07x13 - Water Skipping, Trampolines and Hanging

[bunniefuu]

[Dallas] This is the
Science of Stupid.

[electricity crackling]

[alarms blaring]

Yes, this is the show where
we X-ray stupidity

to reveal the bare bones of science.

Watch as amateur daredevils

throw their bodies on the line

and test the limits of their
scientific understanding.

We'll explain what went wrong and why,

armed with a plethora of principles.

Maybe it's hydrodynamic drag,

the head spinning power
of centrifugal force,

or that troublesome
conservation of energy.

[man yelling]

Whatever it is,
don't try any of this yourself.

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

[electricity crackling]

In this show, we'll explore

the dangers of sudden changes
in velocity

whilst skiing down stairs,

how the inverse square law
might save your life,

and the torque of a trampoline spin.

But first this.

[glass shattering]

[electricity crackling]

[shattering]

[Dallas]
Crossing any body of water on four wheels

can be scientifically challenging enough,

but half those number of wheels

and it's like you've got the
whole of physics against you.

Even a pathetically
small amount of water

can cause quite a bit of trouble.

[bluegrass music]

But if you can't ride through water,

there's another option:

ride on it.

This is Luca Colombo setting
a world distance record

by hurtling across Italy's Lake Como

for 3.4 miles.

[upbeat rock music]

But not only is he a professional,

he's also riding a specially adapted bike

at 46 miles an hour,

so best not to have a go yourself.

Regardless of my advice,
it turns out

that attempting to drive
a motorbike across water

is a thing known as "water skipping."

It's also done on ATVs,
which is tricky enough,

but trying it on two wheels

hardly makes life any easier
or safer, and here's why.

[engine revving]

To avoid simply diving in,

our man's entry must be
as horizontal as possible.

Then to stay on top of the water,

he must have enough
velocity to generate lift.

By pushing water downwards
with his wheels,

he generates a lift force upwards.

Bike wheels are rounded,

so you can lean
when turning on solid ground.

But this gives them
a smaller contact area,

meaning they create less lift
on water than wider ATV wheels.

If he starts to sink,
hydrodynamic drag will rapidly

slow down the bike,
but his momentum means that

he will continue traveling forwards.

[splashing]

Just because it is scientifically possible
to do something,

it doesn't mean it's a good idea.

Boats with their hulls are designed to be
naturally buoyant and stable on the water,

motorbikes less so.

And if you have to go really fast
just to make it across a deep puddle,

well, any problem is gonna
hurt you that bit more,

i.e. don't ever do this.

He's ignored my advice...

[engine revving]

[upbeat rock music]

And my science.

[man, off-screen]
Oh, my God. He's wet.

[Dallas]
Luckily, with this shallow puddle,

his lack of velocity isn't a problem,

as he can still overcome
the water's hydrodynamic drag.

[man]
Oh!

[Dallas] Although I think some
further study is needed--

oh, and a helmet.

Again, he doesn't have enough velocity,

so he starts to sink.

But this time, his wheels
hit the soft mud of the bank.

Its resistance stops the bike,

but his momentum means he keeps going.

[man, off-screen]
You okay?

[Dallas]
I'm fine. Thanks for asking.

[engine revving]

That's more like it.

[woman gasps]

That's less like it.

She didn't have
the velocity to water-skip.

So when she hits a deeper bit of puddle,

the increased hydrodynamic
drag slows the bike

-and she gets an early bath...
-[laughter]

And not much sympathy.

[man, off-screen]
I'm sorry, I've got to keep filming.

You're fine.

[Dallas] [chuckles]
Oh, good for her.

Now, how about a touch more velocity?

Well, that's one way of doing it.

[upbeat rock music]

And that's one way of undoing it.

He certainly had enough velocity

and a nice horizontal entry,

until he let go of his bike.

[electricity crackling]

[exploding]

Randy, Miller, Rudolph, Barani.

No, not members of my now
sadly defunct boy band,

simply trampolining lingo
for moves a bit like these.

[rousing string music]

Gravity-defying rotations around either

your horizontal, vertical, or both axes.

But nailing them is harder than it looks.

♪ ♪

And when I say harder...

[boy grunts]

...I mean more painful.

Yep, bouncing into that spin
is certainly not for novices.

You're dealing with trajectory,
torque, angular momentum,

and possibly even
unwanted horizontal momentum.

It's a lot of science to get wrong,

unless you're this guy.

[dubstep music]

To launch, he applies
a downward and horizontal force

to the trampoline, generating torque,

giving him just enough
angular momentum

and minimal horizontal momentum.

Because once airborne,
his trajectory cannot be changed.

In the air, he tucks in,

increasing the speed of rotation.

On landing, he applies
enough counter torque

to dissipate his angular momentum

and stop rotating.

♪ ♪

Okay, first step,
getting plenty of angular momentum

but not horizontal momentum
right on launch.

Did you know, friends can actually
boost the effect of that bounce

by pushing down hard
in sync with the jumper?

[bombastic music]

Like this.

[boy groans]

Although I wouldn't recommend it.

[boy yelps]

With a little help from his, uh, friends,

he generates enough angular momentum

but also gained some
unexpected horizontal momentum,

misdirecting his trajectory.

And remember, once airborne,

that trajectory can no longer be altered.

He'll find that hard to forget.

[boy groans]

[laughter]

-Now, onto landing.
-[man, off-screen] Yep.

[Dallas]
It's about reducing that rotation

with a little counter torque.

-[boy groans]
-[man laughs]

But a little more than that.

[upbeat music]

On landing, he still has angular momentum

and doesn't apply
quite enough counter torque

to dissipate it,
and gains horizontal momentum.

-[boy groans]
-[man laughs]

Another go?

-I meant on the trampoline.
-[boy] Oh, my gosh.

[man, off-screen]
You okay?

[Dallas]
Now, what else did we learn?

[percussive music]

Ah, yes, tucking can increase
the speed of rotation.

[man]
Ah!

[Dallas]
And the likelihood of doing that.

When he lands, he doesn't
apply enough counter torque

to dissipate his angular momentum,

and gets a fair bit of
horizontal momentum instead.

Nice work.

[crashing]

[electricity crackling]

[engine revving]

[bluegrass music]

A fun team-building exercise.

But can you guess the science

this chap is about to demonstrate?

[shattering]

[electricity crackling]

[shattering]

[bluegrass music]

[Dallas] Did you guess the
science he's about to show us?

[woman, off-screen]
Go for it! Commit!

-[thuds]
-[scattered groans]

[Dallas]
That's right, it's friction.

And for a bonus point: base of support.

As he steps onto the ramp,
there's very little friction

between his foot and the surface.

Thanks to his momentum
from the run up

his foot continues sliding up the ramp.

This means his center of mass
is no longer over his base of support.

-[thuds]
-[scattered groans]

That's gotta hurt.

Maybe that's why they
call it an as*ault course.

[electricity crackling]

[creaking]

Millions of years ago,

our primate ancestors were
masters in the art of hanging,

as we swung about
in our arboreal environment.

But today, where do we stand
amongst our fellow animals

when it comes to this once innate skill?

For example, here we have a raccoon

using its physiological
knack for hanging to survive.

And here we have a human...

[man]
Oh!

[Dallas]
Falling from a tree.

So, how do monkeys
taunt gravity so in the treetops?

Why can sloths spend 90% of their time
hanging about in branches?

And why must cats
always ruin the curtains?

The answer, my learned viewers,

lies not only in the physics,
but in biology.

Animals with an arboreal lifestyle

tend to be better equipped
for hanging about.

Whilst we rely solely on our two hands,

some animals can spread
the force of their weight

across four limbs

with opposable thumbs
on hands and feet.

[dramatic electronic music]

New-world monkeys have
a muscular prehensile tail

which acts as a fifth limb and
can grip like an extra hand.

Some animals make up for
their lack of opposable thumbs

with hook-like claws,

whilst some non-tree dwellers

have powerful jaw muscles
to lock themselves in place.

♪ ♪

Hanging upside down
does have its, well, downside.

Sloths spend so long the wrong way up

that they need special internal adhesions

to anchor their guts to their lower ribs,

or their organs would squash their lungs,

which is clever.

[playful music]

But squirrel monkeys

are clever-er-er-er.

It's hard to believe we share
over 90% of our genes

with our agile primate cousins.

[man grunts]

Especially when you see that.

We don't have gripping feet
or a tail for balance.

[man grunts]

Maybe he was praying for opposable toes?

Speckles here doesn't
have opposable thumbs,

but she can use
her grapple hook-like claws

to dig in...

[crashing]

-And break that lovely lamp thing.
-[meowing]

Cats curved claws
can only help them grip

if the object they dig into
is well-anchored,

-otherwise they're of no help at all.
-[meowing]

That's over 200 pounds of bite force

supporting Derek's body weight.

In fact, jaw muscles
make up a huge percentage

of a dog's head, leaving very
little space for the brain.

[girl, off-screen]
Let go!

[Dallas]
So he might be there for a while.

-[woman, off-screen] Let go.
-[dog whines]

[Dallas]
But you don't have to be big headed,

just proportionally so.

Harold's relatively powerful jaw

means he can support his
featherweight body--

his featherweight and squishy body.

To be fair,
if all you ate were sunflower seeds,

you would have big jaws
and a tiny body, too.

[clattering]

[sizzling]

[bubbling]

Right, it's time to get
your lab coats from the locker

and get ready for today's science lesson,

the part of the show where we place

a particular principle
under the microscope.

Can you guess what it is
from the following?

An unwisely positioned cannon...

[exploding]

A delightful birthday surprise...

-[pop]
-[all shout]

And a high-pressured basketball game.

-[boy] Listen to it.
-[loud pop]

-[boy screams]
-[boy laughs]

[Dallas] The connection is
the inverse square law.

That's a geometric law
that describes how

the intensity of energy,

such as heat, light,
electrostatic, and sound

is inversely proportional to the square
of the distance from the source.

That is, it gets drastically
less intense over distance.

Here's an analogy courtesy of
a little scientific graffiti.

[rousing upbeat music]

Imagine this nozzle as the point source

and the spray paint as the energy.

As you increase the distance
from the point source,

the area the spray covers increases,

and therefore, the intensity decreases.

Triple the distance and
you have nine times the area

but a ninth of the intensity.

Now, imagine this spray
as a sphere of energy

spreading out from the point source,

and this is how
the inverse square law works.

Okay, time for a test.

Question one: How does
distance from a point source

affect the intensity of energy?

[dainty classical music]

Bella's dad is attempting

an entertaining way
to show her the answer.

[man, off-screen]
Bella. Hey, Bella.

[Dallas] She's not interested,
but top marks for effort.

[man, off-screen]
Bella.

[Dallas] As Dad brings
the statically charged balloon closer,

the electric field is powerful enough

to make her hair stand on end.

When he moves it further away,

the sphere of energy
is larger and less intense.

[man, off-screen]
Bella, you want a cr*cker?

[Bella]
Yeah.

[Dallas] At least Dad
learnt a valuable lesson.

[man, off-screen]
You want pizza?

[Bella]
Pizza!

[Dallas]
A child's attention span

is directly proportional to
the amount of food on offer.

Question number two:

How can the inverse square law save lives?

These firefighters
are going to enlighten us.

[sirens wailing]

[flames whoosh]

Or rather, the warehouse is.

Because it's full of magnesium,

which burns with a temperature
of over 4,000 Fahrenheit,

if the firefighters were
close to the point source,

they'd be burnt.

But even a distance of 30 feet or so

is enough for the intensity of
heat to dramatically diminish.

[flames whoosh]

So, they're okay,
thanks to inverse square law.

Third and final question:

How does the inverse square law
affect sound waves?

This bass lover is
using an in-car sound system

to demonstrate the answer...

-[dubstep music]
-[man screaming]

At the expense of a 24-hour migraine.

[laughter]

[man, off-screen]
Couldn't ride the bull!

[Dallas]
It's actually a van, but anyhow,

bass bins are a point source
of sound energy.

So the inverse square law applies,

and the sound waves get less intense

as he escapes to a safe distance.

[man, off-screen]
Couldn't ride the bull!

[Dallas]
Alas, there's no safe distance

from the ensuing ridicule.

Class dismissed.

[laughter]

[electricity crackling]

[clanking]

[Dallas]
Close your eyes

and picture for a moment
the perfect ski slope.

Now, you may be thinking
about the snow-blanketed slopes

of Chamonix,
Val d'Isère, St. Moritz.

What you're less likely to be thinking...

is a set of concrete steps.

[man yells, then groans]

[woman laughing]

Or worse still, the household staircase.

-[man yells]
-[clattering]

He's not going to be too popular

with Mum and Dad when they get home.

And rightly so,
because skiing down stairs

is a particularly dangerous activity.

If you don't damage your mum's
treasured side table,

you will damage
important parts of your body.

And here is the science to explain why.

[electronic music]

Thanks to the steep angle

and reduced friction
offered by smooth skis,

our man will accelerate dangerously fast.

He may find this fun, until he reaches

a flat section where the skis
will be forced to rotate about 30 degrees,

causing a rapid deceleration
in his vertical velocity

but barely any change
in his horizontal velocity

and also a turning effect.

If he can't counteract this
with his upper body

to keep his center of mass
over his base of support,

he's in big trouble.

♪ ♪

This is, without a doubt,
an appalling idea,

aside from the aforementioned
scientific complexity.

Bear in mind that on the ski slope,

you're generally surrounded
by soft, forgiving snow.

On the stairs, you're more likely
surrounded by hard,

unforgiving materials,

like metal, concrete, and wood.

As our friend,
Dave, is about to find out.

[man, off-screen] Dave's got skis on,
and he's going down the stairs.

[Dallas]
But he's all set...

[upbeat rock music]

[Dave groans]

To prove my point.

Dave accelerates to around 15 miles
an hour by the bottom,

where upon his skis rotate
by about 30 degrees,

but he doesn't counter
the rotation with his body

and just, kind of... rolls with it.

[woman, off-screen]
He's fine. He's fine.

[Dallas]
He really doesn't look it to me.

San Francisco's famous mosaic stairs.

Again, not an official ski slope...

♪ ♪

Or a particularly safe one.

[man, off-screen] [chuckling]
Oh, my God.

[Dallas] This chap does
manage to counter the rotation

on the first few flights at least,

but builds up so much velocity
that he loses balance,

catches a ski in the rail,

and learns that concrete
is far less effective

at reducing impact force than snow.

[man, off-screen]
Let's get out of here.

[Dallas] Yeah, good idea.
And yet further proof

as to why skiing down stairs
is really quite dangerous.

[upbeat music]

Please don't try this yourself.

[electricity crackling]

Even top golfers need
somewhere to hone their skills,

and the driving range
is just the place

to develop that powerful swing.

[upbeat music]

-Or just show off.
-[man] Oh, my gosh.

[man]
That was cool.

[Dallas]
But most people at driving ranges

aren't top golfers.

[man yelps, then laughs]

They're more like him.

So, as they say,

practice and, of course,
science makes perfect.

Mike Austin holds the record
for the longest drive in play

at 515 yards, over a quarter of a mile.

To get anywhere near that distance,

you'll need to
understand centripetal force,

inertia, and parabolic trajectories.

[dubstep music]

As he swings the club,

it experiences a large centripetal force,

which keeps it moving in a circle.

However, it tries to continue
in a straight line,

as the head has inertia,
which means

it resists the centripetal force.

He must then hit the ball
just below center

for a good parabolic trajectory
to cover a long distance.

♪ ♪

There's a lot to it,

so we thought it would be useful

to send our researchers into the field

for further investigation.

Researcher number one
is looking for power.

[rock music]

[shattering]

-And he's found it.
-[woman laughing]

As he swings, the club experiences

a large centripetal force.

Inertia tries to resist this force

and send the club in a straight line.

And thanks to his weak grip,
it succeeds.

[woman laughing]

Researcher number two

has positioned a camera
to assess his swing.

[man] Get this on video,
just in case it goes wrong.

[upbeat rock music]

[Dallas]
Scientific perfection.

[man]
I'm going for a second.

[Dallas]
How's he gonna top the first one?

-[plastic clacking]
-Oh, like that.

[man]
Ooh!

[Dallas] His club connects
with the ball too high up,

which produces too little
vertical momentum,

sending the ball too low.

-[plastic clacking]
-[man] Ooh!

[Dallas]
Maybe hit a little lower next time.

-[thwacks]
-[groans]

Yeah, but not that low.

[laughter]

Connect too low beneath the sweet spot

and too much vertical momentum

will mean that ball will find
another sweet spot...

Sweet for your mates, anyway.

[laughter]

[glass shattering]

[electricity crackling]

[shattering]

The science fiction writer
and biochemist

Isaac Asimov reportedly once said,

"Intelligence is an accident of evolution

and not necessarily an advantage,"

which would go some way
to explaining this lot.

-[pop]
-[all shout]

[lively fiddle music]

-[man groans]
-[man] Oh!

♪ ♪

[boy yelps]

[man grunts]

♪ ♪

[man cheering]

[tires screech]

♪ ♪

[clattering]

-[boy] Listen to it.
-[loud pop]

-[boy screams]
-[boy laughs]

-[man] Come on!
-[woman] Oh!

♪ ♪

[exploding]