Kind: captions
Language: en
most people don't know how bicycles
actually work
so we modified this bike to prove it
this video was sponsored by kiwiko more
about them at the end of the show
when you're riding a bike and you want
to turn left i think most people just
imagine you turn the handlebars to the
left
this is a bike to test whether that is
true and it's made by my friend rick
here
and he's got a radio controller that
allows him to lock out the steering to
one side so what he's going to do is as
i'm biking he's going to pick
whether i can turn either to the left or
to the right so go for it
i'm giving it a left turn
it pulls the pin out but you can see
that you can still fully steer
after i've pulled the pin out i've armed
it
there's where it locks okay now the the
that's when your led comes on that just
says turn that way turn left yeah and if
i try to turn right can't i can't and if
i try to turn left you can i can't so
the question is can i successfully
execute this left-hand turn
should we give it a shot i mean he's not
going to tell me whether it's left or
right so i have to look at the led to
know which way i can still turn you let
me know when you're ready
okay
that was meant to be a turn to the right
but there was no chance in hell left
right
all right
flip
right right right
god
if you look closely you can see the
problem
here i'm trying to turn right
but steering that way puts me off
balance
if you could ride this bicycle you would
find it's impossible to turn left
without first steering right and it's
impossible to turn right without first
steering left
this seems wrong i think most people
believe you turn a bike simply by
pointing the handlebars in the direction
you want to go
after all this is how you drive a car
point the front wheels any direction you
like and the car just goes that way
but the difference with a bicycle is
steering doesn't just affect the
direction you're headed it also affects
your balance
imagine you want to make a right turn so
you steer the handlebars to the right
what you've done is effectively steered
the bike out from under you so now
you're leaning to the left and the
ground puts a force on the bike to the
left so the only way not to fall is to
steer the bike to the left
you have made a left turn
if you really wanted to turn right you
first have to counter steer to the left
so you can lean right into the turn
this is something anyone who rides a
bike knows intuitively but not
explicitly turn left
film someone riding a bike towards you
and tell them which direction to turn
and you will find they countersteer
without even thinking about it far left
yeah yeah
that's really clear when you're riding a
bike it's exactly the same as what we
call an inverted pendulum or balancing a
broomstick on your hand if i'm balancing
it and i just start walking toward you
it will always fall away from you if i
want to walk toward you it's easy enough
to do and people inherently know how to
do it if i pull it backward i can now
start walking
that way i have to
initiate the lean yeah to turn into it
if you want to move the pendulum
somewhere you first move the bass in the
opposite direction and now the pendulum
is leaning in the direction you want to
go so you can move with it
and it's the same with a unicycle in
order to go forward first you have to
pedal back so you're leaning forward and
then you can go forward with it
everything you're doing on a unicycle is
is all about keeping that contact patch
right where it needs to be relative to
you you're balancing the broomstick it's
just that on a unicycle you do the
longitudinal balance with the pedals and
you do the lateral balance the side to
side the same as you do with the bike
you essentially sort of small counter
countersteer to get that weight
to get the contact patch out
and then you can pedal and bring it
under you
now i should point out that sometimes
when the steering locked we just happen
to be leaning in the right direction to
execute the turn
right right right right right right
right right right
essentially by sheer luck we had counter
steered before that side of the
handlebars locked down now now i can i
can keep going but yeah but don't turn
left or you don't turn left i can't turn
left now stop now what's interesting
about this is it shows that you can
still ride the bike perfectly well right
it's just you can't turn
left the funny thing is that you
couldn't initiate
the turn right
i mean the wild takeaway is that
steering is not just for turning the
bike steering is for balancing that's
exactly right
why is it hard to balance on a
stationary bike i think most people
believe it's because the wheels aren't
spinning so there's no gyroscopic effect
but that's not it
the truth is you use steering to keep
the bike underneath you but steering
doesn't work when you're stationary your
balance comes not so much from how you
position your body over the bike but by
how you steer the bike to keep it
underneath you
even when going straight you're
constantly making small steering
adjustments to maintain balance
you're moving the contact patch of the
front wheel under you you're doing
exactly what you do when you balance a
broomstick on your hand
so if the rider is responsible for
steering the bike to keep it balanced
how do bikes without riders stay upright
as long as a bike is moving with
sufficient speed it can keep coasting
indefinitely
i first became aware of this phenomenon
through the great videos by
minutephysics which inspired me to make
this video you should definitely check
them out
but it turned out the ground where we
went to test this effect was really
bumpy but the bike still manages to
absorb all these perturbations and
remains stable
so how does it do this
i think most people believe it's the
wheels spinning that creates some sort
of gyroscopic effect that resists
falling over
just like in this demonstration of
gyroscopic procession the wheel stays
upright even though gravity is pulling
it down
but this is not why bikes are stable
just watch what happens when we lock the
handlebars completely so you can only go
straight ahead locked out locked out
whoa
all is happening is the steering is
locked
you just gotta ride it you don't have to
turn you just go straight ride letting
go some people tried going really fast
holy crap this is impossible others
experimented with extreme balancing
techniques
whoa
but even with the gyroscopic effect of
the wheels no one was able to keep the
bike upright for more than a few seconds
this is not safe for a second it is just
as hard to balance on a bike with locked
steering as it is to balance on a
stationary bike no
this one is impossible because you can't
steer the bike back under you
the real reason bicycles are stable
without riders is because they're
cleverly designed to steer themselves
if they start falling to one side the
handlebars turn in that direction to
steer the wheels back underneath them
at least three mechanisms are
responsible for a bike's corrective
steering the first is that due to the
angle of the front fork the steering
axis intersects the ground in front of
where the wheel touches the ground
so if the bike starts leaning to the
left the force from the ground on the
tire turns the wheel to the left if the
bike starts leaning right the force from
the ground pushes the wheel to the right
the front wheel of a bicycle is
essentially a caster wheel like those
you find on strollers or shopping carts
whichever way you drive them the wheel
falls in line and rolls in the same
direction
the second reason for a bike's
corrective steering is that the center
of mass of the handlebars and front
wheel are located slightly in front of
the steering axis so when the bike leans
left their weight pushes the front wheel
to the left if the bike leans right
their weight steers to the right
and the third mechanism is a gyroscopic
effect but it doesn't keep the bike
upright directly it just helps steer if
you have a gyroscope and you push down
on the left hand side the gyro will turn
left
if you push down on the right side it
will turn right
this is known as gyroscopic procession
it seems as though the force you apply
takes effect 90 degrees from where you
applied it
so bikes are stable primarily because of
steering they have built-in mechanisms
for steering themselves in fact you
don't need all three mechanisms to
create a stable bike
researchers created this weird looking
bicycle to prove a point it has no
gyroscopic effect thanks to counter
rotating wheels above the wheels that
touch the floor
plus there is no caster effect because
the front wheel touches the floor in
front of the steering axis
but this bike is made stable by its mass
distribution the force of gravity on
which steers it in the direction of any
lean
understanding how bicycles work is still
an active area of research there is a
program you can use to input all the
different bicycle parameters and see the
range of speeds over which it is
self-stable
and this research is leading to better
bikes this prototype has a smart motor
in the handlebars to actively help steer
keeping the bike upright even at low
speeds
i guess it's fitting that we're still
learning new things about bicycles since
most of us are able to ride one without
any knowledge of how we're actually
doing it
hey this video is sponsored by kiwiko
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