Hey, it's me Destin. Welcome back to Smarter Every Day. So today I'm in California, and I have the great privilege of introducing the MAN, Alan Sailer.
嘿，是我Destin。歡迎回到Smarter Every Day。所以今天我在加州，而且我很榮幸跟你介紹這個人：Alan Sailer。
Alan Sailer is, if you don't know, one of the best high speed photographers that currently does the art. So I'm here in his garden, back behind his house, and we're going to basically study explosions underwater with some firecrackers.
You typically do it with the high speed photography method right?
Yeah, it's just an instant...instant of detonation, and I'm really looking forward to seeing uh...time.
Yeah, exactly! It's not just one moment. This is a M320 Miro Phantom camera, and what do you hope to learn here?
是啊，沒錯!它不只是一瞬間。這是一台M320 Miro Phantom攝影機，你希望在這裡研究些什麼？
I just wanna be impressed, so uh...do it. Three...two...one...zero!
Pretty cool. Let's look at the video.
Oh, we get ripple. Yeah.
OK, so we decided we wanted a lower exposure time and also a higher frame rate. So what we're gonna do is we're gonna change the lens.
About twenty feet... Yup...
Man! The uh... I wonder if that was from impact or if...if the bottle itself... No, it sucks in... There's cavitation appears on the top if you looked at the photograph.
Yeah? Yeah. Alright, let's just look at the video.
Alright, I have a scientific mystery that I need your help figuring out. Let's first define what an explosion is, alright? So basically it's a rapid formation of gas, and you have it contained in some type of mechanical device, and it increases pressure. And that mechanical restraining device will eventually fail and blow outwards, correct? But here's the question. After each shot I would go find the bottle on the ground, and the bottle would be sucked in on the top instead of blown out like you would think. This is counter intuitive, and we have to figure out why.
My theory is that as the bottle blows up on the bottom, it begins to shoot up like a rocket, and when it does this, it starts to wrinkle like grandma legs if you can see it, as it pushes the rest of the bottle forward.
Now, the cap has more mass than the side walls of the bottle, so my theory was that the bottle was pushing the cap, but the cap weighs too much, and so the bottle is outrunning the cap.
Alan on the other hand disagreed with me. My position is that after detonation there's nothing but high pressure in the bottle, but Alan referenced me back to some of his photos from his Flickr stream. He always sees bubbles after detonation. Always. What causes bubbles to form in a liquid? Of course. Cavitation.
A phase diagram is a fancy chart that uses pressure and temperature to describe what state the matter should be in. We're located about right here, which is twenty-three degrees Celsius. Now, there's only a couple of ways we can go from liquid over to vapor. One is we can move along to right here and increase the temperature. I don't think we're heating the water up enough in order to do that.
So I would conclude that Alan is correct. I believe we are lowering the pressure enough that we go beyond this vapor boundary and turn into vapor. And all we have to do to turn it back into a liquid is repressurize.
OK, let's look at the cavitation. Immediately after detonation, we're seeing bubbles all over the bottle. That's interesting, but a hundred and fifty microseconds later on the next frame, all the bubbles seem to be confined in one area. Basically the shock waves are bouncing off the sides of the cylindrical bottle on the inside, and they're bouncing back toward each other, and then they're interfering with each other and creating a low pressure spot. I think that's pretty cool because you can already see the cap beginning to suck in.
On the next frame you can see what I call the "Wrinkly Grandma Leg Effects." Now I think it's pretty interesting that the bubble is collapsing from the left to the right, which might mean that's a compression wave going towards the front of the bottle.
But what's confusing to me is the cap of the bottle is still being sucked in. So I convinced Alan to do a self-portrait with me, but what I didn't realize is this self-portrait would reveal more information than any of the other videos.
At the point of detonation, clearly we have high pressure in the bottle. Then you can see the lid suck in. And then...check that out. The lid shoots off. So that implies to me that you have low pressure, and then high pressure. Once the fluid is blown out of the bottom of that bottle, it begins to pull fluid out of the top of the bottle with it. So we have an oscillation in pressure. Where have we seen something like that before?
Sometimes when I'm drinking with a straw, I like to put my finger over the end of the straw and bring the fluid up out of the cup. And then I'll release my finger and watch what the liquid does. It oscillates. That's pretty cool, and I think that's caused by fluid momentum or the inertia of the fluid itself.
So this momentum effect of fluid applies to what we're doing too. As the fluid is blown out of the bottom of that bottle, you can see that it starts to pull liquid out of the top of the bottle and collapse the side walls of the bottle. That's pretty cool too.
So seriously, thanks for your time. It's way more fun to think this through with you. Anyway, if you want the high speed footage, feel free to download it. Draw me some pictures and show me what you think the shock waves are doing on the video. This guy did it. I don't think he's exactly right, but he took a good stab at it. I'm Destin. You're getting Smarter Every Day. Have a good one.
所以說真的，感謝你的時間。和你一起把這件事徹底想清楚很有趣。不論如何，如果你想要這高速攝影影片，請自行下載。畫幾張圖給我看，告訴我你認為震波在這影片中是怎麼運作的。這個人已經這樣做了。我不認為他完全正確，但他做了很棒的嘗試。我是Destin。你在收看Smarter Every Day。祝你好運。
By the way, Alan Sailer grows very good apricots.
The Russians have developed a way to use cavitation to create a bubble on the front of the torpedo. This is called Super Cavitation. If you fly the torpedo in that bubble, you have way less drag, and you can move that torpedo way fast.