Something I always wondered about...

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nestork wrote:

Here's a bullets journal, taken from a Jack Reacher novel:
First thing out of the barrel of Reacher's Barrett was a blast of hot gas. The powder in the cartridge exploded in a fraction of a millionth of a second and expanded to a super-heated bubble. That bubble of gas hurled the bullet down the barrel and forced ahead of it and around it to explode out into the atmosphere. Most of it was smashed sideways by the muzzle brake in a perfectly balanced radial pattern, like a doughnut, so that the recoil moved the barrel straight back against Reacher's shoulder without deflecting it either sideways or up or down. Meanwhile, behind it, the bullet was starting to spin inside the barrel as the rifling grooves grabbed at it.
Then the gas ahead of the bullet was heating the oxygen in the air to the point where the air caught fire. There was a brief flash of flame and the bullet burst out through the exact center of it, spearing through the burned air at nineteen hundred miles an hour. A thousandth of a second later, it was six feet away, and its sound was bravely chasing after it, three times slower.
The bullet took five hundredths of a second to cross the [parade ground], by which time the sound of its shot had just passed Reacher's ears and cleared the ridge of the roof. The bullet had a hand-polished copper jacket and it was flying straight and true, but by the time it had passed soundlessly over McGrath's head it had slowed a little. And the air was moving it. It was moving it right to left as the gentle mountain breeze tugged imperceptibly at it. Half a second into its travel, the bullet had covered thirteen hundred feet and it had moved seven inches to the left.
And it had dropped seven inches. Gravity had pulled it in. The more gravity pulled, the more the bullet slowed. The more it slowed, the more gravity deflected it. It speared onward in a perfect graceful curve. A whole second after leaving the barrel, it was nine hundred yards into its journey. Way past McGrath's running figure, but still over the trees, still three hundred yards short of its target. Another sixth of a second later, it was clear of the trees and alongside the office building. Now it was a slow bullet. It had pulled four feet left and five feet down. It passed well clear of Holly and was twenty feet past her before she heard the hiss in the air. The sound of the shot was still to come.
Reacher's bullet hit Borken in the head a full second and a third after he fired it. It entered the front of his forehead and was out of the back of his skull three ten-thousandths of a second later. In and out without really slowing much more at all, because Borken's skull and brains were nothing to a two-ounce lead projectile with a needle point and a polished metal jacket. The bullet was well over the endless forest beyond before the pressure wave built up in Borken's skull and exploded it.
Reacher was watching it through his scope. Heart in his mouth. A full second and a third is a long time to wait. He watched Borken's skull explode like it had been burst from the inside with a sledgehammer. It came apart like a diagram. Reacher saw curved shards of bone bursting outward and red mist blooming.
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Ummmm, no. Gravity does *not* cause the bullet's horizontal velocity to decrease.

Ummmm, no. The longer it was in flight, the more gravity deflected it. Vertical motion due to gravity depends only on the length of time that it's been in motion, and is *not* affected in the least by horizontal velocity. A bullet fired from a gun parallel to the ground, and a bullet *dropped* from the same height, will strike the ground at the same instant.
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wrote:

Exactly so.
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On Thu, 20 Dec 2012 16:23:12 +0000 (UTC), Doug Miller

Hey, you spoiled the story! Read your example above of how gravity works on a bullet many years ago, and never saw a better one since. Because no more need be said.
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OK, I read through all the posts. Thanks guys.
I guess the analogy between throwing a ping pong ball and throwing a golf ball speaks loudest to me. Both would start out with the same initial velocity and both would encounter the same amount of air resistance, but the smaller mass of the ping pong ball would be more affected by that air resistance, and slow down much faster.
BUT, if that's true, then it would also apply to objects smaller than a bullet. I'm thinking that there are different size pellets in shot gun shells. Some shot gun shells have lots of tiny pellets, whereas other have a fewer number of large pellets. In both cases, however, the pellets are made of lead (I think) and so the difference in density between the pellets and the surrounding air would be identical. Does anyone know if the shells with fewer large pellets have a longer range than those with lots of small pellets? If air resistance is the key, then it would stand to reason that they would. Larger, heavier pellets should be less affected by air resistance, and therefore slow down less and travel further.
--
nestork


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Correct. Different sizes for different purposes.

Depends on what you're hunting. The ammunition used for squirrel, rabbit, grouse, pheasant, or dove is normally lead pellets, whereas non-toxic shot (steel or copper, for instance) is required when hunting waterfowl.

Indeed they do.

That is exactly what happens.
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This is the reason why depleted uranium is used in projectiles. http://en.wikipedia.org/wiki/Depleted_uranium#Ammunition
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What a load of crap. And air doesn't burn.
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On 12/20/2012 9:39 AM, HeyBub wrote:

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Nestork wrote a post without making coherent use of the subject line.
Nestork's post -> FAIL.
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It all has to do with the mass (weight) of the bullet. The battle ship guns and rifles shoot the bullets at about the same speed. Simple example is to take a ping pong ball and throw it. Then take a pool ball and throw it. You can throw each one about the same speed. Because the pool ball is heavier, it travels the most. You can also take a grain of sand and the pool ball. This may be more of the relationship of the cannon and rifle. The sand grain will not travel as far. It is too light. It is small enough the air resistance is very much less than the pool ball so that takes the air resistance out of the picture.
Hand gun bullets have about 1/3 the speed of the other bullets. This is mainly because of the barrel length. Gunpowder can only burn so fast and the gun can only take so much pressure. Even if the handgun could be made strong enough to handle the pressusre, it would be so heavy that no one would want to carry it around. It would also have so much recoil that it would hirt too much to shoot it.
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The magazine is below the turret and only enough powder to load the guns are actully in the turret at one time. However that still means there could be several thousand pounds of powder in the turret.
There seemed to be two theories as to the cause of the explosion. Sabatoge by someone putting something in the powder. Another is what is called over ramming the charge.
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Harry:
"This is the reason why depleted uranium is used in projectiles."
I wondered about that, too, and now it makes sense from an air resistance point of view. Instead of making the projectile bigger to have more mass, just make the projectile out of a denser material.
Oren: Thanks for sharing that link to those pictures with us.
What surprises me is that no one working behind that gun is wearing any hearing protection! I would have expected that anyone not wearing hearing protection in the turret when a gun like that fires would blow out their ear drums and lose 100% of their hearing instantaneously and permanently. I kinda doubt they took off their hearing protection just to take those pictures. Or, maybe it's not actually all that loud in there?
Those two big cylinders on the top of the breach... Are they like giant shock absorbers? When I've seen movies and TV shows showing modern cannons behing fired, something jerks back and then more slowly slides forward again (if I recall correctly) after each firing. I always presumed the whole idea behind that is to use a shock absorber to reduce the peak stress the steel holding that cannon together and in place has to bear. Kinda like the rubber shoulder pad at the butt end of a rifle; allowing the barrel to move backward as the bullet shoots forward might sacrifice a bit of muzzle velocity, but it makes holding the butt end of the rifle against your shoulder "bearable" when you pull the trigger.
--
nestork


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