"Ken" means sword and "Dama" means ball and it's a sword and a ball.

The French name is bilboquet

There is the spelling, bilboquet

We have some english versions of this toy but not so sophisticated as this one

So, as you can see, a ball is hanging from a string attached to this sword, as we say.

You see, there's a cup here and the challenge is to just tug the ball up and put it in the cup

Now that's of course is very, very difficult to do.

So you shouldn't do this in public... Because the chances of success are very small

[Generic News Channel Song]

[Explosion]

[Crowd Cheering]

[Tadashi Tokieda] Even if you succeed with the large cup

you shouldn't try the smaller cup because that's much, much harder to do of course.

Now, if you're a little mad you say "Ah! I notice that there is"

some space at the end of this stick.

Presumably that's not designed for play of this kind

But you know, if you're ambitious, you might try and miraculously succeed.

There is a place where you can rest you know? So surely I will not be able to do this

but once in ten years or so I may succeed.

But what is demonstrably impossible is you see there's a hole at the bottom of the ball

Is to tug this up and then make it land on the stick

And it's impossible because you see, when i tug it up

the ball starts going in all sorts of orientations

and what are the chances that when it lands, the hole is pointing straight down?

It's very, very unlikely and very, very improbable.

But there's a trick for this:

There's a grand principle in Physics that permeates all parts of the Universe

called The Conservation of Angular Momentum

That means that any body spinning

Once it gets spinning has a tendency to keep spinning exactly the same way

Unless disturbed by external influences

Not only at the same spin, at the same angular speed

but also around the same axis.

So we can begin by spinning the thing

And you see that when I tug it up

you saw that it keeps straight up

Because this axis of spin is vertical

and by the conservation of angular momentum

once it gets spinning it always keeps the same axis.

So, if I spin this and try, what seems impossible becomes possible.

[Crowd Cheering]

[Cheering Intensifies]

[Tadashi Tokieda] You should contrast this with when I don't spin

and how much harder and difficult it becomes

I can do it anyway.

I can reverse the roles of the sword and the ball

I can hold the ball and then swing it

and try to make the sword come into the ball.

This never works.

Hang on. Come on.

Oh!