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Hey Crazies. I absolutely love polarizing filters.
They're a common feature in sunglasses to help reduce glare.
They're used in photography for a similar reason.
But my favorite polarizer effects happen when you have more than one.
How they filter light depends on their orientation.
This allows us to see stress patterns in just about anything transparent,
including your car window.
And how that works is surprisingly straightforward.
Light is literally all we can see.
It's how our vision works.
Light enters our eyes and our brain parses out the information.
Direction gives us a sense of the shapes and sizes of objects.
The wavelength of the light is interpreted as color.
Well, at least for the tiny portion of the spectrum we can actually see.
But light has other properties that we can't see,
at least not without a little help.
That's where a pair of polarized sunglasses can come in handy.
Polarization is just the orientation of a light wave.
It's something we can't normally see.
This is a scientific tool that allows your brain to see polarization.
These lenses interact with the polarization of light, which changes how we see the world.
And we can take advantage of that to see some really cool stuff.
Stuff like this.
Beautiful, isn't it?
What is that? A stress pattern.
It's telling you something about the internal structure of a ruler.
Lots of objects have internal stresses based on how they're made.
Polarizing filters, also known as polarizers, let you see a remnant of that process.
You can tell the plastic in this ruler cooled inward from the edges, forming stress rings.
This wicked cool effect is called "photoelasticity."
But just having a pair of polarized sunglasses isn't quite enough to see it.
The light needs to be uniformly polarized first.
And unfortunately for us, most light is randomly polarized.
That means all the waves from the light source are randomly oriented.
We need them to look like this first. Uniformly oriented.
That's why we need a second filter.
One filter polarizes the light.
A second filter lets you see that orientation.
As we turn the second filter, the light gets dimmer.
Eventually it'll be oriented perpendicular to the first, and no light survives.
It goes black.
Of course, you probably don't have a big bag of polarizers laying around,
but you do have the LCD screen you're watching this video on.
The screen in your phone or connected to your computer already has a polarizing filter in it.
Just open an empty canvas in Microsoft paint or whatever
and you've got yourself a source of uniformly polarized white light.
Now all you need is a pair of polarized sunglasses and you're good to go.
Just rotate the sunglasses in front of the screen and you'll see it go dark, just like with my square filter.
I have one of these taped to my phone camera, so what you're about to see will be as if you're wearing the glasses.
So we've got one polarizing filter in the computer screen and one polarizing filter attached to my camera.
The screen looks a little dark because the filters are perpendicular to each other, or at least close.
But watch what happens when I bring in the clear plastic ruler.
Bam! Stress pattern.
But if the filters are perpendicular, how does any light get through?
The plastic material rotates the light.
Yes, it's true that two polarizers oriented at 90 degrees should block all light.
It's not perfect because the effect is wavelength-dependent, but that's a whole other conversation.
The first one makes the light uniformly polarized,
and the second one will block any light perpendicular to its own axis.
But all bets are off when you stick something in between.
This ruler rotates the light wave as it passes through.
By the time the light gets to the second polarizer, it's not perpendicular anymore.
The effect happens with reflection, too.
Here's a picture of my iris with and without polarization.
It's taken with my phone camera.
The polarizer square is covering both the lens and the flash.
You can see it with any iris, but it's more dramatic with blue and green eyes.
Anyway!
Patterns like this might help you to notice stuff you missed with your own eyes.
The pattern in this protractor seems to be radiating from an off-center point on the edge.
A closer look reveals a tiny chip in the plastic.
Something similar happens with my triangle ruler.
With the polarizers you can see a fine crack in the plastic.
It's obvious the stress has been released at that point,
which deformed the overall pattern quite a bit due to the redistribution of internal forces.
Engineers do this all the time to test parts.
Of course, if the rotation of that light happened uniformly, the ruler would be solid white.
That's not what happened, though. There's a clear rainbow effect.
The rotation the light experiences doesn't just depend on the stress of the material,
but also the wavelength of light.
You can actually see where the forces are greatest within the plastic.
The same thing happens inside your car windows.
These spots are stress points within the glass.
Points of maximum internal force.
See, there are two basic ways to make glass.
Annealing and tempering.
Annealing is pretty straightforward.
The glass is molded and then allowed to cool gradually.
That means there are no particular places within the glass where you see an excess of stress.
Front wheeled sh-...
Front wheeled shields. (Laughing)
Front wheeled-.
Oh no! (Laughing)
I can do this.
The front windshields of vehicles are made with annealed glass,
and so are the windows in your home.
Tempered glass is different.
The glass is still molded, but it's cooled off quickly from the outside,
which distributes the internal forces unevenly.
We end up with high tension in some places and high compression in others.
Why would anyone do that? Safety.
Safety? Safety?!
If you ever end up with your car in a body of water, you're going to be happy with this design.
Water exerts a thousand times the pressure of air, so you won't be able to open your car door to escape.
The only way out is if you can safely break your windows.
But here's what annealed glass looks like when you break it.
You end up with a few large and very sharp pieces of glass.
The water would have thrown several of those at you as it poured in.
And climbing out over any pieces that stayed attached to the door would be dangerous.
Tempered glass, on the other hand...
Ah!
I've got to remember to stop saying that.
The forces on the outside make it incredibly strong to protect you from things like rocks.
It's very difficult to break, as you can see from my first few attempts.
The exterior strength can be overcome, though.
And when it is, the interior forces are ready to tear the glass to shreds.
It just wants an excuse.
If you hit the glass at or near the corner - its weakest point - then and only then will the glass break.
When that happens, the internal stresses will shatter it into a bunch of tiny pieces.
Here's an up close look. It's completely destroyed.
That means if you ever find yourself in that underwater situation,
there won't be any large pieces of glass being thrown at you.
There's no more window.
The water pours in quickly and you can climb out no problem.
Not that I anticipate ever being in that situation, but better safe than sorry.
Anyway, super main ultimate point:
If you have a pair of polarized sunglasses, then you have a powerful scientific tool.
They let you see the orientation of light, a property otherwise invisible to us.
With that new power and an LCD screen,
you can peer into the internal structure of a material.
You can see where it's already under stress even before you do anything to it.
Think about that the next time you see spots in your car window.
Though you may be too busy wondering how I made my 3D animations.
Look no further than After Effects, which you could learn how to use by joining Skillshare.
Skillshare is an online learning community with thousands of classes
for anyone who wants to explore their creativity or learn new skills.
When it comes to 3D animation, you don't always need fancy modeling software.
Sometimes After Effects will do.
If you're unfamiliar,
I would recommend checking out The Ultimate Guide to 3D in Adobe After Effects by Jake Bartlett.
First, he'll walk you through how 3D cameras and lighting work.
Later in the class, you'll learn how to give your objects depth.
Usually that's good enough for me.
But if you need to make spheres or texture surfaces, you'll want to work with something like Cinema 4D or Blender,
both of which Skillshare has plenty of classes on.
If animation isn't your thing, though, they have other classes that might match your interests.
If this sounds like a service you might be interested in, check out Skillshare.
The first 1000 people to use my special link will get a one-month free trial.
It also let Skillshare know you heard about them for me, which helps out the channel.
So are you going to try this stress patterns experiment yourself?
Let us know how it goes in the comments.
Thanks for liking and sharing this video.
A special thanks goes out to my Patreon patrons and YouTube members like Kevin Flanagan,
our new Einsteinium level supporter.
Thanks Kevin!
Don't forget to subscribe if you'd like to keep up with us.
And until next time, remember: It's okay to be a little crazy.
I appreciate all the recommendations that people left in the comments of the last video.
Everyone learns a little differently, so having a large collection of sources in one place can be super helpful.
Thanks to all the commenters and thanks to everyone for watching.