How Does A Bicycle Balance?

We don't understand bicycles!

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Episode Transcript

Speaker 1 (00:08):
Hey, orror, Hey, what image do you get in your
mind if I say the phrase mysteries of the universe?
I think I think of you know, black holes and
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

(00:28):
have to go so far away to find mysteries. M
You mean, like, why is a cartoonists 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 don't understand. Yeah, I've heard

(00:49):
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, but you don't know
what you're talking about, or you know what you're talking about,
but you don't understand. 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,

(01:11):
and sometimes we think it's a simple explanation, but we
sit down to work it out and it turns out
it's much more complicated than we thought. Yeah, it turns
out there are big mysteries even in the things that
a lot of us ride to work every day. That's right.

(01:41):
I'm and I'm Daniel, and welcome to our podcast Daniel
and Jorge Explain the Universe, a production of I Heart 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 in the episod, we're
going to try something a little bit different. So usually

(02:03):
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's 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

(02:23):
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 in maybe hidden in everyday objects. That's right,
So look around you think about whether you understand the

(02:44):
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? You know, the bicycle has

(03:05):
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 fascinating. If you just hold a bicycle and
let go, it's going to fall over, right, But if
you push your bicycle so that's going fast, it doesn't
fall over. It can ride by itself. It's kind of

(03:26):
a ridiculous situation. Do you think about it? Like? Who
thought it to take two wheels and right around and
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 arrive. I guess I'm gonna
have to invent something. They couldn't aford a third wheel

(03:49):
only they only had the raw materials enough for two
wheels or something. You were like inventing a new myth
of the genesis of the bicycle, right, Yeah, well it
seems implausible 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

(04:09):
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. Um. Yeah, there's so there's
two wheels, 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,

(04:31):
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, Um, it's it's fascinating.
But you know, do this experiment in your head. You
remember riding a bike, probably, and it's the faster you go,

(04:52):
the more stable the bike. Seems that at some point
you could even lean back and take your hands off
the handlebars, and it seems like a ridiculous thing to do.
You're going twenty miles an hour and if the if
the handlebars flipped over, you would fly over the front
of the bike. You can 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

(05:14):
onto the handlebars because at high speeds it's so stable. Yeah,
wearing a helmet though, right, we should probably wearing a helmet,
and it's only you know, off the street. Of course,
never ride with without holding the handlebars on the street
because you could cause an accident or or okay, that's right. Actually,
my dad used to commute to work on a bicycle,

(05:35):
and we lived up in the mountains in New Mexico,
and so he could get pretty snowy, and I remember
that he would put um 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
commute to work. He was like, I'm going to commute
to work no matter what the weather is. Sounds like
a Matt Mag's modification there. Yeah. I asked him once

(05:57):
if it was good for the ice, and he said, actually,
it's pretty good for pedestrians too. Let's getting for clearing
the road on pedescans exactly exactly. Um, yeah, so we
understand that, but we don't understand why bikes stand up. Yeah,
it's kind of a mystery. You write it, and uh,
I mean you do. You're doing a lot of the
balancing with your handlebars, right, But a lot of the

(06:20):
balancing and staying up is kind of done for you
when you're riding a bicycle. Yeah, that's right. A lot
of it is 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 how to move your hands and

(06:41):
shift your weight, etcetera to ride the bike. Right. It's
amazing seeing seeing a kid learn to do that. It's
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't do because it's very counterintuitive, right to
ride a bicycle. Yeah, that's right. I mean like if
you're starting to into the right, then you actually you'll
have to teach your body to turn the wheel towards

(07:05):
the right to balance, Yeah, exactly, And you have to
lean the just the right way, and sometimes you have
to lean left to turn right. You can get pretty complicated. Um.
It's sort of in its most extreme form in those
crazy motorcycle races. You see those guys whizzing around turns
like a hundred something miles an hour and their bikes
are leaning so far over that their knees almost scrape

(07:25):
the ground. Right. But basically, if you're at home, and
maybe you don't have a lot of experience of bicycles
and trying 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.

(07:48):
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 at college campus. That's right,

(08:09):
that's right, and asked people on the street. Actually, today's
a sort of a special edition because this quarter at
you see Irvine, I'm teaching freshman physics, which is mechanics,
And the week before we did these interviews, I just
taught about rotation incular momentum, and so my students were
primed for this topic, and so I asked students in

(08:31):
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 gotta get

(08:52):
you know, centrifugal forces. You gotta get your back are
your physics professor, And definitely not. Would it be because
since there's two wheels like the force, and one goes
to thegether, that's why it still keeps going forward. Something
like that. Okay, thanks, umws. There's a talk from the

(09:16):
tire um way we're rotated, the talk of support the rotation.
It's sort okay because it's is it because it's moving?
Chance because like a loane like standing up and want it.
They want to like stand up by itself. So I'm
not sure. Actually I'm not exactly sure, but I'm thinking

(09:39):
it has something to do with maybe cent tripital forces.
The fact that there's constantly like pushing in or like
towards the 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 like other points of contact. I
think that this has to do with either the angular
momentum or rotational inertia the bi So if something is

(10:01):
rotating like a gyroscope, because of its angular momentum, you
will continue to rotate more easily rather than starting or
stopping it from rotating. Great, thanks very much, by I
was moving wise because you're Jesus Christ. It's not because
of Jesus Christ. Um, I have no idea. Thanks all right.

(10:22):
So where are you impressed with your students or none impressed? Um?
I think the scores on the final tell you how
impressed I should be with these students. Um. Yeah, they
seem pretty perplexed, like they could not really apply the
concepts of rotation and anglad momentum to this topic. Um.
I like how they one of them, even God religious

(10:43):
di went like Jesus Christ, I don't even know. Um,
it's tricky. Yeah, it turns out it to be tricky. Um.
But a few folks, you know, repeated what I think
a lot of people imagine is the answer, which is
anglar momentum. Yeah. A lot of people think, oh, it's
some gyroscope effect, some conservation of angular momentum. Maybe they

(11:03):
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's 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,

(11:28):
I just don't want it to click away. That's right,
keep listening. Trust us more to it than just angular momentum.
I mean, it's not even close. It's it's not like
the dominating factor and why bicycles stay up right. Yeah,
that's right. But let's stick into a little bit. Let's
talk about what angle momentum is, how contributes to bikes
staying upright, and then what else is going on? But
first a quick break, what exactly is angular momentum? Yeah,

(12:05):
so let's do it one step a time. Let's just
make sure we have clear in our heads what momentum is,
and then we'll extrapolate from that to angular momentum. Right.
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

(12:26):
if you if you've got something going, it doesn't let's
keep it going that 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

(12:47):
this property is something if it's moving, it like sustained movement,
and it comes 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 the weird thing about the universe. Right, Like
I was talking to a pretty um high level physicism.

(13:09):
They were saying that we don't really know kind of
what inertia on. Hold on, you talked to other high levels.
I'm finding out about this on the podcast What Physics
Cheating on You? Daniel. Well, okay, I'm putting on my
two day list, find other cartoonists to talk to. Technically
happened while we were while we were on a break, Daniel, So, um,

(13:30):
it's not okay, alright, find flaunch your relationship with other physicists.
Go ahead, ahead, doesn't hurt my feelings at all. Go ahead.
It happened before we signed a contract together. Um, but no, no,
this was this was a lamb gross. He's like the
one of the head physicist at CERN, right, he is
a prominent member of the Atlas collaboration and a serious

(13:52):
Higgs physicists. 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 I do things keep
going the way if you don't apply a course of 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're like, well, we noticed this,

(14:14):
and we'll 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, or like why if we have

(14:36):
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,
So 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

(14:56):
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 where the
frontier of sciences that that's right, all right, So that's momentum, right.

(15:21):
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 and with a
whole new concept. Let's just extrapolate from something else we
already know. So we have this concept of linear momentum,

(15:44):
and let's just use the same kind of stuff, the
same ideas to describe spinning, right. And I think it
was something that I would always find interesting, is that
anger momentum is kind of just linear momentum. But if
you apply to things that are kind of connected to
each other, right, Like a wheel is really just a
bunch of atoms stuck together. A wheel is a bunch

(16:05):
of atoms stuck together. Yes, I can confirm that here
on the show. I'm getting an update. Yes, yes, yes,
that's true. The experiment checkt. 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 becomes

(16:25):
almost something else. Yeah, that's right. You have all these objects.
You can think of a wheel is 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. They 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

(16:45):
force that forces gravity that keeps it from just flying
off into space. So in the case of the wheel,
why do the bits of the wheels stay together and
not just fly off. It's because the atoms are holding
them together. So, yeah, there's forces they're moving it in
a circle. But like all things, as you can, you
can describe it in different levels. Right, you can describe
it as a single wheel, you can describe it as
eleven d billion particles. Right. The physics should work in

(17:08):
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, you spin it, it's going
to keep spinning in space for forever unless you slow
it down or apply some force or torque to it.
That's right. Angular momentum is also conserved, right, So if

(17:30):
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,

(17:51):
and so, um, there's lots of consequences of anglid momentum
and the conservation of angle momentum. So it's definitely a thing.
Plays a big role in the shape and the structure
of our of the un verse and our everyday lives. Right.
So angle momentum is definitely a thing. And it seems
relevant to the bicycle because the bicycle has big spinning
things on it, right, right, and angler momentum is also
kind of different. Not just that it's hard to speed up,

(18:14):
horror slow down when something is spinning in space, but
it's kind of hard to change the orientation of it. Right,
When when something is spinning like a wheel out in space,
it's kind of hard. It likes to be It likesly
not just keep spinning, but it likes to keep spinning
in that direction, that's right. Angler momentum is to find
along a spin access, right, And just like if you

(18:34):
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 access 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 wanted to spin the other way, right,
that takes a lot of torque. Or if you have

(18:56):
it spinning in one direction and you want it spinning
around an access that's like a rotated by ninety degrees,
that also takes a lot of torque. Right. So yeah,
it's not just that it spins. You already likes to
spin in the same direction. And so that's why people
assume that's the reason bikes tape upwards, is that up
boards up right right, upright right, yeah, yeah, exactly, because

(19:17):
you imagine that this has an application of the bicycle
that the wheels are spinning, and so the wheels have
angular momentum, and then the momentum is around the axis
or the hub around which the wheels are spinning. And
so if um, 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 access. And for

(19:38):
that 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
gonna mostly stay upright, you know, kind of like a
coin when you coin plus a coin or roll a
coin on the table, it just kind of likes to
keep rolling and stay upright. Yeah. And you can see

(19:59):
this effect in lots of other of things in your life,
like if you ever if you ever have like a
spinning top, right, you know, you can spin a top
and it will 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, um, stuff
like that. You can 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

(20:21):
easy to keep it on your finger. And that's because
it resists changing its direction because the angle momentum is
going in a certain direction already. Right, It's the same thing.
The same effect is in play for the bicycle. And
if you are a few too too many levels into
your inception dream, then the top which just keep spinning forever. Right,
that's right, yeah, exactly, um. And so what happens on

(20:42):
a bicycle While 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 will keep the bike stable.
So it's not like the gyroscope of keeps the bike
from leaning over. It's more that it it turns the

(21:04):
wheel in such a way that if the bike does
start to lean over, it corrects itself. Right. If you
if it falls over the right. Then the forces work
out just the right way so that the bike the
bike um turn, the wheel turns to the right, and
then the bike stays up right. Well, I mean that's
what happens when you're the anglo momentum thing is what

(21:24):
happens when you just toss one wheel down the street, right,
Anglo 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 up up right. Right, Well, I'm saying that the
gyroscope effect, this anglementum does have a role in keeping
the bike up right, like you said, for a single wheel,

(21:45):
but it turns out they did some studies and it's
not enough. Right there, effect is there, it's real, but
it's not enough to keep a bicycle upright. And it
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 that like
if you like if you just take a bicycle and
you lock the steering wheel, meaning you can't steer it,

(22:09):
or like if you just connect two 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. R's right exactly. The front wheel has to
be free to make these corrections right so that the
gyroscope effect and the other effects will talk about in
a minute can correct, the can can turn the wheel

(22:29):
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
gonna 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. If you turn the
wheel to the right, then you're just gonna fall over.
So the key to to keep staying up righting a

(22:50):
bicycle is that the front wheel turns in the direction
that you're falling. Okay, so that's um, hold on, I
think I just fell off my bike. You're mainly mental,
by I hope you're wearing a helmet. That's wearing a
mental helmet. Well, let's let's get let's really dig into
it to sound I'm a bit confused, but we'll get
into it, but first let's take a quick break. Okay,

(23:23):
So Daniel, we know that we're trying to figure out
why bicycles stay upright, and we know that angler momentum
has something to do with it, but it's not, um,
you're telling me, it's not the main factor wise 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 angler momentum? I think that's

(23:44):
impossible because the bike has a spinning wheel and that's
definitely gonna have angle momentum. So what they did was
they built a bike with two more wheels, right, 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 spinings clockwise and the
other one's going to spin counterclockwise right because of the
way they rub. And so if you just attach two

(24:07):
more wheels that touch the original wheels, then they're going
to spin the opposite way, which gives the opposite angleid
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
it would just fall over, right, because kind of like
a bicycle, if you don't push it or anything and

(24:29):
just take your hands off it, it's going to fall
over because it doesn't have any angular 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
balance is almost as well as a normal bicycle, which

(24:52):
is like mind blowing it. For decades, people thought, oh,
it's anglid momentum, it's anglimentum, until somebody finally went out
there and did the experiment in 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 gonna have much less angler momentum, and those bikes

(25:12):
are also pretty well balanced. They stay up, they still
stay up. So this sort of like blew up the
cold concept. People assume for a long time that it
was anglo momentum its gyroscope. I yeah, that makes sense,
but nobody really tried it for a while, and so
the people went out and did the experiments and turns out, Nope,
that's not the answer. Where there actually like physics conferences

(25:33):
around this topic. Yeah, somebody got a paper in science
about this. I mean this is a big deal. Yeah,
I mean talk about like low hanging fruit, right, I mean,
it's not that hard to build this bicycle. Um, you know,
you struggled in grad school for years and years. Did
you get a science paper? I didn't. I had to
work on a ten billion dollar collider. I still didn't
get a science paper. You can make a funky bicycle,

(25:54):
you know, with a hundred bucks and get enough information
for a science paper. That's so, somebody made a bicycle
with a angular momentum and it's still stay upright, Yeah,
it's still could balance. You could push it by itself
and it would it would have all those same behaviors.
It could balance by itself. Yeah, okay, so the secret

(26:14):
is something else about a bicycle. And you're telling me
a little bit earlier that the secret is this that
one of the wheels can move. The secret is definitely
you have to have the front wheel being able to move.
But and and there's lots of reasons why that's important,
and one of them is the the angle of the forks. Right,
So the forks of the thing on the whole, the

(26:36):
front wheel in place, right connected to the handlebars, that's
how you steer, and on most bikes, the angle of
the forks is forwards, right, so the wheel sets a
little bit in front of the handlebars. Yeah, it's it's
kind of curved forward, right, It's not like a straight
m fork down. It's kind of angled and it's it
kind of curves up. Yeah. And I always wondered why

(26:57):
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, fancy, just like you know,
like a whimsy like a little whim whimsical touch. But no,
it turns out that's actually an ancient um part of
the design. Like if you look back at pictures of
old bicycles, even really old bicycles, have that sort of slant,

(27:19):
and the reason is that that also helps the bike
stay upright. You know, what it means is that the
axis that you're steering on right this 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. Right, the
bike touches the ground the bottom of the front wheel,

(27:42):
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 it's one is
sort of following the other. It's sort of like you
know those wheels on a grocery cart and those things
that are like impossible to turn around and you're gonna
go backwards to painting, right. I always get the chopping

(28:04):
card with the broken castor wheel you know that goes out.
You probably are the one who breaks them, right, and
you just return them this door and don't say anything
right exactly. Um 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 this the steering access right, they go backwards. They

(28:28):
always aligned 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 just
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

(28:48):
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 access is tilted, then you
get that same effect. Okay, so way you're saying, Okay,
I'm riding my bicycle. Okay, I'm going down this hidewalk,
and suddenly I start to lean a little bit to
the left, so I'm following falling falling, and you're saying,

(29:11):
there's a because of this access cast effect, and 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 front, the handlebars always turn right they
never stay balanced. If you pick up a bicycle, it's

(29:31):
always like the front wheel is spinning in some crazy direction.
That's because this cast 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 that helps me stay upright, right,
because if I'm leaning left, my front wheel turns left

(29:54):
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 is like whole bicycle research teams now, and they've
built bicycles that have no angular momentum like we talked about.

(30:16):
They also built bicycles that have no angler momentum and
don't have this castor 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 you point to step the fork down like perfectly down,
that's still works, or even backwards right the negative effect.

(30:41):
You can even have the fork sort of pointing in
the wrong direction and a bike will still balance. So
bike with no angle momentum and the negative caster effect
will still keep itself upright. But how does it stay
upright if we if you cancel out this self steering effect?
Nobody knows that I am serious. Like, turns out these

(31:03):
equations are complicated, right, Like figuring out how a bike
balances is not a simple like, oh, do to do
it's angle momentum. We're done. These are complicated effects because
there's lots of forces involved, lots of ways that can pivot,
and so it's still a mystery. You know, Um, there's there.
It definitely is influenced by angle momentum. It's definitely influenced
by this caster effect. It's definitely influenced by this other

(31:25):
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
writing 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

(31:46):
does that make riding your bicycle seem more fun and exciting?
It's it seems a little more dangerous, to be honest.
It's not like the physics is gonna stop working. Like
a whole lot of second we figured out your bike
shouldn't balance and then boom, everybody falls over simultaneous sleep.
That would be awesome. It's still a mystery. There are

(32:08):
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,
counter steering. All sorts of stuff is going on. It's
pretty it's really pretty tricky, but it's important. You know,
if you figure out how bicycle is balance, you could
develop a new bicycle. Right, you could have some breakthrough

(32:28):
in bicycle science. To be just around the corner, you
could you could win the no No No bill bicycle right, 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, all of a sudden, the way
we've been riding bikes for a hundred years is like

(32:50):
old fashioned and clunky and hilarious. Um. There's a guy
in my neighborhood actually who rides a unicycle, which I
think is really impressive. You mean to go place and
not not just in the circus. Oh no, yeah, he
commutes to work on his unicycle. Does put two of
those together to make a bicycle. Maybe the bicycle just

(33:13):
broken half? Um, but he's got one for you know,
nice weather. He's got like a mountain bike unicycle. I've
even seen him like on trails, trails I like struggle
to walk up he's like unicycling up way Like wow,
does he put does he put nails? And no, he's
just got knob tires on it. I think that's more
a testament that's not so much physics. That's just the brain.

(33:35):
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 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,
you know, I'm talking specifically about Jorge's brain. His brain

(33:58):
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 these feedback and figuring out how to control it.
And if and kids. You know, for a long time,
I've had a hard time learning to ride a bike.

(34:20):
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 and just think about it, you are writing
a black hole that's right in our knowledge of the universe. Yeah,
and you know, there's some interesting physics going on there.

(34:40):
We know a little bit about it. There's some of
these effects that are happening to keep your bike up right,
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 happened
this way and there's a torque or whatever. But it
could 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 phyes this tugget every thread we don't understand,

(35:04):
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. That's when you do physics.

(35:26):
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 your
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 carts always broken? That's right? Why?
And no matter where I go, did Jorhey break the
wheels in my shopping cart? Has he been to every

(35:47):
grocery store in the universe. Um yeah, anything that seems
magical and 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,

(36:09):
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 Daniel and Jorge dot com. Thanks for listening
and remember that Daniel and Jorge Explain the Universe is
a production of I Heart Radio. From more podcast from
my Heart Radio. Visit the I Heart Radio, Apple podcasts,

(36:33):
or wherever you listen to your favorite shows.