- So the big news is I'm a wizard now. Check this out. Look,
full goblet, all right. (Narrator gulping) Empty goblet. Replete poculum (Narrator gasping) This is some "Harry Potter" merchandise that you can't get anymore, it must be about 20 years old, this thing, and it's got a really cool mechanism so, well, I had to laser
cut a 2D version, didn't I? I was pretty confident I
knew how this thing worked. Like, you can see the walls
are suspiciously thick and there's something strange
going on at the bottom there, but I cut one in half
anyway just to be sure. And so my 2D model is
based on this outline here, but you'll notice it doesn't work at all. When I fill it up, the water
doesn't get into the sides. And actually on closer inspection, look, there's a little hole on
the outer rim of the goblet. So I need to put a little
hole in mine as well. And once again, I've made the classic 3D-to-2D conversion error. In 3D, the side walls form
one continuous chamber but in 2D it's now two separate chambers. It's also a problem for bell siphons. Will I never learn? So with the hole on both sides,
when I fill up the goblet, air is able to escape
from the side chambers, and so they fill up with liquid as well. So you drink it off. The great part is, as long as you keep your finger over those holes, the water will remain hidden
in those side chambers. I mean, it's not hidden in this version, unless you're also 2D and
you're coplanar with it but, anyway, it means you
can stop the goblet refilling until you deliver the refilling charm. Replete poculum. Refilling charms do appear in the "Harry Potter" series, by the way, Harry uses it in the Half-Blood Prince but we don't know the actual incantation because Harry cast the charm non-verbally. So this uses a similar principle
to the Assassin's Teapot. By putting your finger over one hole, you prevent the water from escaping from the only remaining hole. It doesn't work in exactly the same way as the Assassin's Teapot, they both rely on the fact that for water to escape from a container, air needs to be able to
get in to replace it. That's a consequence of
atmospheric pressure. I won't get into the details of that because I cover it in the
Assassin's Teapot video, but it's something you probably have an intuition for anyway, from the times you've played
with a straw as a kid. But the Harry Potter goblet and
the Assassin's Teapot differ in the way they prevent air
from getting into the chamber. If a container has just one hole, that has to be the exit hole for the water and the entry hole for the air. And that is possible, so long
as the hole is big enough. The air kind of chaotically
bubbles past the water. But if that one hole is so small that surface tension becomes important, then you do need a
second hole for the water to be able to escape; and that's the working principle
of the Assassin's Teapot. But the way the Harry Potter
goblet stops air getting in is more like the way a
chicken waterer works. So look, this thing is full of water. Some of it's coming into the bottom there, and as water is removed via drinking, this is how chickens
actually drink I believe, every chicken carries
this little cup with them and they scoop the water out. Anyway, as the water's removed, more water from the container
moves down to replace it. And the level of the water
never really changes, which is also quite
magical. (imitating chicken) So here's the 2D version. And look, as the chicken
drinks, air bubbles through and the level remains the same. So just like the Assassin's Teapot, this water can't fall out of the container because air can't get in to replace it, but unlike the Assassin's Teapot it's not surface tension that's
stopping the air getting in. Instead, it's the fact that
water is more dense than air and that creates a kind of plug, like the air would have to somehow push this bit of water down to
be able to get in the thing. If that happened, that
really would be magic. Ventus. The goblet works in the same way, air isn't able to get down
and under that barrier because there is water in the way. Actually, this is how
chickens drink, I believe. They've got a little
syringe in their mouths and it comes out, and
then this top, like the... I noticed this cool thing while I was filling
the 2D chicken waterer. The stream is touching
both walls of the container which creates a seal, which means we now have a fixed
volume of air inside here, so as the water level rises a stream must bulge
upwards until it breaks, and then the cycle continues. Another issue with going from 3D to 2D is the volume available
for the hidden chambers. If adding hidden chambers to my 2D version was to double the width of the goblet, then those hidden chambers
would be able to hold exactly the same volume
as the central chamber, but consider this top-down
view of a 3D goblet. If adding a hidden chamber here were to double the width of the goblet, well, the hidden chamber would have three times the capacity
of the central chamber. So I ended up making my hidden chambers quite a bit thicker than the goblet ones. By the way, if you like
the Assassin's Teapot, I've had something in the
works for a little while that I think you'd be
really interested in, something you can own. So if you wanna make sure
you hear the announcement, consider clicking the notification bell. It should be one of my next few videos. So I've got my own laser cutter now. (gentle upbeat music) I've been just cutting loads of stuff and just trying different things, and I've come up with this
thing that I wanna show you. It's not related to the goblet at all, but it's a cool 2D water thing. So Jack Bull asked me the question, "How does water drain?" And I thought about it for
a while and I realized, actually I don't know the answer. Which is to say, "If
you pull the plug out, the water that comes out the plug hole, where does it come from? Does the water drain from
the bottom layer first, or does it drain from the cylinder immediately above the plug hole or is it something in between?" We know that if the body of water has any kind of rotation to begin with, it'll end up swirling
around the plug hole, but what if there is no rotation? I think we need a 2D version. (Narrator mumbling) (machine beeping)
(machine whirring) (water trickling) Well, that's not desperately helpful. If only we had some mutually
point bs from a previous video. Now, because this is 2D we
definitely don't have rotation, but we also have boundary layer effects because of these two
large transparent walls, so this might not be a great
model of what happens in 3D but I still want to see it. So it looks to me like the water is coming evenly from all directions. I hope that answers your question, Jack. I also wondered about if the
container was funnel-shaped, how different would that be? It's easier to see in this one that there's a boundary layer effect. The beads seems slower right
next to the sloped walls. There's this video effect in Premiere Pro editing
software called Echo. It leaves a trail when things
move across the screen. So look, if I turn that
on here, how cool is that? You can get a sense of
the speed of the flow in different places and
the direction of it. It's quite mesmerizing. (gentle music)
(singer vocalizing) ♪ It's not my fault ♪ ♪ You've been lying, saying that I- ♪ - Watching it fill up is pretty cool too. ♪ Drowning by yourself,
now you wanna blame me ♪ ♪ Like you have no options ♪ - I didn't realize this
Premiere feature existed when I made the Convection Viewer video, so I really want to show you that now. How cool is it that you can see little eddy currents that formed, little vortices that
separate from the main flow? That would be really hard to
see without the effect applied. Link in the card in the description if you want to see that video in full. You know, life is full
of little annoyances and it's important to
make peace with that fact, but at the same time I'm the sort of nerd that thinks about optimization a lot. Is there a system I can put in place now, or something that I can do
that will remove annoyances and friction in the future? As a result, I have all sorts
of crazy systems in my life. And thanks to the sponsor
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