(upbeat music)
- This is a toy ballerina,
and this is a little mirror that comes with it.
When the ballerina sees herself in the mirror,
she starts to spin.
It's a cool little toy, but how does it work?
Like, there aren't any moving parts or batteries,
or motors, or anything.
My first thought was that seeing yourself in a mirror,
dressed as a ballerina,
fills you with so much joy
that you simply start to rotate,
and that's certainly my experience.
But I noticed that when you rotate the mirror
through 90 degrees in this direction,
or a quarter tau radians clockwise,
the ballerina spins in the opposite direction,
and that's not true for me.
(loud bang)
The other thing that's different is that if you turn
the mirror upside down, the ballerina stops,
whereas I carry on going,
but perhaps the most significant difference
is that if you give the ballerina a flat bottom,
she doesn't spin at all.
Actually, no, that's true for me as well.
So, what's going on?
Well, I also noticed that if you turn the mirror
through 90 degrees anticlockwise,
the ballerina sticks to the mirror,
so there's got to be at least one magnet involved.
Did you know, I now have
a separate channel for YouTube shorts?
Steve Mould Shorts, yeah?
I don't know, I think it's for people
who don't want to turn their phones.
I don't know, I can't get YouTube on my phone anyway.
It's one of those old flip-flones.
Let's take apart the base of the ballerina.
Look, there's the magnet, and using this compass,
you can see that this is north and this is south.
To simplify things, I'm going to use this magnet here.
It's actually two cube magnets joined end to end,
this is north, this is south,
and I've 3D-printed a base for the magnet
so it can have a rounded bottom like the ballerina.
And to keep the mystery a little longer,
here's the mysterious box that makes the magnet spin.
Look, it spins according to the arrows
I've drawn on the box.
How cool is that?
So, what's going on inside this box?
Well, actually, let's have a look inside the mirror first.
Look, there it is,
at the bottom of the mirror, a little magnet.
We can see north is here and south is here,
and maybe that's a little surprising actually
because it's at an angle, a 45 degree angle,
and presumably that's important because, look,
the manufacturer put a little pen mark on there
so that the people assembling it
would know how to put it in correctly.
And, in fact, that's what I've got inside the box,
a magnet with north and south on the diagonal.
So, when the box is put down like this,
the magnet spins anti-clockwise,
and when the box is flipped onto its side,
the magnet spins clockwise.
So, what's the mechanism.
Well, let's take the magnet out of the box
and the other magnet out of the stand
and push them together with our hands at 45 degrees.
When we do that, what we'll feel is two forces.
Firstly, you'll feel a repulsion force.
That's because you've got a north pole
and a north pole here, close together,
and a south pole and a south pole here, close together.
They repel each other,
but you also feel a second force, a twisting force,
and that's because this north pole
is somewhat close to this south pole
and this south pole is somewhat close to this north pole.
They attract each other,
and that leads to a torque force, a twisting force.
So, what happens when you combine these two forces?
Well, without a rounded bottom, not much,
but when you deploy the patented bottom-rounder 3,000 here,
two things happen.
The first is that that twisting force
causes the contact point to change.
The whole assembly rolls a little clockwise.
So, the contact point is now here,
but the center of the magnet is now here.
It's no longer above the contact point,
but the repulsion force from the magnet
in the box is still acting in aggregate
on the center of the magnets.
So, looking from above, you can see,
here's the contact point,
here's the point being pushed by the magnets,
and so you have a torque force.
The assembly will rotate around the contact point,
but as it moves, the contact point moves as well.
It rolls, like a wheel.
Like if I push this wheel against the ground at an angle,
it causes the wheel to rotate.
It's the same thing that's happening here.
What's really cool is that because there are
no moving parts, no batteries, no motors,
this is actually a source of free energy.
I'm planning to build a giant one to power my house.
The reason you haven't heard of this before
is because spinning ballerina technology has been suppressed
for decades by the big energy companies,
or the energy has come from somewhere that isn't obvious.
That's probably it, isn't it?
In fact, when we had the magnets out
and we were holding them together,
then we felt that repulsion force, well,
when the box magnets
are brought close to the spinning magnets,
the spinning magnets move away,
so the force is acting over a distance.
Work is force times distance moved in direction of force.
In other words, that force that you feel
as you move the magnets is you doing work.
In other words, the energy to dance
like a ballerina comes from within,
and I think I always knew that.
Thanks to Paul Knack for his Instructables project.
The link is in the description.
Isn't it cool, you now know
how headphones work. - Yeah.
I was wondering all the time how they work,
but now we know.
- I was always a tinkerer as a kid,
and my parents really supported it, like they'd let me
take the TV apart to find out how it works.
It didn't always work when we put it back together again.
My kids seem to have the same thing.
I don't know if it's nature or nurture, but either way,
I'm really grateful for the sponsor of this video, KiwiCo,
because it's a STEM project subscription service.
Every month, a box comes in the post.
Everything you need for the project is in the box
so you don't have to run out to the shops
or anything like that.
There are eight different subscription lines
that cover all possible ages.
Like, my daughter here is making headphones for herself,
and it's led to all these conversations, like,
how does the sound get from there to there,
like, how does the speaker work, how do wires work?
There's a magazine of additional activities
around the subject, but it also has this replay value.
Like, obviously, with the headphones,
my daughter's just wearing them everywhere now.
Even if she's not listening to something,
she's got them around the neck.
My wife works in education,
and she thinks about these things quite a lot.
I always hear her muttering when the Kiwi Crates arrive.
She says things like, "Oh, they're working
on their fine motor skills there."
You know, there's always stuff like that going on,
and I just feel like KiwiCo have really thought about,
you know, the different stages of development
for the different age groups and making sure
those are incorporated in the boxes.
It's really interesting to hear
my wife talk about that stuff.
The deal on this one is really good.
If you go to kiwico.com/stevemould,
you get the first month absolutely free,
no strings attached.
The link is also in the description,
so check out KiwiCo today.
And what all did you say? - There's nothing better
than KiwiCo! (Steve chuckling)
(upbeat music)