pesco at July 23rd, 2013 14:57 — #1
felixtannenbaum at July 23rd, 2013 15:10 — #2
Can someone with some sturdy physics knowledge talk about what it is we are seeing? is it the shock wave? does it just sort of collapse on it self? There doesn't seem to be many bubbles, but wouldn't some sort of gas be created?
(I am unable to listen to it at work so I don't know if the two guys discuss it, so pardon me if they answer this in the video)
jandrese at July 23rd, 2013 15:28 — #3
Wow, the guy fired the gun with his hand. He's a braver man than me, I would have worried about backpressure from the water causing the chamber of burst. This seems like the kind of experiment where you would really want to use a gunstand and some rope to actuate the trigger.
radiosilence at July 23rd, 2013 15:30 — #4
This video was filmed at the same time as one for YouTube science channel Smarter Every Day. Destin (the host) uses the same camera setup to fire an AK-47 underwater and talks about exactly what's happening.
radiosilence at July 23rd, 2013 15:33 — #5
See the video I just posted in another reply. The host of that show has fired various gun underwater in previous videos using a stand/string rig to pull the trigger; this is the first time I think he's done it holding the gun himself.
wbeaty at July 23rd, 2013 16:22 — #6
Little-known everyday physics: all underwater bubbles are musical instruments! When stimulated (depth charges, guns, or just by whacking nearby rocks together) they can give out bell-like tones. Clouds of bubbles give out deep bass notes, as when beating meringue or when performing the Hot Chocolate Effect. So, SWIMMING POOL TRICKERY: http://amasci.com/~billb/cgi-bin/instr/instr.html#hot
synesthesia at July 23rd, 2013 16:25 — #7
I'm worried as well. Isn't this super dangerous? Cant shooting some of these guns underwater make the chamber explode?
progo at July 23rd, 2013 16:50 — #8
The evidence shown empirically says no -- for these particular guns. :^)
But, considering all the trouble they went through with the periscope and stuff, it would seem prudent and not a lot of extra work to remotely fire any gun you are abusing with an off-label use, in case it's not as stable and indestructible as you thought it was. The Mythbusters usually don't fire off gun experiments by hand unless they're sure they have complete control of the situation.
synesthesia at July 23rd, 2013 17:35 — #9
yeah, i remember a mythbuster chapter where a shotgun just burst open. Kept me wondering.
phanatic at July 23rd, 2013 17:59 — #10
Shotguns have wide bores, and long and thin barrels. Shotguns don't develop a lot of chamber pressure, but the volume of the barrel means that's a lot of water that needs to be pushed out of the way, and not a lot of material to withstand the pressures that develop.
Both the AK-47 and the handgun shown in this thread have relatively low chamber pressures and short barrels. I'm surprised the AK handles it so easily, though. There's no chance in hell that I'd try this with a gun firing a full-length cartridge.
felixtannenbaum at July 24th, 2013 15:25 — #11
holy crap- that was awesome!!
this guy is like the apex Michelangelo of Rednecks- really a wonderful mind paired with a great relaxed ability to talk.
timquinn at July 24th, 2013 18:07 — #12
Thanks for that. Both of those videos were completely great. I suspect they did some experimenting beforehand to make sure this would not kill them. They don't seem like morons.
thetorchpasses at July 25th, 2013 14:30 — #13
I can give a barely-educated guess as to what's going on...
The gunpowder ignition creates a hot gas (obviously) that expands. The water is denser (obviously) so it keeps the gas contained rather than dispersing as it would in air. As that hot gas expands, it cools, aided by the water. The incompressibility nature of water creates a high pressure situation in the gas bubble, causing it to collapse back in on itself. That rapid collapse in turn causes the gas to heat back up, but not as much as before because the water has absorbed some of the heat. That residual re-heating of the gas causes it to expand, repeating the whole process but to a lesser degree as heat is absorbed by the water.
Or I could be completely and embarrassingly wrong.
pesco at July 28th, 2013 14:57 — #14
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