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SYLVIE DOUGLIS, BYLINE: NPR.

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DARIAN WOODS, HOST:

The saying goes, don't reinvent the wheel. But the wheel has been reinvented many times, and that's a good thing, according to structural engineer and author Roma Agrawal.

ROMA AGRAWAL: I find this expression that we shouldn't reinvent the wheel really annoying...

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AGRAWAL: ...Because the fact is that, ever since we did it - invent the wheel - we have been reinventing it.

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WOODS: This is THE INDICATOR FROM PLANET MONEY. I'm Darian Woods. On today's show, reinterpreting the wheel - how the wheel has cycled through change after change and just how crucial that innovation has been to the modern economy.

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WOODS: Roma Agrawal, structural engineer and author of the book "Nuts And Bolts: Seven Small Inventions That Changed The World (In A Big Way)," welcome to the show.

AGRAWAL: Thank you so much for having me.

WOODS: So obviously, wheels are important in the modern economy - for driving, for trains, for planes - but where else do we use wheels going through a typical day?

AGRAWAL: If you ask somebody what the most important inventions in human history is, I think a lot of people would say the wheel and axle 'cause it is so important. And you've mentioned the - kind of the obvious ones that we can see. But if you think about the fact that you might have a toothbrush with a rotating head - like, an electric toothbrush - I often have a breakfast smoothie which requires some spinny (ph), sharp things to break my fruit down. So these are the kind of very everyday objects that need that spinning action. So there is an absolutely enormous range of applications of the wheels that might not be immediately obvious when you think about it.

WOODS: So let's start with how the wheel was actually invented. I think the collective memory has some kind of image of, like, a stone wheel carved in a cave - maybe some kind of Fred Flintstone-style carriage.

AGRAWAL: Absolutely (laughter).

WOODS: Is that at all what happened?

AGRAWAL: So all of my engineering study and extensive qualifications have led me to believe that the Fred Flintstone car wouldn't work, so you heard that here first.

WOODS: (Laughter).

AGRAWAL: And so yeah, so the wheel was not, in fact, invented for transport. So if I take you back 6,000 years to ancient Mesopotamia, the population was increasing. There was more food to be grown but also to be stored, and the potters were struggling to keep up with demand. So they came up with this idea where they had a pedestal in the ground, and then they took a wheel which had a sort of bump on the bottom, and they spun this wheel. And now you could create pots quickly, robustly, and it almost mechanized this process. So that was actually the first example of the wheel that we can see.

WOODS: We went from a potter's wheel to maybe something that was more like a wheel for transport. In the book, you say the first discovered wheel and car was from around 5,000 years ago.

AGRAWAL: This was in a grave that was found in what is now Russia, where archaeologists found a grave of a man sitting within a four-wheeled cart. So this was the first sort of evolution from the potter's wheel to going to transport. And, to be honest, like, why did it take so long, you know? But when you think about it, it's actually quite a complex thing because gravity is now not helping you. So the potter's wheel - gravity's keeping your wheel in place. That's not the case when you turn it on its side by 90 degrees. And so you're trying to balance a lot of different engineering challenges and restraints in order to make this work.

WOODS: This must have opened up a lot of trading on land that wasn't previously possible.

AGRAWAL: It did. So it was the Yamnaya people that we found with - you know, with these graves and the cart. And from what I understand, they went from being a primarily agricultural, local, community-based people to traveling around. They probably slightly terrified the other people they came across when they trundled up on their wagon. So they spread out. Agriculture changed because, instead of needing dozens of people tilling a field, you could now get an animal. So one family could now run a farm.

WOODS: OK, so that's reinvention of the wheel No. 1. What's the next reinvention that happened?

AGRAWAL: So the next reinvention was the spoked wheel. So that is the wheel, if you imagine, in slightly more modern carts. So this made vehicles lighter and therefore speedier and so would have helped the speed at which stuff could move around, commodities could move around, and people could move around.

WOODS: So how do we get from these kind of wheels 2,000 years ago to something like a - in a bicycle or a car?

AGRAWAL: Yes. So now this is where we didn't reinvent the wheel for quite a long time. So the wire wheel was only invented about 200 years ago. The wire wheel was, in fact, invented for flying machines. So you have these inventors wanting to get up into the air. They're creating these really light, metallic-framed or wood-framed structures, and they have to keep them as light as possible. So somebody came up with this idea of the wire wheel, which is what we now see in our bicycles. And so these are extraordinarily light compared to the clunky, wooden wheels that we had 4,000 years ago.

WOODS: So keeping the wheel strong while also being light is kind of the goal here.

AGRAWAL: Absolutely.

WOODS: Yeah. You know, what would a very modern version of the wheel be - like, a cutting-edge form of wheel?

AGRAWAL: So I think there's two. One is the gear. This is a wheel where you essentially chip away at the edges, and then you can make these teeth interlock. So gears - I think they're pretty much in every machine I can think of. So if you think of a blender or a dishwasher or any kind of mechanism like that, you've got gears in there whirring away.

And the other one that I love is the gyroscope. So the gyroscope has been around for maybe a hundred to 200 years. So the best example I can think of is a top. You set it spinning, and it stays up on a tiny, little point because of this momentum of the spinning, round body that it has. And if you try and give it a very gentle little nudge, it goes, oh, I don't like this. I'm going to push back at you.

So we can use this principle to navigate the International Space Station. So the International Space Station has four giant wheels that they call flywheels. They're about just under a meter in diameter, and they weigh a lot - like, hundreds of kilograms. And they're spinning. So it's almost, like, a little driving mechanism to manage something that's really far away up in space.

WOODS: That's fascinating - so all the way from a potter's spinning wheel to something that keeps astronauts in place in space. That's amazing.

AGRAWAL: Yeah, it's a pretty important invention.

WOODS: So what does this all say about innovation?

AGRAWAL: So I'm trying to think of the Mesopotamian potters. They wouldn't have probably ever imagined that a spaceship would be using this principle to orientate itself, so I think that's one thing to think about - is there's a good possibility that our invention will be used for a completely different purpose. And as much grief as I give this expression, don't reinvent the wheel, there is something to it. But I also think, when things change and develop, it's always good to take a little step back and go, can we just remind ourselves why this thing is exactly this way? Is there something we can tweak about it, as the world changes, to make it better suited? Can we make it better suited for a broader range of people?

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WOODS: Thanks, Roma Agrawal. It has been fascinating to talk to you for THE INDICATOR.

AGRAWAL: Thank you so much for having me.

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WOODS: This episode was produced by Cooper Katz McKim with engineering by Maggie Luthar. It was fact-checked by Sierra Juarez. Kate Concannon edits the show, and THE INDICATOR is a production of NPR.

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