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Old 01-22-2008, 06:12 PM   #21
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Ok.
so is everybody straight?

Yes, a bullet fired truely horizontall from 32 feet high will fall for marginally more than one second regardless of how far it goes. Another identical bullet dropped straight to the ground will fall for the exact same ammount of time. (in Short, to the OP: You teeacher is absolutely 100% right)

Yes, the line of sighting would be other than horizontal to make that happen; no that's not relevant to the concept...

No, weight does not matter at all.

Yes, if an object is going through the air, then drag will slow it's fall (only slightly for a rock, more for a sheet of paper. But that's because of drag, not weight, mass, or density. Those DO, however play into the coefficient of drag, but are inceidental in and of themselves... That's why being in a vaccume would matter in THAT case. Two identical bullets will have identical drag, thus hit the ground at exactly the same time.)
I believe it was Allan Sheppard who demonstrated this to watching school children when he dropped a feather and a hammer while on the moon; As predicted, they hit at the same time. ... taking six times longer than it would have taken on earth, but the exact same time, nonetheless.

Yes, spinning makes the bullet more stable; no, that doesn't matter in this case. IF the experiement were done from 193.2 feet, (making the fall last for 3 seconds) the dropped bullet might have time to flop over and present it's rear, flat surface to the wind making more drag, while a stabilized bullet would present a sleeker profile.. But again that's DRAG, not gravity. In a vaccume, even that would go away.


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Old 01-23-2008, 02:33 AM   #22
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Quote:
Originally Posted by deadin View Post
Think outside the box. The term used was "line of bore" not just plain "bore".
If you want to talk about the hole in the end of the barrel, yes, the sights are above that. However the "line of bore" is the projected line down the center of the bore from the breech to the muzzle and beyond, all the way out into the distance. The same thing with "line of sight". It's not just where the sights are on the barrel, it's all the way to the target when the sights are aligned on the target.
Yer right. And if the bore were completely level, the sights would be adjusted to coincide with the bullet at some point (point of aim). At that time, line of bore and line of sight would be the same.


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Old 01-24-2008, 03:31 AM   #23
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Quote:
At that time, line of bore and line of sight would be the same.
NO! The "line of sight" is a straight line from the rear sight through the front sight and projected out to the target. All in a perfect straight line.
The "line of bore" is likewise a perfect straight line from the center of the rear or chamber of the bore through the center of the bore at the muzzle and projected out to infinity.
The trajectory of the bullet (or "line of flight", if you prefer) is a curve due to the influence of gravity and in order to hit a target at a given range will need to cross the line of sight at the point of the target. This can happen on either the upward path of the trajectory or on the downward path, your choice. It still requires that the "line of bore" be angled upward from the "line of sight".

Now if you really want to confuse the issue, on a pistol the line of sight is sometimes below the line of bore, but this is because recoil will cause the barrel to pitch up before the bullet exits the bore.
It seems counter-intutitive, but a slower muzzle velocity in a pistol can cause the point of impact to rise on the target because of the longer barrel time. (And vice-versa. Higher velocity can cause low hits.)
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Old 01-29-2008, 08:42 PM   #24
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Default Leaning tower of Pizza

Go to the top of the above location and drop a cannon ball and a marble at the same time and they will land at the same time. So says Sir Isaac Newton.

Fire a bullet fast enough that it's trajectory matches the curvature of the earth and (if it doesn't meet an obstruction) about 90 minutes later it will come around and hit you in the back of the head! TFIC So says RED.
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Old 01-30-2008, 03:02 AM   #25
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...
Fire a bullet fast enough that it's trajectory matches the curvature of the earth
...
Mentioning that the experiment breaks down if the projectile attains orbital velocity (the trajectory you mentioned, or about 17,500 mph) is just the kind of thing that made the teachers not like me when I was a kid.
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Old 01-30-2008, 11:48 PM   #26
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Orbital velocity at sea level (or there-abouts) would probably burn the bullet up long before it made it around to the back of your head. (Or you assuming a vacuum?)
Also, if I remember my physics (it's been a long, long time) doesn't orbital velocity have to have altitude calculated in? Something to do with the attraction of gravity is an inverse square function or another. In other words, at sea level it would be a whole lot faster than 17,500 mph.
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Old 01-31-2008, 03:39 PM   #27
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Orbital velosity is relational to the pull of gravity, so Yes, the speed would change as the distance from the planet changes...

But since I ws rounding to the nearest 500mph interval (I did mention it is ABOUT 17,500 mph) the altitude difference is within the rounding's margin of error.

And yeah, for that matter, doing it through the air density at sea level would certainly burn it up before it got far anyway. Even the space shuttle (covered in some pretty high-tech ceramics) has to make sure it gets below a hypersonic speeds before it gets too low, or even IT will melt.
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Old 01-31-2008, 08:51 PM   #28
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Quote:
Originally Posted by Duck View Post
Yes, you do need the vacuum. Air creates resistance that takes a greater effect on a lighter object. Don't believe me? Drop a piece of paper and a rock at the same time. The air resistance restricts the paper's fall. In a vacuum, there is no air so the resistance isn't there.

Sorry, wrong answers.

A free falling bullet "drops" vertically, not horizontally. All free falling objects are affected equally by gravity so the example of the two bullets hitting level ground at the same time is true IF the bullet is actually fired parallel to the ground and that's the basic premise of the question.

Your illustration of air resistance does not apply to the question of two bullets dropping. In fact, it doesn't even apply for your instances; compare the drop times of two rocks or two pieces of paper rather than two dissimular objects and the air resistance on the objects will be equal so the rate of fall will be equal. Actually, the air resistance to the low velocity of drop of a bullet is negligible for the short distance the question is concerned with.



"Also, a bullet actually arcs upwards as it leaves the muzzle. That bullet would have a further distance to fall, so would probably hit the ground last.
No bullet has any magic that makes it "arc upwards as it leaves the muzzle." Neither bullets nor guns even know which way up is.

A bullet's trajectory normally arcs up but only because the line of bore and line of sight are not the same. Gun sights are adjusted to compensate for drop so there are normally two points where the line of bore and the line of sight cross, one is usually less than 100 yards and another at the zero point.


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