07x14 - Tractor Pulling, Snow Biking and Monowheels

[bunniefuu]

[Dallas]
This is the Science of Stupid.

[klaxon blaring]

Yes, this is the show
where the lab coats of science

meet the straitjackets of stupidity.

[man groans]

[Dallas]
Watch and learn as everyday people

attempt acts of jaw-dropping idiocy

with eye-watering results.

We'll clarify what went wrong,

and why,

with the help of scientific principles

such as the transfer of momentum...

inertia...

[boy groans]

[Dallas]
And equal and opposite forces.

So strap in...

[motor whirring]

-And prepare for pain.
-[woman screams]

Watch out,
it's the Science of Stupid.

[glass shatters]

[electricity crackles]

[shattering]

[Dallas]
In this episode,

we'll be looking at how
retraining your nervous system

-may help with flexibility...
-Aah!

[clattering]

[Dallas]
The problems with low rolling resistance

when rollerblading on ramps.

And how the surface tension of water

affects the angle of repose.

[upbeat country music]

But first, this.

[glass shatters]

[electricity crackles]

Formula One, the epitome
of auto racing cool.

I mean, who but the coolest of heads

could handle such powerful engines,

slamming them from naught
to 60 miles an hour

in under three seconds?

Which got me thinking,
if you invented a motorsport

which had even more powerful engines,

would it be even cooler?

It turns out, yes, it would.

Formula One cars have
almost 1,000 horsepower.

Some of these souped-up super tractors

produce ten times that amount.

These are the race horses
of the agricultural world.

Extremely powerful--

[rock music]

Yet surprisingly delicate.

♪ ♪

Tractor pulling is a sport that involves

towing a weight transfer sled
as far as possible

whilst the sled gets effectively
heavier and heavier.

The tractor that can pull it
the furthest wins.

It sounds simple,
but pulling such heavy loads

requires a huge amount of power.

To harness that power successfully

and avoid accidents requires
an understanding of the physics.

[dramatic music]

The sled has wheels at the back

and a pan at the front.

As the tractor pulls it,
a mass shifts forwards

so that more of its weight
is over the pan,

increasing the friction,

making it increasingly harder to pull.

This leads to a large reaction torque

on the body of the tractor,
so over-accelerating here

can lift the front
of the tractor off the ground.

The tractor's engine assembly
must also be strong enough

to handle the power output required.

If not, the engine,
and a few other important bits,

could fail.

[metal clatters]

Huh.

Engine assembly failures,

torque, effective weight.

It's a lot more complicated than it looks.

The motto of the National
Tractor Pullers Association

used to be "pull on Sunday,
plough on Monday."

[man, off-screen]
Oh!

[Dallas] Looks like this guy
is letting his fields

lie fallow this year.

As the mass on the sled comes forward,

it increases the effective
weight he needs to pull.

The huge amount of torque required

lifts the front off the floor.

And when the driver
takes his foot of the gas to stop this,

the front falls with
enough impact force...

[crowd clamoring]

To lose those things.
What are they called again?

[child, off-screen]
Wheels!

[Dallas]
That's it.

This sport is said to have originated

from the horse-pulling
competitions farmers held

to see who had the strongest horses.

In fact, it wasn't until the late '20s
that they started competing with tractors.

[metal clatters]

Should have stuck with the horse.

[dramatic music]

Here, the modified engine
is forcing the flywheel

to spin far faster
than it was designed for,

and centrifugal force
causes it to break apart...

[metal clatters]

And cut the tractor in half.

Oh, that's a tricky insurance claim.

[upbeat country music]

To counter the torque
that can lift the front end,

tractor-pullers often
add weights to their vehicles,

which is just one of a number of reasons

why you want to keep your engine on board.

[crowd clamoring]

[electricity crackles]

[metal creaks]

As you can tell,
I joined a gym recently,

as I wanted to learn how to do the splits.

The instructor asked me
how flexible I was.

"Well, I can't really do Wednesdays."

[rock music]

Our bodies owe their flexibility

to a range of joints
connecting our rigid bones,

restricted by the elastic
limits of our tendons,

ligaments and muscles.

Stretching can improve
flexibility and blood flow

throughout the body, including the brain,

so she probably should
have seen that coming.

In essence, the human body
is very much a compromise

between rigidity,
as provided by the skeleton,

and flexibility, as provided

by a lot of the soft,
springy bits around it,

and a variety of joints.

Cue science.

[dramatic music]

Hinge joints,
such as the knees and elbows,

allow rotation in a single plane.

but ball and socket joints,

such as the shoulders and hips,

allow rotation in multiple directions,

giving a greater range of motion.

♪ ♪

Muscles has viscoelastic properties,

which allow them to relax
and elongate as we stretch.

Thankfully, pain receptors
fire signals to warn us

when our muscles are being stretched

beyond their capacity.

There's a lot of contention
around stretching

and how it affects
your muscles and flexibility.

Some even suggest that stretching

may train your body to ignore
these helpful pain signals.

But whatever the case,

it's always wise to know your limits.

Ball and socket joints
between femur and pelvis

are highly flexible.

And thanks to her trained muscles,

she doesn't appear to be in pain.

[woman]
Aah!

[Dallas]
Until then.

[laughs]

[woman]
That hurt a lot!

[Dallas]
When you stretch, your muscles relax

and can elongate to their limit.

[yelps]

[Dallas] Which does nothing
to improve your balance.

[bright music]

In this pose, her muscles are completely
stretched to their limits,

and incredibly taut.

So when she wobbles slightly,

her muscles are unable to stretch
to compensate and catch her.

[splashing]

Luckily, someone put that pool there,

so she didn't hurt herself.

[exhales]

[Dallas]
Did you know that women have evolved

with a more flexible pelvis than men?

[dramatic music]

[man, off-screen]
Daaaamn!

[Dallas]
Although, he may now be an exception.

The ball and socket joints
between his femur and pelvis

allow him more than enough
motion to do the splits.

It's just his tendons and
muscles that might not agree.

[man, off-screen]
Daaaamn!

[Dallas] That's six months
of yoga in half a second.

-[thudding]
-[grunts]

[electricity crackles]

[metal creaks]

[crumbling]

[Dallas] BMX in a bowl,
it's a dangerous sport

best left to the professionals,

but what science is he about to show us?

[upbeat music]

[glass shatters]

[electricity crackling]

[shattering]

[Dallas]
Did you guess what scientific principle

this BMX'er was about to demonstrate?

[lively fiddle music]

Yes, it's all to do with trajectories.

[boy 1, off-screen]
What the heck?

[Dallas] I think his legs
are stuck between those bars.

[boy 2, off-screen]
Oh my gosh!

[Dallas]
Leaving the bowl,

he has enough vertical velocity
to clear the fence,

but not enough horizontal velocity.

So his trajectory
intersects with the fence,

leaving him presumably
pondering on how lucky he is.

[boy 1, off-screen]
What the heck?

[Dallas]
Please never try that yourself.

[boy 1, off-screen]
That was insane!

[Dallas]
My thoughts exactly.

[electricity crackles]

[metal creaks]

[crashing]

Back in 2010, my personal hero,
Shinji Kazama,

became the first person
to reach both the North

and South Poles on a motorbike.

He's also ridden one up
Mount Kilimanjaro,

Mount Fuji, and much
of the way up Everest,

which prompts two questions.

One: What is Shinji running away from?

And two: How good a vehicle
is a motorbike on snow?

Well, it's this second question

that we're going to attempt
to answer today.

My initial research
suggests they aren't ideal,

but science is all about being
willing to be proved wrong.

[motorcyclist yells]

Okay, not a promising start,

but maybe we'll do better
after we've learnt about

the science of motorbikes on snow.

[dramatic music]

Being relatively heavy
with two small contact points,

motorbikes exert a high ground pressure

and sink into thick, soft snow.

This causes a huge increase
in resistance on the wheels,

slowing them down dramatically--

[thuds]

Unlike our man.

Compacted snow has its own issues.

It can be icy,
and so offer very little friction,

meaning that when you turn,

the wheels can slide out very easily.

[tires screech]

[thuds]

It does sound like
biking on snow is a poor idea,

but if you have to do it,
then some people suggested

driving slowly and
using your feet as stabilizers.

[upbeat music]

Or that shortcut...

♪ ♪

...may not turn out to be
the time-saver you hoped for.

[motorcyclist laughs]

Skinny wheels means
high ground pressure.

Fine on stones, but they cut
right through snow,

resulting in a lot of resistance...

[bluegrass music]

And giving him an unexpected opportunity

to make snow angels.

But remember, that compacted snow

can also be a problem for bikes,
so this...

[clattering]

...is a terrible idea.

[man, off-screen]
Not again!

[Dallas]
Again?

The snow here is old and compact,

which is good,
as the wheels don't sink into it.

But while ground pressure isn't an issue,

[clattering]

the pressure of the ground may well be.

Now, did you hurt yourself?

[man]
Ah, just my knees.

[Dallas] Well, I'd recommend
someone looks at your head, too.

[groans]

Ooh, a specially adapted bike,
a sensible speed, and no jumps.

But have we remembered
that snow's low friction affects braking?

[motor hums]

-[metal clangs]
-[man grunts]

Absolutely not.

He's replaced his front wheel
with a large ski blade,

so he's got much more
contact area with the snow,

so he won't sink into it.

But that ski only works

because the snow's got so little friction,

which makes stopping quickly...

-[metal clangs]
-[man grunts]

...a bit of an issue.

Luckily for him, he's crashed
into the world's nicest man.

[man]
Sorry about that!

[metal clatters]

[bubbling, sizzling]

[Dallas] As the brightest amongst you
will no doubt have deduced

from my dapper attire,
we're at the science lesson.

That's the part of the show
where we focus on

one particular scientific principle.

So, who can tell me

what is being demonstrated
by the following?

This clever roof clearer...

[man laughing]

This motocross scrambler...

Oh, how annoying.

[man laughing]

-[man, off-screen] Is it safe?
-[woman, off-screen] Yeah, totally!

[Dallas]
And this...

[woman, off-screen] Just go fast,
it's better if you go fast.

[Dallas]
Suggestible bank runner.

[woman, off-screen]
[laughs] Oh, my God.

[Dallas] Yes, obviously,
it's the angle of repose.

The steepest angle,
the slope of a granular material

can form without sliding.

No, didn't get it?
Okay, well here's the science.

When you pour wheat grain into a pile,

the slope it creates
rests at the angle of repose.

[upbeat music]

This is the angle formed
by granular materials

when the force of gravity

pulling each individual
grain downwards

and the friction holding
them together are in balance.

The angle of repose is dependent on

the shape and size of the grains.

This gravel is larger and more angular
than the wheat grain,

so it has a steeper angle of repose

♪ ♪

And as anyone who's ever made
a sandcastle will tell you,

the dryness of the grains matters.

Damp sand sticks together
better than dry sand

due to water's high surface tension.

Got all that? Good.

Let's start with an easy one.
What is the angle of repose?

Maybe these guys can show us.

[boy]
I'm running down the slope.

[Dallas]
Yes, I can see that.

[boy]
Too fast, too fast.

[Dallas]
Thanks, lads. [laughs]

These junior scientists have fallen

because of the very steep
angle of repose,

the maximum angle
naturally formed by the sand

when gravity and friction are in balance.

It's nice to know physics.

♪ ♪

[boy]
Too fast, too fast.

[Dallas]
But even better to know your limits.

Okay, question two:
What do you think happens

when a material at the
angle of repose is disturbed?

[rock music]

This guy has managed
to combine two of his hobbies.

No, not skiing and paragliding.

Science and destruction.

♪ ♪

The snow on this slope is
right at the angle of repose,

so it only takes
a small amount of extra mass

to trigger a collapse...

♪ ♪

And the whole thing
becomes a chain reaction,

or, what we call an avalanche.

Fascinating science, potentially deadly.

Okay, last question.

What other factor
can affect angle of repose?

Did you say moisture?
Well done if you did.

[observers clamoring]

You see, the first guy does quite well.

I mean, that slope is almost vertical,

probably thanks to the dirt being moist.

So its particles have more
cohesion and hold together,

until his back wheels disturb them

right in front of the other chap.

[observers clamoring]

Oh, he'll--
he'll have enjoyed that.

[bright music]

Class dismissed.

[glass shatters]

[electricity crackles]

[shattering]

[Dallas]
Ah, the '90s. What a decade.

Dial-up Internet,

eyebrow piercings, and inline skating.

I spent almost every waking minute
trying to perfect my ramp skills,

and I wasn't alone.

By the year 2000,


That is 5 million more
than playing baseball.

Why so very popular?

Well, throw in a ramp,

and you can pull off some sick tricks.

[upbeat music]

[skater grunts]

Sick in the more traditional sense.

And that, ladies and gentlemen,
is a perfect example

of why you should have
the correct safety gear on

whenever you're skating.

You know, like a helmet.

Those spinning wheels
can roll you into a lot of trouble fast,

and when a ramp's involved, even faster,

thanks, of course, to pesky old science.

The rolling resistance between
the inline skate wheels

and the surface of the ramp
is so low

that he'll accelerate very quickly.

So has to stay almost
perpendicular to the ramp

to keep his center of mass
over his fast-moving

base of support with respect to the ramp.

And due to that acceleration,

the skater gains a large
amount of kinetic energy,

which he can use in a variety of ways.

[dramatic music]

Any skating that focuses on tricks

instead of gliding around

is called aggressive inline skating.

And like any type of aggression,

you need to be careful
to ensure no one gets hurt.

Starting out slowly is smart,
but with that low rolling resistance--

[laughter]

That can be quite hard.

[upbeat music]

She tries to stop herself,
but the low rolling resistance

causes the skates
to accelerate backwards,

pulling her base of support
out from under her...

-[woman] Aah!
-[laughter]

[Dallas]
Just like that.

This guy's absolutely shredding it.

-[clattering]
-[yells]

And by "it,"
I mean the skin on his elbows.

Low rolling resistance between
his skates and the ramp

means he gains so much kinetic energy

that when the fence stops his skates...

-[clattering]
-[yells]

...he continues.

Okay, let's get back to basics.

Just a pallet, some bits
of wood and some skates.

This should be fun.

[skater groans]

Should be fun, but isn't.

[man, off-screen]
That hurt!

[Dallas]
This daredevil's run-up means he's got

plenty of kinetic energy for his jump,

but when his skate gets caught,
his mass carries on,

and kinetic energy doesn't
seem quite so much fun.

[skater groans]

[man, off-screen]
That hurt! Ow!

[Dallas] There's only one thing
that can make him feel better now.

[man, off-screen]
Fudge, fudge!

[Dallas]
Yeah, that's the stuff.

[electricity crackles]

[metal creaks]

[Dallas] When I was a boy,
the future seemed so exciting.

It was all about flying cars,
robots, and teleportation.

but fast-forward 40-odd years,
and what did we get?

Well, my fridge texts me when
we're running low on butter.

[phone dings]

Sorry, and milk.

Still, there are some things

that seem to be heading
in the right direction.

Behold, the rise of the single-wheeled
personal transporter.

It's as if someone decided

to distill the very essence
of powered transport.

These are the apex of minimalist vehicles.

Just one powered wheel controlled

by what appears to be pure magic.

But, in fact, it is science.

There are two common designs

for these electrically-powered
single-wheel devices.

Feet in front of and behind the wheel,
or feet either side.

But whichever it is, where you steer

and how fast you go is usually dependent

on how you position your body weight.

[dramatic music]

To accelerate, our man leans forward.

This triggers the motor
inside the wheel to speed up,

bringing the base of support
towards his center of mass.

The more he leans,
the more the vehicle accelerates

to keep him stable.

To turn, he leans from side to side,

but the motor can't help
to stabilize in this direction.

So if he leans too far,

the side of the board
will hit the ground,

resulting in a sudden
increase in resistance.

[thuds]

That seems pretty simple.

Just try not to lean too far,

don't catch the edge of the board,

and remember to avoid obstacles,

and all of this should be child's play.

Some of these one-wheelers

can reach speeds of 19 miles an hour,

but I don't think
he's quite going that fast.

[man groans]

Fortunately.

This speed demon leans too far right,

catches a corner of the board,

and a sudden increase in resistance
slows it dramatically,

but not him.

[man groans]

But one thing's for sure.

No matter how much you lean,

these gadgets can't jump.

In lay terms, we call that a dog,

but a physicist would call it

a sudden of increase of resistance,

and no one gives treats to one of those.

[bright music]

[glass shatters]

[electricity crackles]

[shattering]

[Dallas]
Over 400 years ago, Galileo Galilei,

the father of modern science, said,

"I have never met a man so ignorant

that I couldn't learn something from him."

So, let's watch some
scientific ignorance in action

and learn something.

-[man yells]
-[woman laughing]

[man grunts]

[lively fiddle music]

[skater grunts]

[splashes]

[metal crashing]

[engine revving]

[man grunts]

-[metal clangs]
-[man grunts]

-[clattering]
-[skater grunts]

[crashing]

-[clattering]
-[yells]

[crashing]

-[man, off-screen] Oh!
-[child, off-screen] Wheels!