- [Rob] Are you feeling curious?

- Yeah!

- Today on curious Crew, that is incredible.

We build a better understanding.

Oh, squeeze, oh, squeeze.

Of compression, shear, tension, and torsion.

It's no wonder molecules are a little stressed.

And the science behind.

- Oh, oh no!

- Structural forces.

It's pretty egg-citing.

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

From sweet peas to teens, MSU FCU offers you accounts that go with children.

With financial education, gaming apps, and events, MSU FCU 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.

(upbeat music) - Hi, I'm Rob Stevenson.

And this is- - Curious Crew!

- Welcome to this show, everybody.

We always like to start every episode with a couple of discrepant events because discrepant events stimulate- - Curiosity!

- That's exactly right.

And before I show you the first one, my friends, I've got a question for you, Julia.

I've got a string right here, and I'm curious, do you think that string could support this block if I let them both go?

- No.

- No?

(Rob laughs) You're totally right.

Okay, so clearly I need something stronger.

So I'm gonna use a chain.

Julia, do you think the chain will be able to support this block?

- No.

- You guessed right again.

Now that seems odd, but of course we know that these items work great if there is a load underneath, not so great if the load is on top, 'cause otherwise they just collapse, right?

So string is not gonna be the greatest support for a load.

Here I have what is called a tensegrity table.

If you look at this very closely, you'll notice that the top half is supported by the bottom half with nothing more than string.

We've just established string is not gonna be able to support this block, or is it?

Isn't that odd?

So I've got another example right here that I made out of snap blocks.

Isn't that perplexing?

But I've got a question for you as well, Ollie.

Can I crush a paper cup with my hand?

- Yeah.

- Yeah, I totally can.

No problem at all.

So here's my wondering.

I've got 12 paper cups right here.

Do you think they might be able to support this board and this concrete block without collapsing?

- Yeah, I don't think they'll smush.

- Let's find out.

So I've got some gloves on just to make this a little bit easier to handle this very heavy block.

Let's see what we got.

Look at that.

We've got a couple of interesting discrepant events, and you know what I like to do when we have some interesting discrepant events.

I'm gonna invite three of you to do a little scientific modeling.

So who wants to engage in little modeling moment?

Who'd like to try that today?

Okay, Adia, Kah-Reice, and Nash, you three.

Now I have one more question for you, my friends.

Anybody have a guess what we're gonna be investigating today?

What do you think?

Callan, you got a guess.

What do you think?

- Maybe force.

- We are talking about a special kind of force, actually internal structural force.

It's gonna be interesting.

Stick around, my friends.

This episode will be quite the tour de force.

(upbeat music) - The table is strange.

Did you see the wood parts?

I don't think it could stand without that.

- I noticed that too.

Somehow that works with the strings to make it stable.

- I was also thinking about the cups.

I wonder how few Dr.

Rob could use to still hold up the block.

(upbeat music) - Imagine a house.

It seems pretty stable, but did you know that there are a lot of forces pushing and pulling on it all the time?

That would include the load from the roof, the furniture, the floors, the people, and even the ground pushing on the basement walls.

How can the house withstand all those forces without falling down?

The trick is understanding how to make a structure that can withstand the fundamental loads of tension, compression, shear, torsion, and bending.

Time to unload each one.

(techno music) So if we're gonna understand structural forces, we're gonna start by looking at different objects.

And you're gonna notice on this end of the table, I've got a bunch of objects that are sort of grouped together, and they have something in common.

Julia, can you figure out what these things might have in common?

Now, wait, before you answer, I'm gonna give you a clue.

I'm gonna grab this elastic band and stretch it.

What would happen if I stretch this too far, Julia?

- It would break.

- So that's my clue.

What do you think about those objects over there?

- If they're stretched too far, will they also break?

- They will.

And that's a very interesting structural force referred to as tension when things are pulled apart.

Now, in fact, they don't always break.

Sometimes they'll deform kind of like when you sit on a beach chair and the webbing stretches down.

Now, that tension force is all about pulling molecules apart.

And you know what the molecules are doing?

They're trying to stay together.

But the opposite of that is referred to as compression where we squish molecules.

Now I'm gonna illustrate this with a phone book, and I'm bending this phone book.

And Ollie, I want you to notice carefully.

I've got some arrows on there.

What might the molecules on the top of this be experiencing?

- Tension?

- Exactly.

And how about the ones on the bottom?

- Compression, right?

- Yes, 'cause those ones are getting squished together.

It's really interesting when we have something bending like that.

Now speaking of bending, I know you each have a straw.

That's pretty easy to bend, isn't it?

You guys can bend it up, bend it down, and in fact we can even be thinking about, oh, there's compression on one side, there's tension on the other side.

But what if we get an object that's stiffer than that?

How about this little popsicle stick?

How about that one?

Can you guys bend that one?

Oh, a little bit.

Yeah, you kind of need your thumbs in there though, don't you, to be able to bend it?

Okay, we've got one more.

How about this piece of aluminum?

Can we bend that?

Now aluminum, we think, gosh, how hard can that be?

This is really stiff.

This is really, really stiff.

Now I want you to try something else.

Grab both ends of it and see if you can pull it apart.

(Rob laughing) No chance, is there?

Okay, this is one way we test tensile strength of things.

We can put things in a clamp, in a special machine, and stretch it.

These are actually specimens that material scientists use to see if they can stretch them out and see how much force these molecules can stand before they break.

But look over here.

These ones actually broke.

So you can see in this one, how it starts to get narrower right there.

That's called necking down, and that's going to be an indicator of where it's going to finally fracture.

So we're gonna do our own tensile test with this piece of plastic.

Ollie, here's my wondering.

Do you think this piece of plastic can support this 13 pound can of rocks?

- I'm gonna say no.

- I think that's a really good prediction because I can actually stretch this pretty easily.

But if I take three of these pieces of plastic, and I glue them together, I'm making my own little tensile test.

This is actually strong enough to be able to handle this heavy load.

This is one way we test tensile strength, and believe it or not, engineered materials like this can get pretty strong.

In fact, if you look at this old tennis racket I had when I was a little boy, it's made of wood.

It was a good racket.

But of course the improved tennis rackets now with composite materials can really handle those tension forces much, much better.

So those composite materials are both durable and beneficial.

When you lie in a hammock, the cords on either side get pulled between the hammock and the tree they're attached to.

If we could use microscope eyes and investigate the cord, we would see the molecules are being pulled apart from tension forces, but they are pulling back too.

It's lucky that these cords have good tensile strength.

Otherwise they would break.

Engineers must think about such forces on every structure, buildings, bridges, boat rigging, bicycles, washing machines, ropes, and even your hammock.

Ah, time to get rid of some tension.

(techno music) So we've looked some tension forces.

Now it's time to explore compression.

So think about this.

Whenever we apply a load to something and try to compress it or squish it, those molecules are getting squished together, and they have to try to resist.

That's like me putting this 15 pound weight over on this piece of concrete.

And of course it can resist that compression.

I want you to grab that little block of wood okay?

And you're gonna try to compress it with your hands.

Are you ready?

Let's go for it.

Oh golly.

Oh, squeeze, oh, squeeze it.

You think you can do that, Callan?

- No.

(Rob laughing) - Not so much.

Don't hurt your hands.

Now in fact wood has pretty good compressive resistance.

If I measure that, it's pretty much gonna be the same height.

Now you have something else to test, don't you?

A piece of clay.

Okay, we're gonna try this, you guys.

Let's apply that compressive force.

Are you having any movement there, Nash?

- Yeah, a lot actually.

(Rob laughing) - And Callen totally destroyed hers.

Oh yes.

Okay, so we don't have the same kind of compressive resistance.

And in fact I have to do this 'cause it's just gonna look funny.

I've got a little piece of clay here too.

We're gonna put on the 15 pound weight and- (Rob laughing) It just sort of, it's sort of done.

Okay, now, when I start thinking about something fragile, I think about eggs, and we're gonna try something with five eggs, okay?

These are raw, so I do have to be careful.

Now, I'd like to try to stand the eggs up on end, but because they're round on the bottom, I can't really do that.

And so I'm going to place them inside these little tops to these soda bottles.

And then we're gonna put another little top on top, making a little level platform.

Do you think I'll be able to place a board on top of these eggs and then put the 15 pound weight on without destroying the eggs?

What do you think, Nash?

- I think the eggs will be able to hold it up, but I kinda wanna see the splatter.

(Rob laughing) - Okay.

I'm a little nervous about this.

I'm gonna place this on here.

Oh golly.

Oh golly.

Oh my gosh.

That is incredible.

You might be thinking how?

How can something so fragile as an egg support that?

It all has to do with the shape of the egg and the ability for the shell to resist those compressive forces and distribute the weight all the way around the shell.

And if we use more eggs, we have better support.

You could even say structural forces can be pretty egg-citing.

When people play tug of war, the rope is under tension trying to pull the molecules apart.

Compression is the opposite.

Molecules are squished together, and they try to resist.

Imagine the heel of your shoe.

It gets compressed between your foot and the ground.

Or when you sit on the couch, you compress the cushion, forcing the molecules closer together.

Stiffer objects, like a bridge with a car on it, must withstand a lot of force so the bridge doesn't move, including compressive forces on the top and tension forces on the bottom.

Those are some strong molecules.

- [Audio] Stem challenge.

- So have you been having fun investigating structural forces so far, you guys?

- Yeah!

- That's excellent.

Now, we've been exploring tension and compression, and we've seen how some items have really good tensile strength.

For today's stem challenge, that becomes kind of important.

I've got a piece of thin spaghetti here.

And in fact, if I grab the ends of the spaghetti and pull, this is really quite stable.

Those molecules are not going to let go of those bonds.

Now, if I were to try to compress it, on the other hand, it's going to easily bend and break.

And that's what makes this stem challenge pretty tricky.

You are going to be making a pasta platform.

The top of the platform has to be at least 10 inches off of the table, and it has to be stable enough to support a big book like this.

Now, what pasta are you using?

You're gonna be using thin spaghetti, linguine, and fettuccine.

Are you guys ready to start your builds?

- Yeah!

- Let's do it.

- Like a sturdy base.

What kind of base?

I'm using spaghetti, linguine, fettuccine, gumdrops, marshmallows, and clay.

- I tried using gumdrops, but they didn't work too well.

- [Callan] The gumdrops did work, but not getting the job.

- So the spaghetti's the weakest because it's so thin.

I think that the fettuccine is the strongest because it's the thickest.

Haha!

I am a spaghetti master.

- I started out with just like one linguine and like one fettuccine on each side, and then I ended up changing it and making bundles to make it more stronger.

- The fact that you're using pasta, it's really bendy.

That's the whole challenge is pasta doesn't do well under compression.

I just broke like five pieces.

I'm hoping that it can hold the book.

Okay, that looks good.

- So it looks like you're just about done with your pasta platforms.

So Callan, how about you?

Do you think it's gonna work, and what pasta did you use?

- I don't think it's gonna work, and the pasta I use is the fettuccine and the linguine.

So I see you've got a whole cross section going along the top there.

You can even tilt your camera down just a little bit so we can look at the base of that as well.

So yours is really tall.

So Julia, do you think yours is going to work, and what pasta did you use?

- I think it's going to work, and I used all of the different pasta.

I used one big bundle of fettuccine, and two bundles of linguine, and two bundles of spaghetti.

- Okay, great.

And Ollie, how about you?

Do you think it's gonna work, and what pasta did you use?

- I don't think it's gonna work, but I hope it's gonna work.

I used one column of spaghetti, and then I have it all joined together with singular fettuccine noodles in the center.

- So I'm noticing that a lot of you decided to use clay as a good bonding agent.

So that was an interesting choice.

Okay, let's go ahead and put those cardboard platforms on first, and we'll test each one, one at a time.

So let's put on that book, Callan, and let's see what happens.

Drum roll.

(drum rolls) - Oh no!

(Rob laughing) So this would be an opportunity to redesign.

Obviously pasta platforms, this is a tricky stem challenge.

Okay, Julia, what have we got?

(upbeat music) Oh, it actually supported it.

Okay, and finally, Ollie, let's test yours.

- Okay, moment of truth.

Don't break.

Oh, oh no!

(Rob laughing) - So we're one for three.

Bundling pasta is a great option.

As Julia was discovering, it actually can reduce that bendiness quality.

So try making your own pasta platform and see how heavy a load yours can handle.

(techno music) Now, each of you has a little glue stick, don't you?

Okay, why don't you grab that out?

And what we're gonna be using here is a little stick that would go into a hot glue gun.

I'm using a pool noodle.

Now the first thing I want you to do is, can you guys bend yours so you make a little smile?

Now, I'm looking at the top, and I'm curious, what would those molecules be feeling in the top, Adia?

- Compression?

- Compression, that's exactly right, 'cause they're getting squished together.

And what about the molecules on the bottom of the smile, Kah'Reice?

- They'll be feeling tension.

- That's exactly right.

And together this is referred to as a bending moment.

Whenever we see something bend, we have both compression and tension going on, and I wanna use this board here as a quick example.

This board is from a bookshelf.

Have you ever seen a bookshelf that has way too many books on it?

And you're thinking, oh my gosh, that bookshelf may break.

Well, this one was close to breaking.

Let me show you how.

It's supported on the ends, but it had a lot of weight in the center.

And as a result, you can see how the board has started to bow or warp.

And that's because particle board is not really strong as far as those molecular bonds.

Now, if this were to break, it's going to break on the tension side where those molecules are being pulled apart.

Now, I want you to use your glue stick for something else.

Grab your glue stick, and hold both ends, and twist it.

Kah'Reice, what do you notice about the lines that we have drawn on your glue stick?

- You can notice they're rotating around the glue stick.

- Okay, excellent.

So Adia, what might these molecules feel?

- They're like twisting apart.

- Exactly, so they're twisting apart.

This is called torsion.

Now, there's another one that I wanna show you as well.

So we've got bending and torsion, but let's talk about a force called shear force.

Now to think about shear force, it's either gonna be a pulling or a pushing force, but the strange thing is it's opposite but not in line with each other.

So let's give an example of that.

Scissors are a great example of a shear force when we are cutting paper.

In fact, we've got those pushing opposite each other, and it's able to separate those molecules.

Now it's funny because another name for scissors, shears.

Makes sense.

It's a shear force.

And in fact, we even call this pruning shears.

So we can put a stick in there and separate those.

And of course we also do it with a paper cutter.

Wow, tension, compression, bending, torsion, shear.

It's no wonder molecules are a little stressed, right, guys?

- Yeah.

- Yeah.

- So those molecular bonds sure do endure some structural forces.

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

Hi, I'm Janellyn.

And today I'm with Rita Brown.

Rita, tell me what you do and where we are.

- I am a construction industry consultant, and we are at the Union Carpenters And Millwrights Skilled Trades Training Center in Detroit.

- What do you do as a construction industry consultant?

- I take all of my experience in the construction industry, and I apply it to making our companies stronger, faster, smarter.

Stems everywhere, we're calculating loads, and we do the drawings.

We do the 3D models.

- What's the most rewarding part of working in the construction field?

- Being able to connect with people who are doing the hard work to build our country, because that's what construction's about.

It's about building the infrastructure, building the buildings that we all as a community need.

- Rita Brown helped build my knowledge of careers in construction.

Explore your possibilities!

And now, back to Curious Crew!

(upbeat music) (upbeat music) - We notice the string has good tensile strength.

So the table has to be using that.

- And the wood has pretty good compression strength.

So those center parts must be resisting compression.

- Exactly like how the eggs could support all that weight without breaking.

I bet the cups do something similar to distribute the load of the cement block.

- So they both are resisting compression.

That makes sense.

(upbeat music) - So have you had fun at investigating structural forces today, my friends?

- Yeah!

- Now I know you've been thinking a lot about these phenomena.

So what have you figured out about the tensegrity table, Kah-Reice?

- Well, we think the center string is under tension.

- Right, and the outer strings are under tension too.

- Exactly, and that's what makes a stable system.

- We saw right away that the string and the chain, they could not support the block from above, right?

Now, we know they both have great tensile strength, but as far as compressive resistance, not so much.

They just sort of collapse.

So we have to take advantage of tension.

And as you stated, that center string is under tension.

And if you look at it closely, you can actually tell.

This upper section is suspended by this center string.

So why doesn't it collapse?

And that has to do with these vertical members.

Those are actually supplying the compressive resistance.

So it can't.

So all we have to do is stabilize the corners by pulling them together.

So they're under tension as well.

Now, I've got it stable enough that it can support this block.

Now Adia, what would happen if I put on something heavier.

- The table would collapse.

- You're totally right.

It's still a very fragile system.

Now, it's called a tensegrity table, which stands for tension + integrity.

And in fact, if I look at this one over here, this one's even more fragile because I only have two outer lines under tension compared to three.

What if there are four lines under tension with a rectangular piece?

And we could get it even stronger still.

Something else that we need to talk about, our curious cups.

Nash, what have we figured out there?

- Well, a single cup isn't strong enough to hold the weight of the cement.

However, when you have 12 cups, it's able to handle the weight.

- Good thinking.

Okay, so we know that we can easily crush a paper cup.

And the reason that is so is we're actually applying a force on the sides, and that force isn't very even, and so tension and compression, it fails.

Now, if we can think about a paper cup though, it actually has really good compressive resistance.

Those molecules and the bonds will actually resist that squishing together pretty well, even enough to support a ridiculous load like this cement block.

And just as Nash stated, the more we have, the more weight we can distribute, and the better it can support such a heavy load.

Now, when I start thinking about other things that have pretty good compressive resistance, I think about a soda can.

And in fact, we see something similar with soda cans.

We can easily crush a soda can with our hands, right?

But if we stand them on end, and we apply an even force, we end up having good compressive resistance with the soda can as well.

We can even do this with a single soda can.

It just takes a little bit longer to get it balanced.

And now that you are armed with greater knowledge, you are a force to be reckoned with.

So remember, my friends- - Stay curious!

- And keep experimenting.

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

- [Announcer] Support for curious crew is provided by MSU Federal Credit Union.

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

With financial education, gaming apps, and events, MSU FCU 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.

- It's no wonder molecules are a little stressed, right, guys?

- Yeah!

- Yeah, they're stressed.

Get it?

Stressed.

They're stressed.

Get it?

Stressed.

They're stressed.

Sorry, it was a bad one.

It was a bad one.

(upbeat music) (chiming)