- This is a Peruvian whistling vessel.
You fill it with water and then you tip it back and forth.
And as you do, it makes a whistling sound.
Different vessels, make different sounds.
For example, this one makes the sound of a bird, I guess.
This one makes the sound of a slightly different bird.
This makes the sound of a person, I guess.
I don't know.
I thought I had a good idea of how these things work
just from thinking about it.
But there's one thing I really can't explain.
My theory is that as you tip the thing water moves
from this compartment to this compartment.
As this compartment fills with water, it forces air out
through some kind of whistle that's hidden inside the head.
But if air is free to leave the vessel via the whistle,
then surely as you tip the thing,
you should just get a continuous whistling sound,
but you don't.
You get a warbling sound and I can't figure out why.
When I made the Assassin's teapot video
the only way to see what was going
on inside was to smash one of my teapots.
And a commenter said, "Why didn't you just get a x-ray?"
And I thought, "Yeah, great,
I'll just take it down to my local x-ray shop.
Thanks for the advice."
And then brilliantly, I got an email
from a company called Creative Electron based
in California saying we x-ray things for a living.
If you ever want to see inside something
without smashing it, give us a call.
You might recognize Creative Electrons work
from the Veritasium video about bowling balls.
It's a really good video,
the link's in the card and the description.
But when loads of you sent me the Peruvian whistling vessel
as an idea for a video, I really didn't want to smash one
'cause they're handmade and it just didn't feel right.
So I thought I'll send a few to Creative Electron
see what they can do,
but also, I mean, how cool would it be
to get an x-ray of these things?
So here you go.
This is the first vessel I showed you.
It's the one from the thumbnail.
There's definitely something interesting going
on in the head.
So I asked them to take a closer look with their scanner
and they took images from all around it.
So we can kind of pan around.
How cool is that?
I'm pretty sure that's a whistle,
which seems to support my hypothesis of how it works.
If you're able to view stereograms,
then go cross eyed now to overlap these two images
and you'll be able to see it in 3D.
I didn't need any special photography for that.
It's just that each excessive frame is slightly
to the right of the previous frame.
So putting the next frame side by side
with the previous frame is like having an image
for the right eye and an image for the left eye.
And it's not just for fun, like being able to see it
in 3D really helps to figure out what's going on,
especially with an x-ray where the details can be obscured
by things in the foreground and things in the background.
I made a video not long ago about how whistles work.
So if you want the details,
the link is in the card and the description.
But from everything I learned making that video,
it's pretty clear to me that this is a whistle.
It also explains the holes either side of the head.
Like air couldn't flow through the whistle
if it didn't have anywhere to escape to.
I imagine those holes make the whistling sound
easier to hear as well.
My goal of course, was to make a 2D transparent version
of the Peruvian whistling vessel.
And these x-rays gave me just about what I need for that.
And here it is.
Annoyingly, it doesn't work.
It doesn't make a whistling sound when you tip it back
and forth, it does whistle if I blow through this hole
but that's really not the point.
And actually I think the problem is that it is 2D.
Like the chamber simply isn't big enough.
You need to force air through the whistle at high speed.
But if your vessel is constrained to two dimensions
you just can't get the throughput.
You can increase the volume of the vessel
and therefore the throughput of air by extending it
in the third dimension.
But I really wanted to get something
transparent that worked.
And I had an idea, although I didn't want to smash the thing
I thought maybe I can cut the thing in half
and still have it work.
I thought about getting it cut with a water jet
but the problem is it's not perfectly symmetrical
because it's made by hand.
And with water jet cutting I would get
this perfect flat plane through the whistling vessel.
So, you know, maybe it would intersect perfectly
through the head, but then it wouldn't intersect perfectly
through the spout at the back or vice versa.
So instead this has been cut by hand.
And then I glue this flexible plastic over the cut
and there you go, it works.
How good is that?
Interestingly, this cutaway version doesn't warble
and to begin with, I was disappointed about that,
but actually I think it helps to explain why some
of these vessels warble while others don't.
My original assumption was that if the air channel through
the whistle was really narrow,
that receiving chamber could only fill
with water very slowly.
And so there would be an opportunity for an exchange
of air and water between the two chambers
when the vessel is tipped.
When the vessel is tipped water falls to this part
of the receiving chamber
forcing air towards the exchange pipe.
This wouldn't happen if the receiving chamber were able
to fill up more rapidly.
Like if I drastically reduce air flow
through the whistle in the 2D version
by covering up the vents, then look,
you do get an exchange of air and water
between the two chambers.
In other words, you get a glug.
It's a bit like the glug that happens
in the gluggle jug that I demonstrated in a previous video.
And of course when the glug happens
that will affect the sound of the whistle,
leading to a warbling sound.
In that respect, it's very similar to the gluggle jug.
The only differences being that in the whistling vessel
there is a narrow channel from which the air can escape
in addition to the glugs.
Whereas with the gluggle jug,
there is no escape, only glugs.
I can also initiate glugs by restricting airflow
with this cutaway vessel.
But I have to give it a jiggle to get it started.
And that's because I have to overcome surface tension
in the connecting pipe.
And of course the narrower the pipe
the more important surface tension is.
And by cutting this thing in half
I've reduced the cross sectional area of the pipe.
I've made surface tension more significant
in this cutaway version.
So that might explain why you get warbles
with the uncut vessel, but no warbles in the cut vessel.
So for warbles to take place, you need a narrow escape
through the whistle and you need a wide connecting pipe.
I'm surprised the air has such trouble escaping, actually.
It might be to do with the shape of the whistle.
It seems that the working principle might be similar
to a sports whistle, which I talked about
in the whistles video.
The incoming stream loops around this bulb shape
and interrupts itself.
I'll go into a bit more detail about how that interruption
of the airflow leads to a whistling sound
in the whistling video.
But the point is it's reasonable to think
that it would add some resistance
to the flow of air through the whistle.
It may have a similar working principle
to the Tesla valve, actually.
That's easy to blow air through in one direction
and hard in the other.
But anyway, in support of the hypothesis
that a warbling sound requires a narrow channel
through the whistle and a wide connecting pipe,
we can consider other vessels.
With this vessel there is no warbling.
And look, the connecting pipe is much more narrow.
This vessel warbles much more rapidly than this vessel.
(bird-like whistling)
And that makes sense because the connecting pipe
in this vessel is wider and shorter
than it is in this vessel.
And actually in the x-rays you can compare the whistle parts
and see that actually they seem
to have very similar geometry.
So it's not a difference in the rate of flow of air.
It's a difference in surface tension effects
in the connecting pipe.
The person whistling vessel, as I'm calling it,
has a much wider connecting pipe.
And yet doesn't warble,
which seems to contradict my hypothesis,
except that if you look in the x-ray, you can see
that the whistle mechanism has a much wider pipe.
The air can escape so rapidly
that the chambers aren't given a chance to glug.
And in fact, if I restrict airflow out the whistle
you get incredibly rapid glugs.
(water gently glugging)
Something else about the whistle mechanism on this vessel
it's embedded in the handle
which makes it appear different.
But the mechanism is essentially the same,
except the piped leading up to the whistle
kind of curves upwards.
Meaning that most of the air will escape through the hole
without really interacting much with the whistle mechanism,
which is perhaps why this has a more raspy sound.
One final thing about this vessel
that's particularly nice is that it has a second whistle.
It's only activated on the return tilt
as water comes back into this chamber, forcing air out.
And it only works if you cover this hole.
So that air is forced to go through the whistle instead
of coming out of the hole.
That's nice, isn't it?
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