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I've always wondered...

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Re: I've always wondered...

Unread postAuthor: userjjb » Fri Aug 17, 2007 8:54 am

Pilgrimman wrote:Why is it that when I fire my pneumatic, I can't see any white "steam" come out the muzzle, but when I watch a video of the came shot, the camera seems to pick up the "steam"? It's been irking me for a while... :lol:

I'm a little slow on the draw, but one reason not offered yet is that the CCD in most digital cameras/camcorders are responsive to wider ranges of wavelengths of light than the human eye. Water vapor is transparent to the naked eye but opaque to infrared, so your camera could see the water vapor even though you couldn't.
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Re: I've always wondered...

Unread postAuthor: Gepard » Fri Aug 17, 2007 9:55 am

userjjb wrote:snip>Water vapor is transparent to the naked eye <snip>


Surely not as otherwise we wouldn't see clouds.

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Unread postAuthor: paaiyan » Fri Aug 17, 2007 10:57 am

About the whole blinking thing. Last time I checked, light moved faster than sound, I'm not sure if that's still the case though. </sarcasm>

Since light does move faster than sound, wouldn't you see the vapor before you blinked due to the light reaching your eyes before the sound reachign your ears?
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Unread postAuthor: spud yeti » Fri Aug 17, 2007 11:15 am

You so close to the gun its probably (almost)instantaneous, and your eyes start blinking before you shoot or are blurred, thus not seeing the steam.
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really good quote/phrase here
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Unread postAuthor: paaiyan » Fri Aug 17, 2007 11:18 am

Perhaps when the gun is fired, small amounts of water condense, but not enough for the human eye to notice. When gasses expand, they cool. Perhaps, when these expanding gasses cool and condense some water vapor, the water vapor produces a diffrent amount of infrared radiation than the surrounding environment, thus showing up on the camera due to it's sensitivity to changes in the infrared and ultraviolet spectrums.
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Unread postAuthor: rednecktatertosser » Fri Aug 17, 2007 11:32 am

paaiyan wrote:About the whole blinking thing. Last time I checked, light moved faster than sound, I'm not sure if that's still the case though. </sarcasm>

Since light does move faster than sound, wouldn't you see the vapor before you blinked due to the light reaching your eyes before the sound reachign your ears?


This is true, but you have to account for the fact that there is a projectile in the barrel which is probably not moving faster than the speed of sound, and is therefore blocking the water vapor from exiting the barrel before you hear the report..
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Unread postAuthor: paaiyan » Fri Aug 17, 2007 11:46 am

rednecktatertosser wrote:
paaiyan wrote:About the whole blinking thing. Last time I checked, light moved faster than sound, I'm not sure if that's still the case though. </sarcasm>

Since light does move faster than sound, wouldn't you see the vapor before you blinked due to the light reaching your eyes before the sound reachign your ears?


This is true, but you have to account for the fact that there is a projectile in the barrel which is probably not moving faster than the speed of sound, and is therefore blocking the water vapor from exiting the barrel before you hear the report..


This is true, but I think my last explanation will be my final answer.
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Unread postAuthor: Modderxtrordanare » Fri Aug 17, 2007 1:22 pm

paaiyan wrote:Since light does move faster than sound, wouldn't you see the vapor before you blinked due to the light reaching your eyes before the sound reachign your ears?


Why are we assuming that the blinking obstructing our view of the vapor is caused by the report and not just natural blinking? Or blinking in preperation for the report sub-conciously when you push the trigger.
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Unread postAuthor: paaiyan » Fri Aug 17, 2007 1:24 pm

Ok, blinking theory retracted people, geez. I'll go with the cool gasses interfereing with IR radiation that I said after that.
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Unread postAuthor: joannaardway » Fri Aug 17, 2007 2:21 pm

I usually get the vapour evident to the naked eye, but as the OP has experienced, it does usually seem to show up a bit better on camera.
I think it's a quirk of the camera's CCD because of that.

Also, some experiments of mine with triggered camera flash circuits and cameras prove that the vapour is formed significantly after the projectile has left the barrel. I don't have an exact time figure, but I reckon it could be as much as something of the order of up to 100 ms afterwards.

That's plenty of time to blink before the vapour is formed. However, a blinking reflex is unlikely to be the full explanation.

There is also another assumption being made by people about human reaction.
It is being assumed that there is instant conscious recognition of the vapour. Humans have a small delay between seeing something and conscious reaction to it. Your eyes may well see the vapour as it forms, but you may not register that you've seen it.
Also, given the shock noise, the sensory regions in the brain have their attention on sound, rather than vision at the exact time.

The combination of transparancy, blinking, delayed vapour formation, and the consciousness time, this might be part way to an explanation.
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Unread postAuthor: paaiyan » Fri Aug 17, 2007 2:23 pm

Quit making us look dumd joanna, it's not nice, haha. I knew all that, I was just testing you guys...
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Unread postAuthor: joannaardway » Fri Aug 17, 2007 2:30 pm

Oh crap, I'm not trying to make anyone look dumb... sorry. I think it's genetic... *runs*
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Unread postAuthor: paaiyan » Fri Aug 17, 2007 2:33 pm

Haha, it's all good. I still like my theory. I think it ties in with yours pretty well. My second theory I mean. Now when you say genetic, are you not-so-subtly implying that women are smarter?
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Unread postAuthor: joannaardway » Fri Aug 17, 2007 2:53 pm

paaiyan wrote:Now when you say genetic, are you not-so-subtly implying that women are smarter?

No... but I like that idea.

My planned point was that interest in engineering and good intelligence run in my family.
I have so many weird conversations about sciences.
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Unread postAuthor: Marco321 » Fri Aug 17, 2007 6:35 pm

My coaxial produces water vapor at 40psi. i can see it clearly with my eyes. It did it when it was cold at night and hot during the day. I can prove its water vapor because after a few shots, i had an empty chamber and stuck my finger down the barrel, it cam out wet. The physics also says its water vapor

I believe joannaardway is correct too why it can be seen easier on a camera than to the naked eye.
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