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Author Topic: Gun myth for gun experts to comment on  (Read 767 times)

Dominus Nox

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Gun myth for gun experts to comment on
« on: December 13, 2006, 06:50:46 pm »
A friend of mine told me a gun myth that I wanted to get commentary on.

Basically it goes like this: If you take a gun and fix it to a mount so it is perfectly perpendicular to the ground, and the ground if flat, and you hold an idential bullet to the the the gun fires next to the gun barell and release it the instant the gun is fired and the bullet from it leaves the barell, the two bullets will hit the ground at the same instant.

The belief is that gravity pulls both bullets down at the same speed whether one is moving foeward at high velocity or not, so both will drop at the same rate even if one is moving forward at high speed, and thus both will contact the ground at the same instant, even if the one keeps sliding, skipping or rolling foward and the other just drops straight down.

Any gun experts want to comment on this?
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Kyle Aaron

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« Reply #1 on: December 13, 2006, 09:53:41 pm »
Yes, it's true. And you don't need to be a gun expert to know it - it's late high school physics.
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Dominus Nox

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« Reply #2 on: December 13, 2006, 10:21:57 pm »
Quote from: JimBobOz
Yes, it's true. And you don't need to be a gun expert to know it - it's late high school physics.


I thought so, still it's one of those things that may seem obvious at first glance but has a trick in it.

Thanks for the confirmation.
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O'Borg

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« Reply #3 on: December 14, 2006, 07:11:07 am »
Quote from: JimBobOz
Yes, it's true. And you don't need to be a gun expert to know it - it's late high school physics.
:confused:
It's been a long time since I did physics at school, but isnt normal gravity something like 32 meters per second (squared), whilst the muzzle velocity of a pistol is going to be 900m/s or more?
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flyingmice

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Gun myth for gun experts to comment on
« Reply #4 on: December 14, 2006, 01:08:43 pm »
Quote from: O'Borg
:confused:
It's been a long time since I did physics at school, but isnt normal gravity something like 32 meters per second (squared), whilst the muzzle velocity of a pistol is going to be 900m/s or more?

Those are two perpendicular forces. The gravity acts on both bullets. The velocity downward is the same, but the fired bullet has an additional horizontal component. If there is an upward component to the fired bullet, some of the forces will cancel each other out, and if there is a downward component the two forces will add, but not if they are perpendicular.

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joewolz

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« Reply #5 on: December 14, 2006, 01:30:38 pm »
Yes Nox, it's all true.

Of course, good luck finding a test area...
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flyingmice

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« Reply #6 on: December 14, 2006, 02:04:44 pm »
Quote from: joewolz
Yes Nox, it's all true.

Of course, good luck finding a test area...


Especially since this whole thing assumes perfectly flat (no curvature, no protrusions or dips) ground and a vacuum (no air gusts or lift) to work. Welcome to physics-theory-land! :D

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Dominus Nox

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« Reply #7 on: December 14, 2006, 04:10:12 pm »
Quote from: O'Borg
:confused:
It's been a long time since I did physics at school, but isnt normal gravity something like 32 meters per second (squared), whilst the muzzle velocity of a pistol is going to be 900m/s or more?


32 feet per second, actually, it'd take like 3g to have a downward falling speed of 32 meters per second.
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Dominus Nox

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« Reply #8 on: December 14, 2006, 04:11:19 pm »
Quote from: joewolz
Yes Nox, it's all true.

Of course, good luck finding a test area...


Well, you could theoretically test this with like BBs in a large enclosed area, like a stadium, but it's not necessary.
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O'Borg

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« Reply #9 on: December 14, 2006, 05:14:35 pm »
Quote from: flyingmice
.... but the fired bullet has an additional horizontal component.

-clash

I blame the departmental pre-XMas p!ss up last night for making me misread the original post and think the gun was pointing straight down :o
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Kyle Aaron

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« Reply #10 on: December 14, 2006, 07:11:51 pm »
Quote from: O'Borg
I blame the departmental pre-XMas p!ss up last night for making me misread the original post and think the gun was pointing straight down :o

In which case you shot yourself in the foot and are too busy screaming to read the meters to see which landed first, the dropped round or the fired one.
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O'Borg

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« Reply #11 on: December 14, 2006, 08:05:07 pm »
Quote from: JimBobOz
In which case you shot yourself in the foot and are too busy screaming to read the meters to see which landed first, the dropped round or the fired one.

I think I actually rolled that once as a critical fumble in SpaceMaster. :D
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SunBoy

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« Reply #12 on: December 18, 2006, 10:39:09 am »
Well, I thought at first that the gun was pointing upwards (and I was starting to laugh), then down (and I was starting to scream), then I got it (and I had to start thinking).
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TonyLB

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« Reply #13 on: December 18, 2006, 10:42:51 am »
Quote from: Dominus Nox
Well, you could theoretically test this with like BBs in a large enclosed area, like a stadium, but it's not necessary.
At the kids section of the Air and Space museum near us, they've actually got a device that does this in miniature:  It's a spring-loaded rod, and when you release the catch it hits one BB sideways (pretty hard!) while simultaneously jerking a trapdoor cleanly out from under a second BB at the same level.  You can hear the single, loud "click" as they hit the ground at precisely the same moment.  It's cool. :D
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Nicephorus

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« Reply #14 on: December 18, 2006, 12:33:10 pm »
Quote from: O'Borg
I blame the departmental pre-XMas p!ss up last night for making me misread the original post and think the gun was pointing straight down :o

That's because the original post is written wrong.  The gun should be parallel to the ground, not perpindicular

In theory, it would work, but it would be tricky to actually make it happen in full scale.  The fired round is likely to be deflected up or down a bit by the air unless it's perfectly shaped.