07x15 - Zip Wires, Scooters and Hay Bales

[bunniefuu]

[Dallas]
This is the Science of Stupid.

[klaxon blaring]

-[man groans]
-[Dallas] Yes,

this is the show that fuses science

and stupidity.

Watch as the actions of the few

inform the minds of many,

through misadventure, miscalculation,

and a misunderstanding
of the laws of science.

We'll reveal what went wrong

and why

with the help of key principles,

such as material strength...

[man] Oh! Oh!

[Dallas] ...angular momentum,

and the bane of all
sentient life, fulcrums.

Physics has a cruel streak.

Mess with its rules,
and it'll mess with you.

Watch out.

It's the Science of Stupid.

[electricity crackling]

[glass shatters]

In this episode, we'll be looking at

how bales absorb force,

Newton's third law,

and Amanda's incorrect
application of friction.

[girl, off-screen] Amanda!

[Dallas] But first, this...

[electricity crackling]

So you're thinking about building
your own zip wire.

Well, naturally, you'll have calculated
the ideal angle of descent,

how kinetic energy will be absorbed,

and considered the catenary curve.

[man screaming]

[Dallas] Claimed to be the longest

and fastest zip line in North America,

the professional engineers who built this

will have considered all that science.

-[man] Whoo!
-[man, off-screen] Yeah!

[Dallas] But this improviser...

[man groans]

-[Dallas] ...eh, probably didn't.
-[laughter]

[Dallas] Yes, I'm afraid
it's come to my attention

that people have been
unwisely constructing

their own homespun zip wires

all without adequate training,

equipment, or knowledge
of important science,

such as the always critical
angle of descent

or the occasionally critical
catenary curve,

the curve a supported line forms
when hanging freely

and nothing to do with cats.

Some zip lines form a large catenary curve

and allow a rider to decelerate naturally,

provided there's enough ground clearance.

Cables with much less of a curve
use a brake at the end

to slow the rider down,

safely absorbing the kinetic energy

gained during the descent.

Descent angle affects velocity,

about four degrees being a good target.

Too shallow and it'll be boring.

Too steep

and excessive velocity will make it...

too exciting.

You see, on a professionally
constructed zip wire,

all of the aforementioned science
will have been carefully calibrated

to get you from point A to point B safely.

Point B looks remarkably close here.

[woman] Ah!

[groans]

[Dallas] Yeah, I was right.

Cable significantly steeper
than four degrees.

not to mention...

being really short.

A bit more length to this one

and the angle looks shallower.

[man groans]

[Dallas] But it wasn't perfect.

A taut cable means
very little catenary curve

to help slow you down,

but if the end of your line
is only three feet high,

the ground will do the job instead...

assisted in this case by a wooden post.

[man] That was awesome!

[Dallas] If by awesome, you mean
poorly thought-out and unsafe,

then yes, it was.

[laughter]

[Dallas] Now this does have
better ground clearance.

-[boy] Ah!
-[Dallas] Whee!

Wa-- wait a minute. Is that
a bicycle wheel and handle bars?

And there's minimal catenary curve
to help slow him down?

I hope there's a brake.

-[boy] Ah!
-[laughter]

[Dallas] Ah, good. Yes, there was.

-[boy, off-screen] Uh-oh.
-[Dallas] Alas, the brake

didn't absorb enough
of his kinetic energy,

and he just couldn't hold on.

Well, he is all right?

[man, off-screen]
Are you okay, mate?

-Yeah, right.
-[Dallas] Are we sure?

[man, off-screen] How many fingers
am I holding up?

How many fingers am I holding up?

[boy] Five.

[Dallas] No, that's four.
Thumbs don't count.

[man, off-screen] All good. Two thumbs up.

[Dallas] Yeah, those things.

Right, how about we just
keep things simple?

[indistinct chatter]

[Dallas] Well, perhaps they've got
some clever safety measures in place.

[boy, off-screen]
Get ready to catch him.

[Dallas] Or perhaps not.

[laughter]

[Dallas] Never mind.

An overly stretchy zip line meant

a sudden increase in kinetic energy.

So he couldn't hold on.

Luckily, there was
a convenient swimming pool

to reduce the impact force...

eventually.

And there you go.

Irrespective of catenary curves...

-[man groans]
-[laughter]

[Dallas] ...angle of descent...

-[laughter]
-[Dallas] ...or bicycle wheels,

DIY zip wires are a dangerous idea.

-[woman groans]
-[Dallas] Don't do it yourself.

[electricity crackling]

[creaking, clanging]

In 1985, a vehicle was pioneered

that would one day revolutionize
the way we travel.

[Dallas] That day...

[boy wails]

[Dallas] ...has yet to come.

Okay, so we're not ditching
the motorcar quite yet,

but the electric scooter has become

something of a hit
for folk both young and old

looking for a simpler more portable method

of getting about
and sometimes messing about.

Nevertheless, with some models
now hitting speeds

of around 30 miles an hour,

it would be remiss of me

not to impart a little cautionary science.

An electric kick scooter and rider have
a high combined center of mass

relative to the wheel base,
so poor stability.

The tiny wheels mean
that even a small obstacle

can make for a very bumpy ride.

Start to wobble
and you might put a foot down,

like a kick scooter.

But at speed, the increased friction

may brake the rider more than the scooter.

And there you go.

Electric scooters may be a simple,

relatively accessible mode
of personal transport,

but they do involve
a fair degree of science,

and they can pack a few surprises.

Some people think
you can't do tricks on them.

[woman gasps, laughs]

Are you OK?

[Dallas] But they're wrong.

High combined center of mass,

sufficiently large obstacle...

fabulous flip.

It's Grandma's first trial
on an e-scooter.

She might need some advice.

[man, off-screen] You got
to get it started before it'll go.

[Dallas] Yeah, and you don't have
to push with your foot, Grandma.

It's motorized.

[woman groans]

[man, off-screen] Oh no!

[Dallas] Don't, don't worry, Dad.
It's okay. You're still recording.

Grandma couldn't resist
pushing with her foot

while also accelerating with the throttle,

which unbalanced her.

[woman, off-screen]
Brake! Hit the brake!

[Dallas] She did but with her foot.

[woman groans]

[woman] Is she alright?

[man, off-screen] Is she alright?

[Dallas] She was all right,
but if that high center of mass

was troublesome enough with one person...

-[woman groans]
-[man, off-screen] Oh!

[Dallas] ...it's even more so with two.

-[girls screaming]
-[man, off-screen] Oh-oh!

[girl] Amanda!

[Dallas] Hmm, but was it really Amanda?

Amanda at the back did put her foot down,

introducing friction,

which dragged her foot behind,

which caused their combined center of mass
to fall outside the base of support.

The driver tries to rescue it

by, yes, generating friction
with her foot.

[girls scream]

[Dallas] A collective effort.

[electricity crackling]

[creaking]

[clattering]

[whistle blows]

[Dallas] A penalty kick in
the dying moments of the match,

but can you guess
what science it will reveal?

[glass shatters]

[electricity crackling]

[glass shatters]

[whistle blows]

[Dallas] Did you guess the science

this penalty kick will demonstrate?

Oh, and he saved it thanks to density.

Someone sign up that dog.

Whilst both the ball and Rex the dog
are similar in size,

Rex is much denser

because he's filled with bone, muscle,

and other organs instead of air.

This density means the ball experiences

a much larger acceleration than Rex

and rebounds off him.

Don't worry, Rex is okay.

He's just feeling a bit "ruff."

[crowd cheering]

[glass shatters]

[electricity crackling]

[glass shatters]

[Dallas] Straw and hay.

They look similar,

but prepare to be horticultured.

Straw is the dried, leftover st*lks

of wheat, oats, and barley.

Hay is dried grass, got it?

For livestock, straw makes a cozy bed,

and hay a nutritious snack,

but either one makes
a rural as*ault course.

If you're this guy.

-[man groaning]
-[laughter]

[Dallas] And it turns out
he's not the only one

who thinks leaping about
on bales is a good idea,

but what's bad for your biology

can be beneficial
for the study of physics.

Bales are composed
of irregular interlinking shapes.

This means they can withstand
a relatively large amount of compression.

They also easily deform,

allowing them to absorb a lot of force.

But their loosely bound structure
means they also have

low tensile strength,

so can be easily pulled apart.

You see, those bales are literally packed

with material strength science.

So how about a recap with some help

from our top field researchers?

A bale has a high compressive strength,

so, yeah, it'll take
your weight no problem.

But don't forget, it also has
a low tensile strength,

so can easily be ripped asunder.

-[woman screams]
-[laughter]

[Dallas]
But just not with your face.

Now, foreheads may be rubbish
at absorbing force...

-[woman screams]
-[laughter]

[Dallas]
...but what about the bale?

Well, here's an acrobatic
young physicist to show us.

Here the bale compresses,

absorbing a little force from his hands.

And here too.

Nicely done, but that wasn't
the best example.

[man yells]

[Dallas] Yeah, that was better.

See, squidgy bales
can absorb lots of force.

Hard ground...

-[audience groans]
-[Dallas] ...not so much.

Time for one more?

-[man yells]
-[audience groans]

[Dallas]
Lovely. On to tensile strength.

Remember, low tensile strength means

a hay bale structure
can be easily torn apart.

Now, which of our researchers
is behind this senseless vandalism?

-[cow moos]
-[Dallas] Oh, it's Trevor.

[cow sneezes]

[woman, off-screen]
What are you doing?

That's the last straw, Trevor.

[bell rings]

[liquid splatters, glass shatters]

[bubbling, hissing]

[Dallas] Right, class, it is time
for your science lesson,

the part of the show where we pick
a particular principle

and precisely pick it apart,

but can you guess
what it is from the following?

[woman, off-screen] How did this happen?

[Dallas] Attack of the k*ller car wash.

[woman, off-screen] Oh, look,
it's over there too.

Bubbles! Bubbles inside the car!

[Dallas] Well spotted.

A tossed egg salad.

[laughter]

And a fun foaming experiment.

[laughter]

I meant rubbish.
A rubbish foaming experiment.

[indistinct chatter]

That's right, we're studying
surface active agents,

or "surfactants" for short.

These are compounds found
in substances all around us,

from cosmetics to certain foods,
detergents, and soaps.

Now, surfactants may be commonplace,

but what they do, well, it's pretty weird.

Surfactants are molecules
where one part loves water

and the other part doesn't.

This allows oily substances
to mix with water

as each surfactant part sticks
to its preferred substance.

This dual nature also reduces
the surface tension of water,

so it mixes more easily with air
to form stable bubbles.

On a wet surface,

surfactant molecules sandwich
water molecules in layers,

making that surface even slippier.

Okay, it's test time.

Question one:
we've learnt that surfactants

are two-faced molecules

that mess with the way
substances interact.

But what good is all that in the shower?

The surfactant in shampoo
allows water to mix with grease

and carry it away.

[snickering]

[man] It's still lathering up!

[Dallas] That's because your friends
keep pouring it on your head.

[man] Yeah? That's slow.

[Dallas] But at least your hair
will be nice and shiny.

[laughter continues]

Question two, what happens
when water and air is mixed

with a surfactant?

[children shouting]

[Dallas]
Mom's away, and Dad has imprisoned

the noisy rascals in a foam tower.

[man, off-screen] It’s literally
touching the ceiling!

[Dallas] Yes, thanks
to the surfactants in soap

reducing water tension,

air easily mixes in
to form stable bubbles.

[boy] Mom, come here!

[Dallas] It's just a shame
they're not soundproof.

[boy] Yeah!

[Dallas]
Finally question three:

what effect can surfactants have
on a wet surface?

Here's a clue.

When the water molecules
on his Slip 'N Slide

are trapped between
the soap surfactant molecules,

the resulting layers
can easily slide over each other,

making it super slippy,

turning a regular Joe
into a neighborhood legend.

Take care. Serious injuries
have occurred on Slip 'N Slides,

particularly involving
bigger kids and adults,

but him, he's doing fine.

Class dismissed.

[glass shatters]

[electricity crackling]

[Dallas] When Sir Isaac Newton proposed
his third law of motion,

for every action, there is an equal
and opposite reaction,

he probably wasn't aware of how
almost three and a half centuries later,

it would prove so relevant to the art
of the wakeboard rail slide.

You see, we might say...

it's launching onto a rail
and gliding smoothly along it.

But Sir Isaac Newton would say...

it's action...

reaction.

See what I mean?

And look a little closer,
because there's more

to Sir Isaac's third law
than crash landings.

To launch on the rail,

he pushes down sharply with his legs.

This applies an action force

and the equal and opposite reaction force

from the water provides the boost,

resulting in a pop.

On the rail, he contends with friction,

acting in the opposite direction
to his momentum.

To maintain the dynamic equilibrium
and stay balanced,

he keeps his base of support
under his center of mass.

Otherwise...

Okay, starting with the pop,

one must apply just
the right amount of force.

And at just the right time.

[man groans]

[Dallas] That was a little late,
slash, not at all.

That's better.

This textbook action/reaction
boosted her onto the rail.

[woman] Oh! Ahh!

[Dallas] Shame about
the dynamic equilibrium.

[laughter]

Her center of mass
was pulled beyond her base

and right over the side of the rail.

But another Newtonian boost...

more than made up for it.

Okay, onto friction force.

Wakeboarders love smooth, steel rails
or plastic pipes like this,

because they offer
low frictional resistance,

meaning...

[man grunts]

[Dallas] ...they're slippy,

and not just on your board.

-[man, off-screen] Ohh!
-[laughter]

[Dallas] On your tummy too.

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

[Dallas] Too little action.

-[man] Ahh!
-[Dallas] Too little reaction.

Look, if you're worried about
Newton's third law of motion,

maybe just find a safe place to spectate.

So not there,

Because as Newton says. action...

reaction.

[electricity crackling]

[clanging]

A vision of futuristic efficiency

for twentieth century sci-fi writers,
like H. G. Wells,

the moving walkway

has actually been with us
for over a hundred years.

So you'd think we'd have figured out

how to use them by now.

No, not like that.

[laughter]

Yeah, now you're just being silly.

It's very complicated.

You walk on, amble along a bit,
and walk off.

But how do they work
on a scientific level?

A moving walkway is a wide rubber belt

or continuous sequence of metal pallets

powered by an electric motor.

The motor uses electrical energy

to transform rotational motion

into continuous horizontal motion
in the walkway.

Typically, walkways move
at around 1.4 miles an hour,

about half the average walking speed

of a healthy adult.

Stepping onto the walkway

can produce an abrupt change in velocity,

so moving handrails help with balance.

They're supposed to make
pedestrian travel more efficient,

and yet studies have shown

that they actually
might be slowing us down

because as soon as we step on that belt,

we instinctively tend to stop
or walk slower,

ultimately clogging up
the way for other users.

[laughter]

But this isn't quite what I meant.

These walkways take skiers
straight to the ski slope,

but if those skis make contact
with the static ground,

friction can drag it out from under you,

making the ride...

not so much fun.

Now, hand rails can help,

but they also need
to be on a continuous loop,

which means they don't slow down
or stop at the end.

-[boy groans]
-[laughter]

[Dallas] They just keep going round.

Did you know in Toronto there's a walkway
that travels at 4.5 miles an hour?

That's three times faster
than the average,

so that would have been
a bit more like this.

-[boy groans]
-[laughter]

[Dallas] But in some ways, that's not
really even the fastest walkway.

This is.

[boy] Level 7!

[Dallas] Same mechanics but beware,

that velocity change doesn't just happen
when you get on.

-[man, off-screen] You all right?
-[boy] Yeah.

That was awesome!

[glass shatters]

[electricity crackling]

[glass shatters]

[Dallas] And that, my friends, is your
lot.

Please do not attempt
any of the dangerous stunts

you have just seen.

Renowned aerospace engineer
A. P. J. Abdul Kalam

once proclaimed science is
a beautiful gift to humanity.

It seems it's a gift
some people forgot to unwrap.

[laughter]

-[woman] Ah.
-[laughter]

[man groans]

[laughter]

[man] Ooh-ooh!

[boy] Uh-oh. [groans]

-[woman] Ah!
-[woman groans]

-[man, off-screen] Whoa.
-[girls scream]

[man] Ahh!

-[woman] Ahh!
-[man, off-screen] Ohh!