- [Host] Are you feeling curious?

- [Children] Yeah!

- Today on ""Curious Crew""... - [Host] Nice job!

We get the wheels turning.

- Whoa!

- Whoa.

As we investigate the driving force behind angular momentum.

These guys are on a roll.

- Support for "Curious Crew" is provided by MSU Federal Credit Union, offering a variety of accounts for children and teens of all ages while teaching lifelong saving habits.

More information is available at msufcu.org by the Consumers Energy Foundation dedicated to ensuring Michigan residents have access to world-class educational resources.

More information is available at consumersenergy.com/foundation.

Consumers Energy Foundation, supporting education and building sustainable communities in Michigan's hometowns and by viewers like you.

Thank you.

(upbeat music playing) - Hi, I'm Rob Stevenson and this is... - [Group] "Curious Crew"!

- Welcome to the show, everybody.

We always like to start every episode with a couple of discrepant events because discrepant events stimulate?

- [Group] Curiosity!

- That's exactly right.

And I've got some fun ones for you guys today.

And it's gonna start off with this ramp that I have here going down there.

That little catcher, I call that my caution catcher.

That's appropriate, don't you guys think?

And a couple of discs.

And Shirley Ann, you're gonna help me out here.

I want you to compare those discs.

- They look the same, they're the same weight.

- Okay.

Except I've got blue stripes on one and green stripes on the other.

And in fact, you notice something kind of important.

I took a mass measurement of both of these and they both have a mass of 189 grams, okay?

Now I'm gonna place this on the ramp and let 'em go.

And Shirley Ann, what should happen?

- They should roll.

- (laughs) I love that!

They should roll.

Let's take a look.

They're definitely rolling.

That one definitely won.

Joann, can you hand those back to me?

I wanna see which one won there.

The green won.

Okay, I'm gonna move the green one in the back and let's try this again and see if we get different results.

That green one keeps winning!

What's up with that?

Those discombobulated discs.

Okay, I'm gonna set that aside for a second and we're gonna take a look at another discrepant event which I had hidden right back behind here.

So first of all, what does this look like to you, Torin?

- An egg.

- (laughs) Totally looks like an egg.

I wanna do something with this egg.

I am going to try to spin it.

Okay?

Very carefully.

And I wanna know how long this can spin for and Torin, would you do me a favor?

I've got a little stopwatch there and I'm hoping you can run that as soon as I get it started.

You just hit start and then I wanna know when it stops.

Okay.

You guys ready?

Warming up the hands.

Okay, here we go.

- [Group] Whoa!

- That was it.

Check it out!

- [Child] That's cool!

- So you're noticing it pops right up there?

Oh, now it's getting even more interesting.

So what are we up to so far?

- 19 seconds.

- 19 seconds.

We're just gonna let this thing go.

I've got my discombobulated discs over there.

I've got my PhiTOP spinner that jumped up on its end and now it's spinning like crazy.

I'm hoping I can get three of you to do a little scientific modeling for me.

Try to use evidence throughout the show to revise your thinking to explain these phenomena at the end.

Who would like to participate in some modeling moments?

Okay.

Demetrius and Josie, you three are gonna do this.

So does anybody have a guess what we're gonna be talking about today?

Ethan, what do you think?

- I think we're gonna be talking about a ton of things spinning like on their sides or maybe just upright.

- So things spinning.

You are spot on.

I don't know what gave that away.

We're gonna be talking about spinning things specifically anywhere momentum.

You're gonna wanna stick around.

We're going for a spin.

(upbeat music playing) - All right, let's figure this out.

- I was actually super surprised that the top set up and spun for so long.

- I know it reminded me of a gyroscope spinning on one side and then lowering before it fell on its wheel.

- I was also thinking about the other vent.

The wheels were supposed to have the same mass but one of them kept going faster.

It has to be something different.

- [Host] Isaac Newton helped us realize that when an object is moving in a straight path, it will keep going unless another force acts on it.

If the moving object has more mass or is moving with more speed, it has more momentum and would need a bigger force to stop it.

This is true with spinning objects too.

Like this top, it takes a twist called torque to get it to start rotating.

Then we would say it has angular momentum and will keep going until another force acts on it.

Oops.

Weren't those discrepant events interesting, you guys?

- Yeah!

- Okay.

Now I've kept the ramp here because if we're gonna try to make sense of those discombobulated discs we need to roll a few more things down here and we're gonna start with these.

Okay?

Gentlemen, I want you to handle those for just one second.

You're gonna notice this one's metal.

Maybe that one's kind of a dense wood.

What are you noticing as you compare them?

- Well, this one feels heavier, but-- - They actually have the same mass!

(laughs) Isn't that crazy?

This one does feel heavier though.

I agree with you.

It feels like this one must have more mass.

Now I'm gonna roll these two down the ramp.

And gentlemen, predict for me what do you think is gonna happen?

- I think that the disc will win.

- Think the disc will win?

Let's find out.

3, 2, 1.

That was a really good prediction and thank you Shirley.

And, you're rescuing that over there.

Appreciate that.

I saw my caution catch already, but how about a couple of other ones?

These ones are smaller.

Handle those for me.

What do you notice there?

- These two are kinda the same weight.

There's not much of a big difference but this one is plastic.

- Similar mass.

- Yeah.

- Let's try rolling these down.

Ethan, what might happen this time?

- I think the plastic's gonna win because it's a little heavier than the disc.

- Okay, so we're going for the hoop this time?

Let's see what happens.

Oh surprise!

- The disc won.

- The disc one again.

Okay.

Let's change things up.

Let's use this hoop and a larger disc.

Okay?

Shirley Ann, what do you think's gonna happen if we race these two down?

- I think that the disc is gonna win 'cause it's not hollow like the other one.

The other one's got a hole in the middle.

- Okay.

- It's only on the outside.

- Let's find out.

So the disc won again.

The disc has won every single time.

Every single time, which is really strange.

Let's race the hoops against each other.

Now this one has a lot more mass.

We've already established that this is metal.

This is plastic.

But if I keep them in line with each other with their contact point on the board and let 'em go.

What's really interesting is they run together, - They tie - Which is kind of cool.

I'll do it one more time because that seems kind of odd that that would be the case.

That really looks cool.

Okay, but let's try this.

Thank you so much dear Leanne.

Let's try this with the discs.

We'll take a little disc, a big disc.

I'm gonna try to get 'em in line with each other and let 'em go at the same time.

And surprisingly, they run together.

Now here's the thing we have to understand about this physics principle.

First of all, discs will always roll alike.

It doesn't matter what the diameter is.

I could have a huge disc so big in the studio and roll it against this little one and they will roll similarly down my plane.

Now if I have hoops, hoops will always roll alike too, which is really strange.

But here's where it's fascinating.

When we race a hoop against a disc the disc won each time, right?

Well let's think about why.

Is there anything in the middle?

- [Child] No.

Nope.

- That's what Shirley Ann was talking about.

All the mass is on the outside.

Here, I can't put my finger through there 'cause there's something in the middle.

We've got mass in this, but it is equally distributed.

Now what that means is if we've got mass anywhere near the center of rotation, this is rolling faster always.

As soon as we move the mass out, we raise the moment of inertia and all of a sudden the angular velocity slows down.

And so we will always see that disc beat the hoop.

Now here's one more final question for you.

Let's really think about this.

Imagine I had a sphere, perfectly round sphere.

Yeah, do you think the sphere might roll faster or slower than the disc?

- I think the sphere would win.

All of the mass and stuff is close together so it'll just go down faster.

- And we can pull that mass even closer to the center of rotation, which is absolutely amazing.

Boy, these guys are on a roll.

When we think about the momentum of objects traveling straight, we think about their mass and speed.

But when we think about angular momentum we think about how quickly objects are rolling or spinning.

We also consider how spread out their masses, which we call moment of inertia.

Now, if the mass is far away from the center, then the object will roll slower.

But when there is more mass toward the center, the angular velocity is even faster.

(quizzical tune) So we've been exploring angular momentum, right, you guys?

- Yeah!

- And we've seen how if we move that mass further away from the center, it actually changes the angular velocity.

I've got a great device here called a Hoberman Sphere.

Any of you guys ever play with one of these?

- Yeah, I have a mini one.

- A mini one?

Okay.

And I have a giant one.

I have a giant.

Now the cool thing about these Hoberman Spheres is go ahead, Ian grab that side a little bit.

You sort of lift it up and you'll notice it just sort of collapses in on itself, which is really kind of interesting.

'Cause it's got all these joints all over the place.

Now normally you can throw it around and it'll like expand and it'll shrink.

But I've got it hooked up with a pulley up on top so I can actually pull on my string... - Wow!

- And shrink it or expand it.

Now here's what we're gonna do, Ian I'm gonna ask you to rotate it.

Go ahead.

- All right, - Go ahead.

Grab it both hands, give it a little spin.

What do you guys think is gonna happen if I pull the string and make it smaller?

- Is it gonna spin faster?

- Yeah.

- Okay.

- It's gonna spin faster because it's smaller.

- Oh, look at that.

(laughter) That is totally correct.

And of course when I make it bigger, it slows down.

Right?

Now this makes sense because soon as we move that mass further away from the center, we have more inertia and it can't move as fast.

We call that the moment of inertia, right?

Now what I find fascinating is when the moment of inertia is high, velocity is low.

When moment of inertia is low, velocity is high.

- Yeah.

Yeah.

- This is all about the conservation of angular momentum.

When one is one way, we'll do it again.

Just speed it up and slow it down and make it really slow like that.

- Awesome.

Ken's gonna pull this up for me right out of the way.

Bye-bye, Hoberman's sphere!

Okay, I have something else I wanna show you.

I have a couple of weights tied onto a string and this seems kind of silly and a little obvious but what I'm gonna do is I'm gonna rotate each one of these around each other.

Have any of you guys ever played tetherball before?

- Yes.

- Yes!

- Okay.

And you know how you hit the ball and it goes winding around that post, right?

And then you have to time it just right and sort of knock it back the other way.

Have you ever noticed what happens to the ball as the rope gets wound up and wound up and wound up?

What happens to the ball?

- It speeds up, it gets faster, - It speeds up Exactly.

- Gets faster.

- Exactly right.

And that is a great example of the conservation of angular momentum.

Soon as it gets closer we've got faster speeds and you're gonna start to see this is starting to speed up as well.

As it is getting closer and closer and closer to the center.

And then finally it'll get right to the end and it'll click and eventually unwind.

And of course it does this in reverse.

You can see the speed right there.

Then of course it will start to unwind and eventually get slower and slower and slower.

So the rule is with conservation of angular momentum if there's more inertia, it's going to turn slower.

(laughter) But as soon as we can make that moment of inertia smaller, we can increase that angular velocity, which is really cool.

So the next time you guys are out there with your friends playing tetherball, you can say, "Hey, this is a great example of - [All] Angular momentum!"

- Exactly.

The best example of angular momentum is when ice skaters go into a spin.

Imagine that they start the spin with their arms and one leg out from the body.

But what happens when they bring a leg or arms in?

They speed up a lot.

At first their mass was spread far out.

So there is more resistance in turning.

But the conservation of angular momentum says that when rotating mass is closer to the center, then the object must spin faster.

Wow.

I'd give that a 10.

- [Voice] Stem Challenge!

- So have you guys had fun exploring angular momentum today?

- [Group] Yeah!

- So glad, we've got a great stem challenge for you.

You are about to build an angular momentum straw spinner.

How's that for a mouthful?

Okay, now I know you've all selected your materials.

Are you guys ready to start your build?

- [Group] Yes!

- All right, let's do it!

- I'm so excited.

We get to like each make our own - That (indistinct) has us making angular momentum straw spinners.

- It's a straw with a string going through it and weight on each side.

- I'm gonna start with the string and then I'm gonna go put my objects through.

- Jenelyn's using some really big straws while Torin's just using medium-sized ones.

So everyone at our table has really different contraptions.

- Don't you wanna put the string in first?

- I realized as I was tying the knots it was a little bit harder than I anticipated.

- I got it, I got it knotted.

- How'd you do that?

- I just like knotted it.

You know, they're like, how?

- I don't know.

- So I decided to use the really small straws and I had to get really small thread in order for it to fit.

I used tape on the end of the straw.

And I finally fit it through here.

It took forever.

- The struggle.

- I think stem challenges like this are really really fun because it gives your mind something to do and your hands as well.

- Good job.

- That works.

- Got it.

- Yay!

- Got it.

- Well these are looking good.

Are you guys ready to show these spinners?

- [Group] Yeah.

All right, I've made one myself.

I'm curious what materials you guys used in yours.

Kyries, what did you use in yours?

- I grabbed this practice golf ball, some string.

A straw and a weight.

And I made sure I all got red 'cause red's my favorite color.

- (laughs) The boy likes red.

You and I chose similar materials although I did not use a red string.

I think yours looks a little classier than mine.

Can you show us how yours works?

- Yep.

- [Host] Pulls that string and it'll speed up.

Nice job.

All right gentlemen, what did you use in yours?

- So, I have like a thicker, like a wide bobo straw.

And then I got the biggest weight.

- [Host] Oh my gosh.

- The biggest washer.

And then I have a wooden spool.

- Oh, excellent.

Okay.

And one more.

Shirley Ann, what did you use in yours?

- I used a 40-gram weight and a practice golf ball.

- So we're like twins.

Nice job.

Now this is not too hard to make.

Is it you guys?

- [Group] No.

- So this is something you can certainly make at home.

We have learned though, you have to make sure there's space before you swing it, right?

Because we don't want to knock into anybody else.

(laughter) The interesting thing is because there's a weight on both sides, you can decide which one you want to spin.

And of course once we get them spinning, as Kyrie showed, we can pull in the string and it will speed up showing us that conservation of angular momentum.

Pretty cool.

Should we demonstrate it real quick?

- Yeah!

- Alright, everybody swing 'em.

Let's swing them and pull your strings!

Nice job.

Try making your own spinner.

It's a lot of fun.

Have you ever tried to flip a bottle to land it on its base?

This is difficult if the bottle is full because it will rotate quickly.

The trick is to empty the bottle so it's only a quarter or a third full.

Now when you flip the bottle, some of the water flows to each end.

And when that happens the mass spreads out and slows the bottle down during the rotation.

Not only is this a fun outdoor activity, but also a great example of the conservation of angular momentum.

(quizzical tune) So we've been having fun today, spinning lots of objects but we haven't yet spun people.

(laughter) So I think it's time we should try that.

And Torin, I'm gonna ask you to start us off.

Torin, would you please sit on this little swivel stool here?

And I've got a couple of five pound weights.

Okay?

I'm gonna ask you to hold those.

And when you're ready, give yourself a little spin.

Not too much.

And whenever you're ready, bring out your arms and bring 'em in.

And you report out what does it feel like?

- Okay.

- Try it out.

- Oh boy.

Arms out.

- Whoa!

- What are you noticing when you bring your arms in?

- I go faster.

You go faster, which kind of makes sense, right?

If your arms are out we've got that greater moment of inertia, so we have inertial resistance but as soon as you bring them in, it's closer to the center of rotation and it caused you to spin faster.

Now you're a figure skater, aren't you?

So you've done a lot of spinning in your days, haven't you?

- Yes.

- And when you're nice and tight on the ice, hardly any friction and you're spinning like crazy.

Do it one more time.

Okay.

Spin away when you're ready, bring it in.

Oh yes!

And nice slowing down.

Excellent jump.

Thank you so much.

Demetrius, I feel like you're needed on the stool.

(laughs) Demetrius, I'm gonna have you do something different.

Josie and I have this motor over here and I've got a small bicycle wheel.

We're going to get this thing rotating really fast and then I'm gonna ask you to hold it and move it around and see what happens.

Are we ready?

Okay.

Josie, you fire that up and I'm gonna get it right on here so we can get it spinning like crazy.

All right, Josie, you can turn that off.

And I'm gonna do a careful transfer.

I'm gonna hold the inside and you get a good grip on that.

You ready?

I'm gonna let it go.

Now you change.

Whoa!

- Whoa!

- Whoa.

Can you feel the torque?

- Yeah, - You can totally feel the torque.

And he changes directions and notice he changes directions.

Okay, stand it up again.

Change direction.

- Oh, that feels weird.

- (laughs) We've got a lot of torque going on here.

And in fact, here's the amazing thing.

As you turn it, it changes the angular momentum.

And I'll take that back from you.

Excellent job.

Now, in fact, if there was no friction in that stool, you would be rotating at the same speed as the wheel.

- Oh my goodness!

- In that case, we're really glad there's friction in this too.

Amazing!

When we start thinking about angular momentum not only is it incredibly powerful, it can be a dizzying experience.

You can experience angular momentum yourself.

Place a rolling office chair in the middle of the room where there's plenty of space.

Find a couple of heavy books and hold one tightly in each hand.

Then stretch your arms out to the sides and use your feet to push the floor several times to try to get the chair spinning in place.

Once you're rotating, try pulling your arms and legs into the chair.

Wow!

Stretching out your arms will slow you down.

But don't stand up too soon.

You might be dizzy.

(upbeat music playing) - Are you curious about careers in science?

Hi, I'm Genesis, and today I'm here with Master Q Quiana Powell.

Quiana, can you tell me where we are and what you do?

- I am a master instructor in the art of Tang Soo Do, the Korean style of martial arts.

And we are at Double Dragon Tang Soo Do Academy in Burton, Michigan.

- Hiya!

- I am the first African American female master in our world Tang Soo Do Association.

- How is STEM involved in martial arts?

- STEM and martial arts surprisingly go hand in hand.

So here's where that angular momentum comes from, okay?

Whether we are preparing to do a basic front kick or a straight punch.

All my energy, I built all my energy up and I'm pushing it forward.

I'm breaking through a board.

- Why are you so passionate about Tang Soo Do?

- I love children and I love being able to help them.

Any way that I can do that, by way of martial arts, it's even better.

- Master Q helped me earn my white belt in Tang Soo Do and physics today!

Explore your possibilities.

(upbeat music playing) - And now back to "Curious Crew".

(upbeat tune plays) - So this cap is an example of angular momentum.

We know Dr.

Rob used torque to get it spinning - Right.

And while there wasn't a lot of frictional force, that's eventually what slowed it down.

- Remember how in the disc race, the hoops were always slower than the disc?

Do you think the inside of the discombobulated discs might be different?

- Yeah.

So there might be more mass around the edges like the hoop or maybe even more mass in the middle, like the discs.

- That got me thinking.

Did you guys notice there's wing nuts on the discs?

Maybe we can ask Dr.

Rob to open them up.

- So have you had fun exploring angular momentum today, guys?

- Yeah!

- Me too.

And I'm sure your wheels have been turning as you've been thinking about these discrepant events.

So what have you figured out about the phi top fun spinner here, Ian?

- So we know it took torque to get it started and once it was spinning, it went from its side onto the end, which raised its center of mass and reduced the amount of friction.

- And that's why it was able to to spin for so long.

Plus it's a really cool example of angular momentum.

- It is a really cool example of angular momentum.

I happen to agree.

And we didn't even get to report out how long it took because we closed right out of that clip and it was still going two minutes and 10 seconds.

Torin, you did a great job with the stopwatch.

We appreciate that.

Excellent job.

So here is another wondering that I have, oh I've got a great piece of alliteration coming in my brain right now.

What about these discombobulated discs, Demetrius?

- You know the mass is the same but we think it might be distributed differently inside.

Can we open it up?

- Ooh, he wants to open it up!

I'm sure you all do.

What might we find inside if we do that?

Josie, what do you think?

- We think the one that rolled faster may have more mass in the middle.

- Ooh, okay.

And we remember that the green one went faster, didn't it?

Okay.

- Yeah.

- So I've got some wing nuts here and I'm just gonna loosen these things up and of course we have to have the big reveal because I'm gonna get 'em both off at the same time so we can see what it's gonna look like inside.

You said you think the mass is gonna be more in the middle with the green one.

Now based upon what we've seen... You are correct!

(laughter) Well done.

Now we do have the same mass overall, it's the same four metal spheres but as soon as we get those brought in the center, closer to that center of rotation, the inertia goes down, angular velocity goes up and it rolls faster.

Just like we saw with the speedy rotations, as soon as we get that mass going to the outside, things are gonna go a lot slower.

Gosh, I don't know about you guys but angular momentum gets me dizzy.

(laughter) So remember my friends... - [All] Stay curious!

- And keep experimenting.

Get your curiosity guide and see more programs at wkar.org.

- [Announcer] Support for a "Curious Crew" is provided by MSU Federal Credit Union offering a variety of accounts for children and teens of all ages while teaching lifelong saving habits.

More information is available at msufcu.org, by the Consumers Energy Foundation dedicated to ensuring Michigan residents have access to world-class educational resources.

More information is available at consumersenergy.com/foundation.

Consumers Energy Foundation, supporting education and building sustainable communities in Michigan's hometowns.

And by viewers like you.

Thank you.

- Ow.

- So what did you figure about?

Na, na, na, na.

(laughter) No, Ian, no!

All money.

(laughter) Be sure to put that in closing credits.

(closing tune)