- Hey it's me Destin. Welcome back to Smarter Every Day. If you can't tell, I am on a kayak here. And we have a lot of the kayak. I guess it was a week
ago I uploaded a video to the second channel. And we were trying to fish, right Trent? - [Trent] Yeah. - Oh you're over there. - [Trent] I'm over here. - So we were fishing because
we've been working hard. And we just wanted to relax. The fish weren't biting. We're out here on the kayaks
and we decided to just play with our headlamps in the water. There's milfoil all in the water here. And we discovered
something really really fun with our headlamps underwater here. And I'll just let you watch
a little bit of that video. - [Destin] Okay, you ready to show them? Get your flashlight, go to the other side. So we figured this out. Put your light in the water. And you could see the beam right? Now stick your arm further underwater. And aim up and it bounces
off the top of the water. How cool is that? Neat. Okay now if you go too
far, it'll break through. That's cool, there's a
thing called Snell's window. You know about Snell's window? - [Trent] Nah uh. - If you're scuba diving for example, and you're in the water, and you look up, you could see the sun. But you could see it from a certain angle. So there's this window right above you. Where you could see the light
coming through it beyond that, the light reflects out. And so what Trent student
over there has to do with the index of refraction water. Can I try it? - [Trent] I'm moving with the- Yeah. - [Destin] Here trade the lights with me. Here's the camera. - [Trent] Oh dude that
looks great from over here. - [Dustin] Isn't that neat? - And then it should just bust through. Look at that. You could see the beam goes through. - [Trent] Dude it bends more with the- - Did you see what happens though? Like half the beam
punches through the water. Half the beam doesn't, watch. So the beam in the water goes dark. So coming up, up, up,
then it starts to go dark. And the whole thing punches through. - [Trent] Whoa. - Okay fast forward to now. We've got lasers now because- some people said in the
comments that it would be really cool if we did this with lasers. Do you have those laser goggles? I gotta say this is the only
time I've ever wore lasers. HaHa Laser goggles.. We look like goobers man. Alright so here we go. We got a green laser. It's not waterproof so I have it in a bag. For 532 nanometer laser. And I'm wearing 532 nanometer goggles. Which means I can't see this. I have no idea what's going on. But if I this, okay I can
see that that's green. So what we're going to do
is we're going to continue to play with words I could
not pull from my brain in the last episode, which was: Total Internal Reflection. That's what's going on here. So we're going to play with
Total Internal Reflection. I have a bunch of goodies in my kayak. Okay you ready? - [Trent] You have no
idea how goofy you look. - This makes so much- I love it so much! Alright, so first up. Oh that's heavy, it's
making my kayak move. Okay I have sheet of acrylic. It's moving my kayak cause it's so big. I'm cutting the light off. Gah-lee my nasty mustache. So if we shine this laser into- Oh that looks red. I could see in the the viewfinder. If I shine this laser
into the side of this square acrylic block, you
can see If I'm at a 90-degree angle to the block, the laser
just goes straight through and bounces off the other side and diffuses a little bit, right? But what happens if I angle
this laser and I bounce it. Look at that, the whole block lights up. And reason it lights up, is
because that angle up top is an acute angle and all
that light bounces around on the inside. Dude this works so much better
than I thought it would. Alright so isn't that neat? Okay so if we go down- Let's go down and see if
we can light this block up. Let's do it, boom we hit the corner. Look at that stuff starts bouncing around. So this Total Internal
Reflection is a thing. So if we just go straight
across, you know. Some stays in some stays out but- Oh look at that what just happened? Oh my gosh I'm bouncing it back and forth. Did you see that? You can't see that can you? Do you see that? What's happening? It's bouncing back and
forth on the inside. - [Trent] I can see it
with my goggles over here. - You could see it with your goggles? Okay here we're going to do it this way. Boom, right there. You see it bouncing back and forth? Can you see it? Can you zoom in? - [Trent] It's really
hard to see it on camera. - Is it really? How do you know? You got laser goggles on dude. - [Trent] I can see
through the viewfinder. - So long story short if you
could bounce a laser underneath the angle of incidence, then you can get what's called
Total Internal Reflection. And this happens when you have
two transparent materials. Two transparent materials
like air and water or acrylic and air or acrylic and water. Okay so that's acrylic. Let's move on to the next thing. Do we have the fiber optics? - [Trent] Yes we do. - Let's get the fiber optics on the kayak. Okay Total Internal
Reflection, you totally- Oh I don't need these. You totally know what's up with that. So we get a flashlight,
we got fiber optics. I can't believe we got all
this stuff on the kayaks. So you know that that's
how that works right? So you got the light that's
going into the fibers and it's bouncing around
on the inside of the fiber and it's going all the way through. You know what's about to happen. You know what's about to happen. Where's my laser? (laughs) Oh shoot! Alright here we go. Laser, look at that. Same thing, except I can't see it because I have laser goggles on. But as I move around, I'm
assuming that it's going through the fibers all the way to the end. And the reason it's able
to do that is it's bouncing all the way down the fibers like a pipe. Total Internal Reflection. This is all stuff you know. This isn't new stuff. So we're just demonstrating
that because it's awesome. What happens if I shine
these fiber-optic lasers into the water? Oh it kind of looks like a
laser flashlight inside that. Okay, okay alright so now the
way that fiber-optic works, is really interesting. I happen to bring a bigger version of this fiber-optic with me. This is a large dowel of acrylic
because obviously this is what you take on a kayak. So the way this works- I'm going to cut this off. This is so going to look
like a lightsaber dude. Oh golly. Are you ready for this? Ready, one, two. Whoa. - [Trent] Put your goggles on. - Oh yeah my goggles I'm sorry dude. Thank you. Oh man. Does it look awesome? - [Trent] It does look amazing. - Okay can you see through? - [Trent] I could only
see it through the camera. - Yeah because we're being safe. - [Trent] It looks incredible. Okay so the reason this looks
like a gigantic fiber-optic is because it is. You could tell that it's an
optic cause of the way it is. Alright so you've got this
low angle of incidence here, it's amazing. - [Trent] Put it in the water. - Can I light up the whole water? I can't see that. Is it lighting up the water? - [Trent] We're about to look. Oh my god. - Is it lighting up the water? I've taken up- It's like a big flashlight at the end. I don't care, I'm going to
quit talking and just do stuff. You could make a camera
that would see all the way to the bottom, couldn't you? It's a light pipe. - [Trent] A light pipe. - You could totally see if
it was polished on both ends, you could make a camera
that could would go all the way to the bottom. Alright we brought a gigantic
piece of acrylic on a kayak. So we've done the square acrylic. We've done the fiber-optic,
both small and large. It's time for the Christmas ornament. Okay, we have a Christmas ornament and we've got murky water below. We're going to need goggles for this one. Oh that's acoustically pleasing. You want to hear that. (bubbling) That was really nice so- Oh we got some milfoil in there. Oh it's that's gonna- That's gonna make it more interesting. Just dudes on boats with
lasers, that's all this is. Freakin' lasers on kayaks
that's all this video is. Alright so here we go. We should be able to see the
light go straight through. And I have no idea what's- I can barely see it. You could barely see it. But what should happen- I'm going to turn this off here. But what should happen, is
if I change the angle inside we should get some weird
bouncing that's going on, right? Yeah we do, let's get up here close. So we're straight here. So we're firing straight
inside right there and if I start to bounce things
off the inside by shooting it like across the cord
instead of the diameter, we get all kinds of weirdness. What would be really cool
is if we could take a shadow graph of this, if we could like
blast this onto a large wall we would see all the microbes and little things living inside there. Internal Reflection does
not have to be total. So if you meet this interface
between the glass and the air for example, some of the light goes out some of the light stays
in and so that's why Total Internal Reflection is so cool. Oh look at that, when I hit that seam- You see that? When I hit the meniscus
or whatever that's called at the top where it curves, it just totally blasts the whole bulb. You see what I'm saying? It makes a huge globe so boom. I hit the curve, lights up
straight across doesn't light up. That's fun, we're having fun. We're learning things. We're learning things
on kayaks with lasers. Okay so now it's time for
more good sounds, here we go. I think it's time. You think it's time? - [Trent] It's time. - Laser under water. We're going to see if we
can bounce the laser up off the bottom of the water. Here's the Christmas ornament. Everybody knows what's going to happen. If the angle that hits the top
of the water from underwater is less than 50 degrees, then it'll bounce back into the water. But if it's above that, it'll punch out. I just want to see it from underwater. Okay here we go. Tilt it back down at some point, all of the light should bounce underwater. You should see the beam
get lighter and lighter as I pointed up more that reflected beam. So as it's laying down,
you should see full laser beam in the water. As I tilt it up and it
bounces off the top, that reflected beam should
get lighter and lighter as I go up and then at the
maximum angle once it hits the critical angle, the
one inside should go dark and all the light should
come straight out. Which is completely rad. Alright so in this video we
talked about the ability of light to bounce on the inside
of an object in a certain way called Total Internal Reflection. I would like to tell you
about a book that made me internally reflect as well
it's called Just Mercy by Bryan Stevenson. This episode of Smarter Every
Day is sponsored by Audible. And I just really want
you to read this book. Bryan Stevenson is the guy that
decided to be the lawyer for Anthony Ray Hinton who was
wrongly convicted of murder in Alabama, sentenced to death row. Bryan Stevenson came to his aid and helped Anthony Ray Hinton get out of death row. It's an amazing book. I loved it. I made me reflect internally
about my role in society and how I could help
those without a voice. So please go check this out by
going to Audible.com/Smarter or texting the word smarter to 500-500 The first books free. You can get two free audible originals. This is a big book for me. I mean in terms of making
me think about my place in the world and what kinds of things I could do to help others. So again you could get a free
book or a free 30-day trial in Audible by going to
Audible.com/Smarter or texting the word Smarter to 500-500 I
highly recommend this book. You will totally dig it. So anyway, thank you for enjoying
Total Internal Reflection time with me here on the river. Yeah, that's amazing. That's really cool stuff,
so I hope you enjoyed that. Last thing, feel free to
unsubscribe to Smarter Every Day. If you feel like this video earned it. By unsubscribe I mean you
could unsubscribe and then resubscribe maybe, if it earned it. And then click the bell
to turn notifications on. If not, that's no big deal
but I hope you enjoyed this. I mean like playing with
Total Internal Reflections on a kayak, it's just
absolutely awesome so I hope you enjoyed this half as much as I do. I'm Destin, again feel free to subscribe. Getting smarter every day. Have a good one, bye.
You just know there are some hikers who only saw this from a distance... out on the water, creepy green glow, sometimes lighting up the water itself.
We're going to hear about this from another perspective on /r/nosleep or something someday.
Green lasers underwater is officially one of my favorite things.. as of now
At 11:43 the reflected laser moves because of the surface waves, it reminds me of an experiment Steve Mould did with mirrors on speakers and pointing a laser at them.
Anybody knows of videos exploring that any further?
https://youtu.be/C-V1uXeyGmg
Should Jedi wear goggles so their eyes aren't hurt by their lightsabers? But then they couldn't see the blade...I have several questions.
Just remembered this when you talked about a camera that sees to the bottom. On the Saturn V they used fiber optics to film inside of the fuel tanks.
looks like some fun for u/SeeThroughCanoe
Bill Hammack “The engineer guy” also did a video on this topic a few years ago.
Fiber Optic Cables: How They Work
My biggest question or concern about this video regards the laser breaking the surface and hitting aircraft. Have you ever covered how this works and why it’s a problem for pilots?
I was pretty disappointed that Destin didn't go in to the "why" of this too much (i.e. refractive indexes, Snell's law, angle of incidence, etc). He just kept saying "you already know this". I do, but I didn't learn it until college, in a course I know many others didn't take. It'd be nice to get more in depth on the science on Smarter Every Day, I feel like that's been missing from the channel lately.