07x04 - BMX, Playgrounds and Parking

[bunniefuu]

[Dallas Campbell]
This is the Science of Stupid.

[electricity crackling]

[klaxon blaring]

Yes, this is the show
that blends high-minded science

with low-brow stupidity.

Witness the acts of misguided guinea
pigs

as they bend the rules of science...

[man grunts]

...and feel it
snap back in their faces.

We'll determine what went wrong...

and why

using some of science's
most painful principles...

[man groans]

...such as viscosity,

unstable equilibrium...

and that little rebel
volume of revolution.

-Physics fights fire with fire...
-[woman shrieking]

So duck and cover.

It's the Science of Stupid.

[electricity crackling]

In this show,

we'll be looking
at the fun side of friction,

the trouble with turbulence...

[woman screams]

...and we get our heads around

centrifugal force.

But first, this.

[glass shatters]

[electricity crackling]

Someone once said that
one good turn deserves another.

I think whoever came up with that

had clearly never tried the BMX 720.

Because, although
he makes it look simple...

some make it look hard.

The 720 in "BMX 720"

stands for 720 degrees of rotation

and, as you've seen,
there's plenty of risk involved.

So before we get our heads in a spin,

let's launch ourselves into the science.

First, our cyclist generates
plenty of linear momentum.

On launch, he turns sideways and pushes
off firmly with his back wheel

to generate angular momentum.

He needs enough of this
to complete two spins

so his wheels will be
in the right position when he lands.

He then uses the ramp to gradually
reduce his vertical velocity.

Okay, some tricky science

but if our researchers follow
the rules, they'll be fine.

First things first. We need a solid
ramp.

That's actually a roof, not a ramp.

Is that a good idea?

I didn't think so.

With little run-up, he doesn't generate
enough angular momentum

to complete the second turn.

Meaning he lands with
his wheels 90 degrees away

from where they should be,

and he can't ride out of the landing.

At least he can laugh about it.

[man laughing weakly]

Through the pain.

Here we are, back in the safety
of the skate park.

[man groans]

Relative safety.

This brave BMXer managed
to successfully complete his 720,

but he didn't have enough linear
momentum,

and so his back wheel hit
the top of the ramp...

otherwise known as "a turn for the
worse."

[man groans]

What a beautiful evening
to ride off into the sunset.

-[thud]
-[man screams]

Or into the handlebars.

This unlucky chap managed
to perfectly execute the 720,

but he had too much linear momentum
so overshot the landing ramp.

Thus, his bike immediately lost
vertical velocity,

but he didn't...

until he headbutted the handlebars.

-[thud]
-[man screams]

Face the facts:
you can't beat physics.

[electricity crackling]

[metallic creaking, clanging]

Passing your driving test is one of
those coming-of-age moments,

although there are a few maneuvers
to get your head around first,

like parallel parking.

It's very tricky.

[people shouting, whistle blowing]

And when things get tricky,
it's nice to have some encouragement...

[people cheering]

But even nicer to have some science.

To successfully parallel park,

you need your car to follow
an S-shaped path,

or "sigmoidal curve,"

by making two opposing tight turns.

Firstly, our man turns his steering
wheel in one direction and reverses.

Once the car is at a 45-degree angle,

he needs to lock the wheel
in the opposite direction

and continue to reverse.

This maneuver should be conducted
at low velocity

to avoid hitting the curve or worse.

[man sighs]

Okay, so the key is
to be at the right angle,

but not a right angle,

and then you should slowly reverse in.

Sounds easy enough.

Plenty of space to park there.

Now, let's just take it slowly.

[man chuckling]

Maybe not that slowly.

They've turned too late
and at the wrong angle,

so are miles away from the curb.

[man, off-screen] I love how he's going
as if like he's right next to the car.

He has got eight foot behind him.

[Dallas] Once in the wrong position,
it is hard to correct,

so this lad's not gonna bother.

[man 1, off-screen]
That guy just... [laughs]

[man 2, off-screen] Oh God.

[laughter]

[man 1] Brilliant!

[man 2] He's got out of the car
and she's parking it!

[Dallas] It's obviously tricky,
so we might be here a while.

-[man] Go!
-[all laughing]

[man] Smashed it!

Absolutely smashed it!

[Dallas] This is more like it.

Straight into that tight turn.

Any minute now, they'll achieve
that 45-degree position.

-[metallic crunch]
-Uh, you want to hit the perfect angle,

-not the curb.
-[horn blaring]

The driver starts the first turn well

but doesn't make the follow-up turn,

meaning they're not able to straighten
up.

Seemingly oblivious,

the driver continues to reverse, and...

[metallic crunch, horn blaring]

That got their attention.

[blaring continues]

Yeah, finished quite well, though.

Let's try a different technique.

[man, off-screen] Fourth time lucky!

[Dallas] Hmm, doesn't sound very lucky.

[man, off-screen] Come on,
straighten the wheels.

[Dallas] The driver doesn't have it yet.

Come on, let's hurry this along.

They've made the mistake
of trying to pull in front-first.

Although intuitive,

it's actually harder
to get the back wheels

into the right position
to complete that sigmoidal curve.

[man, off-screen] That's it. Now lock
the wheels the other way.

-Other way.
-[Dallas] Great advice.

Shame they can't hear it.

[men laughing]

I wouldn't laugh at the state
of that parking, gentlemen.

Just look at the state of your van.

-[men laughing]
-I mean, really.

[laughter continues]

-[man, off-screen] Whee!
-[clapping]

[Dallas] Once you've got
your technique down,

you can try a little faster.

[glass shatters, car alarm blares]

That's just about perfect.

[glass shatters]

[electricity crackling]

I love ping-pong,

but that's not how I play it.

Still, they're about
to demonstrate some science.

But can you guess what?

[glass shatters]

[electricity crackling]

[glass shatters]

[Dallas] Did you guess the science
they're about to show us?

[woman] Bobby! I'm... [laughs]

[Dallas] Yes, it's plastic deformation.

Don't be embarrassed if you got it
wrong.

She's the one with egg on her face.

This cheeky husband throws ping-pong
ba*ls

for his wife to knock in the box.

The ba*ls are plastic,

so they deform slightly and bounce off.

However, he has switched
the last ball for an egg.

Eggs are brittle, and so don't deform...

[laughter]

[Dallas] ...but break on impact.

Cracking shot.

[glass shatters]

[electricity crackling]

[glass shatters]

I'm no expert when it comes to dancing,

but even I know that the secret
to impressing everyone at the party

lies in nonchalantly gliding backwards
as if it were magic.

Yes, the king of the dance floor
is he who can moonwalk.

Man, can that guy moonwalk.

[onlookers cheering]

Oh, look at him go.

[Dallas echoing]

And look at him go--oh. Oh, he's gone.

[man grunts, crowd laughs]

Ah, yes, the moonwalk:

iconic, entrancing,

but a bit of a misnomer
in scientific terms.

You see, it's not about the floaty
effect

of a low-gravity lunar landscape.

It's about the slidey effect
of low friction.

Our dancer starts with one foot
in tiptoe position

and the other flat on the floor.

He positions his center of mass
over the tiptoed foot

to decrease the frictional force
on his flat foot.

He slides his flat foot smoothly
backwards

while slowly lowering his tiptoed foot

before simultaneously switching them,

repeating continuously
for the illusion of gliding.

Of course, if you're sliding backwards,

you're going to struggle
to see where you're heading,

but I'm sure we'll be fine.

The great thing about the moonwalk
is you can do it anywhere...

if you can do it at all.

-[man yells]
-[glass shatters]

I think we found out "who's bad."

It's you.

He fails to position his feet
and center of mass correctly,

meaning he's basically
just walking backwards.

Plus, he's not looking
where he's going, and...

he makes a right mess of the moonwalk.

[bell dings]

[man on PA system]
Clean up on aisle three.

[Dallas] Dad dancing, but in a good way.

He's opted for the sock-sliding
technique,

one of my favorites...

but not her favorite.

His moonwalking technique is nice.

He's minimized the friction
between his feet and the floor,

but he's so focused on dancing,

he forgets to look
where he's going, and...

Charming.

Wow, this girl has got the idea.

[girl yelps]

-Almost.
-[girl laughing]

She uses a wet floor
to decrease her friction

instead of distributing
her mass correctly,

and surprise, surprise...

-[girl yelps]
-It didn't work.

[girl laughs]

[school bell rings]

[liquid squelches, glass shatters]

[bubbling]

Quiet, please.

The bell doesn't dismiss you.
I dismiss you.

Now, I hope you've all got
your notepads at the ready,

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

the bit of the show
where we focus our microscopes

on one particular scientific principle.

But can you guess what it is
from the following?

This waterfall clamberer.

[man shouts]

This ambitious cyclist.

[men shouting]

Or this twirly girly.

[girl whimpers]

All right. Hands down.

They are all examples of turbulent flow,

which is the rougher,
wilder sister of laminar flow.

And if you don't know what
either of those are,

here's a bit of science to help you out.

This water initially has laminar flow,

which is smooth, ordered, and
predictable.

A disruption causes it
to transition to turbulent flow,

which is chaotic, disordered, and
random.

As smoke rises,

it naturally transitions from laminar

to turbulent as it interacts with the
air.

And its particles continually
change speed and direction,

leading to the formation
of eddies and vortices.

Turbulence affects both liquids
and gases in similar ways.

For example, the flow of wind and rivers
are both generally turbulent.

Now, let's see who's been paying
attention

with a little pop quiz.

Question one: Is turbulent flow ordered?

I mean, this guy looks pretty in
control.

Maybe it is.

[people exclaiming]

No, it's chaotic and disordered.

[woman, off-screen] Whoo! [laughs]

[Dallas] The water becomes more
turbulent,

and chaos ensues
as these two waves collide,

so he's got little choice
but to go with the flow.

[woman, off-screen] Whoo!

[Dallas] Don't worry. He was fine.

Question two: What features
are generated by turbulent flow?

Well, here's a clue.

This chap is about to get
a very close look at them.

[whooshing]

See you in a bit.

Okay, let's bring him back for the
answer.

As turbulent wave actions
causes those water particles

to change speed and direction,

it forms swirling vortices and eddies,

which can really suck.

[whooshing]

Don't worry. He was
spat out again in one piece...

eventually.

And question three:

see if you can identify
the following examples

of turbulent flow in a gas.

Have you got it yet? I'll give you a
clue.

You can't see it,

but you can feel it.

[woman screams]

If you said wind, well done.

This hot-tubber is trying
to put the cover on.

Unfortunately,
because the wind is turbulent,

it's unpredictable.

A gust suddenly catches the cover,
and...

[cover squeaks]

There's no shame in defeat.

At least your workout's done for today.

Class dismissed.

[glass shatters]

[electricity crackling]

[Dallas] The humble
yet indispensable pulley system

has been with us since at least
the Mesopotamian times,

but over its 3,500 years plus of
history,

it's been used and misused.

[man grunts]

And that is misuse.

In fact, it's incredibly dangerous...

Because a pulley doesn't have to
break...

for you to.

-[man] Oof!
-[woman laughing]

[Dallas] Yes, pulleys can
be found absolutely everywhere,

helping make work easier for everyone.

So let's make our lives run
a little smoother

and check out the science.

A pulley is a simple machine
made up of one or more wheels

and a rope or belt.

A one-wheeled pulley reverses
the direction of force,

so you pull down to lift an object.

With more than one wheel,

you can reduce the force
that you need to lift an object.

This is known as "mechanical advantage."

Pulley wheels can also be connected

by a continuous belt or cable.

This transmits rotary motion and force

from one wheel to the other.

So, let's shift this up a gear

and see those pulleys really get to
work.

That crane is working very hard.

[creaking]

That's it. Have a lie-down.

This is a prime example
of mechanical advantage.

The pulley system in the crane
has given enough mechanical advantage

to lift a very large weight.

However, it moves its load
too far away from the base,

creating a turning effect

that rather overturns the advantage.

[man laughing]

A ski lift is a pulley system
on a continuous loop.

This one is out of control.

and now everyone's looking
for the fastest way off.

[woman screams]

That's one option.

Luckily, no one was seriously injured.

And that really is lucky.

This could have been a lot worse.

[man shouts indistinctly]

Here's a pulley system
supporting the weight

of a young physicist...

-[boy, off-screen] Look at this thing.
-[boy shouts]

[boy laughing]

[Dallas] ...who's studying gravity.

The rope is just as important
as the wheel in a system,

but before this lad is lowered down
from the tree house,

his weight exceeds
the strength of the rope.

[boy, off-screen] We won't let you down.

[Dallas chuckling] Oh, you won't.

[boy screams]

But he will.

-[boy laughing]
-Don't worry.

He was okay.

[electricity crackling]

[metallic creaking]

[clattering]

Are you bored of playing on the same
old traditional roundabouts?

Well, have no fear, because
there's a thrilling new alternative.

The ingenious difference?

It's just a bit tilted.

[boy laughs]

And whilst this pair are looking
pretty proud of themselves,

you know what pride comes before.

[boy gasping]

Pain.

So, the roundabout has been revamped,

and those wonky versions
are popping up everywhere.

but before we get ready for recess,

let's remind ourselves of the science.

When our man steps onto the roundabout,

he exerts a force on it,

giving it angular velocity.

Because of its tilted surface,

this is also produced by gravity

when he stands on either side
of the roundabout.

The faster it spins...

the more he'll feel the centrifugal
force pushing him outwards.

Because there's no handrail,

he must rely on the friction
of his feet to keep him on.

All of this is made harder

when his friend joins in.

It's literally child's play,

providing you don't try
to be too ambitious.

Ooh, we're starting with three riders.
That is brave.

-[girl shrieks]
-[man laughs]

Well, Dad did well.

[man continues laughing]

Dad has a greater mass
than his two children.

When he walks to the top of the ring,

he generates a large turning force

due to gravity.

As the ring moves,
the kids can't run fast enough,

and it pulls their feet out...

[girl shrieks]

...from underneath them.

Yeah, I'm not sure
that was designed for you, Dad.

Maybe try the swings.

Three again?

We know that won't work.

Can one of you get off?

Thank you.

Excellent technique.

It actually looks quite relaxing.

I'd probably just drift off.

[children shouting and laughing]

But maybe not like that.

By laying low,
they increase their stability

whilst their chums underneath
do all the hard work.

But as the spinner gains angular
velocity,

one of our lads fails
to hold on tight enough

and there isn't enough friction
between him and the surface.

Luckily, his doppelganger
was there to catch him...

or that would have hurt.

Ah, a solo rider.

And you are building
some impressive velocity, my friend.

[boy shouts]

Yes, you've earned that lie-down.

As our confident soloist
runs on the roundabout,

he increases its angular velocity.

When he stumbles,
centrifugal force takes hold.

Nice gloves, but maybe a helmet next
time.

[electricity crackling]

[glass shatters]

Well, that's quite enough science
and stupidity for one day.

Please don't try
any of these stunts at home.

At best, you will look ridiculous.

At worst, you could
hurt yourself and your friends.

If you need any more convincing,

then watch this.

[man groans]

[woman, off-screen] Whoo!

-[man grunts]
-[people shout]

[girl giggles]

-[thud]
-[man groans]

[man grunts]

[crowd laughs]

[woman] Bobby! [laughs]

[crowd cheering]

[woman screams]