06x02 - Bob Sled, Backflip and Swegway

[bunniefuu]

[Dallas off-screen] This
is the Science of Stupid.

[screams]

[Dallas off-screen] Yes, this is the
show

where science collides with
stupidity.

You're about the meet the unsung heroes
of the scientific world.

[man] No, no! Ah!

[Dallas off-screen] The untrained, the
unqualified, and the unbelievably daft.

We'll explain what went wrong.

And why.

With the help of principles
like impact force.

The coefficient
of friction.

[man] [bleep].

[Dallas off-screen] And deceleration.
[man] [bleep].

[Dallas off-screen] Tread on the toes of
science,

and it'll hit you where it
hurts.

So, watch out, it's
the Science of Stupid.

In this show, we'll be exploring the
painful side of positive feedback.

The embarrassment caused
by angular momentum.

And revealing how the amplitude of waves
can ruin your holiday.

[screams]

[Dallas off-screen]
But first, this.

[Dallas] Have you ever thought, "I like
trampolines,

but wouldn't it be brilliant if

they were much were much longer
and much, much thinner"?

No? Me neither.

But, the inventor of the
slackline clearly did.

[Dallas off-screen] And, you
know, he might have had a point.

But to be good at slacklining,
you need nerves of steel.

And pants of iron.

[Dallas] Right, so, slacklining
is a bit like tightrope walking,

with an extra helping of bounce.

And if you think that'll make things a
bit tricky, you'd be absolutely right,

and here's the science
to explain why.

Leaping onto the slackline,

his weight and vertical momentum push
him down onto

the line, storing elastic
potential energy within it.

Unlike a tightrope, a slackline moves
dramatically in two dimensions,

so it's harder
to stay balanced.

His challenge is to ensure that his
center of mass remains

over the constantly moving line.

[Dallas] The longest slackline ever
walked was over a kilometer long.

I think we should
start a bit smaller.

This one is so low, he's basically
walking along the ground,

which should make it hard
for him to hurt himself.

Hard, but
not impossible.

The slackliner's weight keeps
the line planted on the ground.

Sadly, he forgot about elastic potential
energy stored in the line.

But, when his foot slips.

He gets
a quick reminder.

This man is going to lean on his friend,
to get him safely onto the line.

[man] [bleep]. Oh.

[Dallas off-screen] Not
that it did him much good.

As he starts to fall, he pushes the line
towards his center of mass,

which science suggests is the right
thing to do to stay balanced.

[man] Oh!

[Dallas off-screen] That's
more like his center of pain.

Once you've mastered the basic line
mount, and, let's be honest,

nobody has so far,

you can add a
little bit of flare.

Why not start your move
with a jump onto the line?

Ah, that's why not.

A slackline mainly resists forces that
go directly downwards.

Our woodland acrobat pushes
backwards, as well as down.

The slackline moves from beneath him,

and his downward force moves further
away from it,

which is a long-winded way of saying.

He eats soil.

Ooh, slackline to
slackline, now this is cool.

In theory.

It was all going so well,

but he fails to keep his center of mass
over the line.

And back he goes
from whence he came.

Is he
laughing or crying?

Yeah, we'll go with laughing,
we'll keep it light.

Oh yes, now, here's a little tip for all
slackliners, do your laces up tight.

Now then, do you like your adrenaline
rush to involve sub-zero temperatures,

a high-velocity
coffin on steel runners,

and a fair to middling
chance of serious injury?

Then bobsled could
be the sport for you.

[man] And they're off!

[Dallas off-screen] Professional
bobsledders can experience up to

five G's on some corners.

That's more than astronauts experience
during a rocket launch.

This is clearly not a
sport for the fainthearted.

In fact, I wonder what it's like when
the fainthearted have a go?

[screaming]

[Dallas off-screen] Oh, I
see, it's a bit like that.

Well, it's a long course,
so we'll leave him to it.

I don't think there's any doubt that
bobsledding is a serious business,

and if you're still keen to have a go,

make sure you turn up at your local
course,

armed with a helmet and
the relevant science.

The sled is accelerated by being pushed
at the top of the course.

From then on, the sloping track means
that the gravity

continues to accelerate it.

Low friction between the runners and ice
means that very little of the sled's

kinetic energy,
or speed, is lost.

But if the base of the sled
hits an obstruction and stops.

The riders still
have a lot of momentum.

On the fastest tracks, sleds could be
hitting speeds of over 90 miles an hour.

[Dallas off-screen] That's why
professional sleds are finely-engineered

machines, that
can cost a fortune.

Our researchers haven't got a fortune,
so they built their own sleds.

What could
possibly go wrong?

Well, there's that,
that, and that.

They have got the low friction right,
but everything else wrong.

No, this is just silly,
you're not proper scientists.

This looks more like it.

[gasps]

[Dallas off-screen] Gravity
provides the acceleration,

but when the sled hits
the snowdrift, it stops.

But, the riders' momentum
means they keep going.

Oh, that is textbook.

[man] Oh, yeah.

[Dallas off-screen] Steep course,
gravity, and low friction

results in
lots of momentum.

[man] Oh no!
[man 2] Whoa.

[Dallas off-screen]
Classic physics.

They steer into the bank,
the runners turn sideways

and suddenly have
a lot of friction.

So, the sled stops,
but the sledders don't.

[man 2] Whoa.

[Dallas off-screen] Ooh, I've just
remembered

our perturbed bobsledder
from earlier.

I wonder how he's getting on?

Looks like he's coming
to the end of the course.

Do you think he enjoyed it?

[man] Ahh, what are you doing?

[man] Not backwards...

...not backwards!

[Dallas off-screen] Bobsledding, the
sport that comes with

a mental health warning.

Now, we all like a bit of backyard kung
fu fun,

but what scientific principle is
this

nunchucker about to show us?

[Dallas off-screen] We asked you what
science this nunchuck ninja

was about to demonstrate.

Jean-Claude Van Damme,
that must have hurt.

Anyway, did you guess
centripetal acceleration?

When he applies centripetal force at one
end, the other moves in

a curved path around his hand.

But, a severe lack of proper control

means those paths intersect with each
other, and then with him.

In quite a painful way.

[Dallas] Okay, it's time for one of our
occasional studies of the natural world,

where we explore the science behind
common environmental phenomena.

And today, we're looking at something
that can be both very impressive

and very scary.

[Dallas off-screen] Yes, he's
gonna surf that wall of water.

And yes, he has chosen the worst
possible moment to fall off.

Hang about, where's he gone?

Oh, there he is.

Hello, are you okay?

Don't worry, he was fine.

[Dallas] Yes, waves are pretty powerful,
and the key to that power lies in the

science of the ocean.

When strong winds beat down on the
ocean, they transfer kinetic energy,

which creates large
chaotic waves.

As the waves move away from the storm,
they calm into a regular pattern,

known as swells.

Approaching the shore, the clearance
between the surface wave

and the seabed decreases,
squeezing the wave upwards.

Since water is a fluid and can't support
itself, it crashes down,

creating those plunging
breakers loved by surfers.

The largest waves ever recorded were
more than 100 feet tall,

so I made it very, very clear to all of
our field researchers

that they needed to be on their A-game.

"This is not a holiday," I said.

Nobody listened.

Rhea forgot that water is a fluid, and
can't support itself when forced

upwards, but it can meter out
some rough justice.

Now, I'm all for the research team
pushing the envelope,

but Chanel here has gone too far and
ignored the dress code,

which clearly
stated smart casual.

[screams]

[Dallas] Not only did Chanel have to
contend with the

seabed squeezing the wave
upwards,

the rock she's standing on adds to the
dramatic vertical crash.

[screams]

[woman] The sea just got me.
We got wet!

[Dallas off-screen] Correct.

Another example of one of our
researchers at the top of her game.

Ah, good, it's Layla,
department head.

I didn't know about the
hula hooping, to be honest.

Layla knows that as waves move away
from the storm that created them,

they settle into regularly-spaced
swells, which means

by my calculations, another one should
be due, yeah, about now.

Yep, there it is.

[Dallas] Okay, okay, settle down,
please,

it's time for today's science lesson,

the part of the show where we study a
specific aspect of science.

And there will be a test later, but
let's start by seeing if you can guess

today's subject matter.

Can you identify which common scientific
principle is being used,

to stunning effect, by this
physicist-c*m-cyclist?

And completely misunderstood
by these giggling students?

Yes, that's right, it's combined center
of mass, the principle that applies

when two or more
objects are coupled.

And here's an example.

A gymnast lifting his partner is raising
their combined center of mass.

The higher is it, the more they are at
risk of a toppling torque.

So, he keeps his base of
support wide, for stability.

However, if the weight of one gymnast
moves to the side,

the other must compensate,

to keep the combined center
of mass over the base.

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

Question one, what happens to the
combined center of mass

when additional weight is added directly
above an object?

[Dallas off-screen] That's right, the
combined center of mass is raised,

and when it's that high, it's hard to
keep within a narrow base of support.

[man] Oh!

[Dallas] The phrase "no pain, no gain"
applies to physics, as well as the gym.

Question number two.

What is the principle risk of a high
combined center of mass?

[Dallas off-screen]
Yup, it's torque.

Our overgrown toddler has significantly
raised the

center of mass of the toy car.

When the wheels hit a rut, he's in no
position to resist the resulting torque,

and loses any respect his
children may have had for him.

[Dallas] Right, the third
and final question.

How can stability be maintained when
multiple objects are coupled?

That's correct, by keeping the combined
center of mass over the base of support.

Arranging themselves in this, err,
unique way,

means that the combined
center of mass of

the riders and bike is still over the
rear wheel on the ground.

She hasn't got the best view in the
world, though. Class dismissed.

[Dallas] Tyson Edwards may not be a
name that most people are familiar with.

But that's a shame, because he's a true
gymnastic hero of mine,

holding the official record for the
highest standing backflip,

at four feet and 6.5 inches.

And Tyson is just one
of many top flippers.

Check out this guy.

[man] Whoa!

[Dallas off-screen] A backflip
from a sitting position.

But not all flippers
are born equal.

[man] Oh my God!

[man] Are you OK?

[Dallas] Okay, there seems to be,
clearly,

more to this flipping business
than we might have first thought.

As ever, the devil is in
the detail, and the science.

He pushes down to generate a reaction
force and produce upwards momentum.

The greater the upwards momentum, the
more airtime he'll have

to complete the flip.

He leans back to create torque and
angular momentum

before he leaves the ground.

Once airborne, the tighter he
tucks, the faster he'll spin.

That's the conservation
of angular momentum.

Quite a lot to remember, but we can
distill it down to jump up,

lean back and tuck in.

So, let's see how our
field researchers get on.

[Dallas off-screen]
Hmm, wedding reception.

Heavy meal, slice of cake,
and a few glasses of wine.

Arguably not the
best preparation.

There was some angular momentum, but
not much upwards momentum, so,

very little airtime.

And, he failed to tuck.

No more cake for you, sir.

That's it, style it out.

Ooh, nice bod.

Nice tan, if you like orange.

Terrible backflip.

Didn't tuck in enough,

and therefore didn't generate sufficient
angular velocity.

[gasps]

[Dallas off-screen] And, from all the
out of shape guys in the world.

That's karma, my friend.

[cheering]

[Dallas off-screen] Okay, could this be
the one where it all comes together?

[man] Ooh [bleep].

[Dallas off-screen] No.

That ditch could have given him extra
airtime,

but adding a twist takes him to
one side,

and into a mound
of earth instead.

[man] Ooh [bleep].

[Dallas off-screen]
Standing backflips?

[man] That's exactly
what I expected!

[Dallas off-screen] Not
as much fun as you'd think.

In 2013, a patent was filed for a
contraption

that would spawn a revolution,

a revolution in pain
and embarrassment.

That contraption was the hoverboard,

a particularly dangerous piece of
equipment.

[Dallas off-screen] Especially in the
hands of someone like him.

If ever the phrase "don't try this
yourself" was especially relevant,

it is now.

A little safer,
but don't show off.

You're the one
wearing a nappy.

And, with a low center of mass,
you've got a distinct advantage.

Ah, sitting down, clever.

Well, it was good in theory.

[Dallas] A hoverboard is one board with
two wheels each with their own motor,

and those motors are controlled by
these footplates.

You lean forwards to go straight and
then backwards to reverse.

Now, you'd imagine standing up on this
would be tricky, but sitting down

should be easier, right?

Well, no, it's not, and the answer to
why lies, as ever, in the science.

[Dallas off-screen] Sitting on a
hoverboard, the rider relies on shifting

his entire center of
mass to start moving.

Because that center of mass is closer to
the ground than if we were standing,

he must lean his body a lot to tilt the
footplates enough to work the motors.

Once that tilt takes the center of mass
away from the wheels,

the rider starts to rotate down, which
causes his bottom to further tilt the

footplates, accelerating
the board even more.

This is known as positive feedback, even
if it doesn't feel like it.

[Dallas] Fail to control your center of
mass, and you'll not only topple,

but you'll accelerate
at the same time.

It sounds like a lot of bother, but I'm
ready to be persuaded.

[screams]

[Dallas off-screen] I think the
jury's still out, to be honest.

With a lot of his bodyweight
behind the board,

his center of mass is behind the wheels,

causing rapid and
unexpected acceleration.

[screams]

[Dallas off-screen] Ooh,
a sideways hoverboard rider,

and a battered bookshelf.

Spinning on one wheel gives him a very
narrow base of support.

He leans too far, creating a rotation
that further increases the tilt of the

board, which causes
it to accelerate.

Another sideways rider.

And what's more, it seems
to be working, this time.

I feel like I jinx
it, sometimes.

It was all going so well, until he leant
to far, shifting his center of mass to

such an extent that he couldn't help
rotating further and accelerating more.

So, that's positive feedback.

Not the best-named
principle, in this instance.

The great Albert Einstein is thought to
have said,

"If we knew what it was we were

doing, it would not be
called research, would it?"

Well, if lack of knowledge is the
qualifying criterion for research,

we've got some Nobel
Prize winners on our team.

See ya.

[man] Oh!

[man] [bleep].