06x10 - Fences, Dinghies and Hang Gliders

[bunniefuu]

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

Yes, this is the show where we try to
extract actual sense

from absolute nonsense.

So, get ready to see amateur researchers
try to find answers to the questions

that literally
no one was asking.

We'll learn our lessons the fun way
while they learn theirs the hard way.

Then we'll stop, reveal what went wrong
and why with principles

like moment of inertia.

Elastic potential energy.

Muscular oscillations.

Test the laws of physics.

And they'll test you.

Watch out, it's the
Science of Stupid.

[man] Go.

[Dallas off-screen] In this show we'll
be learning what not to do

with horizontal force.

The downside
of positive feedback.

And how to plan your
parabolic trajectory.

Not like that.

[man] Oh my God.

[Dallas off-screen]
But first, this.

Apparently, people have been flying
since the late 13th century.

Marco Polo described seeing Chinese
man-carrying kites on his famous odyssey

to the Far East, so I thought that I'd
like to give it a go myself.

Not in a kite obviously, I had something
more practical in mind.

The hang glider, you still get
the same feeling of freedom.

I don't think that's me.

You can loop and soar
amongst the birds.

Yep, that's still not me.

Ah, now this one is me.

[screams]

[Dallas off-screen]
That was six weeks ago

and I'm still finding
bits of plant in my teeth.

Landing a hang glider is really quite
hard to do,

so if you don't enjoy the taste of
hospital food

then I suggest you pay attention to this
science and it all starts by knowing

that the hang glider is
essentially one big air foil.

An airfoil generates lift in part by
forcing the air traveling over it

to go faster than the air
traveling under it.

This creates a pressure differential
with lower pressure above it,

which literally
sucks the glider up.

When landing our pilot tilts the front
of his glider upwards,

which increases lift but lowers his air
speed.

If he gets this right he's
in for a gentle landing.

Tilt too much and the airflow above the
wing will become turbulent,

creating a stall,

a rapid descent and what pilots
euphemistically call a hard landing,

which is just as much
fun as it sounds.

But before you can land you
need to get yourself airborne.

[Dallas off-screen]
Here we go, up, up and

straight
back down on your face.

It's not a great start.

A lack of speed at take-off meant there
wasn't sufficient airflow

over the airfoil to generate enough
lift, so he landed.

[man] Oh, ah.

[Dallas off-screen] A little
sooner than he'd have liked.

Okay, this guy is flying but has he
remembered how important lift is

in avoiding
obstacles on landing?

Like that house, for example.

Insufficient lift means
he can't clear the house,

so he stops with a jerk
through an open window.

Doors are an alternative
way of entering a house.

Ah, nice kit.

Now, he looks professional,

effortlessly gliding through the
picturesque landscape and the

perfect approach for a controlled
landing, and by 'controlled'.

[screams]

[Dallas off-screen] And by
'controlled' I mean rubbish.

Classic case of all
the gear and no idea.

[man] Oh.

[Dallas off-screen] The pilot
here tilts the glider too much

which creates turbulence,
a stall.

[screams]

[Dallas off-screen] And one of those
hard landings we've been talking about.

[man] Oh.

[Dallas] A controlled stall should allow
you to stop on a dime

but if you find yourself still
moving forward a bit on landing,

it is totally acceptable
to run a little.

[Dallas off-screen]
Just remember.

[man] Ow.

[Dallas off-screen] To
keep holding your glider up.

This guy almost got it right but on
landing

he let his control bar hit the
ground.

And that is probably
the worst way to come to a stop.

Actually,
I take that back.

This is the worst way to land.

This poor guy's hang glider has
folded in on itself trapping him

underneath as it spirals
towards the earth.

He's got his parachute that partly slows
him down but because that wing

is still an airfoil it acts like a
propeller, also slowing his descent,

and making him very, very dizzy.

[screams]

[Dallas off-screen] But amazingly he
walks away with just some cuts,

bruises and probably an understandable
hatred of hang gliders.

Now, there's a hypothesis that humans
descended from aquatic apes with our

hairless bodies being
more streamlined.

Now, scientists didn't really go for it,
but it'd certainly explain why I find

nothing more relaxing than messing
about on the water.

This guy must be seriously relaxed, save
some dingies for the rest of us.

Yeah, not so relaxing now.

And dingies are even more peaceful when
you get professional to pilot while

you sit back and enjoy the view.

[screams]

[Dallas off-screen] Yeah,
you're not getting a tip.

Clearly there is an art to staying dry
in a dingy,

so if you want to avoid
being bounced out of a rubber raft,

you better take note of the following
science.

[Dallas off-screen] Inflatable
structures need to contain air at a

greater pressure than their surroundings
in order to remain rigid.

If a dingy is under-inflated, it will
lack flexural strength

and will bend easily with the contours
of the water beneath it.

If there are rolling waves there will be
moments where one end of the boat

is raised by the wave and the other
is briefly suspended.

When this happens the boat bends
and our man takes an early bath.

And, of course, external forces can
accelerate lightweight structures

like dingies quickly and easily.

Well, now that we understand
some of the science,

let's see how our
experimenters get on.

That sea doesn't
look very inviting.

[screams]

[Dallas off-screen] Maybe
it's nicer once you're in.

That dingy is under-inflated, which
means it

lacks flexural strength and as
dingies follow

the profile of the wave, when one end is
raised the dingy bends and she...

[screams]

[Dallas off-screen]
Gets a taste of the sea.

Trainee life savers here so
these guys should be good.

[screams]

[Dallas off-screen]
And yet here we are.

Their boat like any dingy is
lightweight, so external forces can

quickly accelerate it or in this case,
decelerate it.

As they reach the top of the
wave the dingy gets slowed down.

[screams]

[Dallas off-screen] A lot
faster than its passengers.

Keep going with the training lads,
you'll get the hang of it one day.

Good thinking, five people in one dingy

should act as ballast and stabilize the
boat.

Yeah, four.
Four might do it.

Or, or three, that
should be fine.

[screams]

[Dallas off-screen] Guys.

I hope you can swim.

I think we all love an impressive BMX
stunt, but can you guess what science

this biker will reveal?

[Dallas off-screen] Did you guess the
science

this brave BMXer was about to
demonstrate?

Yes, that's right.

It's angular momentum,
or lack thereof.

His run up gives him
plenty of horizontal momentum

but to lift the bike over the bin he
needs to rotate the bike around

the rear wheel to generate
sufficient angular momentum.

He doesn't and when
he hits the bin.

He does get
angular momentum.

But in the wrong direction.

A balance jump can be any jump

where you land on an unstable surface
and have to balance.

To do it well takes extraordinary
strength,

Zen levels of concentration and the

poise of a ninja, especially
if you wanna get high.

Like this.

[Evan] Huh. Yeah!

[cheering]

[Dallas off-screen] Here's Evan Ungar
jumping more than 60 inches from

a standing start, incredibly
this is nearly his own height.

[man] Ready whenever you are.

[Dallas off-screen] A more modest jump
here but he looks like he should have

the strength
to pull it off.

[man] Oh, my back.

[Dallas off-screen] That
puts the dumb into dumbbell.

Jumping high is hard enough but adding
the difficulty of having to balance

on landing only makes things harder.

The jumper needs to apply sufficient
force to the ground

to get enough reaction force to

propel themselves upwards and towards
the object they intend to land on,

in a parabolic trajectory.

When landing on an unstable surface you
need to worry about overcoming its

coefficient of static friction with the
surface beneath it,

resulting in it moving.

So, your best bet is to aim for a point
directly on top

which demands a higher parabolic
trajectory and pinpoint accuracy.

So, if I understood that right,

when you are jumping on something
unstable you are best to jump high

and come down on it almost vertically
and even then, it can skid away.

Sounds like the sort of thing best tried
on a well-padded gym floor.

And not a tiled shopping mall.

[man] You're going
to break your ankle!

[Dallas off-screen] I think his ankle
escaped

but he might need his head tested.

His jump wasn't bad, but he forgot all
about the bin's

low coefficient of static friction with
the floor and that...

Was a mistake.

Oh, good.

A gym and a nice long run up.

[screams]

[man] Oh my God,
are you all right?

[Dallas off-screen] Which
didn't really help at all.

Let's see what went wrong, sufficient
ground reaction force, yup.

Nice high parabolic
trajectory, sure.

Landing directly
downwards, close but...

[screams]

[Dallas off-screen] No cigar.

[man] Oh my God.

[Dallas off-screen] And if you hit a
stack that high slightly off center

you're gonna know about it.

This looks nice and easy, not too high
and with a nice, flat top.

Hard to mess up.

Hard but not impossible.

This gym goer's parabolic
trajectory wasn't high enough

and he catches the edge tipping
it backwards and tripping him.

Onto his face.

Oh, this guy again
but has he learnt anything?

No, no he hasn't.

[man] Oh.

[Dallas] Well, I've got this silly hat
on again, which can mean only one thing.

Yes, it's time for
today's science lesson.

The part of the show where we lean into
our microscopes to peer at one

particular scientific principle,

and don't forget to take notes because
there will be a test at the end.

So, what do the
following have in common?

[Dallas off-screen]
This hover boarder,

this inflatable flop

and this short-circuiting
power supply.

Well, that was exciting.

It's something all students hope for,

positive feedback but I'm not talking
praise for completed homework.

We're gonna look at what happens
when a slight disturbance

induces a runaway reaction which
causes the system to collapse.

Sounds exciting, and it is.

As the Ping-Pong ball hits the mouse
trap it sets it off,

firing the ball on it into another mouse
trap, which sets off more.

So, the action of one event feeds back
into itself increasing in magnitude and

leading to runaway instability.

This is positive feedback.

Yes, that was fun, but
did you learn anything?

Well, let's see.

Starting off nice and easy,
what is positive feedback?

[Dallas off-screen] It looks like this
little car pulling a very heavy trailer

might be
about to show us.

Yes, that's it.

A slight disturbance starts a runaway
reaction, ultimately ending in...

An expensive insurance claim.

Here's another example, this slackliner
is doing fine but a little wobble.

[slackliner] Ah, ah. Ah, no.

[woman] Your glasses, watch out.

[Dallas off-screen]
Leads to positive feedback.

[man] [bleep]. Ah.

[Dallas off-screen] His small
corrections lead to greater instability,

which lead to more corrections,
more instability and then.

[woman] Your glasses, watch out.

[Dallas off-screen] A dip in the world's
least appealing swimming pool.

Okay, time for question two.

Does positive feedback help
improve a system's operation?

Hopefully this electrical engineer can
help shed some light on the matter.

[screams]

[Dallas off-screen] No.

Positive feedback definitely
doesn't improve most systems.

They need better instructions;
those ones are shocking.

The power line is overloaded so it heats
up, which increases its resistance,

which increases the load which
heats the wire even more until.

It's time to find that
fire extinguisher.

Now, where did I put it?

I know, a bit of snow
will sort this out.

Yep, you're a bit late with
that extinguisher, my friend.

[speaking native language]

[Dallas] Alright, the last
question is a bit trickier.

Where in nature can you see
positive feedback in action?

[sheep bleats]

[dog barking]

[man] Oh.

[Dallas off-screen] Yes,
stampedes are another example

of positive feedback.

One member of the group panics

and reacts in a way which panics those
around it.

This escalates resulting
in a group flight response.

[man] Oh.

[Dallas off-screen] So, that's positive
feedback, a strangely upbeat name

for something that
usually ends very badly.

[Dallas] We all like a
light dusting of snow

but sometimes you get
more than you bargained for.

In 2015 a village in central Italy was
inundated with 100 inches

of snow in just 18 hours.

In fact, about 70% of all the earth's
fresh water

is locked away frozen as ice
and snow.

And snow is surprisingly insulating, the
inside of an igloo can be


outside but the best thing about snow.

Is just how pleased
it makes people.

[child] Hi.

[child] It's snowiiiiing!

[child] It's snowiiiiing!

[Dallas] Especially adults when they
realize that they now

have a great excuse not to go to work

but how does a collection of tiny
snowflakes

transform a vast landscape
overnight?

As always, science
has the answer.

When the temperature is near freezing
tiny ice crystals and clouds

can collide, stick together and
become snowflakes.

[Dallas off-screen] Snowflakes that fall
through cold,

dry air produce powdery snow.

Whereas flakes that fall through warmer,
wetter air

melt around the edges and
stick together

producing big, fluffy flakes.

Typically fallen snow has a lot of air
gaps in it,

which means it's very compressible

but once snow has been compressed it can
become very slippery

due to its lower coefficient of
friction.

[driver] Oh.

[Dallas off-screen]
My thoughts exactly.

So, you get different types of snowfall
depending on the type of air

they fall through, and different types
of snow have different properties.

For example.

The snow on these
tracks may look solid.

But it really isn't.

Because this snow has fallen through
cold, dry air it's actually powdering.

Good news for the train.

Slightly less good news
for the passengers.

Yep, sometimes snow can
take you by surprise.

[woman] Snow!

[woman 2] I've never seen
anyone so excited for snow.

[woman] Dude, I'm sorry...

I live in Arizona...

where there's no snow at all.

[Dallas off-screen] Ah then
you'll probably not know,

about its low friction.

-[woman] Ah. Ah.
-[woman 2] Are you okay?

[laughter]

[Dallas off-screen]
So, that's snow.

Lovely stuff.

As long as
you know your science.

[snowboarder] Damn.

[Dallas] If you're a fan of big fences
and, let's face it, who isn't?

Then you should consider heading to
Australia for your next holiday

because its home to both the rabbit
proof fence,

which is a massive 727 miles long and
the even bigger dog fence,

which stretches
more than 3,300 miles.

Impressive stuff.

Especially when you consider how hard

putting them up in the first place can
be.

[woman] Bye bye fence.

[Dallas off-screen] Although it is
easier

if you aren't attempting it
during a hurricane

and take a minute to think about
placement

because a fence in the wrong
place...

[man] Oh.

[Dallas off-screen]
Can be a bit of a pain.

[man] Oh my God, dude!

[Dallas off-screen] And you'll
be relieved to hear there was

only very minor damage to the fence.

Today we shall be exploring
the surprisingly hazardous and

increasingly popular past time
of leaning on a fence.

It sounds easy and it is as
long as you know your science.

Your standard household fence is built
in sections

supported by posts which are
strong and

deeply buried allowing them to withstand
vertical and horizontal forces.

But if the attachment points between the
posts

and the rest of the fence are
poorly made

or damaged they might not
have the required strength.

Generally speaking if left alone fences
are pretty well-behaved and do their job

with the minimum of
fuss and complaint.

It's the human factor that
seems to mess things up.

This young lady's undecided if she wants
to pursue that modeling career.

She's currently on the fence.

[woman] Now give me
a kick, give me a...

[woman] Oh.

[Dallas off-screen]
Now she's over it.

As this aspiring model changes her pose,
she leans in more heavily.

This transfers additional horizontal and
vertical force

causing the end of the fence,

and the end of her
modeling aspirations.

[woman] Are you okay?

[Dallas off-screen] This little girl
scores a basket with no fuss at all.

Let's see if her much larger
friend can manage a slam dunk.

[man] Slam dunk. Oh.

[Dallas off-screen] That
was more dunk than slam.

[man] Slam dunk.

[Dallas off-screen] During his exuberant
celebration he completely forgets

about the fence until it's too late and
it doesn't have the strength

to withstand the impact.

So that's fences.

[man] Oh [bleep].

[Dallas off-screen] The very definition
of passive aggressive.

In the words of Nelson Mandela, there is
no passion to be found playing small.

Well, this bunch of experimenters let
their passion guide them in going big

and failing even bigger, and
for that we thank them.

[music plays through credits]

♪ ♪