04x09 - Ski Jumping, Limbo Dancing & Zip Lining

[bunniefuu]

[Dallas]
This is the Science of Stupid.

[reading onscreen text]

Yes, this is the show where science

and stupidity collide.

As people with a total disregard
for safety

-reach peak stupidity...
-[shrieks]

with bone-crunching results.

We'll reveal where it went wrong

and delve into the science
behind the fail.

With the help of angular momentum,

work and power,

and the coefficient of restitution.

So grab a seat

and prepare
for the eternal struggle

between intelligence and idiocy.

Ohh!

Watch out!

It's the Science of Stupid.

[electricity crackling]

In this show, we'll be looking at...

[cries]

impulse...

lever arms...

[yowls]

...and turning effect.

-But first, this.
-Ohh. Oof.

[electricity crackling]

For me, there's never been a machine

that could inspire my passions
and want of freedom

more than the motorcycle.

It fulfills all my dreams.

Like the thrill of the open road.

The pleasure of riding
with skill and precision.

And then there's this.

Whatever this is.

Now, personally,
when I'm out riding my hog,

there's nothing I love more
than doing a straight-line burnout.

But spinning your rear wheel
while driving forwards

has the potential
for some painful outcomes.

So it's probably good to know
a little bit about the science.

[techno music]

Before revving the engine,

the rider applies the front brake

and then shifts his weight forwards

to keep it over the front of the bike.

This reduces the downwards
force on the rear wheel,

which decreases the static friction,

enabling the wheel to spin in place

when he opens the throttle
and releases the clutch.

As he gentle releases the front brake,

the bike will move forwards
because the rear wheel

is still experiencing kinetic friction,

the resistance present
between two sliding surfaces.

And although kinetic friction
offers less traction

than static friction, it's still enough

to be able to move the bike forwards.

Perfecting a burnout isn't easy,

and you also need
supreme control of the bike,

because that low kinetic friction

allows the wheel to slide
in any direction.

Check out this guy
with all the right moves.

Brakes on, check.

Leaning forward, check.

Decreasing static friction, check.

Using kinetic friction
to ease forward, check.

Controlling the bike...

not check.

Eh, four out of five isn't bad.

[laughter]

Given that kinetic friction
allows motion in any direction,

even a small, unchecked lateral force
causes the wheel to slide out.

[man] I'm so glad I recorded this.

[Dallas] Yeah, me too.

And finally, make sure
you are on a secure surface

when you try to do your burnout,

because, you know, friction.

[laughter]

If upping the thrill factor
is the name of your game,

then I'd recommend my preferred method
of doing straight-line burnouts,

and that's doing it backwards.

Doing it all in reverse?
Difficult? Ha, sure.

But not for this guy.

[man] Whoa! Whoa-oh!

He forgot
one of the basic principles.

You only want a tiny bit of traction
to creep forwards.

Too much,
and with the rear wheel spinning

at around 460 revolutions per minute...

it was wheelie time.

[man] He's all right!

[electricity crackling]

[metal creaking]

When I'm at parties,
people are always asking me

what my favorite scientific principle is,

and I always say the same thing:

gravity, although it has a downside.

That's not true.
I-- I don't get invited to parties.

But what is true is that what goes up

must come down.

[all yell]

One way...

or another.

That looked painful.

Obviously, one way to stop the pain

is to not hit the ground with such force.

Or even better,
to not hit the ground at all,

and for that,
you might want to phone a friend

so you have someone to catch you.

But catching a person
is surprisingly difficult.

Luckily, we're here
to tell you the science.

As the jumper falls,
she has downward velocity.

In order to stop her
before she hits the floor,

the catchers must reduce
her velocity to zero.

This is done by exerting
an upwards force.

This force, exerted over time,
is called an impulse.

To stop the jumper in a controlled way,

the catchers need to position themselves

to be able to apply
a sufficiently large impulse

as close to the jumper's
center of mass as possible.

Flexing their arms and legs
increases the length of the catch.

The longer it takes, the less force
the jumper and catchers will feel,

and the smoother the stop will be.

So if your catcher
stands in the right spot,

flexes as they absorb the impact,

and applies an upward force
over as long a time as possible,

there shouldn't be any problems.

Sounds simple, right?

[woman screams]

But it's a little harder than it looks.

The catcher was in the wrong position,

so couldn't apply an impulse

that was aligned with her center of mass.

But he did manage to grab her legs,

but that only made it worse.

[man] Kevin, get off the roof, dude!

[Dallas] Kevin here is stuck on the roof

and wants to make sure
he gets down safely.

[man] One, two, three!

It's a short drop,
and his friend is right there.

What could possibly go wrong?

-Ow!
-[Dallas] Oh, yeah, that.

Kevin's friend
wasn't in the correct position

to be able to apply an impulse
near Kevin's center of mass.

So Kevin hit the ground
with roughly the same force

as a watermelon travelling
at 150 miles per hour.

[man] Oh, my God! Kevin, are you OK?

[Dallas] Kevin's dreaming
about being a watermelon.

OK, to actually catch someone,

you need to apply an impulse
near to their center of mass.

But you also need to make sure
that you're in a position

where you can use your whole body

to maximize that impulse.

I love a fancy dress party.

Note to self:
if you are planning to crowd surf,

make sure the crowd knows about it.

[screaming]

[indistinct chatter]

[man] They did not catch him.

[Dallas] No, they did not.

Although the one person
who attempted to catch this knight

used outstretched arms
which were far too weak

to provide enough impulse
to stop his descent.

Standing close together, arms linked--

it looks like these guys
know their catching principles.

The person falling doesn't stay rigid,

so she slid through the catchers' arms,

and they couldn't apply
enough impulse to stop her.

Trust is overrated anyway.

[electricity crackling]

Can you guess what scientific principle

these backyard gymnasts
are about to demonstrate?

[electricity crackling]

I asked what science
these amateur acrobats

are about to teach themselves.

Look out. Oh, [bleep].

[Dallas] It's torque.

To stop the bar slipping
when the fellow below does his spin,

the guy on top needs to apply a torque

at his ankles to keep them pointing up.

Unfortunately,
he's not able to maintain it.

Look out. Oh, [bleep].

And our spinner bites the dust.

They might want to practice
on some smaller bars next time.

Or not bother.

[electricity crackling]

Like a lot of young people,
I love the idea

of putting my cap on backwards,
grabbing my deck,

and heading out skateboarding
with my fellow youths.

But then I see this.

This.

And things like this.

[screaming]

And then I decided, hmm, you know what?

I'm fine right here, thank you very much.

However, if the idea of some
bone-crunching fun appeals,

you should know
that being able to remain standing

on your board
isn't only about a gnarly attitude.

It also involves a healthy dose
of friction and balance.

So here's some science
for you radical dudes.

The basics of balance

are to keep your center of mass
over your base of support,

which in this case
means his feet and the board.

Skateboard wheels
are designed to roll easily.

So if he leans too far forward or back,

a turning effect is generated

that accelerates the board
out from under him.

And while the wheels are only designed

to roll forwards or backwards,
a lean too far sideways

can overcome a static friction
and cause a skid.

When on a slope, his weight will act

to accelerate the board down it.

So to stay balanced,
he needs to lean forwards.

But not too much.

So it's just a matter
of keeping your center of mass

over your base of support and avoiding
accidentally overcoming static friction.

Right, let's see
who has been paying attention.

[groans]

[Dallas] Well, not him.

Unless that's what he wanted to do.

Moving his center of mass
outside his base of support

created a turning effect
in line with the direction

of the wheels,
meaning his board accelerated

away from him...

rather quickly.

Maybe it'd be better to find your balance

before adding speed.

[laughter]

Yeah, I'd suggest more practice.

[laughter]

And finding some better friends.

[cheering]

This chap's got a great stance
and plenty of speed,

which is perfect...

if you want to speed across the concrete
on your face.

That puddle helped
to reduce static friction

between the board and the ground,

so when he leaned too far sideways,

his wheels easily lost traction...

and skidded.

[boy] Hey, you good?

[Dallas] Not at avoiding puddles,
he's not.

Once you've got a handle on balance,

you can take it up a notch
and add some more speed.

But with speed comes
a whole extra set of problems...

...as this brave field researcher
is about to demonstrate.

Whoa-ohh!

A speed wobble
is a self-exciting oscillation.

At high speeds, the slightest wobble

can feed off the skateboard's
energy and grow and grow

until either you slow down...

or you're thrown off.

[groans]

[lively music]

Now I'm sure this guy remembers

that even on a small slope,

his weight will help
increase acceleration.

Right?

[screaming]

Wrong.

[screaming]

And that, well,
it's a slightly different take

on the turning effect.

And a rather good reason
to wear a helmet.

[bell rings]

[objects clattering]

[liquid bubbling]

Jones, I've told you a thousand times,
liquid nitrogen is not a toy.

Take Jenkins to the thawing room.

All right, pay attention, class,

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

This is the bit of the show
where we dissect

a specific scientific principle.

So who can tell me
what the following have in common?

This elastic band inspector...

-[groans]
-[laughs]

this junior pizza chef...

and these pillow fighters.

[groans]

That's right, today we are talking

about modes of failure, or in other words,

what happens when a large enough force

is applied to an object
so that it breaks or deforms.

So open your books, take out your pens

and pay attention,
because you are about to get schooled.

Here comes the science.

When we drop this vase,
we can easily see what happens

when a force applied to a brittle object

exceeds its yield strength,
which is the limit of stress

it can withstand.

It breaks.

The molecules in this porcelain vase

are rigidly locked together.

So when we drop it, the stress of impact

creates fractures, and it shatters.

This is known as a brittle failure.

When we drop the same material

but wet and unfired,

it undergoes a plastic deformation.

This permanent shape change
happens in objects

with more flexibly bonded molecules.

Also, the shape of an object
can concentrate stress

in unexpected places,
so a failure can occur

some distance
from where the force is applied.

Got it? Good.

Right, question one,

what type of failure do you see in objects

with rigidly bonded molecules?

[yells, groans]

Yep, they shatter.

The large and sudden force
applied to the chair

causes a brittle failure,
breaking the bonds

holding the tightly knit
molecules together.

That chair will never recover,

but luckily it looks like he will.

[yells, groans]

And when it comes to a brittle failure,

it can be quite... sudden.

The pole is elastic up to a point,

and bending it stresses it most
in the middle.

This concentration of stress
causes a failure

some distance from where
the force is actually applied.

[yells]

My thoughts exactly.

On to question two.

What properties in a material
can lead to a plastic deformation?

Ah, a practical demonstration.

Thanks to our helpful skateboarder,

we can see the car door
is dented but not broken,

meaning the molecules in the metal

must be more flexibly bonded.

I once blew a bubble as big as my head.

And it ended in exactly the same way.

Blowing applies a force that stretches

and plastically deforms the gum

until the extra force of the slap

increases the stress
and bursts her bubble.

That is never coming out
of your eyebrows.

And now, on to our final question.

What happens if you combine
plastic deformation

and brittle failure?

This.

Here we have two separate objects

with different failure mechanisms.

The car is experiencing
plastic deformation,

as the metal dents
to accommodate the stress

of smashing through the house,

while the house itself
is illustrating brittle failure

as the wood and glass break apart.

I prefer to end my drive-throughs
with a burger in my hands.

Class dismissed.

[electricity crackling]

Scientists like me call water
the universal solvent,

due to its ability to dissolve
a huge range of substances.

Luckily, humans aren't one
of the things on water's hit list,

at least when it comes
to the whole dissolving thing.

But you still need
to be careful around it.

Yeah, that's not water.

Yeah, more careful than that.

And certainly that.

As that guy will tell you,
puddles can be very dangerous.

But if you're intent
on messing around in them,

then there are two main problems
you need to overcome,

being able to see the bottom
and not slipping on it.

Any dirt or sediment in the water

increases its opacity
and can obscure the bottom,

making it hard to accurately judge depth

or spot any underwater obstacles.

But the surface of water
can reflect light,

which means that from
certain viewing angles

you may not be able to see the bottom,

even if the water is clear.

And obviously water reduces
the coefficient of friction,

making it harder to get traction
and easier to slip over.

But for a lot of people,
the key thing about puddles

is not getting your feet too wet,

especially if you're wearing
brand-new trainers.

[man] Nakeem and his nice-a*s shoes
about to jump in this puddle.

I do it for the kids.

[laughter]

Whoo!

[Dallas] And that, boys and girls,

is another reminder
to never jump into a puddle

unless you can see the bottom.

Due to the water's opacity,

Nakeem here couldn't judge
the depth of this puddle...

[laughter]

Whoo!

...which was a bit deeper than most.

[laughter]

[woman] Does he have his phone on him?

[Dallas] Well, if he does,
he better be careful then,

'cause he wouldn't want to get it... wet.

[laughter]

Yes, the reflective surface of the water

obscured the bottom--
and that pothole.

My mother always used to say
that the secret to success

was preparation, preparation...

and taking into account
that water will reduce

the coefficient of friction.

It's an odd motto, but
it's stood me in good stead.

[laughter]

[electricity crackling]

I've been told on more than one occasion

that my legs are greatly admired.

-[wolf whistle]
-I know.

It's a tad embarrassing,

but I do like to keep them in shape,

as you never know when you might
need to spring into action.

[whimsical music]

So effortless and agile.

Remember, think of the grace of the cat.

[laughter]

Our animal friends
make getting air seem so simple,

and science explains why.

A large ground reaction force
is needed to get airborne.

A powerful downwards push
from the legs will do this,

so having strong muscles helps.

Smaller animals have an advantage

because they're proportionally
stronger for their size.

[growls]

And to gain extra height,
animals use their legs as levers.

By using the joints as pivots,

the muscles only have
to contract a small amount

to produce significant power

and magnify the distance they can travel.

The longer the lever or leg,

the greater the distance.

Right, so those are the basics.

But just how easy is it
to leap like a legend?

Come on, Tiny.

Up you jump, Brutus.

Eh, not quite.

His ground reaction force was too small,

and shorter legs equals shorter levers,

limiting his ability to extend the jump.

Looks like you're walking
home on your own.

Let's see if this kitty
is a master of feline flight.

[yowls]

Well, not too bad,

but unfortunately
landings are equally important.

You really want a stable surface
to help maintain that hard-earned height.

Better luck next time, Moggy.

[electricity crackling]

And that brings us
to the end of another show,

but in case some of you

have foolishly taken inspiration here
today, don't.

And here's a reminder of why.

[lively fiddle music]

[laughter]

[yells, groans]

[yowls]