reducing the speed of an impact

HarryKeogh

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ok, say you have a rifle set up at point A. it's aimed at point B, a bulleye target 100 yards away.

now you have a sheet of 1/8" steel that you can place at any point between A and B to slow down the bullet (let's assume that the trajectory of the bullet won't change after it strikes the sheet of steel)

now if youre trying to minimize the force of the impact as much as possible would it matter where you place the sheet along the line between A and B?
 
This is a difficult question because we don't have any way to characterize the effect of the steel plate on the bullet, except that it doesn't change the trajectory. In a very simple (an probably not valid case) the sheet would impart a change in velocity dv=constant, so it wouldn't matter where on the range the sheet was.

In more complex cases the effect of the sheet on the bullet's velocity would be something like dv is proportional to 1/v, so the sheet would be most effective when the bullet is moving slower. This seems like a reasonable case, since when the bullet is moving slower it would have to interact with the sheet for a longer amount of time, creating a bigger force.

All this discussion assumes there is air resistance, and the bullet slows as it traverses the range. If this were not the case, it wouldn't matter where the sheet was placed.
 
HarryKeogh said:
now if youre trying to minimize the force of the impact as much as possible would it matter where you place the sheet along the line between A and B?
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Well, if you place the sheet of steel right at point A, i'e. pressed against end of the muzzle of your rifle, I'd guess you could make the barrel of the gun explode.
 
You could go a bit radical and place the steel sheet horizontal and diagonal to the path of the bullet. The bullet cuts the steel like a sheet of paper cut by scissors from one corner to the diagonally opposite one. That'll make it travel through the most metal.
 
And that's very kind of you... but I'm not sure if it's within the rules. :D
 
If there is friction from air, I think putting it towards the end of the path will slow it down the most because there is one case in which a farther plate will actually reverse the bullet's direction.

If the bullet is travelling very far it will slow down to the point where it can't get through the plate. Even if it could get through a plate close to the muzzle, if it travels far enough it will slow down to the point where it simply bounces off the plate. So that's at least one case where a close plate will slow it down, but a farther plate will slow it down much more (in fact, reverse it's direction).

Or if it's difficult to imaginine a bullet being slowed down that much by air, replace the force of the air by imagining firing the bullet straight up against gravity. Assuming it's going under escape velocity, it will go slower, then stop, then fall back. It might blast through a plate a meter from the muzzle, there will always be a point just before the top of its trajectory when it will be going so slow that any plate will cause it to stop and reverse direction.
 
Iconoclast said:

Like Michael said... eh?
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The further a bullet travels from the barrel, the slower it goes.

The slower it goes, the less force it has. This increases the likelihood of the plate stopping or significantly slowing the bullet.

If you're negating air resistance, then just where the hell are you firing this bullet?????
 
DangerousBeliefs said:


The further a bullet travels from the barrel, the slower it goes.

The slower it goes, the less force it has. This increases the likelihood of the plate stopping or significantly slowing the bullet.
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i see. i was just curious though if there was some "balancing" act.

say you put the plate 10 yards away. the plate would slow the bullet then it would travel 90 yards more, slower due to the impact with the plate, with the air able to act on it a longer period of time

or if you put the plate 90 yards away, the bullet will have been a bit slower due to 90 yards of air resistance, it would hit the plate and since the plate can act on it a longer period of time be slowed down more.

so that was my reasoning for posting this thread. would the different resistance of the two different situations above balance out.

but the consensus here (and everyone's knowledge of physics here) seems to confirm the latter scenario would slow it down the most.
 
We had water-level recorders in shelters mounted on observation wells. These seemed to attract the Billy Joe Bobs from miles around, who would shoot at the shelters, damaging the instruments inside. We found the best solution was to place a sheet of steel in the shelter at an angle from vertical. Then, when the yahoos shot, the bullets would be deflected and the instruments would remain safe.
 
pupdog said:
We had water-level recorders in shelters mounted on observation wells. These seemed to attract the Billy Joe Bobs from miles around, who would shoot at the shelters, damaging the instruments inside. We found the best solution was to place a sheet of steel in the shelter at an angle from vertical. Then, when the yahoos shot, the bullets would be deflected and the instruments would remain safe.
Click to expand...

Too bad you can't set the sheet of steel at an angle such that the bullet ricochets and injures the person that shot it.
 
If we're talking real world, the bullet is going to get seriously deformed punching through a steel plate, making it much less likely to even find its target if you put the plate near the gun. And think if the drag a squished bullet is going to suffer compared to the nice aerodynamic shape it left the barrel in.

I think we need to do some field tests.
 
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