Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: DoctorBeaver on 26/04/2007 09:29:11
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This occurred to me while I was posting a silly answer in another thread.
Combustion depends on the presence of oxygen. Guns fire bullets by causing a small explosion in the bullet, which is nothing more than very fast combustion. At altitude there is a lot less oxygen. So, would a gun still fire at the top of Mount Everest?
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An explosive has the oxygen locked up chemically in the explosive, this is how it can burn so fast, and so they are not dependent upon atmospheric oxygen.
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Yes, bullets will also go off underwater for the same reason. They won't go very fast though due to the viscous drag of the water.
Out of interest, Dave, how fast would a bullet travel in water? Take an AK47 for example, which fires bullets at about 1200 miles per hour, in air?
Chris
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Yes, bullets will also go off underwater for the same reason. They won't go very fast though due to the viscous drag of the water.
Out of interest, Dave, how fast would a bullet travel in water? Take an AK47 for example, which fires bullets at about 1200 miles per hour, in air?
Chris
if i may add another question. when criminalists are testing weapons they fire in to a "water" chamber, the bullet goes less than a metre! why is that?
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because 1m of water has about the same amount of stuff in it as 1km of air. There are then some subtleties about shockwaves and defformation of the bullet, but the amount of stuff in the way is the fundamental issue.
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So does that mean i could escape someone with a gun like in the films by diving into the sea and swimming underwater.
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So does that mean i could escape someone with a gun like in the films by diving into the sea and swimming underwater.
Depends on the type of gun and ammo, but most conventional ammo I would doubt would reach more than a foot through water, and even by then it will have lost a lot of energy. High energy jacketed rounds should be better at pentrating water.
The ability if a bullet to pass through water would probably only be slightly more than the ability of the bullet to pass through the soft tissues of the body. Most common hand gun bullets are designed to not leave the body (after all, if a bullet leaves the body, it will be taking some of its energy with it - and to do the maximum amount of damage requires that as much of the energy of the bullet as possible is transfered to the tissue of the target person, and none should be wasted by leaving the body). A high velocity rifle round can easily pass through several people (but they have enough energy that they can afford to waste some of it), and so will have quite good penetrating water.
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Firing a gun under water could be very dangerous. If there is water in the gun barrel the effective inertia of the bullet will be increased greatly because the charge also has to accelerate the water column. this would cause the breech pressure to be much higher and could cause the gun to explode like a bomb if there was air in the barrel this could be compressed and the gun would fire reasonably normally but as has already been said the bullet would not travel very far
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Very interesting. Thank you all
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The American science investigation series 'Mythbusters' tried a series of experiments to see if diving underwater would keep you safe. Their conclusion was - surprisingly ? - that it takes <1m of water to stop bullet; and that as usually bullets are fired into water at a shallow angle, a dive of perhaps 30cm would be sufficient.
What was really impressive about the experiments was that it was only the slower bullets that survived the impact with the water. Anything fired from a gun larger than a small handgun simply shattered into tiny fragments as it hit the water's surface.
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Generally the bullets will go all the way to the bottom of the water. Doh!
The point is that they slow down a lot in the first few feet. Another merit to hiding under water is that, unless they are firing straight down at you, refraction of light means they they will not actually aim correctly at you.
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Generally the bullets will go all the way to the bottom of the water. Doh!
LOL [:D]