07x09 - Moguls, Logs and Starting Gates

[bunniefuu]

[Dallas Campbell]
This is the Science of Stupid.

[klaxon blaring]

Yes, this is the show
that blends science with stupidity.

Watch as amateur stuntmen
and stuntwomen test the boundaries

of nature and fall foul of physics.

We'll explore what went wrong and why.

With the help of some wincing,
juicing principles.

Such as inverted pendulums,

flexural strength

and everyone's favorite...
impact force.

So look out.

It's the Science of Stupid.

[electricity crackling]

In this episode, we'll be learning
some surprising science

on pressure.

Enlightening you
on electric circuits.

[screams]

And we'll be exploring
how to absorb impact while skiing.

Spoiler alert, that's not it.
But first this.

[glass shatters]

[electricity crackling]

[shatters]

We regularly feature some
astounding bike skills on this show.

But today we are looking
at where it all begins.

And if you're into racing
that's the starting gate.

A good start is essential
if you want to get ahead of the rest.

Oh dear. Well, it could be worse.

[announcer]
Here we go big boys!

Main event. Let's do it!

[Dallas]
Yeah! That's done it alright.

[announcer]
Everybody's on the ground.

[Dallas]
Well, not everyone. Look.

[laughter]

BMX start gates help you
accelerate away sooner

because you can push your wheel
against the gate

with your feet already on the pedals.

And then it's on your marks,
get set, science.

The rider starts in a standing
position with his feet on the pedals.

As the gate drops, he throws his body
towards the handle bars

to generate linear momentum.

As he does this, he drives
his feet down on the pedals,

generating as much torque
as possible on the back wheel

and maximizing acceleration.

If the gate drops fast enough,

the rider will be off
in a fraction of a second.

Alas but for a spot of oil
and a little elbow grease.

Gates don't always work quite
so smoothly as you'd like.

But if they do, it's simple.

Throw your weight forwards,
generate torque and you're off.

For this lot, it's child's play.

Unless that happens.

The momentum generated by the riders

throwing their bodies forward
does generate torque.

But sadly it's around the front wheel.

It's not a good start.

Right, let's try again.

[announcer]
Riders ready?

Watch the gate.

[Dallas]
They are ready!

But that gate wasn't.

Here the gate drops too slowly.

So when the riders drive
their feet down onto the pedals

the torque they generate
does maximize acceleration.

But not in the way they'd planned.

Motocross bikes also use start gates.

And also do that.

Getting your wheel stuck in the gate
won't do much for your acceleration.

Ah, finally he's off.
But can he catch up with the rest?

Not really his day, is it?

[electricity crackling]

Your smart phone is millions of times
more powerful

than the computers that first
sent man to the moon.

Nevertheless, you couldn't fit
all that power in your pocket

if not for the lithium ion battery.

But beware. They aren't always
as safe as you'd hope.

[screams]

I'm not sure I still want
to fit it in my pocket.

And it's not just hand-held gadgets
that use lithium ion batteries.

[screams]

Some electric scooters use them.

And they're a lot bigger than phones.

There are now over two billion
smart phone users worldwide.

Most of them probably carrying
one of these seemingly innocent

lithium ion batteries in their pockets.

But as you've just seen,
these batteries can have the potential

to be rather expl*sive. And here's why.

Lithium ion battery cells contain
two oppositely charged electrodes

kept apart by a separator.

All covered in a conductive chemical
called an electrolyte.

Turn on the phone,
and lithium ions flow

from one electrode to another
through the separator

causing current to flow in the circuit
powering the device.

If the separator is damaged,
this can cause a short circuit.

Where excess current can flow
directly between the electrodes

generating heat, fire
and in some powerful devices,

if you're really unlucky, an expl*si*n.

I should probably point out
that fires and explosions

caused by lithium ion
batteries are pretty rare.

But reading the instructions
carefully is always wise.

[screams]

Maybe he missed the bit about
keeping loose change

in the same pocket as
your vape batteries.

Whatever the cause,
one thing's for sure,

his battery shorted leading
to an overload of current.

[screams]

And a pair of hot pants.

Very hot pants.

He was okay though. Eventually.

This guy also narrowly escaped
a trip to hospital.

[man off-screen]
There you go.

[Dallas]
But what happened?

[man off-screen]
The board just burned up.

[Dallas]
And when did this happen?

[man off-screen]
My board just caught on fire today.

[Dallas] Hmm, it looks like
a good bit of kit. Did it cost much?

[man off-screen]
Six hundred dollars down the drain.

[Dallas]
So, what are you going to do?

[man off-screen]
We better call the fire people.

[Dallas] Well, I suspect if you check
the battery you'd find it's defective.

And a short circuit
has caused excess current.

And as the battery in a hover board is
much larger than the one in a phone...

so is the expl*si*n.

And what learnings would you pass
on to other hover boarders?

[man off-screen] People if you got
one of these in your house...

get it out.

[Dallas]
Very wise.

Now, this looks
a bit more scientific.

An engineer checking
a smartphone for faults.

[screams]

I think he's found one.

It looks like he applies
pressure to the battery,

which could have
damaged the separator.

[screams]

Causing a short circuit
and indoor fireworks.

Please, if you do find your
battery device erupting into flames...

leave it well alone.

[electricity crackling]

[clattering]

Ah, piñata!

A fun game for children.

And for adults, an outlet
for repressed aggression.

But what science will it reveal?

[laughter]

[glass shattering]

[electricity crackling]

[Dallas]
Did you guess what science

will be demonstrated by this lady's
unrelenting hunger for sweets?

[screams]

Yes, it's Newton's Second Law of Motion.

Almost 350 years earlier,
Isaac Newton stated--

[woman off-screen]
Don't throw the bat.

[Dallas]
That whenever an object,

i.e. the bat, is subject
to an unbalanced force,

i.e. the resultant force from
the piñata and her swing.

It will experience an acceleration.

Changing its speed, direction
or in this case...both.

[screaming]

He's a clever chap that Newton.

[electricity crackling]

[engine revving]

Ah, the joys of skiing.
Smooth snow blanketed slopes.

A magical experience scuppered
only by the occasional hidden bumps.

Not to mention the obvious ones.

[laughter]

But some people actively seek out bumps.

This is mogul skiing.

A timed freestyle competition
where skiers race

against the clock on a
steep course

absolutely littered with bumps.

Like...

that one.

Oops.

Sorry, too late.

Mogul. It comes from
the Bavarian word for hillock.

But be warned. Those moguls
can be pretty darn dodgy

if you're hurtling downhill
at bone breaking speeds.

And the secret to survival is science...
and rhythm.

As our skier travels
around the peak of a mogul,

he bends his legs to absorb as much
as the impact force as possible.

He keeps the height of his center of
mass as consistent as possible

and over his base of support
for stability.

In the troughs, he extends his legs
like springs.

Pushing the skis into the snow
to create a reaction force

that allows him to turn.

He must do all of this in sync
with every mogul and trough, or else...

So, to sum up, it's all about
keeping your balance

whilst rhythmically soaking up
those bumps and dips.

Personally I'd stick to
the dips you can pop a breadstick into.

But the world of mogul skiing
is full of braver souls than me.

This guy's got rhythm.

[man off-screen]
Oh...

[Dallas]
And now he's got the blues.

Keeping center of mass
at a relatively consistent height here.

And legs rhythmically absorbing impact
until about here.

Then his face absorbed
the impact.

[screaming]

Then his head.

And then his bottom.

[screaming continues]

This guy looks like a pro.

Just not at this.

As he hit the bump,
he was leaning too far to one side.

And about here, was in no position
to absorb any impact with his legs.

But beware in mogul skiing,
not all bumps are equal.

Especially when they're ramps.

[screams]

[bubbling]

Right, it's time
to pick up a pencil,

nab a notebook and get ready
for today's science lesson.

The exciting part of the show
where we illuminate the ignorant

by scrutinizing the science
behind one particular principle.

Can you guess what it is
from the following?

This very practical family car.

[screaming]

[man]
Woo.

[Dallas]
The joys of jet packing.

[screams]

And this water pipe rodeo.

[laughter]

Yes, that is a
fully grown man.

If you said Pascal's law,
you must be a warped genius

with an uncanny knack of spotting
unlikely connections.

So, well done.

But you may not know
how it works.

So here's the low down.

Courtesy of a ball,
a balloon and a lot of water.

When this water-filled ball
is squeezed,

the fluid escapes with even pressure
from the two holes.

According to Pascal's law,

when there's an increase in pressure
at any point in a confined fluid,

there's an equal increase at every
other point in the container.

As this balloon is filled with water,
the pressure builds

and is transmitted evenly around it.

So it will break at its weakest point.

Regardless of where
the pressure is applied.

Thanks to Pascal's law,
hydraulic machines

can transmit and even multiply forces
even to the end of long arms,

helping them
lift heavy loads.

Okay, quiz time.

As pressure is transmitted
equally in a confined fluid,

where will its
container break?

It's dress down day
at the fire academy

and these recruits have offered to
help us with the answer.

Which is...

Ah yes, the weakest point.

The pressure from the pumped
water is relatively constant

along the length of the hose.

So breaks at its weakest point.

Thanks for the answer guys,
but that is rather wasteful.

Right, time for question two.

If a fluid is not completely
confined,

can pressure
still be transmitted along it?

[man off-screen]
There you go.

[exclaims]

[laughter]

[Dallas]
Yes.

Not all of the pressure,
but still quite a bit.

[laughter]

There must be easier ways
to earn your pocket money.

[giggling]

And finally, question three.

What do hydraulic systems
use Pascal's law to do?

[beeping]

Well in this case, it's lifting
a load of heavy palettes.

He studied Pascal's law
and knows that a hydraulic system

can transmit and multiply forces.

But he didn't pay attention
to the seminar on balance.

Class dismissed.

[glass shatters]

[electricity crackling]

[shatters]

With all the other
throwable objects on offer:

ba*ls, paper airplanes, darts;

it does surprise me how much people
like to throw other people.

Although to be fair, without
that, you wouldn't have this.

Dance and acrobatics would
be far less entertaining.

Weddings wouldn't be nearly as much fun.

-[glass shattering]
-[crowd gasping]

And clearing up after a party
would be trickier.

[cheering]

Although considerably safer.

Please don't try that yourself.

Unless you're a trained gymnast
or other expert person thrower,

throwing another human
is a terrible and dangerous idea.

But for the sake
of scientific knowledge alone,

here's how the experts do it.

Our gymnast bends
then extends his arms.

Applying a force
through her center of mass.

Giving her just enough
vertical velocity.

Without giving her too much
angular momentum,

and causing her to flip.

By applying an upward force
as she descends,

he decelerates her significantly.

Safely reducing the impact force.

Some serious science there.

So now you can see why only an expert
should ever attempt this.

I've no proof, but Dad
may not be an expert.

Now I have proof.

No troublesome angular momentum,
but her near horizontal angle

combined with the sloping bank,
meant a muddy treat unsuitable for kids.

[man]
Oh, are you okay, Pup?

[girl]
Ow.

[Dallas] These researchers
are training for a record attempt.

[laughter]

How many ears can
they kick in one day?

Good long launch.

But since the thrower
wanted to duck under,

the one being thrown would have needed
a lot more vertical velocity.

[laughter]

But at least she got
a sympathy laugh from her friends.

Will it be easier throwing
someone will less mass?

Yes, but that's not necessarily
a good thing.

[laughter]

Dad imparts too much vertical velocity.

She hits the screen above and is quickly
decelerated by the impact force.

Luckily for Dad, his daughter...
and his wife...

[woman off-screen]
I'm glad that wasn't me.

[Dallas]
Have a sense of humor.

[electricity crackling]

For our next activity,
let me take you on a trip.

Back through the ages, to a time
when lumberjacks

would hop skillfully across floating
logs to shepherd them down river.

It's hard to believe
that grueling work

is now the inspiration
for a popular sport.

Especially when you see it.

[announcer] I hope you folks
are having a great time out there,

because I tell you, it is unbelievably
exciting to here right in front.

[Dallas]
Yes, this is log rolling.

One log, two competitors
and a mission to spin your opposition...

[screaming]

into very chilly water.

It's come a long way since the old days.

But arguably not in the right direction.

I've always found it tricky enough
balancing on a log on land.

But what with water's
relatively low resistance to movement,

that log is gonna be
shifting around like crazy.

And keeping on top of it,
is a complicated science.

Our man must keep his center of gravity
over the center of buoyancy of the log,

which is in the middle
of its submerged volume.

Any deviation results
in a turning effect on the log.

So to stay balanced,
our man must move

in the opposite direction
to the rotation of the log,

responding to abrupt changes
in angular velocity.

Tricky enough. But if the log
has insufficient buoyancy,

hydrodynamic drag can
slow his feet, leading to...

So to be an elite log roller,
one must first develop

an uncommon sense of balance
and super human agility.

These trainees are practicing
with a land based device.

And it's just as well.
Because the novice on the left

can't keep up with even
the slightest burst of angular velocity.

[man] Oh.

[Dallas]
Leaving the winner to savor his victory.

I mean, what could go wrong now?

[screams]

[laughter]

Well, there's always that, I suppose.

All that angular velocity
means the barrel experiences

a large centrifugal force
pulling it apart.

[screams]

[laughter]

I'm not sure we're ready
for the water yet.

But let's go anyway.

Low resistance to movement
means the log spins very easily.

So it's baby steps technique here.

It didn't work.

Her baby steps couldn't keep up
with the angular velocity

generated by her competitor.

She turns sideways and her foot
slid her center of gravity.

Outside the center of buoyancy.

But what if that buoyancy
is already compromised?

Greg and Jamie
here are heavier,

so their log is a bit sinky.

[man off-screen] Let the log come up,
let the log come up.

[woman off-screen]
What's our fall count?

[Dallas]
So, will the less sinky Greg win?

[man off-screen]
Let's go!

[Dallas]
No. Because as my nan would say,

"Always bet on a shirtless man
in a woolly hat."

The lack of buoyancy meant
more drag on their feet.

But Jamie powered through,
whilst Greg's center of gravity

fell outside the center of buoyancy.

At least the water looks warm.

[glass shatters]

[electricity crackling]

[shatters]

And that gentle viewers is your lot.

Remember please do not
attempt to recreate

any of the dangerous stunts
you've just seen.

And to quote the great Nobel
Prize-winning physicist Heinrich Rohrer,

"Science means constantly
walking a tightrope

between blind
faith and curiosity".

But it's worth remembering
I've never seen anyone

walking a tight rope
on this show without getting hurt.

[screams]

[screams]

[screams]

[screams]

[announcer]
Oh no!

[screams]