The 11th Curiosity Box is currently shipping.
I’m talking ferrofluid, a trammel of archimedes.
I can’t give every item away but you will
also be receiving one of these if you’re
a subscriber.
This is a hui stick.
Aka a gee-haw whammy diddle.
Aka the ouija windmill.
Oh yeah it’s spooky.
It’s just a little rubbing stick and a propeller
stick that has a propeller on one end and
notches on one side.
Now when you rub the rubbing stick along the
notches the propeller stick will vibrate and
the propeller will spin but the direction
it spins in will obey your command.
All you have to do is say the magic word.
Hui.
Hui!
Hui!
Hui?
Who?
E?
How does it work?
Well that’s what we’re gonna talk about
today on Michael’s Toys.
To see how the Hui stick works you need to
come closer or I could come to you.
Now here are my hands and let’s pretend
that they are your hands.
When you hold the propeller stick you hold
the rubbing stick across the notches in the
other but you don’t just rub the rubbing
stick across the notches like this.
No no no.
The trick is that you hold the stick like
this so that when it’s engaged with the
notches you can press against the propeller
stick from one side with your index finger
or from the other side with your thumb.
So as you rub across the notches you are also
dragging a finger and constantly pressing
a finger against one side of the stick or
the other.
And that is what reverses the direction.
Watch this.
I will begin.
Let’s begin with my thumb.
I’ll try to make them far apart so it’s
very obvious when I switch.
Here I go.
I am pressing.
I ‘m constantly pressing against the stick
from the right with my thumb and now here
goes the notch action.
Nice!
We’ve got some rotation and that is in a
counterclockwise direction but now I’m going
to switch so that my finger, my index finger,
presses against the left side of the propeller
stick.
You ready?
Boom.
Whoa!
Reversal!
Pretty cool huh?
But how does it work?
Well to begin this investigation let’s talk
about how the propeller stick moves when the
notches are being rubbed.
Well that should cause up and down motion.
Vertical, straight up and down.
Except not exactly.
No matter how hard you try, there will always
be a little bit of error.
Even if it’s just the width of an atom,
horizontally and that’s really all it takes
for a little bit of rotation to be induced.
You can try this at home.
Take something like a pencil and a roll of
tape or some other ring-shaped object.
Put the pencil through and try to move the
pencil only up and down.
No matter how hard you try, rotation will
always result.
Only if you’re able to move the pencil up
and down right through the exact center of
mass of the ring so you only push it up and
down will you not get rotation but the tiniest
little error from there introduces a torque
which causes rotation and then a feedback
loop makes it stronger and stronger.
This is exactly what’s happening with the
hui stick.
I don’t know if you can tell but the shaft
that connects the actual propeller blades
to the propeller stick is much thinner than
the propeller hole.
Here’s an example that’s been deconstructed.
You see that shaft there’s quite thin and
the hole in the propeller’s pretty big.
This means that as that shaft bounces around
it really does bounce around inside the propeller’s
hole and can push and drag through friction
the propeller around.
To see how exactly those vibrations of the
propeller stick work we got some great slow
motion footage.
Here’s how we made it.
I took a laser measure that shoots out a laser
beam, there’s the dot, and I gripped this
in the same hand as the hui stick and projected
the laser point on a wall across the room
so that when I stroked the notches they would
both, the laser measure and the hui stick,
they would both vibrate together and I could
look at how it vibrated.
Now when I don’t even press a finger against
the propeller stick I still get pretty chaotic
motion.
The propeller stick doesn’t just vibrate
straight up and down.
It does move in circles sometimes but it’s
quite a mess.
It’s definitely not controlled.
But if I press my index finger against the
left side the laser pointer moves clockwise.
And if I press my thumb against the right
side the laser pointer rotates counterclockwise.
And because the shaft has room inside that
propeller hole to move around its circular
motion easily translates into rotation for
the propeller.
But why does putting a finger on the side
lead to circular motion in the first place?
Well there have been many many papers written
about how a hui stick works and they don’t
all agree with each other.
Many explanations just simply say that it
happens and they don’t get into the actual
mechanism but I’ve done a few experiments
on my own and I’d like to present some of
my findings and this is what I believe is
important in the functioning of a proper hui
stick.
I believe that it doesn’t just matter which
side left or right you press a finger against.
It also matters which side top or bottom your
finger is pressing against.
And here’s why.
Let’s pretend that this circle is a front
on view of the propeller stick like this right?
So we’re looking straight at it and the
whole in the middle is the shaft in the middle
that the propeller sits on.
Now if this is that hui stick as I rub across
the notches the stick is pushed up and down.
It’s pushed down when the stick is on the
top of a notch and then as the stick flies
back up because of course my hand is holding
it and producing a torque his way to keep
it in contact with that rubbing stick it goes
up and then it’s pushed down when the stick
is on top of a notch.
Then it comes back up when I’m in a notch
and so on up and down.
But when I drag a finger along the hui stick
my finger is slightly above.
Right?
I’m not reaching down below the middle of
the stick.
I’m on top.
And look at what happens.
Two torques.
Two torques because when I press a finger
against the stick like this I’m creating
a torque that causes rotation in this direction.
But of course the stick doesn’t keep rotating
that way because my steadying hand pushes
the other way.
It produces a counter torque that keeps the
stick in one position.
And it is the interplay between these two
torques that causes spin in a particular direction.
And here’s why.
Let’s go back to our big circle.
If this is the hui stick and my finger is,
let me take this cap off, and my finger is
here.
Let’s say my finger’s up here.
Producing a push, a force, a torque in that
direction and my steadying hand is producing
a torque in this direction.
When the notches are rubbed and the stick
goes up and down when it goes down it temporarily
disengages from my finger’s torque and now
the torque from my steadying hand wins out
and it slightly moves this way before going
back up and reengaging with my finger and
through the finger’s constraint getting
pushed this way only to be pushed back down
away from the finger where the torque from
my steadying hand plays a much more dominant
role and so we get rotation like this.
Rotation that is counterclockwise when seen
from the front.
Let’s see if that can be confirmed by experiment.
I’m gonna put my finger in the upper right
quadrant as seen from the front.
You ready?
Upper right quadrant as seen from the front.
Will I get motion that is to you counterclockwise.
Yes I do.
Now, if instead I put a finger, let me erase
this so that we have a nice clean diagram.
If I instead rub my finger along the other
side on the top so my finger is right here.
That’s a big magnified finger.
If I put my finger here and I push this way
now what happens is that as the notches are
rubbed and the propeller stick, oh wait, if
my finger is pushing this way then my steadying
hand is going to produce a counter torque
in the opposite direction.
That’s very important.
So the hand holding the back of the stick
is always kind of turning it this way.
So oh yeah let’s grab this one.
Now when the propeller stick moves down because
the top of the notch has been reached by the
rubbing stick it disengages with that finger’s
torque and is pushed this way.
Then it flies back up, reengages with the
finger, and that torque brings it back this
way and so on until we get clockwise rotation.
Will a finger dragged along the upper left
side result in clockwise rotation?
I think we already know the answer to this
question.
I’m going to rub my thumb along that side,
what is for you the upper left side and we
will get clockwise rotation.
Pretty amazing.
But if this is true that means that it should
matter whether I’m above or below the middle
of the stick because if we restart our diagram
here putting a finger not on the right above
or the left above but instead down below like
say here, pushing against the stick this way
means that we have to produce a torque that
is moving in this direction with our steadying
hand.
Boy I’m not a very good drawer but I think
the point should be pretty clear.
Now when the stick is pushed down by the rubbing
of the notches it engages with this finger
and is pushed that way but then it flies back
up and now that counter torque from that steadying
hand pushes it a little bit to the right and
so on and so we get clockwise motion.
We got counterclockwise motion when my finger
was in the upper right quadrant but in the
lower right quadrant we should see clockwise.
Let’s try and experiment.
I’m going to begin by putting my finger
on the lower right quadrant.
I’m going to press against that quadrant
as I rub the notches.
We should see some rotation and we do.
We see clockwise rotation but now I’m going
to move my finger up to the upper right quadrant
right now.
And it reverses direction.
Likewise if I rub my thumb along the upper
left quadrant I get rotation in that clockwise
direction but if while I do this I manage
to move my thumb to the lower left quadrant
I reverse directions.
Pretty cool.
Pretty cool.
If this explanation is true then we should
not have controllable rotation direction when
a force is applied that the up and down vertical
motion of the vibrating stick cannot escape.
To try that out I created a hui stick comb.
It’s just like a usual rubbing stick but
its got these teeth on it that allow me to
put a torque directly 90 degrees from the
up and down motion caused by the rubbing of
the notches and because these teeth are quite
long going up and down does not disengage
the propeller stick from that torque like
it would with a finger.
Now let’s see what happens here.
I'm going to start by applying the torque
on what is for you the left side of the stick.
And we get some rotation but watch what happens
when I swap.
No reversal.
Okay here comes the force on the left side
and now on the right.
I am really pushing but the propeller stick
cannot escape from the force and so it cannot
take advantage of the interplay between the
opposite direction of one hand’s torque
and the steadying hand’s opposite torque
which is what I believe leads to the rotation.
Please when you get your hui stick perform
your own experiments.
It is a blast and it's really good exercise
especially for someone with weak hands like
myself so have fun, stay curious, and as always,
thanks for watching.
By the way the shirt that I have been wearing
this entire time comes in box eleven as well.
I talk about cardinal and ordinal numbers
in how to count past Infinity and I love cardinal
numbers.
Cardinal.
It’s a great word and it's a great bird.
Cardinals are a very common sports team mascot.
In fact my middle school, Blue Valley Middle
School was and is the cardinals.
So we started thinking what if we made a shirt
that looked like a jersey or like it represented
a sports team but not just the cardinals but
the transfinite cardinals.
Now the smallest transfinite cardinal, the
smallest amount of infinity is of course Aleph-Null
and there's the symbol for Aleph-Null.
Aleph-Null is how many whole numbers there
are.
It’s how many integers there are.
It's how many even numbers there are and it’s
how many odd numbers there are.
So I wear this shirt with an infinite sense
of pride.
And I hope you do to.
