>> ALEX NICKEL: Woah!
Hey guys, I’m here in the kitchen, let’s get technical.
Recently, I got this, the Curiosity Box by Vsauce, and, in it, came these little beads.
They’re little polymer beads, which grow up to 300 times their size, if you put them in water for 12 hours.
*music*
I don’t have enough space on my SD card for 12 hours.
Anywho, I could talk about the science behind why these beads get so big, but, what I think
is even more mind blowing is how they become invisible under water.
Now you can see it, now you can’t.
Whaaaaaaat?
I put a ball in one of these cups, can you tell which one it’s in?
Vote using by clicking the i in the upper right.
Ok, here’s the answer: psych, there’s balls in both, you just got bamboozled.
Today, let’s get to the bottom of why do these balls magically disappear under the
invisibility cloak of water.
>> RON WEASLEY: What is it?
>> HARRY POTTER: Some kind of cloak.
>> RON: Well, let’s see then, put it on.
WOAH!
>> ALEX: Well, this isn’t magic!
It’s science.
Here, let me give you a hint which will help you find out why this happens.
Check this out: if I stick this straw through the ball like this, then you can see that the ball kinda distorts the straw a little bit.
But, if I take the straw, and put it back into the
water, the distortion disappears.
Ok, so that’s a bit of hint, and to actually start answering this question, we must take
a look at why the straw ever looks distorted in the first place.
You ever notice that?
When you put a straw in water, it looks weird.
Whaaaat?
This occurs because light travels at differents speeds when it travels through different mediums.
Think it this way: let’s imagine that I’m running, well just, just imagine.
Oh come on it’s not that hard.
Let's imagine that I'm running a 5k with my friends, and we're about to reach the finish
line.
Because we're rebels and took a shortcut, we're coming at the finish line at a weird
angle, and, because of that, we stop running and start walking at different times.
Oh, and we’re all holding hands.
That’s actually very important.
The person on the very left is the first to slow down, and then next person slows down,
and the next person, and the next.
Because of this delay in slowing down, the angle of the line perpendicular to the line
of people is changed.
Think about it: because this person is now going slow, this person is going faster than
him, and they’re linked together, the entire line starts to shift to the left until, eventually,
everyone crosses the finish line and slow down.
This also works if you look at it in reverse.
If we go from walking to running instead of running to walking, the new trajectory is
closer to the x axis instead of the y axis.
Also, I want to point out that if the group is just in a straight horizontal line and
not on a diagonal line, there would be no change in the angle of trajectory.
And you can try this at home too!
If you're ever with a group of friends and want to try this out, set a finish line, link
arms, then realize as each of you cross the line and slow down, you end up changing direction
So how do people galavanting along relate to a sipping through a straw in your glass
of water?
*ding ding ding sound effects* Wow I just said the weird metaphor ever said on this
channel!
And remember, I compared fidget spinners to Dumbledore at one point, so.
Essentially, the same effect is happening here, but instead of people running, it’s
light.
As light travels from air into water it’s bent, making the straw bend.
>> TROLL: But Alex, if the straw becomes bent because the light going from air to water
is bent, then why does the straw in the water look like it’s the same angle as the straw
outside but just like it’s cut off a bit.
Whaaaaa?
That is quite possibly the greastest sound effect I've ever made.
Whaaaaa?
Ok Troll, as much as I want to be mad at you for not waiting to watch the whole video, I’m actually
legitimately impressed you’re paying attention.
Congrats, 5 points to Gryffindor!
Well, remember, light changes mediums twice: once when it goes from air to water, and then
once again when it goes from water to air in order to get to your eye.
While that second medium switch causes this straw in the water to be at the same angle
as the straw outside the water, it does cause it to be offset as well.
Also notice that the steeper the angle you tilt the straw at, the more extreme the offset
is.
And, if you put the straw straight up, there’s no offset at all.
Remind you of something?
This whole effect can be modeled with diagrams like these, which Physics students are very
well aware of, as well as an equation, Snell’s law, which looks like this.
Snell’s Law states that index of refraction of the first medium multiplied by the sine
of the angle of incidence of the light ray is always equal to the the index of refraction
of the second medium, multiplied by the sine of of the angle of refraction.
To help you remember Snell’s law, here’s a rap *beatboxing* puuu chu cha puuu chu cha
It. Is. This.
That was real helpful.
While probably about half of you are super familiar with this equation, the other half
probably isn’t, and don’t worry: the equation itself is not that scary, and you don’t
really need to know all of it to help us in this case.
Oooh, now I get why most students in school are dissatisfied with the education system....
Hold up, wait a minute, all good, just a week ago, crew at my house, and we party every
week and so.
But seriously, hold up, I mentioned the index of refraction, but... what is that?
Well, you know how we established that light travels at different speeds in different mediums?
That’s where the index of refraction comes in.
The index of refraction is the speed of light in a vacuum divided by the speed of light
in a medium.
So air, there the speed of light is basically the same as in a vacuum, has an index of refraction
of tiny bit more than 1.
In water, where the speed of light is a lot slower, well, relative to air, the index of
refraction is higher, about 1.33.
Essentially, the slower light moves through a medium, the higher the index of refraction.
Now is a good time to go back to one of the first things I said this video.
These are polymer beads that grow up to 300x their size when you put them in water.
Man, I was so young back then.
So nieve.
But seriously, when the beads soak up that much water, they basically turn into water.
99% of one of those balls is H2O.
This makes these balls have a very similar similar index of refraction as water, since,
because it’s soaked up so much water, light travels through the ball in practically the
same speed it would travel through water, thus making their index of refractions almost
equal.
And, if we go back to Snell’s law, if the 2 index of
refractions are equal, then that means the sine of the angle of incidence and the sine
of the angle of refraction must be equal, which means that these 2 angles must be equal,
which means that light isn’t bent when traveling through these beads, which makes invisible!
We did it, reddit!
Now is a good time to note that the 2 index of refractions aren’t exactly equal, which
is why you can still sorta see a little bit of the ball if you look closely.
If they were exactly equal, then they would be purely invisible, like pouring water into
water.
However, these balls are close enough.
So in conclusion, these balls become invisible under water because they have practically
the same index of refraction as water, which means that light treats the balls and the
water as basically the same substance.
Thanks for watching, DFTBA, and explore on.
There are still balls in there, ok.
*music*
If you got this far in the video, then you probably like mind blowing physics, so, if
you want more, check out this marshmallow experiment.
It's pretty sweet.
Thank you, thank you, no thank you.
Ahh, please click
if you see this, you're an awesome person. thank you for being you.