06x08 - Jet Skis, Bicycles, and Slack Lining

[bunniefuu]

[Dallas off-screen]
This is the Science of Stupid.

Yes, this is the show where
we titrate a touch of science

into a bath full of stupidity,

and then retreat to watch
from a safe distance.

We'll see optimists attempt
to take on the laws of

physics and lose every time.

Then we'll reveal what
went wrong and why,

with the help of such scientific
principles as hydrodynamic drag.

Torque.

And spatial memory.

When physics and fools come together,
it's a match made in pain.

Watch out, it's the
Science of Stupid.

In this show we'll be taking
a deep dive into Pascal's law.

Freezing level.

And elastic potential energy.

But first, this.

Call them what you will, jet-skis,
personal watercraft, boat-orbikes,

nothing beats the feeling
of the wind in your hair,

and the waves lapping
around your delicate toes.

But when you find yourself


from the nearest bit of open water,

you've got to improvise.

A swimming pool
should do the trick.

Yeah, that looks tricky.

This guy's making do with
rain-drenched streets.

It's a bit hard to
see the drains though.

There's one.

[screams]

[Dallas] Even though jet-skis
are designed for lakes and bays,

sometimes you may want them to

go over small bits of
ground,

so you need to find
a way to do without water.

And, if you're gonna pull off
that little trick,

you need to
pay attention to the science.

In water, a jet-ski uses an
impeller that pumps water

out the back of the craft at high

speed, providing thrust that accelerates
him and the jet-ski forwards.

But the impeller can't provide
thrust without water,

so to cross a dry patch of land,

he first needs to build momentum
and approach perpendicular

to a flat bit of shore to minimize

friction with the ground,
which will slow him down.

Okay, sounds pretty simple.

You just have to make up for lack of
thrust with plenty of momentum,

and a perpendicular
approach to the shore.

Let's see how our
brave researchers get on.

But first, let me
give you one last tip.

Watch out for pedestrians, because
jet-skis don't come with a bell.

It's a confident start,
he has enough momentum

and a nice straight
heading for the flat shore.

But a heads up would
be nice next time.

Okay, let's see if we
can improve on that.

Oh, hello.

This guy's trying to pull
right up to his trailer.

Oh, who left that there?

He's an over-achiever, and
it all goes rather too well.

He wants enough momentum to avoid
having to drag his jet-ski,

but low friction with the
hardened ground

means there's
not much to slow him down.

Until there is.

Impressively beaching yourself
is just one of the things

you can do with
your jet-ski on land.

Once you've mastered the
basics,

you can attempt
some more dramatic stunts.

Like clearing a whole island.

He's got the momentum,
and a good approach angle.

So close.

When he hits the land at speed,
the slight slope up the beach

is enough to launch him into a
trajectory and off his craft.

Well, at least
the jet-ski made it.

Are we ready for a flip?

No, we're not.

A sand mound and a crash mat is
good preparation for a trick,

but since the soft sand deforms

and stops the jet-ski, his
flip is more like a flop.

Clouds look so light and
fluffy,

so it would be easy to
assume that they're weightless.

Well, that would be wrong.

Scientists, in fact, have worked
out that the average cumulus

cloud weighs 1.1 million pounds,

that's as much as 100 elephants
floating above your head.

It's bad enough when those
clouds fall as rain,

much worse when they fall as hail.

In a severe hailstorm,

you can be pelted with large bits
of ice traveling at as much as


this one look fairly tame.

[man off-screen] Neat.

[Dallas off-screen] And hailstorms can
be incredibly destructive too.

A single storm in 2001 produced at least
$2.2 billion worth of damage

across several states in
the US, most of it from hail.

Worse still, hail can be deadly.

In 1888, hailstones as big as oranges
fell in India, k*lling 246 people.

So, it should be treated
with caution and respect,

which is easier when you
know what you're up against.

Hail forms inside a
towering thundercloud.

Updrafts push water vapor high up above
the freezing level where it freezes,

making tiny ice particles.

As these ice particles are tumbled
around in the cloud by updrafts

and downdrafts, they can pick up layer
upon layer of ice,

until the hailstones are so big that the

updrafts can't support them
anymore and they fall to Earth.

Hailstones falling towards the ground
are accelerated by gravity,

up to surprisingly high speeds.

So, when your rain starts to feel lumpy,
it's probably best to stay indoors.

[man] The problem is,
my golf ball is right there!

[Dallas off-screen]
Oh, that is a problem.

At least he's got a
helmet, that'll help.

Or not.

Let's not forget that
below the freezing level,

icy hailstones can
melt into water,

which makes an excellent lubricating
layer that no helmet will save him from.

And let's take a second to
remember that the longer

those ice particles are tumbled around

in the clouds,
the bigger they get.

[man] Those are softball sized!

[Dallas off-screen] So these bad boys
must have been through that cycle of

updrafts and downdrafts many times,
picking up layer upon layer of ice.

[man] That's insane.

[Dallas off-screen] The metal roof of a
car should protect you,

but even a marble-sized
hailstone can come

in at more than 30 miles an hour, more
than enough to crack your windscreen.

[woman] Oh my gosh!

-That poor cow!
-[Dallas off-screen] Poor cow indeed.

Scary ice bombs hurtling from the sky

really seem to bring out the best in
people.

Like this guy, protecting a mother goose
and her young from the hammering hail.

Although, after seeing what it
could do to a glass windscreen,

I'm not sure that an umbrella is

quite up to the task.

Ah, yes, two umbrellas,
that'll do it.

There's nothing more relaxing at the
weekend then a spot of gardening,

but what science is this
pair about to reveal?

[woman] OK, wait!

[Dallas off-screen] These two amateur
gardeners are

trying to remove
a stubborn bush,

but did you guess what science
they're about to demonstrate?

Yes of course,
it's turning effect.

Since the rope is attached
above the rear wheels,

when he accelerates and the bush stays

put, it creates a turning
effect that lifts the trike.

And while she's sitting
on the front,

she creates
a turning effect in the

opposite direction, keeping
the nose close to the ground.

But, when she steps off, there's
no resistance to the rotation,

and he takes a tumble.

Slack lines are
really big at the moment.

Really, really big.

And one of the highest slack lines ever
walked, or wobbled, more like,

was 3,280 feet off the ground.

Scary stuff, but you can still
pull off some impressive

tricks without risking your life.

Like this guy, giving an impromptu and
informal demonstration

of his slacklining skills.

Well, I feel like
I've learned something.

Ah, now this guy
knows all the moves.

Butt bounce,
chest bounce, butt bounce,

and of course
classic face plant.

Yep, slacklining tricks can be
the very definition of cool,

all you need is an awesome sense of

style, a good sense of balance, and an
even better sense of science.

Jumping on the slack line,
his kinetic energy is stored as

elastic potential energy in the
line, which is converted back

into kinetic energy to accelerate him
upwards.

For a controlled sequence of
bounces,

he needs to align his
center of mass so the restoring

force from the line
bounces him straight back up

or helps him generate
angular momentum for a flip.

Okay, maybe this isn't
as easy as it looks.

So, let's start simple, can our student
of slack line even stay on the line?

So graceful.

So acrobatic.

He needs to keep his center
of mass over the narrow

slack line to stay balanced,
which admittedly isn't easy.

But at least his friends
seem to have enjoyed it.

This is more like it.

Maybe his bobbing friend is
the secret to his success.

Let's call him Bob.

[man] Yes, yeah.

[Dallas off-screen]
Bob, don't stop.

See what you did?

Bouncing on his belly, this guy
is keeping his center of mass

over the line and receiving

all-important restoring
force on each bounce.

But, when he twists up
into a sitting position,

he's just too far forward,

and that slack line
makes a break for it.

Once you've got a handle on
restoring forces,

you're ready
to turn the slack lines elastic

potential energy
into something majestic.

Ah look, Bob's having a go.

Hey, he's pretty good.

I knew it, he needed
a Bob of his own.

The elastic potential energy
in the line

had the potential
to launch him off in a flip.

Sadly, without any apparent
control over his limbs,

that potential was wasted.

Okay, Liebig condensers away
and notebooks out everyone,

because it's time for today's science
lesson,

that part of the show where
we tune our oscilloscopes to

a particular
scientific principle.

Can you tell me what the
following have in common?

This party popper.

This watery washout.

And this bucket bouncer.

Alright, hands down, it is of course
fluidity, the properties of materials

that don't have a fixed shape.

Now, as I'm sure you all know, the
particles of a fluid

aren't fixed in place, and are free to
move past each other,

which makes fluid materials behave

in some pretty interesting ways.

Unlike solids, fluids can flow,

following the steepest gradient to take
the shape of a constraining vessel,

the speed that it flows is determined by
its viscosity.

Low viscosity fluids like
water flow quickly,

while honey has a higher viscosity

and moves more slowly.

But, if you apply pressure,

Pascal's law says that the
whole body of fluid will be

pressurized until some part
of it can flow to relieve it.

Got that? Let's hope
you were paying attention,

because it's time
for a quick pop quiz.

Question one, what is the difference
between a solid and a fluid?

That's right, fluids will
flow, but a solid won't.

Fluids will also flow out of the way
when a stress is applied.

[man] No it's fine,
stay to the right.

[Dallas off-screen] Why did
I know that was going to happen?

[woman] Oh, it's cold!

[Dallas off-screen] The water flows away
from the advancing bike wheel.

But it flowed away from
her advancing body too.

Right, question two,
what's viscosity all about?

Yup, it determines how
fast a fluid will flow.

Given a nice steep gradient,
water will flow downhill,

and its low viscosity means it will

effectively fall over itself
in its rush to get there.

While the kayakers do
all they can to keep up.

Except him, he's
fine where he is.

On the other hand, something like this

sticky contact cement has high
viscosity.

[man] This is not going
the way I wanted it to.

[Dallas off-screen] And
will flow much more slowly.

The viscoelastic fluid stores
energy as he moves it around,

so the more he stretches it,

the less it's
going to cooperate.

[man] Ah jeez...

...I don't think
this is working.

This is not working.

[Dallas off-screen] Yeah,
you need to, oh, never mind.

[man] Ah, good grief.

[Dallas] Question three, what happens
when you put a fluid under pressure?

It'll try and relieve that pressure,
which can be sudden and painful,

so don't try this at home.

Pascal's law tells us that when you
apply pressure to a liquid,

the whole body
will be pressurized.

So, when the seal gives
out,

the water makes a bid for
freedom, sh**ting out at speed,

and propelling the bottle away at around
three and a half G.

Okay, let's see how that guy's getting
on with his contact cement.

Yeah, pretty much the same.

Okay, class dismissed.

[Dallas] On your typical Sunday
afternoon,

you're sure to find
me clad head-to-toe in lycra,

speeding around my local park.

You see, I've been learning to ride, and
it's all going rather well.

I'm almost confident now to think about
removing those stabilizers.

Riding a bike is just one of those
wonderful

outdoor activities that anyone
can try.

From young cowboys.

Well, not him.

To intrepid granddads.

Yeah, not him either.

Okay, so maybe riding a bike
isn't so simple after all.

Perhaps a spin through
the science will help.

Staying stable on a bike is a delicate
balance of lean and steer.

He needs to make sure that the
combination of all forces acting on him,

such as gravity and
centrifugal force,

are balanced,
so the bike remains upright.

But the bike is self-stabilizing
up to a point,

when it leans
to the left the wheel turns,

which straightens up the lean and steers
it back the other way.

All he has to do is make
sure he doesn't lean too far.

Oh, so that's
how to ride a bike.

I think that the time has come to take
off those training wheels,

and really test our skills.

It's Georgie's first ride.

[woman] There he goes.

[Dallas off-screen] He needs absolute
focus and concentration,

so nobody distract him.

[woman] Georgie!

Oh my gosh.

[Dallas off-screen] Yeah,
that was totally your fault.

[woman] There he goes.

[Dallas off-screen]
After a quick push from dad,

Georgie does well to balance
gravity and centrifugal force.

Even as he's pedaling, the bike can
self-correct the small side to side

lean, which helps him keep
it in a straight line.

[woman] Georgie!

[Dallas off-screen] But when he gives in
to the temptation to put his feet down,

his leans sends him weaving,
which he rescues just in time.

[woman] Oh my gosh.

[Dallas off-screen]
To crash into the car.

[woman] Whoops!

[Dallas off-screen] Of course, you can
avoid obstacles by simply

steering out of the way.

[woman] Tati turn baby.

Turn!

[Dallas off-screen] But it
does take a bit of practice.

Our peddler in pink is working
hard to keep her bike stable,

and leaning into the turn is the

right thing to do, but that
was the wrong place to do it.

She was fine, just like all
of our junior experimenters.

I love a bit of gardening.

Tilling the soil is a
great way to pass the time.

But over in Emerson, Arkansas,

they've clearly got too much time on
their hands.

Time that they use for.

The world championship
rotary tiller race.

For nearly 30 years competitors
have been training hard

for the annual opportunity to race their

pent-up ploughs
along a 200-foot course.

Clearly this is a highly
complex sport,

there must be
a lot of strategy involved.

[man] I don't have no
strategy, just hold on and go.

[Dallas] Well, while hold on and go
might be the order of the day for some,

if you want to rotavate yourself
to victory it's probably worth

ploughing through
the science too.

Rotary tillers have motorized
wheels equipped with blades

that dig in and shear the soil,

but if the tiller isn't held
in place,

the soil's internal
friction can resist the blades

movement to propel it forwards.

But those motorized wheels
can't be steered,

which makes
the tiller hard to maneuver.

If he gets uneven traction, then
the vehicle will veer

to the side, leaving him in the dust.

Okay, so keeping pace and avoiding
uneven traction is all you need

to make it to the finish line.

Sounds simple.

Wrong.

With such uneven ground, the two tiller
wheels dig in different amounts

and get uneven and
unpredictable traction.

A bit more on the left pulls it
to the right,

and by letting go
he's committed it to its fate,

and the crowd to theirs too.

Oh look, color-coordinated.

But there's nothing rosy
about flipping your tiller.

Uneven traction on the uneven ground
sends him straight for the hay bales,

and then the dirt.

Red and green should never be seen, pink
and brown, upside-down.

On your marks, get set, till.

Looking good, he's got a nice stride,
and red's into the lead,

and, oh, he's down.

That's nice, he's gone
to check on his rival.

Oh no, that's just a tiller
with a mind of its own.

They both suffered the effects of uneven
traction here pulling them to the side.

And while our man in red
manages to ride it out,

his low-slung rival is left
languishing in the dirt.

I wonder what happened.

[man] You get on, and it starts taking,
you know, it starts gaining speed,

it pulls to the left, and I didn't have
enough strength to pull it back

and get back in line.

[Dallas off-screen] Yeah, uh-huh, I see.
Yeah, that makes a lot of sense.

To paraphrase the
great Neil DeGrasse Tyson,

science doesn't care whether
you believe in it or not,

it'll hurt
you just the same.

And, if you need a reminder,
take a little look at this lot.

[music plays through credits]

[man] How am I gonna
turn that camera off?