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.