06x12 - Parkour, Boats and Bicycles

[bunniefuu]

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

Yes, this is the show where
we put the fun into the

fundamentals of physics.

Prepare yourself to see
foolhardy field researchers do

foolish things without
fully thinking them through.

We'll dissect what went wrong
and why with the help of such

scientific principles
as curvature gradients,

negative feedback
and Pascal's law.

In the battle between physics
and foolishness there's only

ever one winner, so don't
try any of this at home.

Watch out, it's the
Science of Stupid.

In this show we'll be exploring the pain
of poor trajectory.

[laughter]

The problems with
Aeolian regimes.

[man off-screen]
Holy [bleep].

[Dallas off-screen] And what
happens when balanced forces

-become unbalanced.
-[man] Oh!

[Dallas off-screen]
But first, this.

While I've mastered
the foot jam,

perfected my double peg grind
and done so many supermen

that, frankly,
I've grown bored,

there's one bike trick that's
always been my Achilles' heel.

It's the ledge drop,
or 'the drop-off'.

[Dallas off-screen] These
guys seem to have the hang

of it though.

It's almost as if they were born with a
bike between their legs.

But I'm not sure this
guy has a handle on it.

[moans]

Jumping drop-offs isn't
technically difficult,

but it can be dangerous,
so it's best left to the

professionals, those with
courage and an understanding

of the science.

[Dallas off-screen]
Preparing for a ledge-drop,

he keeps the combined center
of mass over his base of

support to avoid any
unwanted rotation.

By launching with sufficient
velocity and without any

angular momentum, he can keep
the front wheel raised as

gravity pulls the bike
down, so when he lands,

the back wheel touches the
ground first while he keeps a

center of mass securely
over the center of the bike.

Well, it all sounds
relatively simple,

but you really want to avoid
to landing on your front wheel

first, since all that weight
in one spot means your forward

and downward momentum can
introduce a talk that can send

you tumbling to the floor.

So let's start with
something easy.

[Dallas off-screen] I'm
sure he'll nail this stunt,

hands down.

Or face down.

It's the classic error.

He rides off the ledge
but leans too far forward,

so when the front wheel hits
the ground his center of mass

is ahead of him,
introducing torque,

which leaves him
a bit red-faced.

Okay, a bit more
advanced here.

This guy is planning to
ledge-jump off this roof.

There's a bit of a crowd, so
I'm sure he's keen to make a

good impression.

And he does, off his
face, in that flowerbed.

His jump off the roof is good,
as is his bounce off that

house, but thanks to some
rotation during the descent

and his angle of
approach is too steep,

leading to that dreaded
front wheel landing.

[moans]

And that, ladies
and gentlemen,

is exactly why you
shouldn't try this yourself.

[whistles]

A flawless start, he obviously
hasn't forgotten his science,

but he has forgotten his bike.

A good run-up builds velocity,
but at the crucial moment he

spins around, transferring
forward momentum from the bike

to himself, meaning he
leaves the bike behind,

and you really do need that.

[moans]

In the world of bike stunts,
there's still room for

innovation, but I'm
not sure 'the ledge,

flop and splosh' is destined
to become a classic.

[man] That was nice!

[Dallas] I was at the beach the
other day thinking that I'd

really like to break
a world record,

but a quick look on the
Internet revealed that the

world's largest pile of
sand was more than 3,860 feet.

That's easily taller than the
Burj Khalifa and I just don't

have time for that.

Luckily, my other world record
attempt is still going strong.

I'm currently competing to
be the world's oldest man.

[Dallas off-screen] Still,
sand dunes aren't great.

After all, sliding down
one is loads of fun.

[screams]

Although driving
up a sandy bank...

[man] Holy ****!

[Dallas off-screen] Looks
a little more challenging.

[man off-screen] Woo!

[Dallas off-screen]
And running down them?

[laughter]

Well, that just looks awful.

Dunes form in what's known
as an Aeolian regime.

It's a landscape that's
dominated by the actions

of the wind.

[Dallas off-screen] When wind
gives sand kinetic energy,

piling it up around
debris and then itself.

Sand is a granular material
that can provide reaction

force like a solid.

But it can also flow like a
liquid under sheer stress.

The slope of the dune is
partly determined by sand's

angle of repose, which is
the maximum angle that it

can support itself.

Dunes shift over time, but if
you want to see some then a

pretty safe bet would
be to head to Australia,

home of the Simpson Desert and
the world's largest parallel

sand dunes, each one
stretching up to 100 miles

long, which is nearly as
impressive as what our team

of testers have been
getting up to.

[Dallas off-screen] Our
Australian research team here

are testing the way the
bodyboard interacts with the

granular material of the dune.

Apparently quite well.

[laughter]

But I'm not sure he
thought that through.

The gradient of the dune means
that he has momentum with both

forwards and
downwards components.

But when he reaches the bottom
the board levels out and is

slowed by the sand, which
means all his meals will taste

a bit gritty for a while.

[laughter]

In Peru, one of our testers
has borrowed a high-powered

pickup and seems
to be having fun.

[woman off-screen] Oh no.

[Dallas off-screen] Yeah,
that's going to be an awkward

chat with the owner.

When the truck drives
off the top of the dune,

it starts to rotate forwards
while at the same time the

sand allows the front
wheels to dig in,

causing more friction and
allowing angular momentum to

lift the back wheels
off the ground.

He's going to find it tricky
getting out of that truck.

[grunts]

[man off-screen]
Hey, hey, hey, hey.

[Dallas off-screen] I wonder if dirt
bikes handle dunes any better.

[grunts]

[man off-screen] [Bleep].

[Dallas off-screen]
Well, clearly not.

As the rider reaches
the peak of the dune,

his heavily loaded rear
suspension decompresses,

giving the bike
angular velocity.

And because the dune
then drops away,

he has lots of airtime in
which to rotate forwards.

I'm sure it's just a
one-off accident though.

[screams]

Maybe not.

Perhaps we should just draw
a line in the sand and accept

that the best form of
transport for this terrain

is a camel.

[screams]

So majestic.

We've all got a bit
carried away at a party,

but what science is this rooftop reveler
about to reveal?

[Dallas off-screen] Did you guess what
science our overexcited partygoer

was about demonstrate?

[grunts]

Yes, it's reaction force.

In this case, far too little.

To back-flip off the roof,
he needs to generate enough

reaction force with his legs
to accelerate him up and over,

but there's too low a
coefficient of friction

between feet and roof, and
without that reaction force

this flip was a flop.

[man] Yeah!

[Dallas off-screen] He still seems
pretty pleased with himself though.

[cheering]

It was boats that allowed the
Vikings to reach America



It was boats that meant
the Polynesian people could

colonize remote Pacific
islands almost 3,000 years ago,

and it was boats that
helped trade food,

spices and ideas
across the globe.

Boats have been vital to
humanity's shared history.

[Dallas off-screen] So you'd
have thought that after all

this time we'd be
better at them.

[man off-screen]
Don't fall in already.

Oh, oh!

[Dallas off-screen]
But we aren't.

We really, really aren't.

I guess some people have difficulty
finding their sea legs.

[man] Jonny, Jonny, Jonny!
Get him!

[Dallas off-screen]
It's okay,

his friend seems to
have found them for him.

Landlubber.

Yes, moving around
on boats is tricky,

so if you want to avoid any
nautical nonsense then I would

suggest paying attention
to the following science.

[Dallas off-screen]
As the boat moves,

our man needs to constantly
adjust his feet and body

position to keep his center of
mass over his base of support

as the boat moves beneath him.

This is called
dynamic equilibrium.

Problems arise when
something gets in the way,

making it impossible to adjust his feet
and his base of support.

[screams]

Slippery surfaces with little
friction can compound the

problem, sending our man off
balance and into the drink.

So to stay on a boat it's all
about dynamic equilibrium,

avoiding obstacles and
trying not to slip.

Sounds hard not to get your
socks wet, but let's see.

[Dallas off-screen] He's moored to the
bank and got two oars,

so this should be a doddle.

[laughter]

Well, just the one wet sock
is better than expected.

When this sailor plants
his foot back on dry land,

he gets a reaction force that
pushes the boat far away from

the shore and a lack of
dynamic equilibrium

makes his friend very happy.

[laughter]

Oh, nice moves.

This guy's got twinkle toes.

[man] Oh!

[Dallas off-screen]
But not sea legs.

[laughter]

Moving around the
pole, his foot slips,

sending his center of mass
away from his base of support.

He can't adjust his feet to
maintain dynamic equilibrium,

which unfortunately stops him
from finishing that routine.

Does having four legs make
boat balancing easier?

[man] Come on, up.

Good boy.

[Dallas off-screen] Our initial
experiments suggest yes.

His canine companion jumps up
and pushes his center of mass

backwards, making his feet
slip due to lack of friction,

sending him over the side.

Who said dogs were
a man's best friend?

It's time for today's
science lesson,

hence the ridiculous hat.

This is the part of the show
where we like to break down

one key scientific principle
to see how it works.

Now, who can tell me what
the following have in common?

[Dallas off-screen]
This back-flopper.

This gong.

[woman] Louder!

[Dallas off-screen] Bonger.

And this classroom-banger.

Yes, today's lesson is
all about pressure waves,

which you should know are
longitudinal waves that

propagate energy through
oscillations in line with the

propagation direction.

Clear? No?

Well, alright,
maybe this'll help.

[Dallas off-screen] The
expl*si*n from this commercial

bird-scarer sends a pressure
wave outward which we

experience as a
very loud sound.

Explosions release a lot
of energy very suddenly,

which propagates outwards
as a pressure wave.

The intensity of the wave
decreases from the energy

source according to
the inverse square law.

As distance doubles,
intensity is quartered.

It is also worth noting
that pressure waves can move

through compressible air,
incompressible liquids and

inelastic solids, and can
also overcome the material

strength of rigid solids.

Got that?

Good, because it's
time for a test.

Question one.

What causes a pressure wave?

[Dallas off-screen] What
better place to find out than

in a secluded wood
using a porta potty?

Yeah, that is
fairly conclusive.

A pressure wave is caused by
the sudden release of energy.

Like that.

The expl*si*n sends a blast
wave outwards which is too

great for the plastic
of the toilet to absorb.

And so it doesn't.

Question number two.

Do pressure waves just
move through the air?

[Dallas off-screen]
The answer is no.

They can move
through solids too.

As that driver has
just discovered.

When an underground
pipe explodes,

the force from the pressure
wave is enough to break the

tarmac in the road, throwing
debris into the path of the

car and leaving the
driver a little shaken.

Pressure waves will also pass
through water and because it's

virtually incompressible,
it's the perfect medium

for destruction.

[man off-screen] Oh [bleep]!

[Dallas off-screen] Why does everyone
keep breaking toilets?

[man off-screen] Oh, [bleep]!

[Dallas] Right,
the third and final question.

How can you keep yourself
safe from a pressure wave?

[man off-screen] 'Murica.

[Dallas off-screen] This
man knows the answer.

[man off-screen] Woo!

[Dallas off-screen] The
expl*si*n from the banger

produces a big pressure wave,
but they stay safe because

according to the
inverse square law,

as distance doubles,
intensity is quartered.

[man off-screen] Woo!

[Dallas off-screen] Which
means he's up on his science.

[man] Yeah!

[man] She gone!

[Dallas off-screen] If
not his gender politics.

So that ends our lesson
on pressure waves.

Class dismissed.

[Dallas] The modern sport of parkour was
developed in France in the 1980s,

based on the training
methods of George Hébert.

Who created the
'parcour du combattant',

a type of military
obstacle course.

Recently it's
become quite trendy,

but it is best left to the
professionals who understand

friction, trajectory
and horizontal momentum.

Unlike these guys.

[Dallas off-screen]
Practitioners aim to get

from one point to another
in the fastest and coolest

way possible.

But it doesn't always work
out the way they'd like.

Painful when you're
messing around in the park.

But potentially lethal when you're
leaping between buildings.

[woman screams]

I really can't think of a
better example of something

you shouldn't try yourself.

Parkour is not a pursuit
for the faint-hearted and it

definitely helps if you've
got a grip on the science.

So today we're going to look
at one specific jump known as

the parkour press, which
involves a short or no run-up

jump to a narrow
landing point.

[Dallas off-screen] Our
athlete needs to push off with

both horizontal and vertical
momentum so that he can bridge

the gap but also land with the maximum
possible downward motion.

The right trajectory is also
important as failure to plot

the correct path may result in under or
overreaching his target,

both of which would be bad.

And friction is key on landing
as its resistance can stop his

momentum, sliding
him forwards.

Well, that looks like
something that I could

practice for the next 35 years
without achieving any tangible

improvement, but luckily I've
got a note from my doctor

excusing me from any
physical exertion.

[Dallas off-screen]
Unlike my friend Otto here.

[Otto] Are you videoing?

[man] Yeah.

[Dallas off-screen] But after that I'm
sure he can get a note too.

Otto plots a good
trajectory for himself.

But with a bit too much
horizontal momentum and not

quite enough friction
to land on his feet.

[laughter]

I'd just like to point out how
dangerous parkour can be and

that attempting stunts
like this is a bad idea.

[screams]

This parkour practitioner has
perfect technique as she jumps

across the first
three railings,

but lacks horizontal
momentum on the fourth,

and with only her toes
reaching the rail,

that was a friction fail.

[screams]



Resistance training has been
a big thing in the world of

'keep fit' for quite some time
and one of the most popular

variants of this form of
exercise is known as a

suspension workout.

[Dallas off-screen] It's
apparently a great way

to work on your core.

[screams]

But you might want to wear something a
bit more appropriate.

And this guy really needs
to read the instructions.

Clearly this suspension
workout business isn't quite

as straightforward
as one might hope,

so if you want to avoid
injury or embarrassment then

I suggest you pay
attention to this science.

[Dallas off-screen]
Resistance is a large part of

a suspension workout.

It's important for our man to retain
good body tension and grip.

If these aren't strong,
exercise will fail.

When holding the stretch, it's
important to keep all forces

balanced so our man makes sure
his weight and friction match

the tension in the resistance
band and the reaction force.

And if they aren't balanced,
it'll be all pain and no gain.

If you're game to give
suspension workouts a go,

just remember, keep all forces
balanced and more importantly

keep yourself balanced.

[Dallas off-screen] We're
gonna start off with some

low-level exercises to avoid
any unnecessary injuries.

[screams]

That was unnecessary.

This maneuver is ambitious
on rings because they're a

moveable base, making
it harder to balance.

So when she attempts to get
into an upright position,

she has too much momentum
which means that only briefly

is her center of mass
over her base of support.

This chap seems more confident
and he's giving his muscles

a really good workout.

But like any good
exercise regime,

he'll feel it in the morning.

[laughter]

In his original position,
the forces are balanced,

but when he tries to turn
around a lack of grip means

they're no longer in balance and he gets
a lesson in gravity.

[laughter]

Isaac Newton, eat
your heart out.

Perhaps we'd be better off starting with
a different angle.

That's not really
what I meant.

Well, that's all for now, but
I will leave with you with

this thought from the American
theoretical physicist,

Steven Weinberg.

'The effort to understand the
universe is one of the very

few things which lifts human
life a little above the level

of farce and gives it some
of the grace of tragedy.'

I don't think he was talking
about this lot though.

[woman off-screen] Oh no!