Slow Motion of an AK-47 Underwater (Part 1) - Smarter Every Day 95

Hey it's me Destin. This week on Smarter Every Day I'm gonna trick you into learning science using a gun and a high speed camera. You remember the old pistols underwater video? Well this week I'm gonna do it with a better high speed camera, and a bigger gun. [music] [power tools] OK here's the setup. This is my dad's AK-47. First things first. The weapon is clear. So, on the back of this thing there's a little tab that the stock for the weapon, you can see it's captured right here, so all I've done is I've created the reciprocal of that out of metal. So we have that on this side, and on the other side we capture it with a J-bolt. So you can see, clicked in position. And here, captured with a J-bolt. If you don't know your way around an AK-47 it's pretty simple. You just take the top cover off, take this spring out, and then you can pull the bolt back. And when you pull the bolt back which is located right here you see this large piston. Now this piston is what operates the mechanism that re-chambers the next round. It's pretty simple the way these things work. As a bullet travels down the barrel, it passes a port right here, and this port allows gases to flow into a cylinder which drives this piston back, which moves the bolt and the bolt re-chambers another round out of the magazine. So here's the question. As the gas flows into the cylinder and begins pushing down this piston, what happens to all this water? My hypothesis is that it's going to slow the bolt down but we're gonna use the high speed footage to determine if this is correct. We have a little bolt cover here and we've painted the end of it white so that we can measure the velocity of it in a high speed video. First shot, air. As you can see here we're firing directly into this dirt burm. 3..2..1.. [gunshot] [several gunshots] [slowed down gunshot] Alright, time for water. [music] 3..2..1.. [gunshot] [laughs] That's a lot more water than last time. [music] OK we're gonna see if it still works. See if I owe dad another weapon. [gunshot] Still works. Alright so what's the answer? Does the bolt come back faster when the gun is in the air, or when the entire thing is under water? Before I show you the answer I need to apologise to you. If you look back at the pistols underwater video you can see that I just blew out the back side of the aquarium but the sides stayed intact. On this one I used tempered glass instead of normal plate glass. On tempered glass if you just break the edge the entire pane will shatter so obviously I messed up the experiment. I apologise for that. So here you go. Look at the difference between air and water. Enjoy. [music] So I've got two theories about why water is faster. Well if you think about it, if you have a round in the chamber you have a big column of water in front of it. So you have to accelerate all of that mass instead of just the mass of the bullet. That makes sense because you can look here and see that the primer's blown out, indicating that there's higher chamber pressure when we do that. That means that there's more force pushing on this piston. Also water is incompressible whereas air is compressible. That means that the pressure information gets to the piston faster. Alright well I hope you enjoyed that. My intent was to make something that you not only learn from that you enjoyed and earn your subscription, but unfortunately I kind of goofed up the aquarium thing so maybe I can earn your subscription on part 2 of this video. If you want to see that, just click where I'm at now or click the outtakes and you can check it out. Don't try this. I've got a little bit more experience than you might think. Anyway, I'm Destin. You're getting Smarter Every Day. Have a good one. [music] (Destin) I think now is a good time to discuss the terms of our agreement. - You replace the gun if it harms it in any way. [laughs] - Now wait, this doesn't sound like a discussion, it sounds like a mandate. [laugh] 3..2..1.. [click].. [laugh] Oh it was a bad round. - Yeah your tarp idea was terrible. [laugh] Completely in the wrong spot. (Destin) The tarp, to catch all the glass. [vacuum cleaner] It's a lot more fun if you pretend you're an elephant, picking up peanuts. Now you may have noticed there was a bubble of air that came out here through these ports. We'll talk about that in part 2 of the video. [ Captions by Andrew Jackson ] captionsbyandrew.wordpress.com Captioning in different languages welcome. Please contact Destin if you can help.

Channel: SmarterEveryDay

Views: 2,728,612

Rating: 4.8969102 out of 5

Keywords: Smarter, Every, Day, Science, Physics, youtube edu, Education, Math, Smarter Every Day, experiment, nature, demonstration, slow, motion, slow motion, education, math, science, science education, be smart, edu science, what is science, Physics of, projects, experiments, science projects, ak-47, AK47, underwater, rifle, assault rifle underwater, assault rifle

Id: W5K6YymPe_M

Length: 6min 15sec (375 seconds)

Published: Mon Jun 24 2013

Reddit Comments

[u/generalmook]

That was surprisingly enjoyable to watch. I'm gonna have to go through this guy's videos now.

[u/Crabski]

Sweet video as always, Destin!

I noticed from the underwater footage that, upon firing, a large amount of gas actually leaks out of the elbow connection on the bolt chamber. Is that an intentional design choice, or just a flaw in the construction? The only reason I can think of for why you might want that to happen is to regulate the pressure on the bolt so you don't damage the spring when firing a bullet with too much gunpowder packed into it.

From watching the video, though, it looks to me like it's just an unavoidable escape of gas through the connection between the two parts. Now I'm wondering if that happens to all AK-47s, or just this particular one. Either way, it's amazing how much the whole thing rattles and shakes around during discharge!

[u/TheLiberalSoup]

you really love fluid dynamics, dont you?

[u/sbjf]

For anyone wondering, this is the complete operating mechanism of an AK http://www.youtube.com/watch?v=q7d8wvEKoy0

[u/RogerMexico]

Pretty much sums up how I feel about Smarter Every Day posts.

[u/[deleted]]

I wonder if he has an AR-15 underwater firing footage.

[u/Yamaharacer]

That was awesome experiment sir . Thank you.

[u/xHaZxMaTx]

Awesome video and awesome music! Reminds me of Ratatat's early stuff. Definitely gonna have to check out more of his stuff.

[u/[deleted]]

I find it very fascinating how fast the cracks in the glass form. I mean, everything moves very slowly and then out of a sudden half of the glass is shattered!