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  • 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.

The 11th Curiosity Box is currently shipping.

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B2 中高級

回族棒子 (The Hui Stick)

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    林宜悉 發佈於 2021 年 01 月 14 日
影片單字