03x03 - Biking, Street Luge and Uneven Bars

[bunniefuu]

[Richard] This is the
Science of Stupid.

[electricity crackling]

[glass shatters]

Yes, this is the show
where science lifts the lid

on the heroically stupid.

Who for reasons best known to themselves,

have abandoned reason,

common sense

and any regard for personal safety.

But thanks to them, we can examine

the science behind some key principles.

From trajectories...

[groaning]

To material strength.

And of course, everyone's favorite...

conservation of momentum.

So strap in...

[tires screeching]

Hold on tight, because this is...

the Science of Stupid.

[electricity crackling]

In this show
we'll explore reaction forces,

rotations,

[screaming]

and compressive strength.

[man, off-screen] Oh!

[Richard] Which that didn't have.

But first, this.

[glass shatters]

[electricity crackling]

If a Canadian Minister of Sport
describes something

as the ultimate laxative,
you know it must be scary.

And that thing is luge.

A sport tailor-made
for adrenaline junkies.

Which is fine if you're
in Austria, like him.

But what if you live in Arkansas?

No problem. Welcome to street luge.

It combines all the fun of luge
with all the fun of a street.

Plus the added dangers of...haystacks.

[screams]

Friends...

and fellow competitors.

[scraping]

[man] I just slid into you...
from the back

and couldn't get off ya.

[Richard] Yeah. I think he knows that.

Yes, if you like the idea of skateboarding

but are too lazy to stand up,

street luge could be
the perfect sport for you.

But before you head on down that hill,
check out the science.

Lying down results
in a low center of mass,

which helps with stability.

To turn left and right,
he shifts his center of mass.

This changes the angle of the wheels

which alters his turning radius.

The small size of the wheels

means that even the tiniest bump
has a large effect.

To brake, he puts his feet down
and uses friction with the ground.

But there are other ways... of stopping.

So lean that center of mass
left to go left,

right to go right and hope your boots

do the job if you want to stop.

All sounds very simple until you hear that

the speed record for one of these things

is 97.81 miles an hour.

So you can see why it doesn't take much

for it all to go a bit wonky.

From this angle, you get a great view

of the rider shifting
his center of mass to steer.

Left, right...

[screams]

Uh, wrong.

At this speed, he couldn't
turn quickly enough

and he shifted his center of mass...

[screams]

right off his sled.

I'm no expert,

but I don't think the straw helped much.

Done correctly, that leaning technique
helps you overtake.

Done incorrectly...

it helps you overturn.

And the tighter the turn,
the more you have to lean.

[grunting]

And that applies to all of you.

[groaning]

Now, as well as the purists,
there are also those

who are a little looser
with their interpretation of street luge.

As long as it has wheels

and they're on their back, they're happy.

I said, on your back!

[slide whistle trills]

[screams]

Thank you.

With tiny wheels and only feet for brakes,

perhaps ramps aren't the best... idea.

That's why.

[man] Ow... That's it. I'm done.

[Richard] I think so too.

He's got a special track.

[screams]

Oh, it didn't help.

[whimpers]

And that's because once airborne,

those small wheels are unable to provide

any steering... unlike the wall.

Still, he seemed happy.

[laughter]

So what happens if you try
and make things a little easier

by increasing the wheel size
and using handles to help steer?

[groaning]

Pretty much the same.

Yes even though he did have bigger wheels,

unfortunately he hit a bigger bump.

Or, more specifically... his friend.

[electricity crackling]

To anyone who thought stacking
one thing on top of another

was an activity confined to the safety
of a supermarket shelf,

I suggest you think again.

Because there's a whole world out there
just waiting to be stacked.

[woman, off-screen] Okay.

[Richard] There's chair stacking...

[screams]

And climbing.

[laughter]

[shouting]

School desk stacking.

[screaming]

All right, how about
some quiet reading now?

And who needs computer games
if you've got stacking skills?

Now, where is there a slot?

To your left.

Left a bit more.

A bit more...

and jump.

I think it was left a bit more.

You see, from organizing
your kitchen cupboards

to building the great Pyramids of Egypt,

it's quite obvious that stacking
is an essential life skill.

So here are the scientific secrets
to a strong, stable stack.

For maximum stability, you need
a large base of support

and a center of mass roughly
in the middle near the bottom.

Use objects with
a high compressive strength

that won't buckle under pressure.

And make an interlocking structure

with high friction between the objects

so they don't move position.

So it's all about
getting your structure right,

making sure that what
you're stacking won't collapse

and that you have enough friction
to stop things slipping off.

Now we've got our science goggles on,

let's see some stacking in action.

Just your everyday
back garden bin tower...

[man, off-screen] Oh!

[Richard] Slash circus apparatus.

[laughter]

Now this happened because,

A, the low compressive strength

of the plastic bin causes it
to buckle when he jumps.

And B, because it was a stupid idea.

[man, off-screen] You good?

[Richard]
No. And his stacking's rubbish too.

[groaning]

These drinks crates have good
compressive strength.

However...

[clattering]

Without an interlocking
structure between stacks,

they're more like dominoes.

[clattering]

Talking of dominoes...

Now, this guy has got a fantastic
interlocking structure.

Just pop that one... there.

Oh...

Well, that's 16 hours of your life
you won't get back.

And that's because although
the structure was good,

the friction between the dominoes wasn't.

Causing them to easily move.

Ha-h*. Butterfingers.

These chaps are adding mass
to their stack,

which could help increase stability.

[glass shatters]

But trying to drink it won't.

[glass shatters]

Now, they seem to
have got everything right.

Interlocking structure... good stability,

the right amount of friction...

[screaming]

Um, who was supposed to be
doing the catching?

[electricity crackling]

[shouting]

What scientific principle is this
Ronaldo wannabe about to demonstrate?

[laughter]

[glass shatters]

[electricity crackling]

[Richard] So have you guessed the
science

this young soccer fan is going to show us?

Yup. It's Newton's second law.

The ball is filled with concrete,

and the greater the mass,
the greater the force

required to move it...

Which he didn't have.

I'm just glad he didn't try
and head the ball.

[electricity crackling]

Have you ever arrived at the top

of a flight of stairs and thought,

what's the stupidest thing
I could possibly do?

No, me neither.

But not everyone
is as sensible as you and me.

For example, I would never
dream of doing this.

[cheering]

And that's why.

Don't get me wrong,

this biking down stairs...
does look exciting.

[slo-mo yelling]

In fact, I wish I could do it.

[man] Oh!

[Richard] And so does he.

Now, there are safer ways
of going down stairs.

My personal favorite is walking.

But if compelled
to ride a bike down stairs,

it's worth knowing that
behind the pain and danger

are some important scientific principles.

Such as velocity and momentum.

Velocity is often a good thing

because the faster you ride,
the more stable the bike.

But that velocity needs to be directed
in a straight line down the steps.

And to remain balanced,
the rider needs to lean back.

Also, if the front wheel
stops too quickly,

his momentum will rotate him forwards.

And...

he'll fall off.

[meowing]

So to ride down stairs successfully,

you need to keep your speed up,
point straight downhill

and avoid any sudden braking.

Now we know the science,
who wants to see a tumble?

Sorry, I meant to say,
a carefully controlled descent.

[man, off-screen] Come on!

[Richard] Hmm, not enough speed.

[laughter]

Oh, very poor center of gravity.

Oh, but a lovely rotation.

Remember, speed helps stability.

But don't forget to brake.

How about this chap?

[laughter]

Not content with going over
just his front wheel.

His sudden side-stop meant his momentum

sent him over both.

Little showoff.

Now, this rider is going
to try something different...

[shouting]

And that was different.

He's decided to demonstrate rotation
whilst on his side.

Before transferring
the rest of his momentum...

to the floor.

Oh, better. Good center of mass...

Good speed...

Now, that's how to do it.

And that's not.

Finally, while cycling is a great way
of meeting people...

[screams]

Don't assume that at 20 miles an hour...

they want to meet you.

[bell rings]

[sloshing]

[bubbling]

And now it's time
for today's Science Lesson,

hence the silly hat.

Yes, it's the part of the show
where we shine the spotlight

on a particular scientific principle.

To reveal today's subject, a little quiz.

What have the following
activities got in common?

[boy] First shot.

[grunts] Oh, sh**t...

[Richard] Any guesses?

How about this?

[glass shattering]

[laughter]

No? What about this?

[yelping]

[laughter]

The answer is ricochet.

[b*llet ricochets]

Or in basic terms, stuff bouncing off
other stuff.

But there is a lot more to it than that.

[b*llet whizzes]

All right, here's the science.

According to the law
of conservation of momentum,

the angle of approach will be mirrored
by the angle the ball is deflected at.

The same law states that momentum

will always be retained by the object...
or transferred to a new object.

And the coefficient of restitution

means that the rubber ball will ricochet
further than the wooden ball.

Because on impact, it can deform more

and stores more energy
before releasing it.

Now, have you been paying attention?

Because it's time for a test

on our three key pieces
of ricochet science.

First question. If a ball hits an object

at 0 degrees, what degree
will it bounce off at?

[indistinct chatter]

Can you guess?

[gasping]

Yup. 0 degrees.

Remember, angle of approach
and angle of deflection are...

[laughter]

the same.

See?

Exactly the same.

[groaning]

There are times however,

when the angles work in your favor...

And times when they don't.

And that's one of them.

[crying]

Question two. Momentum from
a ricocheting object

is always retained or transferred.

But transferred to what?

Correct! The object it hits.

That was a low transfer.

[woman] Oh!

[Richard] And that was a high one...

relatively speaking.

Two transfers of momentum here.

Bat to ball.

[groans]

Ball to... those.

[mumbling]

Momentum here is conserved at around


[groans]

Which is similar to a baseball traveling
at nearly 40 miles an hour.

Right where you don't want it.

And finally question three
of our science lesson.

How does the coefficient
of restitution affect bounciness?

For some reason best known to himself,
this young man has decided to test

the coefficient of restitution
of his mobile phone.

A low coefficient, so not much bounce.

But increase the force...

[groaning]

And you get a bit more.

Yeah, pretty much your dad's reaction
when you ask him for a new phone.

So that's your science lesson for today.

Ricochet, interesting in theory...

painful in practice.

[glass shatters]

[electricity crackling]

Most people accept that hopping

from one small elevated position
to another

is something best left to squirrels.

And you are about to see why.

Here's a squirrel.

Here's a person.

[screams]

Now let's try... jumping.

Squirrel.

Person.

[screams]

But our obvious limitations

haven't stopped some people
setting a new benchmark

and creating the art of post jumping.

[woman, off-screen] Just do it.

Just that pole!

[Richard] Or at least trying to.

Amazing as it may seem,

post jumping is not
an official Olympic sport.

Or an unofficial one, for that matter.

But it does share something
with the world's other great sports.

And that is science.

On launch, he bends
his leg and pushes hard.

Increasing reaction force.

This generates enough horizontal
and vertical momentum

for the optimum trajectory.

On landing, he flexes
his ankles, knees and hips.

Decreasing impact force by nearly 20%.

And a two-footed landing provides

a larger base of support
for more stability.

Okay fine in theory, but how will
our squirrel wannabes

grapple with this science
in the real world?

Where posts come in all shapes and sizes.

Let's find out.

Just to get on the post,

you need that ground reaction force.

[groans]

But not that force.

Let's move on to taking off from a post.

[screams]

Not quite.

Yeah, poor ankle control
leads to loss of balance...

and force is applied
in an unwanted direction.

Maybe try a wider post.

[groans]

No, I meant wider all round.

And maybe ease off the momentum.

[boy] I'm going to jump here to there.

[Richard] I wouldn't.

But at least you've got a flatter post,
which should help.

[groans]

Although I have been known to be wrong.

Insufficient momentum
means that his trajectory

is just too short.

Lovely belly flop though.

[laughter]

[electricity crackling]

When Nadia Comaneci became
the first Olympic gymnast

to score a perfect ten
in the uneven bars in 1976,

everyone thought wow, where will the sport
go from here?

Well, nearly 40 years later, we now know.

[grunts]

Not far. Well, for him at least.

Maybe it's a lack of decent facilities...

[screams]

Or it could just boil down to a lack...
of technique.

Whatever the reason, I think that
before anyone else dons a leotard

and starts swinging, me included,

we should hear what science
has to say about it all.

By holding on and letting herself drop,

centripetal force pulls her
towards the bar, making her rotate.

This means she has angular momentum.

And the more she tucks in,
the faster she will rotate.

When she lets go,
the centripetal force disappears

and her inertia takes her
on a straight path to the second bar.

Well, it all makes perfect sense to me.

But then, I'm not the one
spinning around like a washing machine.

So let's see if it makes sense
to people who are.

Let's start with getting
the basic swing right on one bar.

[screams]

Oh, you off?

Well, great linear velocity.

Just wrong time and wrong direction.

Anyone else?

[screams]

Not enough angular momentum

and too much gravity.

One bar didn't go terribly well,
so let's move on to two.

And it's worth considering
that the force exerted

on a top gymnast's arms when they spin,

is the equivalent of holding 3 1/2 times
their own body weight.

Which makes this guy's display
even more impressive.

Alley-oop!

Oh, nice turn.

Bravo.

Now, this is more gentle swaying,
so less centrifugal force.

Wrong way.

[grunts]

Yeah, let's see how a pro does it.

Okay, maybe not.

She nailed her angular momentum,

overdid her linear velocity

and learned that not all body parts
grip the bar quite as well as hands do.

I made the same mistake last week.

[glass shatters]

[electricity crackling]

So what can we conclude from all of this?

Well, there are many ways in which science
can help keep you safe.

But if you decide to do something stupid,
there are many ways it won't.

[shouting]

[screaming]

[screaming]

[laughter]

[groans]