- Are you feeling curious?

Oh, yes.

Today, on "Curious Crew," whoa, that was cool, we take a spin, whoa, it went flying, investigating the science of centripetal force.

Let's get rolling.

- [Narrator] Support for "Curious Crew" is provided by MSU Federal Credit Union.

From sweet peas to teens, MSUFCU offers you accounts that grow with children.

With financial education, gaming apps, and events, MSUFCU provides the tools and resources to make learning about finances fun and interactive.

Also 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) - Hi, I'm Rob Stevenson and this is - [Group] "Curious Crew."

- Welcome to this 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 today.

First, let me describe what we're gonna look at just in this part of my table in front of me.

You're gonna notice I have two glasses.

I've got this water glass and I've got this fancy glass and in between them, I've got a little ping pong ball.

Now, I'd like to think of a way I can get this ping pong ball into this water glass without touching it with my fingers.

Julia, what do you think I should try?

- I think maybe you could try using the fancy cup and picking up the ping pong ball and then moving it to the other glass.

- Let's try that little strategy there so I can push it over.

That totally worked.

Now, that's an easy way to do it.

Let's try one that's a little bit more scientific, shall we?

Watch this.

(glass rattling) Isn't that cool?

(laughs) Okay.

I'm just going to place this aside for just one moment, and set up my second discrepant event.

Now, this one requires a penny and a hanger.

Now, you'll notice this is an ordinary wire hanger, but I've bent it into the shape of a rhombus.

And on the very end of it, I have this little cap because the end was kind of jagged and I didn't want anybody to get hurt.

Now, what I'm going to attempt to do is place a penny on top of this and try to swing the entire thing around.

Okay?

Kha'reice, what might happen if I try this?

- I think once you swing it around, the penny won't fall off because of the momentum pushing on both sides.

- Okay.

Oh, I appreciate your faith in me.

I'm a little nervous, actually.

I'm gonna put on some safety glasses just to make sure I'm careful and change my angle slightly here.

(gentle upbeat music) (upbeat music) Whoa, that was cool.

And that was a very good prediction, Kha'reiece.

Now, I'm gonna ask you guys to be thinking about these two discrepant events.

And I'm gonna invite three of you to do a little scientific discussion and collaboration to see if you can use evidence throughout the show to explain these phenomena at the end.

Okay?

Who wants to do a little modeling moment today?

Okay, how about Tauren, Ian, and Rishabh?

I'm gonna have you three do this.

What do you think we're gonna to be investigating today?

Anybody have a guess?

What are we gonna gonna talk about?

Adia, what do you think?

- I think we're gonna be talking about circular motion.

- Oh, excellent.

Now, you were thinking about the circular motion of the ball inside the glass and also the hanger and the penny swinging around my finger.

That is outstanding.

We're going to be exploring the force that ensures uniform circular motion.

And that force is centripetal force.

It's gonna be interesting, so stick around.

(upbeat music) - Let's see if we can figure this out.

- Well, I noticed that the ball really started to lift in the glass when Dr.

Rob spun it faster.

So maybe increasing the acceleration made a difference.

- It reminded me of different spinning rides at an amusement park, like roller coasters that can go upside down and still stay on the track.

- Or maybe like those hanging swing rides that lift when they spin faster.

Maybe those are examples of centripetal force.

(upbeat music) - Centripetal means center seeking.

So a centripetal force is a force that acts on something traveling in a circular path.

A tether ball is a great example.

When you hit a tether ball, the rope has tension toward the pole that prevents the ball from going off in a straight line and gravity pulls down on the ball.

When the ball is struck, it travels in a horizontal circle around the pole.

And it is the centripetal force that causes it to travel in that circle.

A good hit will increase the speed and cause the ball to rotate a little higher.

That is until it winds up around the pole.

Great hit!

(bright music) So now we are going to do a little investigation and you even have some supplies there yourselves.

Adia, tell me what you've got set up for this investigation?

- We have a piece of string taped to a ping pong ball.

- And I have a piece of string attached to a tennis ball.

Kha'reice, if I were just to lump this string and this ball in my hand and throw it, what'll happen?

- Well, once you release the tennis ball from your hand, the string will follow up behind it.

- Okay, so it's just going to trail off this direction until gravity pulls it down.

We know that with inertia, right?

Things are just gonna keep traveling until another force acts on it.

In that case, it's going to be gravity.

Now, we're gonna try something different.

I'm actually going to just put my finger through a loop in the string here.

And I am gonna throw the ball, but watch what happens.

Okay, so I've thrown the ball, but it couldn't go straight because it's captured by the string.

This is centripetal force.

Centripetal force means center seeking.

And because the ball is stuck with the string, it can't get away.

All right, let me see yours.

Okay, now I got a question.

Can you feel a little tug on your hand from the ball?

- Yeah.

- Even though there's not a lot of mass, you can feel that pull on the string.

You can actually feel the centripetal force.

Now, here's another wondering, what if I'm swinging the ball around and when it comes down in this part of the arc, I let it go?

And Kha'reice, what might happen if I let it go right there?

- It'll glide and fall.

- Okay, you think it's gonna go flying off that way?

Okay, let's take a look.

I'm gonna start my swing again.

And I'm gonna attempt to let it go at the bottom of the arc, right there.

Oh, it went flying!

Okay, that was a good call.

Now, you might have noticed as soon as I let it go, the centripetal force is gone because the string's no longer holding it.

So it continues on its path in a straight line.

Let me show you this another way.

I've got a little golf ball here inside an embroidery ring, and I'm just going to get the ball moving.

Now, we've got circular motioning happening here, which also means we have centripetal force.

This time, It's the embroidery hoop that's forcing it to keep turning back and turning back and turning back.

The ball cannot get away, okay?

So it's trapped.

If I lift it up, do you think I might be able to catch it in the dust pan?

Let's see if I can do it.

Let's see.

Okay, I have to time it just right, right there.

And I got it.

Okay, now let's think about what's happening.

When we've got centripetal force going on, we have acceleration that's going towards the center, but at the same time, if I were to let that ball go right there and let it get out, it's gonna continue along with velocity.

If I let it go here, it would go this direction.

If I let it go here, it would go this direction.

If I let it go here, it would go this direction.

Centripetal force is a center seeking force when we have circular motion.

Isn't that amazing?

According to Sir Isaac Newton's First Law of Motion, all mass has inertia.

That means an object that is holding still will stay that way.

Or an object in motion will travel in a straight line until another force acts on it.

Our planet earth is moving in space and should travel off in a straight path.

But the gravity from the sun's mass is so great, it pulls the earth toward the sun.

The result is that the earth and the rest of the planets follow a relatively circular path around the sun.

And that inward force from gravity, is referred to as the centripetal force.

The force changes the direction of motion without even changing its speed.

Amazing!

(bright music) (upbeat music) So we've got some fun investigations here, but I wanna stop and revisit this idea of centripetal force.

Ian, what does the word centripetal mean?

- Doesn't it mean center seeking?

- It's exactly right.

And so when we are spinning things around, they're trying to get back to the center.

There's a force that's pulling them back towards the center.

I have a water bottle here filled with some colored water and there's a string tied on the neck of the bottle that goes through this little tube and the string continues and it's tied to this little practice golf ball on the other side.

Now, the first thing I wanna do is I want to get a mass measurement of both this golf ball and the water.

So this one is coming in at six grams.

So we just gotta keep that in mind.

And the bottle is coming in at 157 grams.

So this is a lot more mass.

Now, there's one thing I wanna illustrate.

There's a relationship between mass and centripetal force.

Okay?

Julia, here's a question for you, how can this six gram mass ball lift this more massive water bottle?

What could I do?

- Well, since we've been talking about centripetal force, I'm going to assume that it has to do with spinning.

- You are so clever.

(laughs) Okay, I am going to spin this string.

Now, as soon as I start to spin it, the centripetal force is going to be the string trying to pull the ball back towards the center.

But watch closely (upbeat music) (string rattling) and observe that.

Ian, what are you noticing?

- It looks like the string's getting longer above your hand and the bottle's being lifted up.

- Isn't that cool?

And in fact, when I go faster, we get the string to lengthen above my hand and we have enough force to actually lift up this more massive bottle.

Crazy, six grams, 157, that's pretty impressive.

The power of centripetal force.

Now, we've got another investigation.

Julia, you have this at home and I have it right here.

What is this other investigation?

What have we got?

- It's a balloon that has a dime, a penny and a quarter on the inside.

- Okay, so three different coins.

And Julia, which one is the most massive coin?

- The quarter.

- The quarter.

We are gonna get this spinning and see if we can get these coins rolling inside the balloon.

You guys try it.

I'm gonna try it here.

Oh yeah, I've got, 'em moving now.

Once you get 'em moving, they actually lift up into the balloon.

At some point, I want you to stop shaking it and let them just settle down.

Notice, they're moving back into the center.

We've got friction that's taking place from the latex.

We've got gravity that's slowing them down, but I really am curious, which coin is the last of yours that was moving?

Julia, what was last for you?

- The quarter.

- The quarter.

Oh, and I see Ian's is still going.

Mine was the quarter also.

What was your last one, Ian?

- Same, the quarter.

- Because it's more massive.

In fact, more massive objects are gonna be experiencing greater centripetal force.

We actually have a great formula in physics that says force equals mass times acceleration.

So if we change the acceleration, if we change the mass, we're actually affecting the force.

Pretty cool.

This is one that you can try at home.

Balloon, some coins, let's give it another whirl, you guys.

Try it, it's fun.

(coins rumbling) Have you ever seen a toy car or a marble go upside down in a loop on a track?

You may have even seen a motorcycle drive upside down in a sphere at the circus.

In each case, the object must be traveling fast enough to stay against the track when upside down.

As the object travels faster and pushes against the track, the round track also has a normal force that pushes back on the object toward the center.

All the while, gravity is pulling down on the object, but with enough speed, the object will complete the loop and never lose contact with the track.

Wow!

(triumphant music) - [Narrator] STEM challenge.

- Have you had fun learning about centripetal force so far, guys?

- Yes.

- Yeah.

- Awesome.

We have a fun STEM challenge today.

In fact, we are going to make a centripetal spinner toy.

Now, I know you guys have a lot of materials that you're gonna be working with, so I'm gonna have you start your build and then we're gonna come back together when you're all done.

And you're gonna show us how it demonstrates centripetal force.

Are you guys ready?

- Yeah.

- Yeah.

- All right, let's get rolling.

- [Kha'reice] Kind of hard to get the fan even.

- [Julia] It's like an octopus.

- Dr.

Rob had us making centripetal spinners out of paper.

- centripetal spinners.

- [Kha'reice] Sometimes you just can't take shortcuts.

For all three of us, tape was definitely a big problem that was going on.

- I think the hardest part is probably taping it without moving the paper because it ruins the distance between the strips and it doesn't look right.

- I need three hands.

The way the top is built, it's not easy to stick the tape to the top and to the paper.

- The colors are brown, orange, and yellow.

It looks like a turkey jumping up and down.

- It's cool to watch the centripetal spinner while it's spinning, and it's really easy to do.

- [Kha'reice] All done.

- So it looks like you guys are just about finished with your centripetal spinners.

So hold them up.

Let's see what they look like.

Oh, those are nice looking.

Oh yeah, go ahead.

Take it for a spin.

Fabulous.

Adia, what are you noticing when you're spinning it?

- When you spin it, the paper start to lift up on the stick and it starts to expand.

- Okay, excellent.

So you see that bulging effect as well as it lifting up on the stick.

I'm guessing the others noticed that as well.

Now, what's actually experiencing that centripetal force?

Can you tell what it is, Julia?

- The papers are causing the centripetal force because they're attached to the stick.

- Exactly, right, so as we spin the stick, they would normally just fly away.

But because they're captured at both the top and the bottom, they can't.

So they're experiencing that centripetal force.

Now, you guys made yours out of paper.

You can also make this out of really flexible ribbon.

Now, the interesting thing about flexible ribbon is when you spin it, I see that same thing that lift, that bulge.

But when I stop it, sometimes I can get it to go into like a little figure eight because the bottom keeps spinning and it twists on itself, which is really kinda neat.

Let's take 'em for a spin, you guys.

Grab your spinner, let's spin 'em.

Try making your own centripetal spinner.

Let's get rolling!

Many of the rides we enjoy at amusement parks make a spin or a rotate.

And each one uses centripetal force that pulls us back toward the center of the rotation.

If you are on one of those rides, you can actually feel that inward force.

You can feel the seat pushing you back into the circle and preventing you from traveling off in a straight line.

Although it may feel like there is a force pushing you out, it is actually the centripetal force pushing you in.

Careful, don't get dizzy.

(bright music) So I've got some fun investigations I wanna share with you two.

And we're gonna be using what I call my centripetal tray.

And this is kind of interesting.

It's just this plastic disc with these three strings that come up to another string and I can hold it right at the top.

Now, what we're gonna do though, requires a little bit more space.

So I've actually already done this outside, but I want you guys to make some predictions on what you think is gonna happen.

Then I'll show you the clips.

I'm going to place a cup of water right on top of this.

And I'm going to attempt to swing it around in a circle.

Okay?

Tauren, what do you think is gonna happen?

- I think depending on the speed, the cup will either fall off or stay on.

- Oh gosh, okay, let's take a look and see what happened.

(upbeat music) Wasn't that cool, you guys?

- Yeah.

- So Tauren, was your prediction correct?

- I mean, it was half right.

- Okay, we're gonna try this again, though.

I'm gonna go in a different direction.

What if I tried to swing it around the top of my head?

Kinda like I'm doing a lasso.

What do you think?

- I think the water will still stay in the cup.

- You guys have such faith in me.

This one made me a little nervous.

Let's take a look.

(upbeat music) So Rishabh, how'd you do with your prediction?

- I think I nailed it.

- Pretty amazing though, right?

I mean, my gosh.

Okay, I thought for sure I was gonna bump something, but it worked out.

Rishabh, did you notice the water though?

- Yeah, so like the level stayed exactly the same.

- Okay, and that part is really strange.

Whether it's going up over this way or around my head, this way, that water's staying the same.

And this is because we've got forces acting on it, gravity and centripetal force.

And because both of those forces are at play, everything stays in relative position.

Now, I'm gonna try this one more time.

This is gonna seem a little crazy.

I'm gonna put this block of wood on my centripetal tray with a golf ball balanced onto a tee, really small surface area.

Do you guys think I can do this?

Swing it around?

We'll see.

- Yeah.

(upbeat music) How about that?

Let me tell you, it's hard at the end though, because if I bump it, it's gone, right?

It's just gonna fall off.

Now, these were meant to be done outside, but I can actually do this with a small apparatus right inside here.

Take a look at this.

I'm gonna put this glass on this little contraption.

I'm gonna hold it right up at the top and just swing it around.

Now, what's amazing is the glass doesn't fall off.

Now, I don't wanna bump anything 'cause then it's gonna spill.

But you can imagine with the shape of this, the centripetal force is acting through this whole system, keeping it relative with gravity and centripetal force, so it all stays put.

Now, there's one more thing I wanna show you, this one's really interesting.

I'm gonna be taking this pool noodle, place a dowel through here and I've got these rings.

These rings are knotted together.

It's called a torus knot.

And I'm just gonna put this together and I want you to watch it closely as we see the centripetal force acting on these rings.

And what's really cool, I'm gonna open it up and I'm gonna let it go right onto my arm.

We'll see if I can roll it up from one arm to the next.

Isn't that cool?

(upbeat music) (rings rattling) Centripetal forces at work.

Amazing.

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

Hi, I'm Genesis, and today I'm here with arts professor, Jae Won Lee.

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

- We're in the Kresge Art Center at Michigan State University and I'm a ceramic artist.

- How is STEM incorporated into your job?

- We need to know our geology and chemistry to develop our glaze recipes.

We need to know raw materials from the earth use what effect.

(fire crackling) Technology is also part of ceramics education because we are working on the potter's wheel with the centripetal force, the turning point.

With the electricity invented in history, people could use that electric potter's wheel so we can get to this point of speedy production.

(upbeat music) - Jae Won lee sculpted my understanding of science and ceramics.

Explore your possibilities.

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

(upbeat music) - We've seen that there's always acceleration towards the center of the curve path and the examples of centripetal force.

- In the case of the ball, the curve balls of the glass kept changing the ball's direction in a circular motion.

- And like with the penny, the hanger was applying that force.

In both cases, when they were moving quickly, that force was stronger than gravity.

(upbeat music) - So have you had fun learning about centripetal force today?

- [Group] Yeah.

- Excellent.

Now, I know three of you have been doing a lot of thinking about these discrepant events that we had at the beginning of the show and you've probably got your wheels spinning.

So what have we figured out about this anti-gravity ball, Ian?

- We think that when you rotate the glass, it makes an inward centripetal force in the ball so it keeps going in a circle.

And the faster you spin it, the greater the force from the ball.

- Yeah, the ball falls out due to gravity when you slow it down.

But we also wondered about the shape of the glass.

We wanted you to try it with the water glass instead.

- Okay, I will do that.

I promise.

But let me talk about what you just mentioned.

First of all, 'cause I happen to agree with you.

We've got the glass that's responsible for the centripetal force this time.

It's keeping the ball from getting away, forcing it back into that circle, that center seeking travel of motion there.

And you also are correct that as we speed it up, the force increases, so we can lift it and just as you mentioned, let gravity do the rest once it slows down.

Now, your claim about the shape of the glass is really important.

So you're noticing the taper on the glass right here.

That really makes a difference.

In fact, as the ball is traveling on the inside wall of the glass, that narrow part of the glass forces it upward, which is really kind of establishing some lift.

And the more we see it, the more it goes up, kind of like those centripetal coins that we saw with the balloon.

So I'm gonna do your investigation now.

Let's see how we do.

All right, with a straight walled glass.

Okay, there it goes.

I got it going.

I got it going.

Oh no.

Okay, I got it going.

I got it... Yeah, you're gonna notice that I don't get any lift.

And so every time we lift the glass, it just rolls away on a tangent.

It will not work.

So if you wanna try this at home, here's the rule.

You have to find an object where the mouth of the jar or the glass is narrower than the sides.

I can even do it on something this big.

I'll move these over, just to keep things safe.

(ball rattling) Oh yes.

And let that drop down due to gravity, but we got some great centripetal force in there, don't we?

Awesome, okay.

So Rishabh, talk to me about this poised penny.

- Well, we think that this time the hanger's providing the Centripetal force, keeping the penny balanced.

So as long as you don't bump anything, the penny will hold its position.

- So we have the hanger providing both the circular motion and the centripetal force.

Now, this is a really interesting activity, definitely one better to be done outside, but there's a safer activity where you can enjoy some centripetal force fun.

How many of you have yo-yos at home?

Excellent.

You take your yo-yo outside and you practice and perfect the around the world trick.

You'll feel that tug of the yo-yo, centripetal force in action.

It's too much fun.

So remember my friends.

- [Group] Stay curious.

- And keep experimenting.

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

- [Narrator] Support for "Curious Crew" is provided by MSU Federal Credit Union.

From sweet peas to teens, MSUFCU offers you accounts that grow with children.

With financial education, gaming apps, and events, MSUFCU provides the tools and resources to make learning about finances fun and interactive.

Also by the Consumer's 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.

- (laughs) I hate to brag, but I was the second grade yo-yo champion in my class.

Around the world?

- Ooh.

- Oh.

(yo-yo ratting) - Huh?

still got it.

(balloon thudding) (bright music)