Daniel and Kelly’s Extraordinary Universe - How Does A Bicycle Balance?

Episode Date: April 30, 2019

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This is an I-Heart podcast. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System

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I know how overwhelming it can feel if flying makes you anxious. In session 418 of the Therapy for Black Girls podcast, Dr. Angela Neal-Barnett and I discuss flight anxiety. What is not a norm is to a lot. allow it to prevent you from doing the things that you want to do, the things that you were meant to do. Listen to therapy for black girls on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Hey, Jorge, what image do you get in your mind if I say the phrase, mysteries of the universe?

Hmm, I think I think of, you know, black holes. what's inside of them, and what happened at the beginning of time, and where is the universe going to go? Those are all wonderful mysteries, and I'd love to dig into them, but what if I told you you don't have to go so far away to find mysteries? Hmm. You mean, like, why is a cartoonist hosting a podcast about science? Yeah, that's exactly the point. It turns out that there are deep, unanswered physics questions all around us. You don't have to travel to the edge of the galaxy to find something we'd do. don't understand. Yeah, I've heard about this, that in the objects we use every day, there might be things that even physicists don't know how it works. Yeah, it turns out physicists don't know what we're

talking about all the time. Wait, you don't know what you're talking about, or you know what you're talking about, but you don't understand it. No, that's the exact job of physics, is to look around us and say, do we really know how this works? Can we actually understand it? And sometimes we think there's a simple explanation, but we sit down to work it out. It turns out it's much more complicated than we thought. Yeah. Turns out there are big mysteries, even in the things that a lot of us ride to work every day.

That's right. Hi, I'm Horan. And I'm Daniel. And welcome to our podcast, Daniel and Horan. Howe Explain the Universe, a production of IHeart Radio. In which we look around for weird things in the universe that don't make sense and try to explain them to you. Sometimes we look far, sometimes we look pretty close to home.

That's right. Today on the episode, we're going to try something a little bit different. So usually we talk about the big things out there in the universe, all the big fundamental questions about what the universe is made out of and where is it going and what happens inside of crazy things like black holes. But today, we're going to try something a little different. That's right. Some of those are big, sexy questions that affect the human condition and the context of your life.

But we think sometimes there are mysteries of physics right here in front of us that can give us deep insights into the way things work and how we live our lives. So this might be the first of a series of episodes in which we tackle a question that's kind of close to us or maybe hidden in everyday objects. That's right. So look around you. Think about whether you understand. the way the world works around you. Why doesn't your house fall down? How do the lightning rods work?

All these things that are happening around you, do you really know how they work? Do physicists even know how they work? So today on the podcast, we're going to talk about why don't bicycles fall over? No, the bicycle has been around for a long time. People have been putting their butts on those funny seats and peddling around for decades and decades and decades.

But the physics of a bicycle is fast. If you just hold a bicycle and let go, it's going to fall over, right? But if you push your bicycle so that it's going fast, it doesn't fall over. It can ride by itself. It's kind of a ridiculous situation if you think about it. Like, who thought to take two wheels and ride around in them? That's right. It seems like it wouldn't balance, right?

It seems much more natural to have three wheels or four wheels, right? Maybe somebody was just short of wheels. And they were like, dang it, I ordered three wheels on the internet, only to a ride. I guess I'm going to have to invent something. They couldn't afford a third wheel. That's right. They only had the raw materials enough for two wheels or something. Here we're like inventing a new myth of the genesis of the bicycle, right?

Yeah. Well, it seems impossible because it's hard to balance, right? You need at least, you know, like a chair needs at least three legs to stand on. It's kind of weird to think that someone would think of a vehicle that only rides on two wheels. Yeah, that's right. Not many people invent chairs with just two legs. right for that same reason that would be pretty odd yeah there's so there's two wheel all these two wheel contraptions we have motorcycles we have bicycles it is

amazing it's not something that I would have considered inventing but it works you see bikes everywhere and you go to Europe and India and China and there's all over the world there's thousands and millions and millions of bicycles being used every day but the physics of it is still a bit of a mystery yeah how do bicycles stay up apparently physicists don't really have a good answer right Yeah, that's right. It's fascinating. But, you know, do this experiment in your head. You remember riding a bike, probably. And the faster you go, the more stable the bike seems. And at some point, you could even lean back and take your hands off the handlebars. And that seems like a ridiculous thing to do. You're going 20 miles an hour. And if the handlebars flipped over, you would fly over the front of the bike and hurt yourself. But miraculously, almost, it seems pretty stable. And I remember discovering this as a kid that you could ride your bike without holding onto the handlebars because at high speeds it's so

stable. Yeah, wearing a helmet though, right? We should point a helmet and only, you know, off the street, of course, never ride without holding the handlebars on the street because you could cause an accident. Or in the highway, right? It's sort of amazing. Or on the highway, that's right. Actually, my dad used to commute

to work on a bicycle and we lived up in the mountains in New Mexico and so it could get pretty snowy. And I remember that he would put nails and studs in his wheels on purpose, like sticking out so that he could grip the ice. Yeah, he was a pretty hardcore commute to work.

He was like, I'm going to commute to work no matter what the weather is. Sounds like a Matt Max modification there. Yeah, I asked him once if it was good for the ice, and he said, actually, it's pretty good for pedestrians, too. It's good for clearing the road on pedestrians. Exactly. Exactly.

Yeah, so we understand that, but we don't understand why bikes stand up. Yeah, it's kind of a mystery. You ride it. I mean, you're doing a lot of the balancing with the handlebars, right? But a lot of the balancing and staying up is kind of done for you when you're riding a bicycle. Yeah, that's right. A lot of it's done for you. And I think there's also a fascinating area there where your brain has like incorporated the mechanics of a bicycle into your, into itself, right? It's like learning how to ride a bike is basically learning how to map where you want the bike to go to how to move your hands and shift your weight, et cetera, to ride the bike, right? It's amazing seeing a kid learn to do that. It's a really complicated thing.

Like imagine a robot learning to ride a bicycle. That's a really hard task. That's something that robots still can. do. Because it's very counterintuitive, right, to ride a bicycle? Yeah, that's right. I mean, like if you're starting to lean to the right, then you actually have to teach your body to turn the wheel towards the right to balance

out. Yeah, exactly. And you have to lean to just the right way. And sometimes you have to lean left to turn right. It can get pretty complicated. It's sort of in its most extreme form in those crazy motorcycle races. You see those guys whizzing around turns at like a hundred-something miles an hour. And their bikes are leaning so far.

over that their knees almost scrape the ground. Right. But basically, if you're at home and maybe you don't have a lot of experience of bicycles, try this experiment at home. Borrow a bicycle, or if you have one, take it out, and then hold it out either on the street or on the sidewalk or maybe ideally kind of in a little bit of a downhill, and then just give it a big push forward, and you'll see that the bike keeps going straight. It doesn't immediately fall over. Exactly. And so that's the topic we want to address today. why does the bike stay up?

And so before we dug into it, I thought, well, let's find out what people think. Let's see what people think the answer might be. Yeah. So you went to your local mecca of bicycles, right, a college campus? That's right. That's right. And asked people on the street, actually, today's a sort of a special edition because this quarter at UC Irvine, I'm teaching freshman physics, which is mechanics.

And the week before we did these interviews, I just taught about rotation, angular momentum. And so my students were primed for this topic. And so I asked students in my freshman physics class this question. So the interviews you'll hear are with students in my class. Cool. So think for a moment. And if you think you know the answer, why a bicycle stays upright.

So think about it for a second and then listen to these answers. Here's what they had to say. Why does a bicycle balance? Oh, you have to get the motion going, you've got to get, you know, centrifugal forces, you've got to get your balance. Are you a physics professor? And definitely not. Would it be because since there's two wheels, like the force and one goes to the other, that's what like it still keeps going forward? Something like that?

No. No? Okay. Thanks. Because there's a torque from the tire. and when you rotate, the talk support the rotation, so you won't find out. Okay. Because it's moving by chance?

Because like standing up, it wouldn't stand up by itself. So I'm not sure, actually. Okay, great. I'm not exactly sure, but I'm thinking it has something to do with maybe centripetal forces. The fact that there's constantly pushing in or like towards a, center of the bicycle wheels. So as opposed to where it's not rotating, it's kind of unstable because it doesn't have any other points of contact. I think that this has to do with either the angular momentum or rotational inertia, the bike. So if something is rotating like a gyroscope

because of its angular momentum, we'll continue to rotate more easily rather than starting or stopping it from rotating. Great. Thanks very much. of Jesus Christ. I have no idea. Thanks. All right. So were you impressed with your students or not impressed? I think the scores on the final tell you how impressed I should be with these students.

Yeah, they seem pretty perplexed. Like, they could not really apply the concepts of rotation and angle of momentum to this topic. I like how they want to even got religious. They just went like, Jesus Christ, what? I don't even know. I know. It's tricky. Yeah, it turns out it to be tricky. But a few folks, you know, repeated what I think a lot of people imagine is the answer, which is angular momentum. A lot of people think, oh, it's some gyroscope effect, some conservation of angular momentum. Maybe they haven't worked through the details in their mind, but that's sort of the most common answer. Yeah, I imagine a lot of people listen to this podcast. You know, you've probably read a few science books, maybe, or are into signs,

and you probably think you know the answer. And I imagine most people think it has something to do with angular momentum. And so before you click off, because you think you know the answer, you should know that the answer is not angular momentum. You just gave it away. Well, I just don't want it to click away. That's right. Keep listening.

Trust us. There's more to it than just angular momentum. I mean, it's not even close. It's not like the predominating factor in why bicycles stay upright. Yeah, that's right. But let's dig into it a little bit. Let's talk about what angle momentum is, how it contributes to a bike staying upright, and then what else is going on?

But first, a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush. Parents hauling luggage. kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass.

The injured were being loaded into ambulances. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and law. and order criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop.

Listen to the new season of Law and Order Criminal Justice System on the IHeartRadio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly and now I'm seriously suspicious. Oh, wait a minute, Sam. Maybe her boyfriend's just looking. for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot.

He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them.

I mean, do you believe him? Well, he's certainly trying to get this person. person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts,

or wherever you get your podcast. The U.S. Open is here, and on my podcast Good Game with Sarah Spain, I'm breaking down the players from rising stars to legends chasing history, the predictions, well, we see a first time winner, and the pressure. Billy Jean King says pressure is a privilege, you know.

Plus, the stories and events off the court And, of course, the honey deuses, the signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very fancy, wonderfully experiential sporting event. I mean, listen, the whole aim is to be accessible and inclusive for all tennis fans, whether you play tennis or not. Tennis is full of compelling stories of late. Have you heard about Icon Venus Williams' recent wild card bids? Or the young Canadian, Victoria Mboko, making a name for herself.

How about Naomi Osaka getting back to form? To hear this and more, listen to Good Game with Sarah Spain, an Iheart women's sports production in partnership with deep blue sports and entertainment on the Iheart radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHart Women's Sports. What exactly is angular momentum? Yeah, so let's do it one step at time. Let's just make sure we have clear.

you're in our heads what momentum is, and then we'll extrapolate from that to angular momentum. Okay. So momentum is just, you know, the property of some object to keep going when you've pushed it or to, you know, not go when you haven't pushed it. It's, you know, essentially it's the same as inertia, right? Like if you got something going, it doesn't, let's keep it going. It wants to keep going. Yeah, exactly.

So we say momentum is conserved. That just means if something is moving, right, it has a certain amount of momentum. that momentum is not going to change unless you apply a force to it, right? And that's really what forces are. Forces are changes in momentum. And so momentum is just this property is something, if it's moving, it likes to stay moving. And it's connected to inertia. It comes from the inertia.

The mathematical expression for momentum is mass, which is inertia, times velocity. Right. So something with more mass has more inertia and therefore more momentum for the same velocity. And that's a weird thing about the universe, right? Like, I was talking to a pretty high-level physicist, and they were saying that we don't really know kind of what inertia is. Hold on. Hold on. You talk to other high-level physicists?

I'm finding out about this on the podcast. What? I've been physics cheating on you, Daniel. Oh, my God. Well, okay, I'm putting on my tutel list. Find other cartoonists to talk to. Technically, it happened while we were on a break, Daniel. So it's not.

Okay. All right, fine. Flaunt your relationship with other physicists. Go ahead. Go ahead. It doesn't hurt my feelings at all. Go ahead. It happened before we signed a contract together.

But no, no, no. This was Alam Gross. He's like one of the head physicists at Cern, right? He is a prominent member of the Atlas Collaboration and a serious Higgs physicist. Yeah, so he's thought a lot about mass. That's probably where you're going. He said physicists don't really know what inertia is.

Like, why do things keep going the way if you don't apply force to them? Yeah, you're right. it's an observation, right? We call these things laws sometimes as if we like know why they happen or why the universe works this way. But a lot of times it's just observation. We'd like, well, we notice this and we'd be able to describe it mathematically and write

it down. That doesn't mean we know why, right? It doesn't mean we couldn't imagine the universe that was different. So we don't know why things have inertia, right? We have the Higgs boson, which tells us how things get mass. And that tells us where mass comes from. But we don't know why mass means inertia, right? We don't know how that all works.

Yeah, or like why if you have more mass, it's harder to stop and or to get going. Yeah, exactly. Deep mystery of the universe. Such a basic question. We don't even know how to test it or grapple with it, right? It's just one of those things we just sort of accept and move on. And maybe someday somebody's going to figure it out probably by like poking some other mystery. Maybe even by trying to solve the mystery of an everyday object that's around us.

Yeah, like the bicycle. Yeah, that's why it's important to never let go. of mysteries, right? Even things that seem mundane, right? Blenders and bicycles and whatever, they can hide secrets to the universe. I mean, the unicycle, that's all news, but the bicycles were the frontier of science is at, right? That's right. All right, so that's momentum, right? People are pretty familiar with momentum. Well, there's another kind of momentum, right? Things like to keep moving forward if you've pushed them. Things also like to keep spinning, right? And that's what we call angular momentum. And this is one of my favorite tricks in physics. It's like, let's be lazy.

Let's not describe something new with a whole new concept. Let's just extrapolate from something else we already know. So we have this concept of linear momentum. Let's just use the same kind of stuff, the same ideas to describe spinning. Right. And I think something that I always find interesting is that angular momentum is kind of just linear momentum, but if you apply to things that are kind have connected to each other, right? Like a wheel is really just a bunch of atoms stuck together. A wheel is a bunch of atoms stuck together. Yes, I can confirm that here on the show.

Hold on wait. I'm getting an update. Yes, yes, that's true. Okay, good. The experiments, check out. Okay, good. But what I mean is, like, the angular momentum of a wheel is really just a linear momentum of all the particles inside of it.

But because they're connected together, it sort of becomes almost something else. Yeah, that's right. You have all these objects. You can think about wheels. They're just a bunch of atoms. But if the atoms weren't connected to each other when you spun it, then it wouldn't hold together, right? And so it's the bonds between the atoms that hold them together.

You think of like, you know, the moon going around the Earth, right? Why does it move in a circle? It moves in a circle because there's a force. That force is gravity that keeps it from just flying off into space. So in the case of the wheel, why do the bits of the wheel stay together and not just fly off? It's because the atoms are holding them together. So, yeah.

There are forces there moving it in a circle. But like all things, you can describe it in different levels, right? You can describe it as a single wheel. You can describe it as 11 billion particles, right? The physics should work in every case. It's just sometimes the math is really hairy and sometimes the math is really simple. And so the end result is that it behaves as if the spinning was like linear momentum, right? Yeah.

If you spin it, it's going to keep spinning in space for forever, unless you slow it down and apply some four. force or torque to it. That's right. Angular momentum is also conserved, right? So if something is spinning, it's going to keep spinning until you apply the rotational version of force, which we call torque, right? And so that's why, for example, the moon doesn't fall into the earth, right? Because it has too much angular momentum, right? That's why the solar system hasn't collapsed into a black hole because the spinning keeps it from falling in, right? And so there's lots of consequences of angular momentum and the conservation of angle momentum. So it's definitely a thing. It plays a big role in the shape and structure of the universe and our everyday

lives, right? So angular momentum is definitely a thing. And it seems relevant to the bicycle because the bicycle has big spitting things on it, right? Right. And angular momentum is also kind of different. It's not just because it's hard to speed up or slow down when something is spinning in space, but it's kind of hard to change the orientation of it, right? Once something is spinning, like a wheel out in space, it's kind of hard. It likes to be, it likes to not just keep spinning, but it likes to keep spinning in that direction. That's right. Angular momentum is defined along a spin axis, right? Yeah. And just like if you push something in a certain direction, it likes to go not just in any direction, but in that direction. If you spin something,

then it likes to keep spinning around the same axis of rotation that it started. Yeah, like around the same line that goes through the hub of the wheel. Yeah, exactly. And so if you have it spinning one way and you want it to spin the other way, right, that takes a lot of torque. Or if you You have it spinning in one direction, and you want it spinning around an axis that's, like, rotated by 90 degrees. That also takes a lot of torque, right? So, yeah, it's not just that it spins. It likes to spin in the same direction. And so that's why people assume that's the reason bikes tape upwards, is that up, upwards, up?

Right side up, right. Upright, yeah. Yeah, exactly, because you imagine that this has an application of the bicycle, that the wheels are spinning, and so the wheels have angular momentum, and that momentum is around the axis, right, the hub, around which the wheels are spinning and so if the bike just goes in the same direction then it's going to resist falling over

because it has some angular momentum around that axis and for the wheels to spin in another direction would require some sort of torque and it's kind of like if you just take one wheel and you roll it down the hill or roll it down the street it's going to mostly stay upright kind of like a coin when you coin

toss a coin or roll a coin on a table it just kind of likes to keep rolling and stay upright. Yeah, and you can see this effect in lots of other things in your life. Like if you ever have a spinning top, right? You know, you can spin a top and it'll stay upright. And it can even like do crazy things. Like, you know, move, you can balance it on the tip of your finger, right? Stuff like that.

You could never balance a top that wasn't spinning on your finger unless you're some sort of magician or juggler. But if it's spinning, then it's really pretty easy to keep it on your finger. And that's because it resists changing its direction. direction because the angular momentum is going in a certain direction already, right? So the same effect is in play for the bicycle. And if you are a few too many levels into your inception dream, then the top would just keep spinning forever, right?

That's right. Yeah, exactly. And so what happens on a bicycle? Well, on a bicycle, for example, if your bicycle starts to fall over, right, then the gyroscope effect is essentially going to turn the wheel. It's going to turn the wheel a little bit in the direction. that the bike is falling, and that'll keep the bike stable. So it's not like the gyroscope effect keeps the bike from leaning over.

It's more that it turns the wheel in such a way that if the bike does start to lean over, it corrects itself, right? Right. If it falls over to the right, then the forces work out just the right way so that the bike, the wheel turns to the right, and then the bike stays upright. Well, I mean, that's what happens when you're, the angular momentum thing is what happens when you just toss one wheel down the street, right? Angle momentum is keeping that one wheel upward,

but you're saying that when I put two of them together on a bicycle, that's not the main thing that's keeping the bicycle upright. Right. Well, I'm saying that the gyroscope effect, this angle momentum, does have a role in keeping the bike upright, like you said for a single wheel. But it turns out they did some studies and it's not enough, right? The effect is there, it's real, but it's not enough to keep a bicycle upright.

And that kind of makes sense. I mean, the wheel is not very heavy on a bicycle. And it doesn't go that fast. So it's not a huge amount of momentum now. Oh, I see. Like if you just take a bicycle and you lock the steering wheel, meaning you can't steer it. Or like if you just connect to wheels with a bar and toss it down the street,

it would keep going, but it wouldn't keep going upright as far as a bicycle would. That's right, exactly. The front wheel has to be free to make these corrections, right? so that the gyroscope effect and the other effects we'll talk about in a minute can correct the, can turn the wheel to correct for any leaning. That's the key to staying upright, that if you start to lean, you want to turn the wheel. Like, imagine you're riding a bike and you start to fall over to the left. What are you going to do? Well, if you turn the wheel a little bit to the left, then you're sort of going to ride into it and you'll stabilize.

Right. If you turn the wheel to the right, then you're just going to fall over. So the key to staying upright on a bicycle is that the front wheel turns in the direction that you're falling. Okay, so that's, hold on, I think I just fell off my bike. Your mental bike? I hope you're wearing a helmet. I was wearing a mental helmet. Well, let's get, let's really dig into it because I'm a bit confused.

But we'll get into it, but first let's take a quick break. December 29th, 1975, LaGuardia Airport. holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. terrorism law and order criminal justice system is back in season two we're turning our focus to a threat that hides in plain sight that's harder to predict and even harder to stop listen to the new season of law and order criminal justice system on the iHeart radio app apple podcasts or wherever you get

your podcasts my boyfriend's professor is way too friendly and now I'm seriously suspicious. Oh, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone.

Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him

because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. The U.S. Open is here. And on my podcast, Good Game with Sarah Spain, I'm breaking down the players from rising stars to legends chasing history. The predictions will we see a first-time winner and the pressure.

Billy Jean King says pressure is a privilege, you know. Plus, the stories and events off the court and, of course, the honey deuses, the signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very fancy, wonderfully experiential sporting event. I mean, listen, the whole aim is to be accessible and inclusive for all tennis fans, whether you play tennis or not. Tennis is full of compelling stories of late. Have you heard about icon Venus Williams' recent wildcard bids or the young Canadian Victoria Mboko making a name for herself. How about Naomi Osaka getting back to form?

To hear this and more, listen to Good Game with Sarah Spain, an Iheart women's sports production in partnership with deep blue sports and entertainment on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHeart Women's Sports. Okay, so Daniel, we know that. we're trying to figure why bicycles stay upright and we know that angular momentum has something to do with it

but it's not you're telling me it's not the main factor why bicycles stay upright yeah that's right and they did this really cool experiment to discover that they said can we build a bicycle that doesn't have angular momentum you might think well that's impossible

because the bike has a spinning wheel and that's definitely going to have angular momentum so what they did was they built a bike with two more wheels and these wheels spin the other way. Okay, it's a crazy looking bicycle. But, you know, if you attach, if you put two wheels together and one spins clockwise, then the other one's going to spin counterclockwise, right, because of the way they rub. And so if you just attach two more wheels that touch the original

wheels, then they're going to spin the opposite way, which gives the opposite angular momentum and the opposite gyroscope effect. So you basically have a bicycle with no gyroscope effect. No angular momentum, or like zero angular momentum. And so you would think that, you would think that it would just fall over, right? Because it's kind of like a bicycle. If you don't push it or anything and just take your hands off it, it's going to fall over because it doesn't have any anger or momentum or it's not going. That's right.

But the universe came up with a surprise for us, right? Which is why we do experiments. This is why we don't just sit in a cave somewhere like the Greeks and think about the universe. We go out and test these ideas because the universe is full of surprises. And it turns out that that bike balances almost as well as a normal bicycle, which is like mind-blowing. decades, people thought, oh, it's angular momentum, it's angular momentum, until somebody finally went out there and did the experiment and checked. And, you know, another experiment you can do is

you can shrink the wheels, right? If the wheels are really, really small, like the size of skateboard wheels or something, or roller blade wheels, then they're going to have much less angular momentum. And those bikes are also pretty well balanced. They still stay up. They still stay up. So this sort of like blew up the whole concept. People had assumed for a long time that it was angular momentum, it's gyroscopy, yeah, yeah, yeah, that makes sense. But nobody really tried it for a while. And so people went out and did the experiments and turns out, nope,

that's not the answer. Were there actual physics conferences around this topic? Yeah, somebody got a paper in science about this. Really? I mean, this is a big deal. Yeah, I mean, talk about like, low-hanging fruit, right? It's not that hard to build this bicycle. You struggled in grad school

for years and years. Did you get a science paper? I didn't. I had to work on a $10 billion collider. I still didn't get a science paper. You can make a funky bicycle with 100 bucks and get enough information for a science paper. That's pretty good. So somebody made a bicycle with no angular momentum and it still stay upright. Yeah, it still could balance. You could push it by itself and it would have all those same behaviors.

It could balance by itself. Okay, so the secret is something else about a bicycle. And you were telling me a little bit earlier that the secret is that one of the wheels can move. The secret is definitely you have to have the front wheel being able to move. And there's lots of reasons why that's important. And one of them is the angle of the forks, right? So the forks are the thing on the hold the front wheel in place, right, connected to the handlebars. It's how you steer.

And on most bikes, the angle of the forks is forwards, right? So the wheel sits a little bit in front of the handlebars. Yeah, it's kind of curved forward, right? It's not like a straight fork. down it's kind of angled and it's it kind of curves up yeah and I always wondered why that was and I always thought oh that's just like it looks cool or I don't know it's sort of a nice design or whatever a fancy just like you know like a whimsy like a little whimcical touch but no it turns out that's actually an ancient part of the design like if you look back a pictures of old bicycles even really

old bicycles had that sort of slant and the reason is that that also helps the bike stay upright. What it means is that the axis that you're steering on, right, the fork, the direction, is in front of, it hits the ground, a line along that axis hits the ground in front of where the bike is actually touching the ground. Hmm. Right. The bike touches the ground on the bottom of the front wheel. Right.

But the steering axis hits the ground ahead of that. And so what that means is that it's sort of following it. It's not perfectly aligned these two things. Yeah. Yeah, and so what that means is that one is sort of following the other. It's sort of like, you know those wheels on a grocery cart, those things that are like impossible to turn around and you're going to go backwards, it's a pain, right?

I always get the chopping cart with a broken caster wheel, you know, that goes out the you probably are the one who breaks them, right? I mean, you just return them to store and don't say anything, right? Exactly. No, you know those wheels, they do this funny thing where if you push forwards, then they follow the direction of motion, right? because they're sort of behind the steering axis, right? They go backwards.

They always align in the direction where you're pushing. Yes, exactly, right? Which is why it's so hard to turn them around because they're aligned in some other direction. Well, it's a similar effect for the bicycle, right? What that means is that if the bicycle starts to lean to the left, for example, then because of this angle, gravity in the force from the ground is going to turn the wheel in such a way that the wheel turns in the direction

that you're falling, which again helps the bike right itself. And so because this angle axis is tilted, then you get that same effect. Okay, so wait, you're saying, okay, I'm riding my bicycle. Okay, I'm going down the sidewalk, and suddenly I start to lean a little bit to the left.

So I'm falling, falling, falling, and you're saying there's a, because of this axis castor effect, then my wheel automatically, without me having to steer it, is going to turn to the left. Turn to the left, yeah, exactly. You know how if you pick up a bicycle, right, the front, the handlebars always turn, right?

They never stay balanced. If you pick up a bicycle, it's always like the front wheel is spinning in some crazy direction. That's because this caster effect and also because the center of mass of the handlebars and the wheel are not quite on top of each other. And that's another effect that contributes to the wheel turning in the direction that you're falling. Okay, and that helps me stay upright, right? because if I'm leaning left, my front wheel turns left because of these effects. And then now that's actually going to help me pick myself back up. That's right, exactly.

And so these are all small effects that help a bike stay upright. And the cool thing is that you can build all sorts of crazy bicycles. And they've done this as like whole bicycle research teams now. And they've built bicycles that have no angular momentum, like we talked about. They also built bicycles that have no angular momentum and don't have this cast. wheel effect, right? They angle the fork in the other direction. And I've seen this video, they can still get the bicycle to balance by itself, even without the castor wheel and without angular momentum. Meaning you point the fork down, like perfectly down, that still works.

Or even backwards, right? The negative effect. You can even have the fork sort of pointing in the wrong direction, and a bike will still balance. So a bike with no angular momentum and the negative castor effect will still keep itself upright. But how does it say upright if you cancel out this self-steering effect? Nobody knows. That's the awesome part. I am serious.

Nobody knows? Turns out these equations are complicated, right? Like figuring out how a bike balances is not a simple like, oh, do-do-do, it's angle momentum, we're done. These are complicated effects because there's lots of forces involved, lots of ways it can pivot. And so it's still a mystery, you know?

it definitely is influenced by angle momentum it's definitely influenced by this castor effect it's definitely influenced by this other thing with the center of mass about where the balance point is on a bicycle but the truth is that it's still a bit of a mystery wait so you're telling me every time I ride a bicycle I am riding on a mystery of the universe

that physicists don't know how it works you're basically riding a black hole around town that's what I mean oh my god does that make writing your body bicycle seem more fun and exciting. It seems a little more dangerous, to be honest. It's not like the physics is going to stop working. Like, hold on a second, we figured out your bike shouldn't balance, and then, boom, everybody

falls over simultaneously. That would be awesome. It's still a mystery. There are lots of effects there we don't understand. It's complicated. You know, lots of things about how people turn. You know, you lean to the right and then turn to the left. Yeah.

Counter-steering. All sorts of stuff is going on. It's really pretty tricky. But it's important. If you figure out how bicycle is balanced, you could develop a new bicycle, right? We could have some breakthrough in bicycle science to be just around the corner. Wow. You could win the no-no-bel bicycle price.

Yeah, or, you know, you could make a zillion dollars, whichever you prefer. But it could be that somebody comes up with a better way to make a bicycle, and that sweeps the world, right? and all of a sudden the way we've been riding bikes for a hundred years is like old-fashioned and clunky and hilarious. There's a guy in my neighborhood actually who rides a unicycle, which I think is really impressive. You mean to go place, not just in the circus?

Oh, no, yeah, he commutes to work on his unicycle. Does he know you can put two of those together to make a bicycle? Maybe the bicycle is a broken half. But he's got one for, you know, nice weather. he's got like a mountain bike unicycle i even seen him like on trails trails i like struggle to walk up he's like unicycling up no way way like wow does he put does he put nails and screws on it when it's icy no he's just got knobby tires on it i think that's more a testament that's not so much physics that's just the brain like it's incredible what the brain can

maneuver and accomplish if you put your mind to it and so even though physicists haven't figured out what the equations that the control bicycle are your brain has, right? Your brain has an intuitive grasp of how a bicycle works and how to manipulate it. Right. Well, not just me, like little kids. No, I'm talking specifically by Jorge's brain. Oh, okay. You're incredible people. Jorge's brain is amazing. It's amazing that I can do what a three-year-old can do. Yeah, exactly. But you're right. Three-year-olds are excellent at this, right? But that's what three-year-olds do. They're like mapping their control of the world, right? They're interacting with the world and getting all this feedback and figuring out how to control it. and kids for a long time I've had a hard time

learning to ride a bike but if you start by just teaching them the balance these push bikes then they're great at it right it doesn't take them very long to learn to balance wow well that's pretty cool

so the next time you ride your bicycle just think about it you are riding a black hole that's right in our knowledge of the universe yeah and you know there's some interesting physics going on there we know a little bit about it there's some of these effects that are happening to keep your bike upright but there's

definitely something else going on in there that we don't understand. And it could be something mundane. It could be like, oh, it turns out these forces happen this way and there's a twerk and whatever. But there's always the possibility when you don't understand something that there could be a deep secret of the universe revealed, right? That's why physicists tug at every thread we don't understand, hoping that one of those threads is going to unravel the fabric of the universe and teach us something deep about the way when the world works. Yeah. Or at least you'll get to work Yeah, with a little bit of exercise. Exactly, and you'll look really cool, and you'll be fit from all that biking.

Yeah, that's right. Just remember to wear a helmet when you do physics. And so that's why we think the physics of everyday objects is fascinating. So if there's something in your world that you don't understand, something you'd like to understand, why does this happen? Why does it work this way? How come it doesn't work this other way? Send us a suggestion. Why are shopping cards always broken? That's right.

And no matter where I go, did Jorge break the wheels on my shopping cart? Has he been to every grocery store in the universe? Yeah, anything that seems magical in your everyday life, let us know. We'll try to kill the magic. See you next time. If you still have a question after listening to all these explanations, please drop us a line we'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge, that's one word,

or email us at Feedback at Danielandhorpe.com. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal, just a chaotic, chaotic scene.

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