03x18 - BMX, Inflatables and Racing

[bunniefuu]

[Richard]
This is the Science of Stupid.

[electricity crackling]

-[glass shatters]
-[alarm blares]

Yes,

this is the show
where science meets stupidity

head-on, without a safety helmet.

You're about to be exposed
to experimentation

of the hazardous kind,

where scientific pioneers
push the boundaries

of fundamental principles like:
angular momentum,

the conservation of energy,

and combustion.

Strap on your safety goggles.

It's the Science of Stupid.

[electricity crackling]

In this show,

we'll see how kinetic energy
keeps you on target...

-[groans]
-...or not.

The downside of momentum,

and how a little airflow

can be a drag.

But first, this.

[glass shatters]

[electricity crackling]

[glass shatters]

For any parent, a child's first scoot

on their baby kick scooter
is a nervous affair.

The initial wobble as they set off,

that perilous little crack in the tarmac,

it's enough to set the heart racing.

Of course, fast-forward ten years,

and those same parents
are faced with the likes of this.

The topsy-turvy joys
of the scooter backflip.

Oh, did I say "joy"?

I didn't mean it.

You see, some flippers

aren't quite so good as others.

I'm talking to you.

Whilst the scooter backflip trick

can be flipping fun,

it can also be flipping painful.

Reason enough to pay close attention
to the science.

He hits the ramp at speed
for maximum jump height.

To flip, he leans back,

pulling the handles up towards him.

Bending his legs reduces
his moment of inertia.

Which means he spins faster.

To land,

he distributes his weight evenly

between both wheels for stability.

So get up high,
spin as quickly as possible,

oh, and don't bail out early,

because if you do, you might end up

facing the nasty side
of the conservation of momentum.

But more of that later.

Let's start with
that take-off from the ramp.

The first ingredient is speed.

The second is pain.

Well, certainly if you don't
bend your knees enough.

Stretching out increased
his moment of inertia,

slowing down his spin.

He had a soft mat to land on, but...

[boy, off-screen] You didn't land on it.

[Richard] No, no, he didn't.

Can he do it?

Nope.

Good speed and great take-off angle,

but by not tucking in,

his moment of inertia is too large

for him to complete his spin in time.

Maybe try it over there next time.

I think they're foam bricks.

Right, how's his spin?

It's...

not ideal.

[groans]

Okay, spin not going great.

Best we crack the landing.

Remember, it's about
distributing your weight

evenly over both wheels.

I did say over both wheels, not feet.

Bail out, and the law of
conservation of momentum

means you let go
and the scooter keeps going.

Catch!

[laughter]

Or vice versa.

[wails]

When the scooter stops,

you carry on.

Oh, I really think
you should stop, seriously.

[wails]

[woman screams]

[electricity crackling]

[clattering]

[whooshes]

In the annals of history,

the bow and arrow has been
as much a symbol of pride

as it has a highly effective weapon.

The modern bow in the right hands

can be a thing of wonder.

Here's one in the hands of a little kid.

[boy] Pull.

[Richard] Nice!

[fast-forwarding sounds]

[boy] Boo-ya.

[Richard] That's what I was gonna say.

In the hands of a middle-aged man...

Wait for it.

-[bow thwacks]
-[groans]

[Richard] Still a thing of wonder.

-[bow thwacks]
-[groans]

Like, I wonder why he bothered.

[laughter]

You can see why for thousands of years

the bow and arrow
was such a devastating weapon.

In the hands of the untrained amateur,

it can unleash just as much
pain and misery

as it did in the Dark Ages.

And that's largely down
to kinetic energy and pressure.

As he pulls back on the string,

he's generating and storing

elastic potential energy in the bow.

When he releases it, that potential energy

is converted into kinetic energy.

Propelling the arrow forwards.

And the sharp point of the arrow

provides an extremely high local pressure,

so it punctures the target

with ease.

So the first things
to remember are to pull hard,

to generate and store lots of
elastic potential energy,

and release to convert it
into kinetic energy.

Simple, but deadly.

Therefore, a bow and arrow
should only ever be used

under strict, professional supervision.

[Calvin] My name is Calvin and this is
the Montana tooth pull.

[Richard] Oh, dear.

Ow.

[Richard] Just a little
kinetic energy there,

but enough to avoid the dentist.

[man, off-screen] Got it.

[Richard] Yeah, I just hope
that was the right tooth.

[man] Right here is what we call...

redneck fireworks.

And make sure you have
your safety glasses on.

[Richard] Okay, I still don't feel safe.

Just draw back nice and easy

for elastic potential energy,

and release for kinetic.

[girl screams]

Okay, I think you forgot the last bit.

[laughter]

Ah, now you're talking.

Japanese archery
is a truly ancient art form,

demanding precise control
of elastic potential energy.

[bow thwacks]

Oh, not so precise
in the modern era then.

At least, not for her.

Remember that kinetic energy
packs a punch.

A standard 35-pound bow
has been known to send an arrow

over 1,640 feet.

[thuds]

Oh, I think you needed
a couple of feet to the left there.

Not to mention, a new camera.

[laughing]

[man] I shot Robert two weeks ago
with a blowgun.

Now he's going to get his revenge.

[Richard] That sounds like
a really bad idea.

[man, off-screen] All right.

[groans]

[Richard] You see, that sharp point
creates lots of local pressure,

too much for his homemade padding.

[groans]

So maybe you need better armor,
or better friends.

[man] Son of a *****!

[groans]

[electricity crackling]

[creaks]

[rumbles]

[Richard] Can you guess
what scientific law

this young lady is about to celebrate?

[glass shatters]

[electricity crackling]

[glass shatters]

So what science
is she about to demonstrate

with her nice bottle of bubbly?

[yells]

[laughter]

It's Boyle's law!

Given a constant temperature,

the smaller the volume
a gas is forced to occupy,

the higher its pressure will be.

So when the gas cartridge
finally opens,

the compressed air rapidly expands,

firing the confetti out with it.

-[yells]
-[laughter]

Let's face it, another perfect celebration
of eye-popping science.

[laughter]

[electricity crackling]

[rumbling]

The simple kite has spawned

an industry of exhilarating fun.

In fact, modern kite technology is,

in some cases, evolving faster

than man's ability to harness it.

[man, off-screen] Hey, hey!

[Richard]
Well, it certainly is in his case.

But take that kite
and add a set of wheels,

and the sky's the limit.

Or the ground, if you're him.

[wails]

Yes, be it landboarding or kite buggying,

the addition of wheels to the humble kite

has allowed people
to hurdle down the beach

at exhilarating speeds.

Great fun.

It's also increased the possibility
of being catapulted into the air,

and then dumped violently onto the ground.

To avoid that,

you need to understand lift and friction.

A kite's aerodynamics

convert oncoming airflow

into upwards or sideways lift force.

Whilst on the ground,

sideways friction at the wheels

keeps you rolling forwards.

Changing the kite's angle
alters the airflow

and changes the magnitude
and direction of the lift force.

This allows you to control
your speed and direction,

even enabling you to pull of jumps...

sometimes.

Mastering the kite buggy

is about keeping it
within the wind's power zone,

and then controlling that airflow.

But, of course, you won't get anywhere
without a bit of lift.

Can you get lift without airflow?

Quite right. No, you can't.

Here's a man with the wind in his sails...

-[tires screech]
-[wails]

...and sand in his eyes.

Friction at the wheels
keeps you rolling forwards,

but dig in on a turn,

and too much friction
will send you rolling over.

-[tires screech]
-[wails]

Okay, we've kept things
on terra firma with friction,

and we've used
a little airflow to get going.

Now it's time for a jump.

So you need to pull hard
on that kite for more force

to lift you off the ground.

Landboards work on
much the same principles

as kite buggies,

with near identical results.

If your lift force suddenly drops...

so do you.

Enough lift will leap you
across that pond.

Well, he made it across.

Shame his board didn't.

So remember, plenty of airflow,

large lift force, and sideways friction.

Get it right and you're flying.

[metal clanks]

Oh, who put that fence there?

[bell rings]

[clattering]

[gurgling]

[beaker shatters]

We've come to the part of the show
where I don the cap of pedagogy.

That's teaching to you.

Yes, it's the science lesson,

where we turn our attention

to a particular scientific principle.

Can you guess today's theme
from the following?

A man with too much time on his hands...

-[trap snaps]
-[man] Ohh!

-[traps snapping]
-[groaning]

[Richard] A high velocity shave...

-[screaming]
-[laughing]

and, well, him, doing that.

[retching]

[breathing heavily]

If you didn't guess,

our theme is the sensory system,

how our bodies process information

from our surroundings,
like touch or taste,

and how it can help us
avoid nasty situations

by making us feel, you guessed it, pain.

Here's how it works.

The sensory system uses receptors
to detect external stimuli,

which are relayed
as electrical signals to the brain.

Pain receptors called nociceptors

alert us to excessive mechanical stimuli,

like sharp or blunt pressure,

extreme temperatures,

or potentially harmful chemicals,

like in a chili.

This often results
in an automatic reflex,

intended to pull you away from danger,

or warn others.

So that's the science.

Now for a test. Question one.

Can you think of a way
of annoying your sensory system

with a chemical stimulus?

Yep, it's by eating something.

But not just anything.

Oh...

-[laughing]
-[groans]

[man] That's disgusting!

[Richard] That's right, something acidic,

like super sour sweets in their case.

[yells]

Question two.

You're about to see someone experiencing
some mild discomfort,

thanks to their nociceptors,

but is it A: mechanical, or B: chemical?

[indistinct chatter]

See what you think.

-[woman 1] Ready?
-[woman 2, off screen] Just do it.

-[screams]
-[laughter]

[screams]

[Richard] His pain was due to

the temporary deformation
of skin follicles.

-[screams]
-[laughter]

So it's mechanical.

[yelps]

[man] Why did you do it again for?

[Richard] 'Cause it was funny.

[man] What you do it again for?

[laughter]

[Richard] In moist parts of the body,
like the mouth,

it's easier for a potentially
harmful chemical

to trigger nociceptors.

And question three is,

how does our body protect us
from the hidden dangers

of those nasty chemicals?

He's eating a ghost chili,

one of the hottest chilies in the world.

I wonder how his nociceptors will react.

[laughter]

Oh, perfectly.

With involuntary reflexes
such as coughing...

[coughs]

...and wincing.

[groans]

And, uh, heavy blowing.

[boy] It's really hot.

[Richard] Yes, and that's because
the body's sensory system

reacts as if it were a physical burn.

[groans]

Perhaps try something milder next time.

[groans]

Like a ladle full of cinnamon.

[coughing]

[woman] Ahh!

[Richard] Oh, I might be wrong.

[groans sharply]

Cinnamon powder contains
a nasty, caustic chemical

that can damage your lungs,

and cause just as impressive
a reaction as chili.

So that's your science lesson for today.

Nociceptors are rather sensitive,

so, please, don't taunt them.

[woman]
Over and out.

[glass shatters]

[electricity crackling]

[glass shatters]

[Richard] It's not the greatest feeling
in the world,

breaking down on the side of the road.

But at least when
the professionals turn up

with their recovery truck and trailer,

you know your vehicle, whatever it is,
is in safe hands.

Well, that's what I used to think.

So, rule one...

[metal scraping]

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

[Richard] Keep your
trailer's handbrake on.

[man, off-screen]
Yeah, that didn't work at all.

[Richard]
Ah, touch of paint, you'll be fine.

Rule two,

make sure the ramp is attached.

And rule three,

watch out for obstructions.

[man] Hey!

[Richard] Like helpers.

[man] Hey!

[Richard] Phew, that was close.

Almost hit him.

The problem is that when loading
any vehicle onto a trailer,

there are so many variables at work,

like momentum, gravity, and traction.

Here's the science.

You need force to move a vehicle
up the ramp.

A run-up builds momentum,

but the steeper the ramp,

the more momentum is needed
to overcome gravity.

Torque supplied by the wheels

combines with traction of the tires

to propel the vehicle forward,

so it comes to rest on a stable base.

Ideally.

So it's a little force to beat gravity
and plenty of traction

to keep you on the straight and narrow.

But first, let's tackle
that old devil, gravity.

When going against gravity,
a winch can help,

providing it doesn't snap.

[man, off-screen] Oh, ****.

[Richard] I'm assuming
one of those cars is his.

He's about to use
a high velocity approach.

[man] As you can see I am a little scared.

[Richard] Yeah, I can see why.
But give it a go anyway.

[engine revs]

Oh, maybe the velocity
wasn't high enough.

For a steep angle like that,

he had too little momentum,

caught the edge and then the ground.

[engine revs]

Of course, the bigger the mass,

the more momentum you need
to counteract gravity.

Although sometimes,
momentum can be the problem.

Lots of momentum
and a long wheel base

sent the tracks bouncing
right off the truck.

That effort really tanked.

[electricity crackling]

Men in Lycra throwing each other
around the ring

was television gold for me as a kid.

I loved it.

But little did I know
that these wrestling gods

were also titans of body mechanics.

You see, these professionals

are experts in staging pain and violence.

[all exclaim]

I repeat, staging.

[groans]

He's not an expert,
and that's real pain.

[groans]

You should really
leave this to the professionals,

because they are experienced

in reducing the massive impact force

of wrestling moves like the body slam.

And here's how they do it.

Raising his opponent's center of mass,

he rotates it around a pivot

by generating a turning force.

The closer the mass is to the pivot,

the smaller the turning force needed

to rotate and slam him back down.

The opponent can then
reduce the impact force

by spreading out

and landing on a soft surface.

The key here is that it's the use
of clever body mechanics

rather than strength
that makes the real difference

when lifting the opponent up.

Although that's not to say
that size doesn't matter.

Here's a family wrestling scenario.

I wonder who will win.

Little mass of little brother

or big mass of big brother?

[screams]

I'd say big brother.

Near perfect pivot point,

sufficient turning force,

well ex*cuted slam.

So technique was good.

I just wouldn't advise
trying it with your siblings.

-[groans]
-[woman] Hey, Bailey.

[Richard] Bigger mass to slam here,

so can he provide
a big enough turning force?

Yes, he can.

[laughter]

The further away
his mass is from his pivot,

the larger the turning effect
from his opponent's weight.

But if you do wanna cut the door in half,

maybe try a saw next time?

Still unclear on the dangers
of slamming other people?

Well, remember, wrestlers do their thing
on sprung canvas,

which allows them to lose momentum
over a longer period of time,

thereby reducing the impact force.

Soft surfaces can do this.

Hard surfaces definitely do not.

So need I ask what category
a wooden table comes under?

-[wood cracks]
-[laughter]

Evidently, yes, I do.

But not all soft surfaces
are good for wrestling.

Friends, for example, are bad.

Reducing the impact force is okay.

Sharing the pain is not.

Need I say, this is extremely dangerous,

so please leave it to the pros

and do not try this yourself.

[glass shatters]

[electricity crackling]

[glass shatters]

We've come to the end
of another gleeful romp together

across the field of scientific endeavor.

Please, do not try
any of the stunts you've just seen,

or you're unlikely to be enjoying

any more gleeful romps ever again.

Goodbye.

[screams]

-[bow thwacks]
-[groans]

[woman] Ahh!

[screams]

[groans]

[girl screams]

[man, off-screen] Hey, hey!

[man, off-screen] Oh.

[groans]