03x05 - Motorcycle Wheelie, Hamster Wheel and Trampolines.

[bunniefuu]

[Richard]
This is the Science of Stupid.

[electricity crackling]

Yes, this is the show that puts the "fun,"
into the fundamentals of physics,

selecting the elite
of the intellectual lightweights.

We stand back,
as they make questionable quantum leaps

and senseless scientific breakthroughs.

Through their mastery
of misadventure,

we can tackle key principles,
such as moment of inertia,

the ups...
and downs of pendulum theory,

and friction, or the complete lack of it.

Only the most foolish
will make the cut.

So, sit back.

It's the Science of Stupid.

[glass shatters]

[electricity crackling]

In this show, we'll be bowled over
by elastic potential energy,

blown away by fluid pressure,

and we'll see how center of mass
affects stability.

But first, this.

[glass shatters]

[electricity crackling]

For me, learning to snowboard
was full of firsts.

It was my first silly hat,
the first time I fell off a chairlift,

and how could I possibly forget
my first front flip?

He certainly won't.

Although that wasn't exactly planned.

But as confidence grows,

so do the stunts.

[bleep] [bleep]

Till eventually you're
pulling off massive flips like this.

[groans]

I never did get
the hang of landing either.

[crowd oohs]

[man groans]

Combining
an accurately judged jump

with just the right amount
of angular momentum

while speeding down
a snow-covered mountain

might sound easy.

It doesn't, and it isn't, and here's why.

To perform a back flip,

a man first needs to become airborne
by hitting a ramp at speed.

Before takeoff, he needs to generate
a reaction force

by pushing down on the ramp,

whilst moving his center of mass backwards
to start the flip.

He can increase his angular velocity
by tucking his arms and legs in,

or decrease it by spreading himself out,
ready for the perfect landing.

[crash]

Before you start pulling gnarly flips,

you need to be hitting
your ramp at the right speed

to pull off the trick.

This ramp is too small.

And so was the flip.

[man, off-screen] You all right?

[Richard] Doubt it.

This ramp looks great,

but does the boarder
have enough velocity?

[man groans]

No, he doesn't.

Hitting the ramp
at just eight miles an hour

meant he only had enough airtime
to rotate 180 degrees.

Turning his flip into a flop.

[man groans]

As you approach your ramp,
consider Newton's third law:

Every action
has an equal and opposite reaction.

You need a reaction force from the ground
to generate angular momentum and flip.

Or simply put, push down on ramp

and twist in the direction
you want to flip.

That's not a flip.

Oh, but those are!

Once airborne,
it was too late for this rider

to generate a reaction force.

But he did, when he hit the ground,

with his bottom,

and then his head,

and then his bottom again.

When it comes to angular momentum,
less isn't always more.

[man laughing]

Catching his head on the ramp
reduced his angular momentum,

so he had enough for one flip,
but not enough for two.

Another boarder
with his sights set on a double flip.

[man] Yeah!

[Richard] Bingo!

By crouching whilst flipping,
he increased his angular velocity,

allowing him to pull off
a flip to be proud of.

[man] Yeah!

[Richard] Now what comes after pride?

[man groans]

Oh, yeah, I remember now.

[man groans]

[electricity crackling]

I shall never forget the day

the old man swapped my tricycle
for a proper bike

and let me freewheel down a hill,
wind in my hair.

That feeling of sudden
and absolute horror.

The dull thud of
childish bone against tree.

So for little kids at least,
three wheels can be safer than two.

But are they safer than four?

Well, not when he's driving.

Give a trike to a bigger kid,
and you get...

-[man groans]
-...bigger crashes.

[man, off-screen]
Are you all right, man?

[Richard] Probably not.

[man groans]

You can see
why cars and bikes are so popular.

It doesn't really pay to cut corners
when it comes to wheels, and here's why.

A trike's triangular wheelbase
puts its center of mass closer

to the edge of its base of support,
resulting in poor side-to-side stability.

With someone on it,
a relatively high combined center of mass

also makes it more likely
to pivot over obstacles,

particularly when moving down hills.

Add to that, small wheels
and poor suspension,

and things aren't looking good.

So it's the geometrical proportions
of rider and trike

that make things a touch precarious.

Your only hope of an injury-free ride
lies in an obstacle-free surface.

Like this, and a toddler will have
a lower center of mass, so more stable.

But if the radius of your wheel
is no higher than the curb,

you ain't going over, sweetie.

Well, at least not with your trike.

Don't worry, she was back
on it in no time.

When descending, it's important to keep
your center of mass as low as possible.

[man yells]

That was a bit high.

His looks better.

He's keeping nice and low.

And now he's nice and wet.

Of course, there are some obstacles
that you'll never overcome,

like that tree.

[groans]

Even so,
best not to throw yourself against them.

[man] Ooh!

[Richard] We've seen
how three-wheelers react

when they accidentally collide
with obstacles,

but sometimes they hit them on purpose,

at speed.

[laughter]

Yep, I'm talking about ramps.

This hill's not as steep.

[man] Ohh!

[Richard] But the jump is.

Hitting the ramp at 22 miles an hour

gave enough airtime
for that high center of mass

to rotate him into a nosedive,

and the ground became the obstacle.

[man 1] You're gonna need
stitches dude.

[man 2] No it's good.

[Richard] It's not.

-[man] Ohh!
-[Richard] And you will.

[electricity crackling]

Dearly beloved, let us gather together

for the wedding of
our beautiful bride and groom.

But which principle of science
is about to make this a day to remember?

[glass shatters]

[electricity crackling]

So is there any scientific reason

why this couple cannot be joined together
in holy matrimony?

[minister] The rings please.

Yes, the coefficient of friction.

The low coefficient of friction

between the best man's posh
shoes and the platform

meant that his center of mass moved

outside his base of support
and he took a dive.

And on the subject of diving...

[bride screams]

[bridegroom] No! Oh my God!

[Richard] Is this what they call
a bridal shower?

Looks more like a kind of bath to me.

[guest, off-screen] Oh, my God.

[electricity crackling]

[Richard] Back in the '70s,
well before the rise of games consoles,

high-tech fun for kids took the form
of a device known by many names:

Skippy ball, hippity hop, hoppity hip.

But I always knew it as the space hopper.

Unfortunately,
they didn't come with instructions.

[girl] Hi everyone. I'll be doing the
space hopper of epic-ness.

[Richard] This sounds good.

-[girl groans]
-Huh. Disappointing.

We did eventually work out
how to ride them.

-[man, off-screen] Oh!
-[Richard] Well, almost.

[man, off-screen] Oh!

[Richard] For the benefit of mankind,
it's only right that we try to understand

the complex science behind
these extraterrestrial bouncy things.

To bounce on a space hopper,
the rider must drop down on it,

generating elastic potential energy
as the air inside compresses.

As it rebounds, this is converted
into kinetic energy,

which is transferred to the rider.

By landing towards
the front of the hopper,

her center of mass is propelled forwards.

So she must keep a firm grasp
of the hopper's horns,

ensuring her center of mass remains
above her base of support.

A space hopper gets some of its bounce
from the PVC they're made of.

It's the same stuff they use
to make plastic footballs.

But space hoppers are much heavier.

So don't kick them at your little brother.

People just see
that bright orange grinning face...

-[man] Ohhh!
-[laughter]

[Richard] ...and kick it!

By kicking it hard and storing
lots of elastic potential energy,

he manages to generate
enough kinetic energy

for a 30-mile-an-hour kick.

[laughter]

And yes, the man in the sombrero
thinks it's hilarious.

Space hoppers aren't
supposed to be kicked.

It's cruel.

They're supposed to be bounced on,

but before you can do that,
you need to be balanced,

which means your center of mass

has to be above
the hopper's base of support.

[cheering, yelling]

Nice kinetic energy.

Just keep the center of mass
over base of support,

and you will win.

Oh.

Oh, dear.

Still, your opponent's kinetic energy
is so rubbish you'll win anyway.

Can he keep his center of mass
in the right place?

[laughter]

Well, yes.

Just a shame about the base.

A jump directed off-center

caused the hopper
to roll his base of support

out from under his center of mass.

Hard to hold those horns
when you stand up anyway.

[bell rings]

Pipe down at the back,
it's time for your science lesson.

Now, there'll be a test at the end
of this tutorial, so pay attention.

The pressure is on!

So, who can tell me
what high-powered pumps

have in common with
smashing bottles of fizz, and...

air-hose hijinks.

Cheeky.

[laughter]

Yep, today's lesson
is fluid pressure.

So we'll be looking at

how gases and liquids behave
under pressure.

Bring on the science!

Gases are compressible,

which means you can squeeze more molecules
into a given volume.

According to Boyle's law,
this increases their pressure until--

Liquids, according to Pascal's principle,
are almost incompressible,

which means they do not change
their volume when pressure is applied.

But all fluids will try to
alleviate pressure where possible

by flowing into an area of lower pressure,

and the smaller the aperture,
the faster the flow.

That was the science.

The question is,

how well will you stand up
to the pressure of my grueling exam?

Question one:
How can you increase

the velocity of a liquid
flowing through a pipe?

You force it through a small hole.

A firefighter's hose can squirt water
directly into flames,

or directly above them.

Don't worry about the burning house,
next-door's lawn will look great.

This hole is much bigger,
but make it bigger still...

[man screams]

...and the velocity drops.

[man screams]

And so did he.

Turning our attention
to gases under pressure now.

Question two: What do you get when
a container exceeds its tensile strength,

leading to a rapid release of molecules?

Any ideas?

[expl*si*n]

Yeah, that.
And it's called an expl*si*n.

And here's another one.

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

[Richard] And another bad idea.

[man, off-screen]
It reminds me of Back to the Future,

when they take off!

-[man 1, off-screen] Yeah.
-[Richard] Yep.

I imagine they ignited
flammable gases in milk bottles, too.

Don't try it at home.

Of course if rapidly expanding
gases under pressure are your thing...

[man speaking native language]

That was one car airbag,

one very brave scientist,

and one very sore bottom.

[laughter]

And now we come
to our third and final question.

We've seen liquids under pressure,
we've seen gases under pressure.

But what would happen
if you were to combine the two?

Cram lots of gas into a confined space,
and any liquid with it...

[screams, groans]

...will be
put under pressure too.

Cheer up.

You could be living with this chap.

He's mixed up a little treat
for his girlfriend.

[man] Ketchup.

Apparently if you mix this stuff with it,
it turns into a ketchup b*mb.

[Richard] That doesn't sound good.

I hate ketchup.

[woman screams]

And so does she.

He mixed bicarbonate of soda with ketchup

and created a gas, shook it up,
and you know the rest.

[laughter]

Yeah, laugh it up, buddy.

You'll be cleaning that stuff up
for months.

This can be dangerous,

so please don't try it yourself.

And so ends our lesson on fluid pressure.

Remember, fluids under pressure

will try to head somewhere
with less pressure.

Usually...

[man, off-screen] Can't see it.

[Richard] ...pretty quickly.

[glass shatters]

[electricity crackling]

If you're good at juggling,

then you can put your skills to use
at children's parties.

But if you're good at football juggling,

you could become
an international soccer star.

I know which one I'd choose.
I love jelly.

Ball juggling is the perfect way
to showcase your skills...

[laughter]

...or spills.

I'm sure no one noticed.
Got away with that.

Practice is the key
to keepie-uppie perfection.

Although it can be a frustrating process.

I don't think
that's part of the routine.

The world record
for keeping a ball off the ground

using just the feet,
legs and head is 26 hours,

and no, I have no idea
how he went to the loo either.

It's time for the science.

A kicked ball follows
a curved parabolic trajectory.

He uses small upward kicks
to keep this parabola short,

ensuring his center of mass

remains above his base of support
to maintain balance.

As he kicks,
this base becomes smaller.

He can counteract this
by alternating feet,

bringing the base of support
back under the center of mass.

So the secret to ball control
is to use short, controlled kicks.

And where better to demonstrate
your silky skills than on the field?

[man 1] Go on, Dave!

[man 2] Ah!

[man 3] I might have just
lost an eyeball.

[Richard] This is why you should practice
ball juggling.

You can do
keepie-uppie anywhere,

but just because you can,

it doesn't mean you should.

Her initial kicks had short,
controlled parabolas.

But when she threw in the tricks,
the kicks became less precise,

and the parabola became harder to control.

Football is a game of two halves,

and so is that light.

Balance is also key for keepie-uppie.

Standing on one foot cuts
your base of support by more than half.

Although the question isn't

how this puzzle-twizzling ball juggler
keeps his balance,

It's how did he solve the cube
without peeling off the stickers?

Alternating feet allows him

to keep center of mass
above his base of support.

Is he Irish dancing now?

Oh, that's blown it.

With one leg on the ground,
he had a solid base of support.

With one leg on his football,
he didn't stand a chance.

[electricity crackling]

I was thrilled when I was told
we were doing a piece on tackle.

I love fishing.

But it turned out we're not talking about
carbon rods and bait boxes.

We're looking at this sort of tackle.

[man, off-screen] Oh my God!

[Richard] And it isn't reserved
for the sports field.

When tempers fray...

[crowd] Ohh!

[Richard] ...even a harmless game
of musical chairs...

[woman] Argh!

[Richard] ...can fall apart.

Thankfully, heavy contact
during parlor games isn't essential,

but if you do want to play rough
with the boys with odd-shaped ba*ls,

you'll do well to get to grips
with the science first.

The tackler builds momentum
to increase impact force.

By focusing his weight
behind his shoulder,

he transfers as much
momentum as possible.

And by applying the force away from
the ball carrier's center of mass,

he'll create a turning effect
to bring him down.

To sum up,
create as much momentum as possible

and strike off-center
for that turning effect.

It certainly sounds simple,

so let's begin with getting
plenty of momentum.

[man] Wouldn't that be something
like slamming somebody?

[laughter]

-[Richard] That'll do it.
-[man groans]

Lots of momentum.



And there you have two trellises.

Oh, and a broken friend.

[man] This is exactly what
I was talking about.

We have to do stuff like this.

[Richard] There are other activities
you could try,

like football.

This man is either
severely underdressed,

or he's not part of the game.

Well, it was a little high,

but tackling above the center of mass
can also result in a turning effect.

The higher the hit, the greater the turn.

Maybe he just wanted to cuddle.

Group hug.

In a lot of sports,
a high tackle is ill*gal.

[man] Right let's go.

[Richard]
In whatever this is...

[man screams]

...it should be too.

[man] There we go!

[Richard] But there are other ways
of decreasing stability.

Like sitting on top of a tall thing
balancing on a wheel.

Yup.

In this case, wherever you hit,

he's going down.

[man] Ouch!

[Richard]
My thoughts exactly.

[man 1, off-screen] That was a high hit.

[glass shatters]

[electricity crackling]

[Richard] Once again, we've come to the
end of another Science of Stupid.

I always find it hard to say good-bye,

but not as hard as
endoplasmic reticulum.

That's really tricky. Good-bye.

[lively fiddle music]

-[man 1] Oh-ohhh!
-[man 2] Ohh!

[groans]

[man] Ohh!

[man, off-screen] Ah!