Speaker 1: Hey, orror, Hey, what image do you get in your
Speaker 1: mind if I say the phrase mysteries of the universe?
Speaker 1: I think I think of you know, black holes and
Speaker 1: what's inside of them, and what happened at the beginning
Speaker 1: of time and where is the universe going to go?
Speaker 1: Those are all wonderful mysteries, and I'd love to dig
Speaker 1: into them. But what if I told you you don't
Speaker 1: have to go so far away to find mysteries. M
Speaker 1: You mean, like, why is a cartoonists hosting a podcast
Speaker 1: about science? Yeah, that's exactly the point. It turns out
Speaker 1: that there are deep unanswered physics questions all around us.
Speaker 1: You don't have to travel to the edge of the
Speaker 1: galaxy to find something we don't understand. Yeah, I've heard
Speaker 1: about this that in the objects we use every day
Speaker 1: there might be things that even physicists don't know how
Speaker 1: it works. Yeah, it turns out physicists don't know what
Speaker 1: we're talking about all the time, but you don't know
Speaker 1: what you're talking about, or you know what you're talking about,
Speaker 1: but you don't understand. No, that's the exact job of
Speaker 1: physics is to look around us and say, do we
Speaker 1: really know how this works? Can we actually understand it,
Speaker 1: and sometimes we think it's a simple explanation, but we
Speaker 1: sit down to work it out and it turns out
Speaker 1: it's much more complicated than we thought. Yeah, it turns
Speaker 1: out there are big mysteries even in the things that
Speaker 1: a lot of us ride to work every day. That's right.
Speaker 1: I'm and I'm Daniel, and welcome to our podcast Daniel
Speaker 1: and Jorge Explain the Universe, a production of I Heart Radio,
Speaker 1: in which we look around for weird things in the
Speaker 1: universe that don't make sense and try to explain them
Speaker 1: to you. Sometimes we look far, sometimes we look pretty
Speaker 1: close to home. That's right. Today in the episod, we're
Speaker 1: going to try something a little bit different. So usually
Speaker 1: we talk about the big things out there in the universe,
Speaker 1: all the big fundamental questions about what the universe is
Speaker 1: made out of and where's it going and what happens
Speaker 1: inside of crazy things like black holes. But today we're
Speaker 1: going to try something a little different. That's right. Some
Speaker 1: of those are big sexy questions that affect the human
Speaker 1: condition and the context of your life. But we think
Speaker 1: sometimes there are mysteries of physics right here in front
Speaker 1: of us that can give us deep insights into the
Speaker 1: way things work and how we live our lives. So
Speaker 1: this might be the first of a series of episodes
Speaker 1: in which we tackle a question that's kind of close
Speaker 1: to us or in maybe hidden in everyday objects. That's right,
Speaker 1: So look around you think about whether you understand the
Speaker 1: way the world works around you. Why doesn't your house
Speaker 1: fall down? How do the lightning rods work? All these
Speaker 1: things that are happening around you. Do you really know
Speaker 1: how they work? Do physicists even know how they work?
Speaker 1: So today on the podcast, we're going to talk about
Speaker 1: why don't bicycles fall over? You know, the bicycle has
Speaker 1: been around for a long time. People have been putting
Speaker 1: their butts on those funny seats and peddling around for
Speaker 1: decades and decades and decades. But the physics of a
Speaker 1: bicycle is fascinating. If you just hold a bicycle and
Speaker 1: let go, it's going to fall over, right, But if
Speaker 1: you push your bicycle so that's going fast, it doesn't
Speaker 1: fall over. It can ride by itself. It's kind of
Speaker 1: a ridiculous situation. Do you think about it? Like? Who
Speaker 1: thought it to take two wheels and right around and
Speaker 1: in them? That's right? It seems like it wouldn't balance, right.
Speaker 1: It seems much more natural to have three wheels or
Speaker 1: four wheels. Right. Maybe somebody was just short of wheels
Speaker 1: and they were like, dang it, I ordered three wheels
Speaker 1: on the internet, only to arrive. I guess I'm gonna
Speaker 1: have to invent something. They couldn't aford a third wheel
Speaker 1: only they only had the raw materials enough for two
Speaker 1: wheels or something. You were like inventing a new myth
Speaker 1: of the genesis of the bicycle, right, Yeah, well it
Speaker 1: seems implausible because it's hard to balance, right. You need
Speaker 1: at least, you know, like a chair needs at least
Speaker 1: three legs to stand on. It's kind of weird to
Speaker 1: think that someone would think of a vehicle that only
Speaker 1: rides on two wheels. Yeah, that's right. Not many people
Speaker 1: invent chairs with just two legs, right, for that same reason.
Speaker 1: That would be pretty odd. Um. Yeah, there's so there's
Speaker 1: two wheels, all these two wheel contraptions. We have motorcycles,
Speaker 1: we have bicycles. It is amazing. It's not something that
Speaker 1: I would have considered inventing, but it works. You see
Speaker 1: bikes everywhere, and you go to Europe and India, and China,
Speaker 1: and there's all over the world. There's thousands and millions
Speaker 1: and millions of bicycles being used every day, but the
Speaker 1: physics of it is still a bit of a mystery. Yeah,
Speaker 1: how do bicycles stay up? Apparently physicists don't really have
Speaker 1: a good answer, right, yeah, that's right, Um, it's it's fascinating.
Speaker 1: But you know, do this experiment in your head. You
Speaker 1: remember riding a bike, probably, and it's the faster you go,
Speaker 1: the more stable the bike. Seems that at some point
Speaker 1: you could even lean back and take your hands off
Speaker 1: the handlebars, and it seems like a ridiculous thing to do.
Speaker 1: You're going twenty miles an hour and if the if
Speaker 1: the handlebars flipped over, you would fly over the front
Speaker 1: of the bike. You can hurt yourself. But miraculously, almost
Speaker 1: it seems pretty stable. And I remember discovering this as
Speaker 1: a kid, that you could ride your bike without holding
Speaker 1: onto the handlebars because at high speeds it's so stable. Yeah,
Speaker 1: wearing a helmet though, right, we should probably wearing a helmet,
Speaker 1: and it's only you know, off the street. Of course,
Speaker 1: never ride with without holding the handlebars on the street
Speaker 1: because you could cause an accident or or okay, that's right. Actually,
Speaker 1: my dad used to commute to work on a bicycle,
Speaker 1: and we lived up in the mountains in New Mexico,
Speaker 1: and so he could get pretty snowy, and I remember
Speaker 1: that he would put um nails and studs in his
Speaker 1: wheels on purpose, like sticking out so that he could
Speaker 1: grip the ice. Yeah, he was a pretty hardcore commute
Speaker 1: commute to work. He was like, I'm going to commute
Speaker 1: to work no matter what the weather is. Sounds like
Speaker 1: a Matt Mag's modification there. Yeah. I asked him once
Speaker 1: if it was good for the ice, and he said, actually,
Speaker 1: it's pretty good for pedestrians too. Let's getting for clearing
Speaker 1: the road on pedescans exactly exactly. Um, yeah, so we
Speaker 1: understand that, but we don't understand why bikes stand up. Yeah,
Speaker 1: it's kind of a mystery. You write it, and uh,
Speaker 1: I mean you do. You're doing a lot of the
Speaker 1: balancing with your handlebars, right, But a lot of the
Speaker 1: balancing and staying up is kind of done for you
Speaker 1: when you're riding a bicycle. Yeah, that's right. A lot
Speaker 1: of it is done for you. And I think there's
Speaker 1: also a fascinating area there where your brain has like
Speaker 1: incorporated the mechanics of a bicycle into your into itself. Right.
Speaker 1: It's like learning how to ride a bike is basically
Speaker 1: learning how to map where you want the bike to
Speaker 1: go to, how to how to move your hands and
Speaker 1: shift your weight, etcetera to ride the bike. Right. It's
Speaker 1: amazing seeing seeing a kid learn to do that. It's
Speaker 1: really complicated thing. Like imagine a robot learning to ride
Speaker 1: a bicycle. That's a really hard task. That's something that
Speaker 1: robots still can't do because it's very counterintuitive, right to
Speaker 1: ride a bicycle. Yeah, that's right. I mean like if
Speaker 1: you're starting to into the right, then you actually you'll
Speaker 1: have to teach your body to turn the wheel towards
Speaker 1: the right to balance, Yeah, exactly, And you have to
Speaker 1: lean the just the right way, and sometimes you have
Speaker 1: to lean left to turn right. You can get pretty complicated. Um.
Speaker 1: It's sort of in its most extreme form in those
Speaker 1: crazy motorcycle races. You see those guys whizzing around turns
Speaker 1: like a hundred something miles an hour and their bikes
Speaker 1: are leaning so far over that their knees almost scrape
Speaker 1: the ground. Right. But basically, if you're at home, and
Speaker 1: maybe you don't have a lot of experience of bicycles
Speaker 1: and trying this experiment at home. Borrow a bicycle or
Speaker 1: if you have one, take it out and then hold
Speaker 1: it out either on the street or on the sidewalk,
Speaker 1: or maybe ideally kind of in a little bit of
Speaker 1: a downhill, and then just give it a big push
Speaker 1: forward and you'll see that the bike keeps going straight.
Speaker 1: It doesn't immediately fall over exactly. And so that's the
Speaker 1: topic we want to address today. Why does the bike
Speaker 1: stay up? And so before we dug into it, I thought, well,
Speaker 1: let's find out what people think. Let's see what people
Speaker 1: think the answer might be. Yeah, so you went to
Speaker 1: your local mecca of bicycles right at college campus. That's right,
Speaker 1: that's right, and asked people on the street. Actually, today's
Speaker 1: a sort of a special edition because this quarter at
Speaker 1: you see Irvine, I'm teaching freshman physics, which is mechanics,
Speaker 1: And the week before we did these interviews, I just
Speaker 1: taught about rotation incular momentum, and so my students were
Speaker 1: primed for this topic, and so I asked students in
Speaker 1: my freshman physics class this question. So the interviews you'll
Speaker 1: hear are with students in my class. Cool. So think
Speaker 1: for a moment and if you think you know the
Speaker 1: answer why a bicycle stays upright? So think about it
Speaker 1: for a second and then listen to these answers. Here's
Speaker 1: what they had to say. Why does a bicycle balance? Oh,
Speaker 1: you have to get the motion going. You gotta get
Speaker 1: you know, centrifugal forces. You gotta get your back are
Speaker 1: your physics professor, And definitely not. Would it be because
Speaker 1: since there's two wheels like the force, and one goes
Speaker 1: to thegether, that's why it still keeps going forward. Something
Speaker 1: like that. Okay, thanks, umws. There's a talk from the
Speaker 1: tire um way we're rotated, the talk of support the rotation.
Speaker 1: It's sort okay because it's is it because it's moving?
Speaker 1: Chance because like a loane like standing up and want it.
Speaker 1: They want to like stand up by itself. So I'm
Speaker 1: not sure. Actually I'm not exactly sure, but I'm thinking
Speaker 1: it has something to do with maybe cent tripital forces.
Speaker 1: The fact that there's constantly like pushing in or like
Speaker 1: towards the center of the bicycle wheels, so as opposed
Speaker 1: to where it's not rotating. It's kind of unstable because
Speaker 1: it doesn't have any like other points of contact. I
Speaker 1: think that this has to do with either the angular
Speaker 1: momentum or rotational inertia the bi So if something is
Speaker 1: rotating like a gyroscope, because of its angular momentum, you
Speaker 1: will continue to rotate more easily rather than starting or
Speaker 1: stopping it from rotating. Great, thanks very much, by I
Speaker 1: was moving wise because you're Jesus Christ. It's not because
Speaker 1: of Jesus Christ. Um, I have no idea. Thanks all right.
Speaker 1: So where are you impressed with your students or none impressed? Um?
Speaker 1: I think the scores on the final tell you how
Speaker 1: impressed I should be with these students. Um. Yeah, they
Speaker 1: seem pretty perplexed, like they could not really apply the
Speaker 1: concepts of rotation and anglad momentum to this topic. Um.
Speaker 1: I like how they one of them, even God religious
Speaker 1: di went like Jesus Christ, I don't even know. Um,
Speaker 1: it's tricky. Yeah, it turns out it to be tricky. Um.
Speaker 1: But a few folks, you know, repeated what I think
Speaker 1: a lot of people imagine is the answer, which is
Speaker 1: anglar momentum. Yeah. A lot of people think, oh, it's
Speaker 1: some gyroscope effect, some conservation of angular momentum. Maybe they
Speaker 1: haven't worked through the details in their mind, but that's
Speaker 1: sort of the most common answer. Yeah, I imagine a
Speaker 1: lot of people listen to this podcast. You know, you've
Speaker 1: probably read a few science books maybe or are into signs,
Speaker 1: and you probably think you know the answer. And I
Speaker 1: imagine most people think it's has something to do with
Speaker 1: angular momentum. And so before you click off because you
Speaker 1: think you know the answer, you should know that the
Speaker 1: answer is not angular momentum. You just gave it away. Well,
Speaker 1: I just don't want it to click away. That's right,
Speaker 1: keep listening. Trust us more to it than just angular momentum.
Speaker 1: I mean, it's not even close. It's it's not like
Speaker 1: the dominating factor and why bicycles stay up right. Yeah,
Speaker 1: that's right. But let's stick into a little bit. Let's
Speaker 1: talk about what angle momentum is, how contributes to bikes
Speaker 1: staying upright, and then what else is going on? But
Speaker 1: first a quick break, what exactly is angular momentum? Yeah,
Speaker 1: so let's do it one step a time. Let's just
Speaker 1: make sure we have clear in our heads what momentum is,
Speaker 1: and then we'll extrapolate from that to angular momentum. Right.
Speaker 1: So momentum is just you know, the property of some
Speaker 1: object to keep going when you've pushed it, or to
Speaker 1: you know, not go when you haven't pushed it. It's
Speaker 1: you know, essentially it's the same as inertia, right, Like
Speaker 1: if you if you've got something going, it doesn't let's
Speaker 1: keep it going that it wants to keep going. Yeah, exactly.
Speaker 1: So we say momentum is conserved. That just means if
Speaker 1: something is moving, right, it has a certain amount of momentum.
Speaker 1: That momentum is not going to change unless you apply
Speaker 1: a force to it, right, And that's really what forces are.
Speaker 1: Forces are changes in momentum. And so momentum is just
Speaker 1: this property is something if it's moving, it like sustained movement,
Speaker 1: and it comes it's connected to inertia. It comes from
Speaker 1: the inertia. The mathematical expression for momentum is mass, which
Speaker 1: is inertia times velocity. Right, So something with more mass
Speaker 1: has more inertia and therefore more momentum for the same velocity.
Speaker 1: And that's the weird thing about the universe. Right, Like
Speaker 1: I was talking to a pretty um high level physicism.
Speaker 1: They were saying that we don't really know kind of
Speaker 1: what inertia on. Hold on, you talked to other high levels.
Speaker 1: I'm finding out about this on the podcast What Physics
Speaker 1: Cheating on You? Daniel. Well, okay, I'm putting on my
Speaker 1: two day list, find other cartoonists to talk to. Technically
Speaker 1: happened while we were while we were on a break, Daniel, So, um,
Speaker 1: it's not okay, alright, find flaunch your relationship with other physicists.
Speaker 1: Go ahead, ahead, doesn't hurt my feelings at all. Go ahead.
Speaker 1: It happened before we signed a contract together. Um, but no, no,
Speaker 1: this was this was a lamb gross. He's like the
Speaker 1: one of the head physicist at CERN, right, he is
Speaker 1: a prominent member of the Atlas collaboration and a serious
Speaker 1: Higgs physicists. Yeah, so he's thought a lot about mass.
Speaker 1: That's probably where you're going, he said. Physicists don't really
Speaker 1: know what inertia is, Like why I do things keep
Speaker 1: going the way if you don't apply a course of them. Yeah,
Speaker 1: you're right, it's an observation. Right. We call these things
Speaker 1: laws sometimes as if we like know why they happen
Speaker 1: or why the universe works this way. But a lot
Speaker 1: of times, it's just observation. We're like, well, we noticed this,
Speaker 1: and we'll be able to describe it mathematically and write
Speaker 1: it down. That doesn't mean we know why, right, It
Speaker 1: doesn't mean we couldn't imagine the universe that was different.
Speaker 1: So we don't know why things have inertia. Right. We
Speaker 1: have the Higgs boson, which tells us how things get mass,
Speaker 1: and that tells us where mass comes from. But we
Speaker 1: don't know why mass means inertia, right, We don't know
Speaker 1: how that all works, or like why if we have
Speaker 1: more mass it's harder to stop and or to get going. Yeah, exactly.
Speaker 1: Deep mystery of the universe such a basic question. We
Speaker 1: don't even know how to test it or grapple with it, right,
Speaker 1: So it's just one of those things we just sort
Speaker 1: of accept and move on, and maybe someday somebody's going
Speaker 1: to figure it out, probably by like poking some other mystery,
Speaker 1: maybe even by trying to solve the mystery of an
Speaker 1: everyday object that's around us. Yeah, like the bicycle. Yeah,
Speaker 1: that's why it's important to never let go of mysteries, right,
Speaker 1: even things that seem mundane, right, blenders and bicycles and
Speaker 1: whatever they can hide secrets to the universe. I mean,
Speaker 1: the unicycle, that's all news. But the bicycles where the
Speaker 1: frontier of sciences that that's right, all right, So that's momentum, right.
Speaker 1: People are pretty familiar with momentum. Well, there's another kind
Speaker 1: of momentum, right, Things like to keep moving forward if
Speaker 1: you've pushed them. Things also like to keep spinning, right,
Speaker 1: And that's what we call angular momentum. And this is
Speaker 1: one of my favorite tricks in physics. It's like, let's
Speaker 1: be lazy. Let's not describe something new and with a
Speaker 1: whole new concept. Let's just extrapolate from something else we
Speaker 1: already know. So we have this concept of linear momentum,
Speaker 1: and let's just use the same kind of stuff, the
Speaker 1: same ideas to describe spinning, right. And I think it
Speaker 1: was something that I would always find interesting, is that
Speaker 1: anger momentum is kind of just linear momentum. But if
Speaker 1: you apply to things that are kind of connected to
Speaker 1: each other, right, Like a wheel is really just a
Speaker 1: bunch of atoms stuck together. A wheel is a bunch
Speaker 1: of atoms stuck together. Yes, I can confirm that here
Speaker 1: on the show. I'm getting an update. Yes, yes, yes,
Speaker 1: that's true. The experiment checkt. But what I mean is
Speaker 1: like the angular momentum of a wheel is really just
Speaker 1: a linear momentum of all the particles inside of it,
Speaker 1: but because they're connected together, it sort of becomes becomes
Speaker 1: almost something else. Yeah, that's right. You have all these objects.
Speaker 1: You can think of a wheel is they're just a
Speaker 1: bunch of atoms. But if the atoms weren't connected to
Speaker 1: each other when you spun it, then it wouldn't hold together, right,
Speaker 1: And so it's the bonds between the atoms that hold
Speaker 1: them together. They think of like you know the moon
Speaker 1: going around the Earth, right, why does it move in
Speaker 1: a circle. It moves in a circle because there's a
Speaker 1: force that forces gravity that keeps it from just flying
Speaker 1: off into space. So in the case of the wheel,
Speaker 1: why do the bits of the wheels stay together and
Speaker 1: not just fly off. It's because the atoms are holding
Speaker 1: them together. So, yeah, there's forces they're moving it in
Speaker 1: a circle. But like all things, as you can, you
Speaker 1: can describe it in different levels. Right, you can describe
Speaker 1: it as a single wheel, you can describe it as
Speaker 1: eleven d billion particles. Right. The physics should work in
Speaker 1: every case. It's just sometimes the math is really hairy,
Speaker 1: and sometimes the math is really simple, and so the
Speaker 1: end result is that it behaves as if the spinning
Speaker 1: was like linear momentum. Right, you spin it, it's going
Speaker 1: to keep spinning in space for forever unless you slow
Speaker 1: it down or apply some force or torque to it.
Speaker 1: That's right. Angular momentum is also conserved, right, So if
Speaker 1: something is spinning, it's going to keep spinning until you
Speaker 1: apply the rotational version of force, which we call torque. Right.
Speaker 1: And so that's why, for example, the Moon doesn't fall
Speaker 1: into the Earth right because it has too much angular momentum. Right.
Speaker 1: That's why the solar system hasn't collapsed into a black
Speaker 1: hole because the spinning keeps it from falling in right,
Speaker 1: and so, um, there's lots of consequences of anglid momentum
Speaker 1: and the conservation of angle momentum. So it's definitely a thing.
Speaker 1: Plays a big role in the shape and the structure
Speaker 1: of our of the un verse and our everyday lives. Right.
Speaker 1: So angle momentum is definitely a thing. And it seems
Speaker 1: relevant to the bicycle because the bicycle has big spinning
Speaker 1: things on it, right, right, and angler momentum is also
Speaker 1: kind of different. Not just that it's hard to speed up,
Speaker 1: horror slow down when something is spinning in space, but
Speaker 1: it's kind of hard to change the orientation of it. Right,
Speaker 1: When when something is spinning like a wheel out in space,
Speaker 1: it's kind of hard. It likes to be It likesly
Speaker 1: not just keep spinning, but it likes to keep spinning
Speaker 1: in that direction, that's right. Angler momentum is to find
Speaker 1: along a spin access, right, And just like if you
Speaker 1: push something in a certain direction, it likes to go,
Speaker 1: not just in any direction, but in that direction. If
Speaker 1: you spin something, then it likes to keep spinning around
Speaker 1: the same access of rotation that it started. Yeah, like
Speaker 1: around the same line that goes through the hub of
Speaker 1: the wheel. Yeah, exactly. And so if you have it
Speaker 1: spinning one way and you wanted to spin the other way, right,
Speaker 1: that takes a lot of torque. Or if you have
Speaker 1: it spinning in one direction and you want it spinning
Speaker 1: around an access that's like a rotated by ninety degrees,
Speaker 1: that also takes a lot of torque. Right. So yeah,
Speaker 1: it's not just that it spins. You already likes to
Speaker 1: spin in the same direction. And so that's why people
Speaker 1: assume that's the reason bikes tape upwards, is that up
Speaker 1: boards up right right, upright right, yeah, yeah, exactly, because
Speaker 1: you imagine that this has an application of the bicycle
Speaker 1: that the wheels are spinning, and so the wheels have
Speaker 1: angular momentum, and then the momentum is around the axis
Speaker 1: or the hub around which the wheels are spinning. And
Speaker 1: so if um, if the bike just goes in the
Speaker 1: same direction, then it's going to resist falling over because
Speaker 1: it has some angular momentum around that access. And for
Speaker 1: that for the wheels to spin in another direction would
Speaker 1: require some sort of torque. And it's kind of like
Speaker 1: if you just take one wheel and you roll it
Speaker 1: down the hill or roll it down the street, it's
Speaker 1: gonna mostly stay upright, you know, kind of like a
Speaker 1: coin when you coin plus a coin or roll a
Speaker 1: coin on the table, it just kind of likes to
Speaker 1: keep rolling and stay upright. Yeah. And you can see
Speaker 1: this effect in lots of other of things in your life,
Speaker 1: like if you ever if you ever have like a
Speaker 1: spinning top, right, you know, you can spin a top
Speaker 1: and it will stay upright, and it can even like
Speaker 1: do crazy things like, you know, move you can balance
Speaker 1: it on the tip of your finger, right, um, stuff
Speaker 1: like that. You can never balance a top that wasn't
Speaker 1: spinning on your finger unless you're some sort of magician
Speaker 1: or juggler. But if it's spinning, then it's really pretty
Speaker 1: easy to keep it on your finger. And that's because
Speaker 1: it resists changing its direction because the angle momentum is
Speaker 1: going in a certain direction already. Right, It's the same thing.
Speaker 1: The same effect is in play for the bicycle. And
Speaker 1: if you are a few too too many levels into
Speaker 1: your inception dream, then the top which just keep spinning forever. Right,
Speaker 1: that's right, yeah, exactly, um. And so what happens on
Speaker 1: a bicycle While on a bicycle, for example, if your
Speaker 1: bicycle starts to fall over, right, then the gyroscope effect
Speaker 1: is essentially going to turn the wheel. It's going to
Speaker 1: turn the wheel a little bit in the direction that
Speaker 1: the bike is falling, and that will keep the bike stable.
Speaker 1: So it's not like the gyroscope of keeps the bike
Speaker 1: from leaning over. It's more that it it turns the
Speaker 1: wheel in such a way that if the bike does
Speaker 1: start to lean over, it corrects itself. Right. If you
Speaker 1: if it falls over the right. Then the forces work
Speaker 1: out just the right way so that the bike the
Speaker 1: bike um turn, the wheel turns to the right, and
Speaker 1: then the bike stays up right. Well, I mean that's
Speaker 1: what happens when you're the anglo momentum thing is what
Speaker 1: happens when you just toss one wheel down the street, right,
Speaker 1: Anglo momentum is keeping that one wheel upward. But you're
Speaker 1: saying that when I put two of them together on
Speaker 1: a bicycle, that's not the main thing that's keeping the
Speaker 1: bicycle up up right. Right, Well, I'm saying that the
Speaker 1: gyroscope effect, this anglementum does have a role in keeping
Speaker 1: the bike up right, like you said, for a single wheel,
Speaker 1: but it turns out they did some studies and it's
Speaker 1: not enough. Right there, effect is there, it's real, but
Speaker 1: it's not enough to keep a bicycle upright. And it
Speaker 1: kind of makes sense. I mean, the wheel is not
Speaker 1: very heavy on a bicycle and it doesn't go that fast,
Speaker 1: so it's not a huge amount of momentum that like
Speaker 1: if you like if you just take a bicycle and
Speaker 1: you lock the steering wheel, meaning you can't steer it,
Speaker 1: or like if you just connect two wheels with a
Speaker 1: bar and toss it down the street. It would keep going,
Speaker 1: but it wouldn't keep going upright as far as a
Speaker 1: bicycle would. R's right exactly. The front wheel has to
Speaker 1: be free to make these corrections right so that the
Speaker 1: gyroscope effect and the other effects will talk about in
Speaker 1: a minute can correct, the can can turn the wheel
Speaker 1: to correct for any leaning. That's the key to staying upright.
Speaker 1: That if you start to lean, you want to turn
Speaker 1: the wheel. Like imagine you're riding a bike and you
Speaker 1: start to fall over to the left. What are you
Speaker 1: gonna do? Well, if you turn the wheel a little
Speaker 1: bit to the left, then you're sort of going to
Speaker 1: ride into it and you'll stabilize. If you turn the
Speaker 1: wheel to the right, then you're just gonna fall over.
Speaker 1: So the key to to keep staying up righting a
Speaker 1: bicycle is that the front wheel turns in the direction
Speaker 1: that you're falling. Okay, so that's um, hold on, I
Speaker 1: think I just fell off my bike. You're mainly mental,
Speaker 1: by I hope you're wearing a helmet. That's wearing a
Speaker 1: mental helmet. Well, let's let's get let's really dig into
Speaker 1: it to sound I'm a bit confused, but we'll get
Speaker 1: into it, but first let's take a quick break. Okay,
Speaker 1: So Daniel, we know that we're trying to figure out
Speaker 1: why bicycles stay upright, and we know that angler momentum
Speaker 1: has something to do with it, but it's not, um,
Speaker 1: you're telling me, it's not the main factor wise bicycles
Speaker 1: stay upright. Yeah, that's right. And they did this really
Speaker 1: cool experiment to discover that. They said, can we build
Speaker 1: a bicycle that doesn't have angler momentum? I think that's
Speaker 1: impossible because the bike has a spinning wheel and that's
Speaker 1: definitely gonna have angle momentum. So what they did was
Speaker 1: they built a bike with two more wheels, right, and
Speaker 1: these wheels spin the other way. Okay, it's a crazy
Speaker 1: looking bicycle, but you know if you attach if you
Speaker 1: put two wheels together and one spinings clockwise and the
Speaker 1: other one's going to spin counterclockwise right because of the
Speaker 1: way they rub. And so if you just attach two
Speaker 1: more wheels that touch the original wheels, then they're going
Speaker 1: to spin the opposite way, which gives the opposite angleid
Speaker 1: momentum and the opposite gyroscope effect. So you basically have
Speaker 1: a bicycle with no gyroscope effect, no angular momentum, or
Speaker 1: like zero angular momentum, and so you would think that
Speaker 1: it would just fall over, right, because kind of like
Speaker 1: a bicycle, if you don't push it or anything and
Speaker 1: just take your hands off it, it's going to fall
Speaker 1: over because it doesn't have any angular momentum or it's
Speaker 1: not going that's right. But the universe came up with
Speaker 1: a surprise for us, right, which is why we do experiments.
Speaker 1: This is why we don't just sit in a cave
Speaker 1: somewhere like the Greeks and think about the universe. We
Speaker 1: go out and test these ideas because the universe is
Speaker 1: full of surprises. And it turns out that that bike
Speaker 1: balance is almost as well as a normal bicycle, which
Speaker 1: is like mind blowing it. For decades, people thought, oh,
Speaker 1: it's anglid momentum, it's anglimentum, until somebody finally went out
Speaker 1: there and did the experiment in checked. And you know,
Speaker 1: another experiment you can do is you can shrink the wheels. Right,
Speaker 1: if the wheels are really really small, like the size
Speaker 1: of skateboard wheels or something, or roller blade wheels, then
Speaker 1: they're gonna have much less angler momentum, and those bikes
Speaker 1: are also pretty well balanced. They stay up, they still
Speaker 1: stay up. So this sort of like blew up the
Speaker 1: cold concept. People assume for a long time that it
Speaker 1: was anglo momentum its gyroscope. I yeah, that makes sense,
Speaker 1: but nobody really tried it for a while, and so
Speaker 1: the people went out and did the experiments and turns out, Nope,
Speaker 1: that's not the answer. Where there actually like physics conferences
Speaker 1: around this topic. Yeah, somebody got a paper in science
Speaker 1: about this. I mean this is a big deal. Yeah,
Speaker 1: I mean talk about like low hanging fruit, right, I mean,
Speaker 1: it's not that hard to build this bicycle. Um, you know,
Speaker 1: you struggled in grad school for years and years. Did
Speaker 1: you get a science paper? I didn't. I had to
Speaker 1: work on a ten billion dollar collider. I still didn't
Speaker 1: get a science paper. You can make a funky bicycle,
Speaker 1: you know, with a hundred bucks and get enough information
Speaker 1: for a science paper. That's so, somebody made a bicycle
Speaker 1: with a angular momentum and it's still stay upright, Yeah,
Speaker 1: it's still could balance. You could push it by itself
Speaker 1: and it would it would have all those same behaviors.
Speaker 1: It could balance by itself. Yeah, okay, so the secret
Speaker 1: is something else about a bicycle. And you're telling me
Speaker 1: a little bit earlier that the secret is this that
Speaker 1: one of the wheels can move. The secret is definitely
Speaker 1: you have to have the front wheel being able to move.
Speaker 1: But and and there's lots of reasons why that's important,
Speaker 1: and one of them is the the angle of the forks. Right,
Speaker 1: So the forks of the thing on the whole, the
Speaker 1: front wheel in place, right connected to the handlebars, that's
Speaker 1: how you steer, and on most bikes, the angle of
Speaker 1: the forks is forwards, right, so the wheel sets a
Speaker 1: little bit in front of the handlebars. Yeah, it's it's
Speaker 1: kind of curved forward, right, It's not like a straight
Speaker 1: m fork down. It's kind of angled and it's it
Speaker 1: kind of curves up. Yeah. And I always wondered why
Speaker 1: that was. And I always thought, oh, that's just like
Speaker 1: it looks cool or I don't know, it's sort of
Speaker 1: a nice design or whatever, fancy, just like you know,
Speaker 1: like a whimsy like a little whim whimsical touch. But no,
Speaker 1: it turns out that's actually an ancient um part of
Speaker 1: the design. Like if you look back at pictures of
Speaker 1: old bicycles, even really old bicycles, have that sort of slant,
Speaker 1: and the reason is that that also helps the bike
Speaker 1: stay upright. You know, what it means is that the
Speaker 1: axis that you're steering on right this the fork the
Speaker 1: direction is in front of it hits the ground. A
Speaker 1: line along that axis hits the ground in front of
Speaker 1: where the bike is actually touching the ground. Right, the
Speaker 1: bike touches the ground the bottom of the front wheel,
Speaker 1: but the steering axis hits the ground ahead of that.
Speaker 1: And so what that means is that it's sort of
Speaker 1: following it. It's not perfectly aligned, these two things. Yeah, yeah,
Speaker 1: And so what that means is that it's one is
Speaker 1: sort of following the other. It's sort of like you
Speaker 1: know those wheels on a grocery cart and those things
Speaker 1: that are like impossible to turn around and you're gonna
Speaker 1: go backwards to painting, right. I always get the chopping
Speaker 1: card with the broken castor wheel you know that goes out.
Speaker 1: You probably are the one who breaks them, right, and
Speaker 1: you just return them this door and don't say anything
Speaker 1: right exactly. Um No, you know those wheels they do
Speaker 1: this funny thing where if you push forwards, then they
Speaker 1: follow the direction of motion right, because they're sort of
Speaker 1: behind this the steering access right, they go backwards. They
Speaker 1: always aligned in the direction where you're pushing. Yes, exactly right,
Speaker 1: which is why it's so hard to turn them around
Speaker 1: because they're aligned in some other direction. Well, it's just
Speaker 1: similar effect for the bicycle. Right. What that means is
Speaker 1: that if the bicycle starts to lean to the left,
Speaker 1: for example, then because of this angle gravity in the
Speaker 1: force from the ground is going to turn the wheel
Speaker 1: in such a way that the wheel turns in the
Speaker 1: direction that you're falling, which again helps the bike right itself.
Speaker 1: And so because this angle access is tilted, then you
Speaker 1: get that same effect. Okay, so way you're saying, Okay,
Speaker 1: I'm riding my bicycle. Okay, I'm going down this hidewalk,
Speaker 1: and suddenly I start to lean a little bit to
Speaker 1: the left, so I'm following falling falling, and you're saying,
Speaker 1: there's a because of this access cast effect, and my
Speaker 1: wheel automatically, without me having to steer, it is going
Speaker 1: to turn to the left, turn to the left. Yeah, exactly.
Speaker 1: You know how if you pick up a bicycle right
Speaker 1: the front, the front, the handlebars always turn right they
Speaker 1: never stay balanced. If you pick up a bicycle, it's
Speaker 1: always like the front wheel is spinning in some crazy direction.
Speaker 1: That's because this cast effect, and also because the center
Speaker 1: of mass of the handlebars and the wheel are not
Speaker 1: quite on top of each other. And that's another effect
Speaker 1: that contributes to the wheel turning in the direction that
Speaker 1: you're falling, okay, And that that helps me stay upright, right,
Speaker 1: because if I'm leaning left, my front wheel turns left
Speaker 1: because of these effects. And then now that's actually going
Speaker 1: to help me pick myself back up. That's right, exactly.
Speaker 1: And so these are all small effects that help a
Speaker 1: bike stay upright. And the cool thing is that you
Speaker 1: can build all sorts of crazy bicycles. And they've done
Speaker 1: this is like whole bicycle research teams now, and they've
Speaker 1: built bicycles that have no angular momentum like we talked about.
Speaker 1: They also built bicycles that have no angler momentum and
Speaker 1: don't have this castor wheel effect. Right, they angle the
Speaker 1: fork in the other direction, and I've seen this video.
Speaker 1: They can still get the bicycle to balance by itself
Speaker 1: even without the castor wheel and without angular momentum, meaning
Speaker 1: you you point to step the fork down like perfectly down,
Speaker 1: that's still works, or even backwards right the negative effect.
Speaker 1: You can even have the fork sort of pointing in
Speaker 1: the wrong direction and a bike will still balance. So
Speaker 1: bike with no angle momentum and the negative caster effect
Speaker 1: will still keep itself upright. But how does it stay
Speaker 1: upright if we if you cancel out this self steering effect?
Speaker 1: Nobody knows that I am serious. Like, turns out these
Speaker 1: equations are complicated, right, Like figuring out how a bike
Speaker 1: balances is not a simple like, oh, do to do
Speaker 1: it's angle momentum. We're done. These are complicated effects because
Speaker 1: there's lots of forces involved, lots of ways that can pivot,
Speaker 1: and so it's still a mystery. You know, Um, there's there.
Speaker 1: It definitely is influenced by angle momentum. It's definitely influenced
Speaker 1: by this caster effect. It's definitely influenced by this other
Speaker 1: thing with the center of mass about where the balance
Speaker 1: point is on a bicycle. But the truth is that
Speaker 1: it's still a bit of a mystery. Wait, so you're
Speaker 1: telling me every time I ride a bicycle, I am
Speaker 1: writing on a mystery of the universe that physicists don't
Speaker 1: know how it works. You're basically riding a black hole
Speaker 1: around town. That's what I mean. Oh my god, does
Speaker 1: does that make riding your bicycle seem more fun and exciting?
Speaker 1: It's it seems a little more dangerous, to be honest.
Speaker 1: It's not like the physics is gonna stop working. Like
Speaker 1: a whole lot of second we figured out your bike
Speaker 1: shouldn't balance and then boom, everybody falls over simultaneous sleep.
Speaker 1: That would be awesome. It's still a mystery. There are
Speaker 1: lots of effects there we don't understand. It's complicated. You know,
Speaker 1: lots of things about how people turn. You know, you
Speaker 1: lean to the right and then turn to the left,
Speaker 1: counter steering. All sorts of stuff is going on. It's
Speaker 1: pretty it's really pretty tricky, but it's important. You know,
Speaker 1: if you figure out how bicycle is balance, you could
Speaker 1: develop a new bicycle. Right, you could have some breakthrough
Speaker 1: in bicycle science. To be just around the corner, you
Speaker 1: could you could win the no No No bill bicycle right, yeah,
Speaker 1: or you know, you could make a zillion dollars whichever
Speaker 1: you prefer. But it could be that somebody comes up
Speaker 1: with a better way to make a bicycle and that
Speaker 1: sweeps the world right, all of a sudden, the way
Speaker 1: we've been riding bikes for a hundred years is like
Speaker 1: old fashioned and clunky and hilarious. Um. There's a guy
Speaker 1: in my neighborhood actually who rides a unicycle, which I
Speaker 1: think is really impressive. You mean to go place and
Speaker 1: not not just in the circus. Oh no, yeah, he
Speaker 1: commutes to work on his unicycle. Does put two of
Speaker 1: those together to make a bicycle. Maybe the bicycle just
Speaker 1: broken half? Um, but he's got one for you know,
Speaker 1: nice weather. He's got like a mountain bike unicycle. I've
Speaker 1: even seen him like on trails, trails I like struggle
Speaker 1: to walk up he's like unicycling up way Like wow,
Speaker 1: does he put does he put nails? And no, he's
Speaker 1: just got knob tires on it. I think that's more
Speaker 1: a testament that's not so much physics. That's just the brain.
Speaker 1: Like it's incredible what the brain can maneuver and accomplish
Speaker 1: if you put your mind to it. And so even
Speaker 1: though physicists haven't figured out what the equations that control
Speaker 1: bicycle are, your brain has right, your brain has an
Speaker 1: intuitive grasp of how a bicycle works and how to
Speaker 1: manipulate it, right, Well, not just me like little kids,
Speaker 1: you know, I'm talking specifically about Jorge's brain. His brain
Speaker 1: is amazing. It's amazing that I can do what a
Speaker 1: three year old can do. Yeah, exactly, But you're right,
Speaker 1: three year olds are excellent at this, right. But that's
Speaker 1: what three year olds do. They're like mapping their control
Speaker 1: of the world. Right, they're interacting with the world and
Speaker 1: getting all these feedback and figuring out how to control it.
Speaker 1: And if and kids. You know, for a long time,
Speaker 1: I've had a hard time learning to ride a bike.
Speaker 1: But if you start by just teaching them the balance
Speaker 1: these push bikes, then they're great at it. Right. It
Speaker 1: doesn't take them very long to learn to balance. Wow,
Speaker 1: well that's pretty cool. So the next time you ride
Speaker 1: your bicycle and just think about it, you are writing
Speaker 1: a black hole that's right in our knowledge of the universe. Yeah,
Speaker 1: and you know, there's some interesting physics going on there.
Speaker 1: We know a little bit about it. There's some of
Speaker 1: these effects that are happening to keep your bike up right,
Speaker 1: but there's definitely something else going on in there that
Speaker 1: we don't understand, and it could be something mundane. It
Speaker 1: could be like, Oh, it turns out these forces happened
Speaker 1: this way and there's a torque or whatever. But it
Speaker 1: could there's always the possibility when you don't understand something,
Speaker 1: that there could be a deep secret of the universe revealed. Right.
Speaker 1: That's why phyes this tugget every thread we don't understand,
Speaker 1: hoping that one of those threads is going to unravel
Speaker 1: the fabric of the universe and teach us something deep
Speaker 1: about the way when the world works. Yeah, or at
Speaker 1: least you'll get to work. Yeah, with a little bit
Speaker 1: of exercise exactly, and you'll look really cool and you'll
Speaker 1: be fit from all that biking. Yeah, that's right. Just
Speaker 1: remember to wear a helmet. That's when you do physics.
Speaker 1: And so that's why we think the physics of everyday
Speaker 1: objects is fascinating. So if there's something in your world
Speaker 1: that you don't understand, something you'd like to understand your
Speaker 1: why does this happen? Why does it work this way?
Speaker 1: How come it doesn't work this other way? Send us
Speaker 1: a suggestion. Why are shopping carts always broken? That's right? Why?
Speaker 1: And no matter where I go, did Jorhey break the
Speaker 1: wheels in my shopping cart? Has he been to every
Speaker 1: grocery store in the universe. Um yeah, anything that seems
Speaker 1: magical and your everyday life let us know. We'll try
Speaker 1: to kill the magic. See you next time. If you
Speaker 1: still have a question after listening to all these explanations,
Speaker 1: please drop us a line. We'd love to hear from you.
Speaker 1: You can find us at Facebook, Twitter, and Instagram at
Speaker 1: Daniel and Jorge That's one word, or email us at
Speaker 1: Feedback at Daniel and Jorge dot com. Thanks for listening
Speaker 1: and remember that Daniel and Jorge Explain the Universe is
Speaker 1: a production of I Heart Radio. From more podcast from
Speaker 1: my Heart Radio. Visit the I Heart Radio, Apple podcasts,
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