped down as you look out at the targets. On top of that you would never be firing perfectly parallel to the ground, the weapon would certainly have to pointed upward slightly if you wanted to hit anything.

In a perfect situation the 2 bullets would hit the ground at the same time, I'll take the word of the people smarter than me who figured out all those formulas.... but I can see how the required conditions would make the comparison nearly impossible. Under typical firing conditions (not in a laboratory, or on paper) it would be correct to say that the bullet fired from the gun stayed aloft longer than a bullet dropped from the height of the muzzle, because at the very least you must have the barrel pointed slightly upwards. The ground is almost never perfectly flat either, and even if you are firing uphill, I'd hope you're smart enough to not be pointing the gun right into the side of a hill.

[Sh0rtbUs]

You would think rifling would have an effect on its drop rate.

[BrokenArrow]

i meant the heat rising from the ground, heat rises, so the bullet going through that heat would rise also...

[Wolfmaster]

i think the bullet's too small to really be affected by rising heat.

[Figisaacnewton]

Ya, i know its hard to believe, but the math says if you drop a bullet, and shoot one across a really wide flat open plane, they'll hit the ground at the same time.


about rifling, that simply makes the bullet travel straighter, andcut through the air better. doesn't counteract gravity.

[Aevion]

Yep yep. It's best if you think of velocity as two seperate pieces: horizontal and vertical.

No matter how fast the object travels horizontally, it will still fall at the same rate vertically. This is because the vertical forces acting upon a horizontally immoble object are the same as those acting upon a horizontally hypersonic object.

There are a couple special situations to this. If you can get an object to move fast enough so that its rate of fall matches the curve of the earth (so that the object travels far enough on the curvature of the earth so that the ground "drops away" at the same rate as the bullet is falling), then you've achieved what we know as orbit.

If you have an object that produces lift, such as an airplane, then you can counteract gravity.

[phyte]

Yep yep. It's best if you think of velocity as two seperate pieces: horizontal and vertical.

No matter how fast the object travels horizontally, it will still fall at the same rate vertically. This is because the vertical forces acting upon a horizontally immoble object are the same as those acting upon a horizontally hypersonic object.

There are a couple special situations to this. If you can get an object to move fast enough so that its rate of fall matches the curve of the earth (so that the object travels far enough on the curvature of the earth so that the ground "drops away" at the same rate as the bullet is falling), then you've achieved what we know as orbit.

If you have an object that produces lift, such as an airplane, then you can counteract gravity.

I was in error in my first post, you are all right, of course a bullet will not rise, as there is no force acting on the bullet to influence it to rise. I believe that I made an error of recalling a ballistics diagram rather than thinking about the forces that are at play.

Thanks all.

[Dowding]

I have a masters degree in Physics, so maybe I can help here.

When talking about basic mechanics, we should really be talking about acceleration first, rather than speed or its directional equivalent, velocity.

In a vacuum, a bullet fired on the horizontal plane will drop the same distance in a given amount of time as any object of any mass dropped at the same point. This is because the acceleration due to gravity (approximately 10m/s/s in our everyday environment) is a constant regardless of mass.

Acceleration is the rate of change of velocity, so each object (the bullet and the dropped object) accelerate downwards at the same rate, so at any point in time after the bullet is fired, they have the same vertical velocity and therefore have moved the same distance.

In reality, air resistance counteracts the acceleration due the gravity and anyaerodynamic effects acting on the bullet (due to its rotational motion induced by the gun barrel rifling). As a result of this, the drop distance will be affected.

[keef_haggerd]

wow we have some smart people on this forum!

[BrokenArrow]

OKAY earlier in this thread i said that i had read somewhere that heat can cause a bullet to rise, i was half right. in tom clancy's nonfiction 'a guided tour of a marine expeditionary unit' he talks about firing the M40A1 sniper rifle:

'In less than a second, the round flies out to the target, and the adjustment process begins. you look at the grass and dustclouds to evaluate the wind and heat shimmer to help adjust the scope to help adjust the scope to compensate for crosswinds and heat updrafts that "loft" the round.'

so while i was not entirely correct that heat causes a bullet to rise, from that passage it appears that it does have some effect on the bullets flight. the heat does offset (though not completely) the bullet's drop.

Okay i had to redeem myself at least a little after getting totally shut down

there is alot of interesting stuff in this book though, anyone who wants to see how a real MEU works should pick it up.

[Wolfmaster]

i'm reading a book by tom clancy right now. a novel called debt of honor. nice book.

[BrokenArrow]

that is a good one.

[Wolfmaster]

i know. i've read around 100 pages so far. i really like it. i plan on getting other books by him from the library when i'm finished with this one.

[BrokenArrow]

if you can try to read them in order, they make alot more sense

anyway what was this thread about again?