What-if 0081: "Catch"

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What-if 0081: "Catch"

Postby mathmannix » Tue Jan 28, 2014 3:55 pm UTC

Catch!

Is there any way to fire a gun so that the bullet flies through the air and can then be safely caught by hand?

Ed Hui, London


Image

This picture reminds me of the people that fire their guns into the air every New Year's Eve. Or the news report in the movie Indepenence Day that told people in Los Angeles not to shoot up at the alien spaceships, as they could inadvertently start an interstellar war.
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Re: What-if 0081: "Catch"

Postby EpicanicusStrikes » Tue Jan 28, 2014 4:29 pm UTC

People have got to stop using Mythbusters to prove... well... anything. I don't care how 'sciency' they try to appear. It's still just a TV show and not worth consideration as hard evidence of anything other than "it's cool when things explode".

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Re: What-if 0081: "Catch"

Postby squall_line » Tue Jan 28, 2014 4:30 pm UTC

Spoiler:
Image


Is this a case of the inking not going over the original tracing, or is the cop looking around so fast that her head and arms are a blur and in "bullet time"?

Also, I think that the Mythbusters posited (I don't consider most of their "conclusions" to be even close to scientifically rigorous enough to be called conclusions) that the only way for an upward-fired bullet NOT to be lethal on return to earth is if it was fired directly in the air and fell back to earth base-first. Otherwise, on the parabolic arc, it would fall with the same velocity at which it left the ground, less a little bit for air resistance. This coincides with the mention of the rotation of the bullet when caught at its apex.

edit: Randall fixed the image. Dang. Spoiler-tagged the image, since it's irrelevant now.
Last edited by squall_line on Tue Jan 28, 2014 6:12 pm UTC, edited 1 time in total.

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Re: What-if 0081: "Catch"

Postby cellocgw » Tue Jan 28, 2014 4:32 pm UTC

What if we tried bigger bullets? :twisted:

And aside from losing even more aiming accuracy, could always fire off a non-rifled gun. No rotational momentum that way.

So maybe use a marshmallow gun and someone sitting in a tree house. That has potentially enjoyable side-effects.

Obligatory: waaaaah not every drawing has title-text.
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Re: What-if 0081: "Catch"

Postby jpvlsmv » Tue Jan 28, 2014 4:43 pm UTC

If you throw a (loaded) .22LR gun off Mt Thor with a timer to pull the trigger just before it hits the ground, how high does the bullet go? Is it easier to catch the bullet that way?

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Re: What-if 0081: "Catch"

Postby Klear » Tue Jan 28, 2014 5:09 pm UTC

Reminded me of Gone with the Blastwave.

Also, the last three or so pictures don't seem to have alt-text =(

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Re: What-if 0081: "Catch"

Postby Steax » Tue Jan 28, 2014 5:45 pm UTC

EpicanicusStrikes wrote:People have got to stop using Mythbusters to prove... well... anything. I don't care how 'sciency' they try to appear. It's still just a TV show and not worth consideration as hard evidence of anything other than "it's cool when things explode".


You have a general point, but they did an experiment involving shooting guns into ice and showing us the results of that. They get to piggyback on their reputation and their channel that they're not faking it, unlike a lot of YouTube videos. That's pretty valid evidence.
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Re: What-if 0081: "Catch"

Postby Peregrine Crow » Tue Jan 28, 2014 5:52 pm UTC

Steax wrote:
EpicanicusStrikes wrote:People have got to stop using Mythbusters to prove... well... anything. I don't care how 'sciency' they try to appear. It's still just a TV show and not worth consideration as hard evidence of anything other than "it's cool when things explode".


You have a general point, but they did an experiment involving shooting guns into ice and showing us the results of that. They get to piggyback on their reputation and their channel that they're not faking it, unlike a lot of YouTube videos. That's pretty valid evidence.


Agreed, a lot of mythbuster results are dubious to say the least, but when the hypothesis they are testing is along the lines of "if you do x then y may happen" and they do x and y does in fact happen then that is pretty compelling evidence for their hypothesis.

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Re: What-if 0081: "Catch"

Postby jozwa » Tue Jan 28, 2014 5:56 pm UTC

"Goodnight, Moon" made me laugh. :D

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Re: What-if 0081: "Catch"

Postby rhomboidal » Tue Jan 28, 2014 6:04 pm UTC

Tragically, the fired bullets missed the Wizard of Oz's balloon and punctured Glinda the Good Witch's bubble, causing her to horrifically plummet into a crowd of innocent Munchkins.

That's what happens when people don't understand realistic physics.

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Re: What-if 0081: "Catch"

Postby mathmannix » Tue Jan 28, 2014 6:05 pm UTC

rhomboidal wrote:Tragically, the fired bullets missed the Wizard of Oz's balloon and punctured Glinda the Good Witch's bubble, causing her to horrifically plummet into a crowd of innocent Munchkins.

That's what happens when people don't understand realistic physics.


But... the bubble was only a foot or so in diameter until just before she emerged, IIRC? So... she'd be trapped in tinymode?
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Re: What-if 0081: "Catch"

Postby Gamil » Tue Jan 28, 2014 6:14 pm UTC

There's one thing missing from the answer in this one. There's a pretty good chance that the bullet would also be tumbling. During the transition from supersonic to subsonic, the center of pressure on a bullet shifts forward. There are many factors that contribute to a bullets stability (spin, length, center of mass, aerodynamics, etc). But, your typical .22 long rifle ammunition, regardless of spin, will be tumbling when it leaves the transonic region.

Tumbling bullets are about as accurate as a musket ball and with the increased drag, I'm wondering if a .22LR would even reach 1 km high.

http://en.wikipedia.org/wiki/External_b ... ic_problem

As far as myhtbuster's answer to a bullet falling back to earth, it depends a lot on the round. A short bullet with a flat tail from a pistol would likely travel slowest with the base first. But, rifle bullets are much longer in order to maintain stability and accuracy over long distances. Many also tend to have tapered tails for better aerodynamics, so the slowest decent would be sideways or tumbling.

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Re: What-if 0081: "Catch"

Postby sep332 » Tue Jan 28, 2014 6:27 pm UTC

I'm pretty sure firing a gun *straight* up isn't likely to kill anyone. The terminal velocity of a bullet falling straight down isn't high enough to do that much damage. However, firing a gun up at an angle keeps enough of the sideways momentum that it could kill someone at quite a distance. Check it out: reports of people being killed by guns fired into the air have victims that were quite a distance away from the shooter, not close-by.

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Re: What-if 0081: "Catch"

Postby speising » Tue Jan 28, 2014 6:29 pm UTC

squall_line wrote:Also, I think that the Mythbusters posited (I don't consider most of their "conclusions" to be even close to scientifically rigorous enough to be called conclusions) that the only way for an upward-fired bullet NOT to be lethal on return to earth is if it was fired directly in the air and fell back to earth base-first. Otherwise, on the parabolic arc, it would fall with the same velocity at which it left the ground, less a little bit for air resistance. This coincides with the mention of the rotation of the bullet when caught at its apex.


why would the terminal velocity of a falling bullet have any relation to the muzzle velocity? this "less a bit" should be dominant from this height, shouldn't it?

edit: wikipedia says 90m/s for a typical .30-06 bullet, whatever that may be.

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Re: What-if 0081: "Catch"

Postby rhomboidal » Tue Jan 28, 2014 6:32 pm UTC

mathmannix wrote:
rhomboidal wrote:Tragically, the fired bullets missed the Wizard of Oz's balloon and punctured Glinda the Good Witch's bubble, causing her to horrifically plummet into a crowd of innocent Munchkins.

That's what happens when people don't understand realistic physics.


But... the bubble was only a foot or so in diameter until just before she emerged, IIRC? So... she'd be trapped in tinymode?

If my understanding of fantasy physics is correct, her bubble bursting would've immediately rendered her into full-size. It's an as-of-yet not clearly understood phenomenon of quantum magic.

EpicanicusStrikes wrote:People have got to stop using Mythbusters to prove... well... anything. I don't care how 'sciency' they try to appear. It's still just a TV show and not worth consideration as hard evidence of anything other than "it's cool when things explode".

"Mythbustersbusters"

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Re: What-if 0081: "Catch"

Postby january1may » Tue Jan 28, 2014 6:35 pm UTC

jpvlsmv wrote:If you throw a (loaded) .22LR gun off Mt Thor with a timer to pull the trigger just before it hits the ground, how high does the bullet go? Is it easier to catch the bullet that way?

I wrote (and calculated) a long complicated answer, with a bunch of links, and then lost it :cry:

Briefly: if we somehow manage to make the gun shoot straight up despite it falling, roughly 700 meters (aka about 60% of the way up). The gun would be moving down pretty fast, so the speed of the bullet relative to the mountain would be muzzle velocity minus the speed of the gun - which comes out to roughly 250 m/s; I tried to estimate from that, but this link gives a specific figure for a .25ACP round, which is close enough considering the roughness of my estimates (besides, they gave the same approximate figure anyway).
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Re: What-if 0081: "Catch"

Postby EpicanicusStrikes » Tue Jan 28, 2014 6:36 pm UTC

Peregrine Crow wrote:
Steax wrote:
EpicanicusStrikes wrote:People have got to stop using Mythbusters to prove... well... anything. I don't care how 'sciency' they try to appear. It's still just a TV show and not worth consideration as hard evidence of anything other than "it's cool when things explode".


You have a general point, but they did an experiment involving shooting guns into ice and showing us the results of that. They get to piggyback on their reputation and their channel that they're not faking it, unlike a lot of YouTube videos. That's pretty valid evidence.


Agreed, a lot of mythbuster results are dubious to say the least, but when the hypothesis they are testing is along the lines of "if you do x then y may happen" and they do x and y does in fact happen then that is pretty compelling evidence for their hypothesis.

I remember that. They had to revisit it because the first time around they 'simulated' icy conditions. Their target material was always the wrong hardness by the time they got around to actually testing the myth.

The second time was performed in more natural conditions, and only then confirmed.

I like it when they can confirm things. It's great. But when they claim something is busted? Based on their limited engineering experience? No. No, man. That's not cool. An ancient builder may have had decades if not generations to work the bugs out of an idea. Mythbusters then tries to duplicate that in a matter of... weeks? Months? I don't know their shooting schedule. When they fail, they claim that old-man Chinese McGenius couldn't have done any better with an entire lifespan to get it right.

Or they just get the myth itself wrong. Driving a car backwards in the snow to get better traction? I saw that. Clearly none of them learned how to drive in a snowy climate, otherwise they would have taken a front-heavy, rear-wheel drive vehicle with no traction control uphill. Go forward? The engine acts as a pivot, forcing the drive wheels to move to the side and break forward momentum. Stuckness occurs. Going up the hill in reverse allows the engine to act as a stabilizer and a straight-line run is achieved with greater success.

But did they think of that? Nooooooo.....

I kept trying to call them and correct them during that episode, only to be told something about pre-taping, harassment, and that they were a place called 'Pizza Hut', anyway. Damn producers will say anything to avoid admitting mistakes.

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Re: What-if 0081: "Catch"

Postby Moose Anus » Tue Jan 28, 2014 6:42 pm UTC

jpvlsmv wrote:If you throw a (loaded) .22LR gun off Mt Thor with a timer to pull the trigger just before it hits the ground, how high does the bullet go? Is it easier to catch the bullet that way?
It would go about the same height as if you just stood down there and fired.

When a gun fires, an extremely high acceleration happens to the bullet for a very short time. After that, it relies on velocity to get where it needs to go. A bullet fired up loses velocity due to gravity, which is an acceleration.

In this experiment, when you throw the gun off the mountain, it will accelerate due to gravity along with the bullets inside. When the timer goes off and the bullet is fired, its high acceleration will overcome the acceleration due to gravity by a large degree, so that the bullet will have roughly the same initial velocity it would have if the gun were not falling.

It would probably be harder to catch the bullet because it would be harder to aim.
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Re: What-if 0081: "Catch"

Postby Barstro » Tue Jan 28, 2014 6:48 pm UTC

jozwa wrote:"Goodnight, Moon" made me laugh. :D


My vote is for "we're in the northern hemisphere", but the moon was a close second.

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Re: What-if 0081: "Catch"

Postby cellocgw » Tue Jan 28, 2014 7:22 pm UTC

mathmannix wrote:
rhomboidal wrote:Tragically, the fired bullets missed the Wizard of Oz's balloon and punctured Glinda the Good Witch's bubble, causing her to horrifically plummet into a crowd of innocent Munchkins.

That's what happens when people don't understand realistic physics.


But... the bubble was only a foot or so in diameter until just before she emerged, IIRC? So... she'd be trapped in tinymode?


Couldn't happen -- Glynda travels in a bobble so bullets will have no effect.
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Re: What-if 0081: "Catch"

Postby Peregrine Crow » Tue Jan 28, 2014 8:29 pm UTC

EpicanicusStrikes wrote:<*cutting out the parts I'm actually responding to and leaving the part I found funny*>
I kept trying to call them and correct them during that episode, only to be told something about pre-taping, harassment, and that they were a place called 'Pizza Hut', anyway. Damn producers will say anything to avoid admitting mistakes.


Yeah, their results have to be taken with a considerable grain of salt and filtered with a reasonable amount of common sense. But it is usually enough to at least get a basic idea of the physics involved, so it is still interesting to watch.

Also, in their defence, apparently there is often a lot of footage of the team testing alternative scenarios that is left on the cutting floor, which makes it look like they are taking mayor leaps in logic on the show. (Note: this is in defence of the mythbusters themselves, it is definitely still a problem with the show). The aftershow sometimes goes deeper into this.

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Re: What-if 0081: "Catch"

Postby rmsgrey » Tue Jan 28, 2014 8:42 pm UTC

Moose Anus wrote:
jpvlsmv wrote:If you throw a (loaded) .22LR gun off Mt Thor with a timer to pull the trigger just before it hits the ground, how high does the bullet go? Is it easier to catch the bullet that way?
It would go about the same height as if you just stood down there and fired.

When a gun fires, an extremely high acceleration happens to the bullet for a very short time. After that, it relies on velocity to get where it needs to go. A bullet fired up loses velocity due to gravity, which is an acceleration.

In this experiment, when you throw the gun off the mountain, it will accelerate due to gravity along with the bullets inside. When the timer goes off and the bullet is fired, its high acceleration will overcome the acceleration due to gravity by a large degree, so that the bullet will have roughly the same initial velocity it would have if the gun were not falling.


What?

The falling bullet/gun will have a certain downward velocity. When the timer fires the bullet, the bullet will leave the gun with the same velocity relative to the gun as if the gun were not falling, but relative to the ground, the bullet's velocity will be the sum of the bullet's velocity relative to the gun and the gun's velocity relative to the ground. The gun's velocity relative to the ground will be the velocity from falling plus the velocity imparted by the recoil.

It's true that, during the time the bullet is traversing the gun-barrel, the acceleration due to gravity only has a negligible effect on it, but the acceleration due to gravity during the entire time the gun is falling is going to have a significant effect on the speed of the bullet relative to the ground.

If you tried the experiment in a vacuum - fired a bullet straight up, reloaded the gun, then dropped it from the maximum height the bullet reached, rigged so that it would fire a bullet straight-up just before impact, then the bullet would be (neglecting recoil effects) stationary relative to the ground when it emerged from the dropped gun - in both cases - going upward from a stationary firing and falling from the peak height - it would have experienced exactly the same acceleration - precisely what's needed to cancel the velocity relative to the gun...

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Re: What-if 0081: "Catch"

Postby EpicanicusStrikes » Tue Jan 28, 2014 8:44 pm UTC

Peregrine Crow wrote:Yeah, their results have to be taken with a considerable grain of salt and filtered with a reasonable amount of common sense. But it is usually enough to at least get a basic idea of the physics involved, so it is still interesting to watch.

I'll go along with that. I also enjoy being proven wrong when I go into an episode making assumptions. Like how you can actually slide down a sheet by inserting a knife and holding on. I was watching an old movie with my grandfather when I was a kid, and he swore that would never work, and I believed him.

Of course, that didn't take into account the horizontal seams, but hey...

Does anyone remember one of the revisits of the Archimedes Heat Ray? The one with the self-proclaimed, NASA polymath genius? The one who never actually managed to demonstrate his device working, and even when filming it himself he 'shut it down' our of fear of 'setting the neighborhood on fire'?

Did anyone find it suspicious that a polymath would have mastered so many skills, except for how to properly secure his own experiment when shipping cross-country? Or did he just expect a random shipping company to know how to do a better job than a super-genius?

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Re: What-if 0081: "Catch"

Postby january1may » Tue Jan 28, 2014 10:01 pm UTC

rmsgrey wrote:
Moose Anus wrote:
jpvlsmv wrote:If you throw a (loaded) .22LR gun off Mt Thor with a timer to pull the trigger just before it hits the ground, how high does the bullet go? Is it easier to catch the bullet that way?
It would go about the same height as if you just stood down there and fired.

When a gun fires, an extremely high acceleration happens to the bullet for a very short time. After that, it relies on velocity to get where it needs to go. A bullet fired up loses velocity due to gravity, which is an acceleration.

In this experiment, when you throw the gun off the mountain, it will accelerate due to gravity along with the bullets inside. When the timer goes off and the bullet is fired, its high acceleration will overcome the acceleration due to gravity by a large degree, so that the bullet will have roughly the same initial velocity it would have if the gun were not falling.


What?

The falling bullet/gun will have a certain downward velocity. When the timer fires the bullet, the bullet will leave the gun with the same velocity relative to the gun as if the gun were not falling, but relative to the ground, the bullet's velocity will be the sum of the bullet's velocity relative to the gun and the gun's velocity relative to the ground. The gun's velocity relative to the ground will be the velocity from falling plus the velocity imparted by the recoil.

It's true that, during the time the bullet is traversing the gun-barrel, the acceleration due to gravity only has a negligible effect on it, but the acceleration due to gravity during the entire time the gun is falling is going to have a significant effect on the speed of the bullet relative to the ground.

If you tried the experiment in a vacuum - fired a bullet straight up, reloaded the gun, then dropped it from the maximum height the bullet reached, rigged so that it would fire a bullet straight-up just before impact, then the bullet would be (neglecting recoil effects) stationary relative to the ground when it emerged from the dropped gun - in both cases - going upward from a stationary firing and falling from the peak height - it would have experienced exactly the same acceleration - precisely what's needed to cancel the velocity relative to the gun...


I've mentioned most of the above (including the "stationary in vacuum" part) in the original (lost) version of my post. I actually initially thought the resulting speed would be tiny even considering air resistance, but my calculations turned out differently.
And that "plus" in the description of relative velocities should really be "minus", because the two velocities you're adding are in opposite directions, and thus have opposite signs. But you probably know that already.
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Re: What-if 0081: "Catch"

Postby Moose Anus » Tue Jan 28, 2014 10:03 pm UTC

rmsgrey wrote:
Moose Anus wrote:
jpvlsmv wrote:If you throw a (loaded) .22LR gun off Mt Thor with a timer to pull the trigger just before it hits the ground, how high does the bullet go? Is it easier to catch the bullet that way?
It would go about the same height as if you just stood down there and fired.

When a gun fires, an extremely high acceleration happens to the bullet for a very short time. After that, it relies on velocity to get where it needs to go. A bullet fired up loses velocity due to gravity, which is an acceleration.

In this experiment, when you throw the gun off the mountain, it will accelerate due to gravity along with the bullets inside. When the timer goes off and the bullet is fired, its high acceleration will overcome the acceleration due to gravity by a large degree, so that the bullet will have roughly the same initial velocity it would have if the gun were not falling.


What?

The falling bullet/gun will have a certain downward velocity. When the timer fires the bullet, the bullet will leave the gun with the same velocity relative to the gun as if the gun were not falling, but relative to the ground, the bullet's velocity will be the sum of the bullet's velocity relative to the gun and the gun's velocity relative to the ground. The gun's velocity relative to the ground will be the velocity from falling plus the velocity imparted by the recoil.

It's true that, during the time the bullet is traversing the gun-barrel, the acceleration due to gravity only has a negligible effect on it, but the acceleration due to gravity during the entire time the gun is falling is going to have a significant effect on the speed of the bullet relative to the ground.

If you tried the experiment in a vacuum - fired a bullet straight up, reloaded the gun, then dropped it from the maximum height the bullet reached, rigged so that it would fire a bullet straight-up just before impact, then the bullet would be (neglecting recoil effects) stationary relative to the ground when it emerged from the dropped gun - in both cases - going upward from a stationary firing and falling from the peak height - it would have experienced exactly the same acceleration - precisely what's needed to cancel the velocity relative to the gun...
I should stop making stuff up. So if you're standing on the ground and you could see the bullet the whole time because the gun is transparent, at the time it's fired it would look like the bullet stays stationary, and the gun smashes quickly downwards. Neat!
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Re: What-if 0081: "Catch"

Postby rmsgrey » Tue Jan 28, 2014 10:16 pm UTC

january1may wrote:And that "plus" in the description of relative velocities should really be "minus", because the two velocities you're adding are in opposite directions, and thus have opposite signs. But you probably know that already.

Velocity is a directed quantity - "minus" only makes any sense when the two velocities are along the same line, which generally won't be the case unless there's some form of stabilisation....

Moose Anus wrote:I should stop making stuff up. So if you're standing on the ground and you could see the bullet the whole time because the gun is transparent, at the time it's fired it would look like the bullet stays stationary, and the gun smashes quickly downwards. Neat!


Only in a vacuum - on Earth, the effects of the atmosphere are very important - the gun's terminal velocity is going to be much lower than the bullet's velocity when it leaves the gun, so the bullet will still have a respectable velocity relative to the ground when the gun fires after being dropped - I'd have to do some research to get actual figures - january1may's already done the calculations, and reports that the bullet would still fly up about 60% of the original height.

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Re: What-if 0081: "Catch"

Postby january1may » Tue Jan 28, 2014 10:25 pm UTC

Moose Anus wrote:
rmsgrey wrote:
Moose Anus wrote:
jpvlsmv wrote:If you throw a (loaded) .22LR gun off Mt Thor with a timer to pull the trigger just before it hits the ground, how high does the bullet go? Is it easier to catch the bullet that way?
It would go about the same height as if you just stood down there and fired.

When a gun fires, an extremely high acceleration happens to the bullet for a very short time. After that, it relies on velocity to get where it needs to go. A bullet fired up loses velocity due to gravity, which is an acceleration.

In this experiment, when you throw the gun off the mountain, it will accelerate due to gravity along with the bullets inside. When the timer goes off and the bullet is fired, its high acceleration will overcome the acceleration due to gravity by a large degree, so that the bullet will have roughly the same initial velocity it would have if the gun were not falling.


What?

The falling bullet/gun will have a certain downward velocity. When the timer fires the bullet, the bullet will leave the gun with the same velocity relative to the gun as if the gun were not falling, but relative to the ground, the bullet's velocity will be the sum of the bullet's velocity relative to the gun and the gun's velocity relative to the ground. The gun's velocity relative to the ground will be the velocity from falling plus the velocity imparted by the recoil.

It's true that, during the time the bullet is traversing the gun-barrel, the acceleration due to gravity only has a negligible effect on it, but the acceleration due to gravity during the entire time the gun is falling is going to have a significant effect on the speed of the bullet relative to the ground.

If you tried the experiment in a vacuum - fired a bullet straight up, reloaded the gun, then dropped it from the maximum height the bullet reached, rigged so that it would fire a bullet straight-up just before impact, then the bullet would be (neglecting recoil effects) stationary relative to the ground when it emerged from the dropped gun - in both cases - going upward from a stationary firing and falling from the peak height - it would have experienced exactly the same acceleration - precisely what's needed to cancel the velocity relative to the gun...
I should stop making stuff up. So if you're standing on the ground and you could see the bullet the whole time because the gun is transparent, at the time it's fired it would look like the bullet stays stationary, and the gun smashes quickly downwards. Neat!

Nope. It would look like the gun smashes quickly downwards, and the bullet was smashing downwards with the gun and then suddenly slowed down and went stationary.
In other words, the effect you describe would mainly occur outside the gun, so you don't need it to be transparent :D (it also only happens without air resistance, but you hopefully got that already).

rmsgrey wrote:
january1may wrote:And that "plus" in the description of relative velocities should really be "minus", because the two velocities you're adding are in opposite directions, and thus have opposite signs. But you probably know that already.

Velocity is a directed quantity - "minus" only makes any sense when the two velocities are along the same line, which generally won't be the case unless there's some form of stabilisation....

We're talking about the vertical component, right? Obviously if the gun doesn't fire straight up (which it realistically won't, but that's beside the point), there would be some complicated vector addition involved, but we're talking about what happens if it does - in which case both velocities are (mainly) vertical, and the minus sign makes perfect sense.
There are two films that I particularly like.
One of them is a science-fiction dramatic comedy involving a boy who accidentally travelled in time. Extremely popular when it originally came out in 1985, it retains a major cult following to this day.
The other one, of course, is Back to the Future.

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Re: What-if 0081: "Catch"

Postby Flumble » Tue Jan 28, 2014 10:53 pm UTC

Moose Anus wrote:I should stop making stuff up. So if you're standing on the ground and you could see the bullet the whole time because the gun is transparent, at the time it's fired it would look like the bullet stays stationary, and the gun smashes quickly downwards. Neat!

That depends on the weapon used.
A gun falling from Mount Thor would pick up a velocity of about 110m/s (oh how I love WA :D), so when the muzzle velocity is 110m/s, the bullet will indeed stay put for a moment and then fall down.
Since the muzzle velocity of black powder muskets ranges from about 120m/s to 370m/s (and modern guns start from there), the bullet flies upward (anywhere from 10m to 3½km some height heavily depending on drag) despite the gun punching a hole in the ground.

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Re: What-if 0081: "Catch"

Postby january1may » Tue Jan 28, 2014 11:06 pm UTC

Flumble wrote:
Moose Anus wrote:I should stop making stuff up. So if you're standing on the ground and you could see the bullet the whole time because the gun is transparent, at the time it's fired it would look like the bullet stays stationary, and the gun smashes quickly downwards. Neat!

That depends on the weapon used.
A gun falling from Mount Thor would pick up a velocity of about 110m/s (oh how I love WA :D), so when the muzzle velocity is 110m/s, the bullet will indeed stay put for a moment and then fall down.
Since the muzzle velocity of black powder muskets ranges from about 120m/s to 370m/s (and modern guns start from there), the bullet flies upward (anywhere from 10m to 3½km some height heavily depending on drag) despite the gun punching a hole in the ground.


We're talking about .22LR (the gun/bullet mentioned in the original WI), so the muzzle velocity is 380 m/s (the figure in the linked article).
I couldn't find how to do the velocity calculation you just did above (though I did try to use WolframAlpha), so I just estimated the gun's velocity as 130 m/s, assuming the terminal velocity for such a large heavy object was probably going to be higher. That said, your 110 m/s figure doesn't really change the calculations significantly (considering the roughness of my other estimates).
There are two films that I particularly like.
One of them is a science-fiction dramatic comedy involving a boy who accidentally travelled in time. Extremely popular when it originally came out in 1985, it retains a major cult following to this day.
The other one, of course, is Back to the Future.

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Re: What-if 0081: "Catch"

Postby Guttersnipe » Tue Jan 28, 2014 11:22 pm UTC

Does the third image contain the classical mistake of drawing a bullet with a case soaring through the air?

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Re: What-if 0081: "Catch"

Postby cryptoengineer » Wed Jan 29, 2014 12:54 am UTC

Guttersnipe wrote:Does the third image contain the classical mistake of drawing a bullet with a case soaring through the air?


It sure looks like it.

I shoot recreationaly, both pistol and rifle. The muzzle velocity of a bullet is affected by many factors, including (but not limited to) weight of the slug, how much and what type of propellent it's loaded with, and the length of the barrel. The lowest you're likely to see would be a .22 CCI CB Short, at around 700 fps. This is used mainly for target shooting or when quietness is an overriding concern, since it doesn't undergo a transition from supersonic to subsonic it can be more accurate. A .22 CCI Velocitor will be over 1400 fps. A .17 Hornady HMR can exceed 2500 fps. A 30-06 (standard round used by US in WW2) with the right load can reach 3500 fps. Compare this to the cited 300fps terminal velocity of a .30 slug

Other points:
Muzzle velocity is much higher than terminal velocity - the Mythbusters crew were simply wrong on that. Air resistance is a very important factor.
When the bullet drops through the sound barrier it can lose stability from buffeting, and start to tumble, reducing terminal velocity further.
Too much stabilization can also have bad affects on long range accuracy

ce

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Re: What-if 0081: "Catch"

Postby phlip » Wed Jan 29, 2014 1:45 am UTC

cryptoengineer wrote:Muzzle velocity is much higher than terminal velocity - the Mythbusters crew were simply wrong on that.

Which episode are we talking about now? Because I don't recall them ever claiming otherwise...

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Re: What-if 0081: "Catch"

Postby Klear » Wed Jan 29, 2014 2:45 am UTC

phlip wrote:
cryptoengineer wrote:Muzzle velocity is much higher than terminal velocity - the Mythbusters crew were simply wrong on that.

Which episode are we talking about now? Because I don't recall them ever claiming otherwise...

Yeah, here it is: http://en.wikipedia.org/wiki/MythBusters_(2006_season)#Bullets_Fired_Up

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Re: What-if 0081: "Catch"

Postby thevicente » Wed Jan 29, 2014 2:47 am UTC

(didnt read all above)

I forgot what was the question when I reached the end of the page.

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Re: What-if 0081: "Catch"

Postby phlip » Wed Jan 29, 2014 3:15 am UTC


Right, yeah, I'm still not seeing the part where Mythbusters claimed that terminal velocity > muzzle velocity?

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Re: What-if 0081: "Catch"

Postby Gelrir » Wed Jan 29, 2014 4:54 am UTC

During the development of body armor for the U.S. military during WW2, there was concern about "detrusion" or the dent you get behind non-perforated armor. Edward Corey, an officer in the US Navy, volunteered to be shot with an M1911 pistol at a distance of 15 feet. This started with a vest-type garment, but at some point they tried a glove made of Doron, initially with a lot of padding. They worked down over many shots to just 1/16th inch of Doron, with essentially no padding. With the more padded versions of the glove, "... the bullets were literally picked out of the air and caught as if catching marbles flipped at the hand."

... from "Flak Jackets", by Simon Dunstan, Osprey Publishing, 1984; page 16

The actual experiment is apparently described in "Webster, A. P.: Development of Body Armor. Hospital Corps Quarterly, Volume 18:31-33, October 1945." I haven't been able to find a physical copy or online copy of that report; you can apparently got one on abe books or biblio for $18.

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Re: What-if 0081: "Catch"

Postby Flumble » Wed Jan 29, 2014 5:45 am UTC

january1may wrote:I couldn't find how to do the velocity calculation you just did above (though I did try to use WolframAlpha), so I just estimated the gun's velocity as 130 m/s, assuming the terminal velocity for such a large heavy object was probably going to be higher.

I assumed a gun weighing 5kg, having an area of 10x10cm facing the wind on average, having a drag coefficient of 1/2 (more aerodynamical than a model rocket) and moving through default atmosphere. (you can edit the values in the table on that WA page and then hit enter to update the calculations) If all is well, I'm less than 50% off... for some firearm that can fire .22LR munition.


january1may wrote:That said, your 110 m/s figure doesn't really change the calculations significantly (considering the roughness of my other estimates).

Ah yes, I forgot to mention that explicitly: dropping the gun doesn't affect the velocity of the bullet radically. I'm not sure about the effects on the maximum height, though.

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Re: What-if 0081: "Catch"

Postby mojacardave » Wed Jan 29, 2014 11:17 am UTC

EpicanicusStrikes wrote:People have got to stop using Mythbusters to prove... well... anything. I don't care how 'sciency' they try to appear. It's still just a TV show and not worth consideration as hard evidence of anything other than "it's cool when things explode".


Still no link to this comic? Do I have to do everything myself?

http://xkcd.com/397/

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Re: What-if 0081: "Catch"

Postby cryptoengineer » Wed Jan 29, 2014 5:29 pm UTC

phlip wrote:

Right, yeah, I'm still not seeing the part where Mythbusters claimed that terminal velocity > muzzle velocity?


I was referring to squall_line's earlier post, where he said:

squall_line wrote:Also, I think that the Mythbusters posited (I don't consider most of their "conclusions" to be even close to scientifically rigorous enough to be called conclusions) that the only way for an upward-fired bullet NOT to be lethal on return to earth is if it was fired directly in the air and to back to earth base-first. Otherwise, on the parabolic arc, it would fall with the same velocity at which it left the ground, less a little bit for air resistance.


At no point did I claim they said it would fall back faster; the thing the MBs were wrong on (or maybe just squall_line) is the 'little bit' slower part; air resistance is
reducing the terminal velocity to 1/2 to 1/5 of muzzle velocity. Since energy goes with the square of the velocity, the injury is greatly reduced.

Just to be clear: Firing into the air is a Really Bad Idea. People do die from it. Most often it's from bullets shot at an angle. In that case, they reach earth again
with a much larger fraction of their original velocity.

CE

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Re: What-if 0081: "Catch"

Postby ps.02 » Wed Jan 29, 2014 5:31 pm UTC

Flumble wrote:Ah yes, I forgot to mention that explicitly: dropping the gun doesn't affect the velocity of the bullet radically. I'm not sure about the effects on the maximum height, though.

How much of muzzle velocity is attributable to bracing the gun and absorbing the recoil? My brain is too fuzzy this morning to do the math on that. Intuitively it seems like the bullet would come out noticeably slower if the gun is in free fall, as opposed to braced against the ground or your shoulder, but my intuition could be wrong. Perhaps the ratio of gun to bullet mass is already great enough for the difference to be negligible.

Of course the greater point is that there's no way a bullet fired from a weapon without anyone bracing or aiming could ever be easy to catch. What you really need is an automatic weapon firing dozens of bullets upward in your general direction. You might eventually get lucky and catch one. One would hope you're also wearing some sort of face shield.


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