07x16 - Off Road Buggies, Cartwheels and Swing Seats

[bunniefuu]

[Dallas] This is the Science of Stupid.

[klaxon blaring]

Yes, this is the show where we extract

scientific sense

from senseless idiocy.

[man] Whoa.

[Dallas] Gaze in disbelief

as amateur stuntmen
and women

struggle with scientific principles...

[men shout]

[Dallas]
...and suffer the consequences.

[woman grunts

[Dallas]
We'll reveal what went wrong

and why.

Perhaps it's impact force

or possibly ground pressure,

or maybe they just didn't get
turning effects.

Either way, don't try this at home

or anywhere else, for that matter.

Watch out.

It's the Science of Stupid.

[electricity crackling]

In this show, we'll explore
the potential pain

of misunderstanding
electrical grounding...

-[electricity zaps]
-[children scream]

[Dallas] Complications with
cartwheels and backflips

and friction failure

when jumping on stuff on a trampoline.

But first, this.

[electricity crackling]

[glass shatters]

Think you can handle
the ultimate in off-roading,

bone-rattling ruts,

wheel-swallowing mud pits,

vertigo-inducing rock faces?

Well then, what you're gonna need
is a lightweight machine

with a steel roll cage

and serious suspension.

You are gonna need a buggy.

That's not quite what I had in mind.

That's more like it.

Yup, we're looking at customized

or specially built all-terrain buggies

designed to navigate the toughest terrain,

providing, of course, the driver
has swatted up on their science.

Our man's specialized suspension
creates additional ground clearance

and has greater travel,

which means his wheels
have more vertical movement.

The more the wheels can move,

the larger the bumps
and obstacles they can tackle.

The roll cage's geometric design
and steel tubing

enhances its stability and strength,

which is essential, since buggies
can have a high center of mass,

making them less stable
when tackling very steep obstacles.

[crashes]

So these kinds of buggies tend
to be over-engineered in some ways,

but they're also often designed
to have no unessential weight,

like doors or windscreens,

which can give them
a high power-to-weight ratio...

which means they can really shift.

But not always in the way you'd want.

[both yelling]

-[man] Are you good?
-[woman] Yeah. Are you okay?

[Dallas] Everything's going smoothly
until they hit a bump,

which creates an upward force

too large for the suspension to absorb...

[woman] [yells]

[Dallas] ...which sends them into a spin.

[woman] [screams]

[Dallas] They were protected
as the roll bars

maintained structural integrity.

[woman]
I hit my head, but I think I'm OK.

[Dallas] Which is more than I can say
for the rest of the vehicle.

Let's try an even bigger bump.

Go on. You can do it.

Yeah, that tree is not gonna help much.

You can see that power-to-weight ratio
in effect there.

Nice. And to cope with hard landings,

the suspension has plenty of travel,

but when it hits the tree,

the axel is gone, and so goes the wheel.

[man] You lost something!

You're gonna need that.

[Dallas] Yeah, thanks for
the expert appraisal, guys.

[man] [indistinct]

[Dallas] So that was uphill.

How about downhill?

Is that any easier?

[men shout]

[Dallas] Uh, no. Not really.

The slope is so steep

that the buggy is almost vertical

when the front wheels hit the ground.

Then its momentum pushes
the center of mass

outside the smaller base of support.

[men shouting]

[man] Yep! That's what I thought
was going to happen.

[Dallas]
Why did you do it, then?

[electricity crackling]

[creaking, clanging]

[Dallas]
Here at the Science of Stupid,

we're no stranger
to high-risk trampoline antics.

We've seen backflips, front-flips,

side-spins, double-jump super bouncing,

and even trampolining goats.

We've seen it all... or so we thought.

-[man] Ah!
-[laughter]

[boy] Oh! Ow!

[Dallas] And now we have seen it all.

That was a couple of dangerous
and ill-advised examples

of what I can best describe
as people bouncing on things,

on trampolines, space hoppers,

inline skates, scooters,
you name it, people do it.

Now, seasoned skateboarders

do actually legitimately use trampolines

to perfect their tricks
with specialized boards,

and here's one now

with some equally special science.

[Dallas] As a trampoline deforms,

kinetic energy is converted

into elastic potential energy,

which is returned to him
by the elastic restoring force,

bouncing him high.

So control is critical.

His flat board with no wheels

provides enough friction
to prevent him slipping.

And even when styling it out...

he lands as vertically as possible

so the elastic restoring force

doesn't bounce him off course.

So with the right landing,

a practice board's flat surface
should offer enough friction

to prevent a slip.

But add wheels,

and you're only being held back
by rolling resistance,

which is generally lower than friction.

Theory, of course, is one thing,

but science is nothing
without empirical evidence.

-[boy] Ow!
-[Dallas] That'll do.

Take one less-than-vertical landing

combined with low rolling resistance
from spinning wheels,

and what do you get?

-[boy] Ow!
-[Dallas] Yes, pain.

So what's the answer?

Well, even with wheels,
these gentle vertical jumps

help keep his bounce under control.

[boy 1]
Higher, let's jump really high.

[boy 2] Alright.

[Dallas]
I'm not sure that's a good idea.

[boy] [screams]

[Dallas] See what I mean?

Landing hard to one side
of the board meant

he overcame friction,

allowing elastic restoring force

to send the board heading for next door...

-[boy] [screams]
-[Dallas] ...until his friend caught it.

By removing his scooter's wheels,

this lad has removed
the low rolling resistance factor.

[boy] Oh!

[Dallas] But he might have forgotten
about that critical vertical landing.

And... yup. Confirmation.

That's about 30 degrees from the vertical.

-[boy] Oh!
-[Dallas] But what if your ride

is less wheelie and more bouncy?

A space hopper compresses
as it hits the trampoline.

Both are squishy, and both generate
an elastic restoring force,

offering what scientists would call

"a highly elastic collision."

-[boy] Ah!
-[Dallas] Unlike that.

That is an inelastic collision.

-[boy] Ah!
-[Dallas] See? No bounce.

All of our bouncing stunts
were silly and dangerous.

Please do not copy them.

[boy] Ah!

[glass shatters]

[electricity crackling]

[Dallas] This strutting peacock seems

to have let the title
"best man" go to his head,

but can you guess what science

he and the maid of honor
are about to display?

[glass shatters]

[electricity crackling]

[glass shatters]

[Dallas] We're back with our best man

and his trusting accomplice.

Did you guess what science
they're about to demonstrate?

[guests cheers and whistling]

[woman] Oh, oh, oh!

[Dallas] Yes, that's right.
It's conservation of momentum.

She generates momentum with her run-up...

and when she jumps on his back,

he can't apply enough force to stop her,

so conservation of momentum means

she transfers some of
that momentum to him.

[guests exclaiming]

[Dallas] No, you can't just
style it out, my friend.

You nearly took out the maid of honor

and not in a romantic sense.

[glass shatters]

[electricity crackling]

[glass shatters]

I've recently started gymnastics classes,

and I noticed that I was taller
than everyone else.

Then I realized
it was because they were eight.

Anyway, I persevered,

and last week I did my first cartwheel.

But that was just the start.

Next, they wanted me to add a backflip.

Wow, mine was nothing like that.

-[man] [grunts]
-[Dallas] Yeah, that was more like me.

Cartwheel to backflip,

two already tricksy moves

all tied together
by our good friend science.

His run-up generates
linear momentum for the cartwheel,

which in turn generates angular momentum.

He pushes off evenly
with his feet aligned,

using his linear momentum
to launch him into the air

for the more demanding backflip.

Once airborne,

he can tuck in to increase
his angular velocity,

or spin speed, by up to three times,

ensuring he gets all the way around

to land safely.

Has all that linear
and angular momentum flipped you out

and made your head spin?

Well, don't worry. I'm sure the next lot

will be able to straighten it out.

Yep, even I can do that.

Is she gonna show us how to do
a cartwheel into a backflip?

-[girl] Ah!
-[Dallas] Eh, no.

She builds momentum with her cartwheel

but lands with her feet
in the wrong place,

so only pushes up with one
foot and doesn't tuck,

which means she can't generate
enough angular velocity

and her backflip belly-flops.

Okay, we're getting closer.

Can this guy get more angular velocity?

-[man] [screams]
-[Dallas] He did,

but kind of lost it halfway through.

Good angular momentum in cartwheel,

nice angular velocity in flip,

but he slightly misdirected
the old push-off.

He was actually going
for a different move than the rest,

but we'll never know what.

Don't forget, tucking in
can almost triple that flip speed.

[man, off-screen] Do or die!

-[woman] Whoo-hoo!
-[man] Oh-h*-h*!

[Dallas] But you don't always want that.

Just look how much
lovely momentum he generates

with his cartwheel
and he tucks in so tight,

his angular velocity just won't stop

until the floor makes him stop.

-[man] Oh-h*-h*!
-[Dallas] And on that note,

I'm off to my next class.

Clarinet.

[school bell rings]

[liquid splatters, glass shatters]

[bubbling, hissing]

If you've spotted the rather dapper hat,

then you've probably already guessed.

It's time for the science lesson,

that part of the show
where we unscrew the casing

of a particular principle

and tinker with the workings within.

So can you guess which principle

we're talking about from the following?

This stormy wedding...

[thunder booms]

Wow, that guy's got a big flash.

This power line...

getting some extra charge for free...

[man] [squeals]

-[crowd] [chattering]
-[electricity zapping]

[Dallas] And this shocking as*ault course.

People pay money for this, you know.

[man] Oh my God.

[Dallas] That's right.
Today we are discussing

electrical grounding.

Grounding is used as
a safety measure in electrical devices

in case of a fault,

and to understand how it works,

first you need to know
that for a current to flow,

there needs to be an imbalance
of charge between two locations.

This is what we call "voltage"

or "electric potential difference."

To set a conductor's
electric potential to zero,

our man connects it to Earth.

This is grounding.

The electric potential of Earth
can often be taken to be zero,

as it can absorb or dissipate
a large amount of charge

without significantly changing
its potential.

Current will flow from any potential
greater than zero to ground,

given a conductive path.

It'll do this through the easiest route,

and if he's not insulated,
this could mean...

-through our man.
-[electricity zapping]

Before I go on, I should warn you

never to mess around with electricity.

It can be deadly.

Now for a test. Question one.

What is required for current to flow?

[man] [singing]

[Dallas] This treetop crooner
is about to show us.

[man singing]

-[man] Ai!
-[Dallas] That's right.

It is a difference in electric potential.

The power line has
a high electric potential

compared to the tree,

which has zero electric potential,

as it's earthed in pretty much
every sense of the word.

When his metal broom touches the line...

-[man] Ai!
-[Dallas] ...like that,

he provides a conductive path,

giving him some new moves

and really getting his show off to a bang.

On to question two.

What happens when there is

a large potential difference
between two places,

but no path connecting them?

These metallic balloons
are touching the line,

but there's no path to ground,
so no fireworks--

unless one were to touch that...

[expl*si*n booms]

Oh.

Maybe he should tie
the party balloons to the door.

[man, off-screen] Woo! Good Lord!

[Dallas] Right. Third and final question.

How do you stop current
from flowing through you

due to a potential difference?

Looks like these guys understand
their electrical grounding,

because they're standing
on plastic and wood,

which are insulators,

so don't let the current flow through.

[man, off-screen] All three are safe...

as insulators are underneath them.

[Dallas] Yeah, that's what
I just said, sort of.

Yes, the zero electric
potential point of the Earth

shouldn't be a problem for them unless--

[man, off-screen] Joe at the end
has taken his shoes off.

He now has no insulator.

[Dallas] Well, someone suggests that.

-[all scream]
-[Dallas] These guys know science,

but not enough to not play with voltage.

Class dismissed.

[all scream and laugh]

[glass shatters]

[electricity crackling]

[Dallas] Next, we are taking a break
from crazy stunts and mad activities

to delve into a bit of biology.

We all use them every second of every day,

from the smallest eye movements

to the highest-impact workouts,

muscles.

We take them for granted, but should we?

[boy] Ready for my...

Oof!

[Dallas] When they
don't work as expected...

[boy] Get it off.

[Dallas] They can cause
quite a bit of trouble.

Kids and heavy weights is obviously
not such a good idea.

[indistinct chatter]

There are over 650 skeletal muscles
in the human body,

and the largest is the gluteus maximus,

which is your posterior.

So ironically, our largest muscle
is the one we use to sit around on.

Let's look at the science
behind how our muscles function

and sometimes malfunction.

Muscles are activated by our nerves
triggering a reaction

between the proteins actin and myosin,

which causes individual
muscle cells to contract.

Exercise can cause muscle cells
to enlarge long term,

known as "hypertrophy."

It involves the production
of more actin and myosin,

enabling muscles to contract
with greater force.

Cramps are involuntary contractions
of a muscle,

sometimes caused by a buildup
of lactic acid during exercise.

Hiccups are also muscle related,

caused when the diaphragm
is sent into spasm

by the brain sending a signal
to force it downwards,

pulling air into the nose and mouth.

[baby fussing]

Charles Osborne from the US

started hiccupping in 1922

and finished in 1990.

That's 68 years of hiccupping


That is enough to drive you bonkers.

[man] This has been going on
for 20 minutes.

[hiccups, laughs]

[Dallas] As his diaphragm is forced
down...

[man] I can't get rid of it.

[Dallas] ...his lungs pull air in
through his nose and mouth.

The sudden change in pressure
makes part of the throat snap shut,

which causes the "hic' sound.

[man] [hiccups, laughs]

[Dallas] And it doesn't sound
like clearing up any time soon,

so let's move on to
the more visible muscles...

like those beasts.

A rigorous training regime means
this chap's muscle cells

have enlarged,

meaning more of those actin
and myosin proteins

and more muscle contraction force.

-[man] Ah!
-[Dallas] But not quite enough.

This young man is about
to have a muscle problem

while simply relaxing.

Can you guess what it is?

[people laughing]

[man, off-screen]
You're too big for that thing.

[people shouting and laughing]

[man] I got a cramp.

[Dallas] That's right, sir.
It is, of course, a cramp.

As he hits the cold water,
the sudden temperature change

may have caused
a muscle spasm in his leg...

[man] I got a cramp.

[Dallas] ...which results in cramp.

Oh well. It could be worse.

[man] I'm dying.

Bye!

[electricity crackling]

[creaking, clattering]

[Dallas]
You might have a preconceived idea

that swing seats are
a romantic place to hang out

and contemplate life with a loved one...

but are they?

Looks like a nice place
to relax with your nearest and dearest.

-[chain creaking]
-[men shout]

[laughing]

[Dallas] Well, that's the end
of that bromance.

[man] [groans]

[Dallas] I was actually gonna get
one of those for our garden,

but I never realized
they were so perilous.

Let's see if good old science
can ease my troubled mind.

To get onto a swing seat,

our man must sit down carefully.

If he jumps onto it,

some of his horizontal momentum
could be transferred to the seat,

causing it to swing away.

Once on the seat, he must
take care how far he swings,

because if the combined center of mass
of his body and the swing

moves outside the legs of the seat,

then a turning effect will be produced,

causing it to pivot.

Our team was surprised that there was
so much science involved

in operating something so simple.

Therefore, some of our researchers agreed

to head out into the field

to see if the theory works in practice,

starting with that transfer
of horizontal momentum.

[man] Ah!

[Dallas] Yep, that seemed
to work just fine.

As he lands, most of his
horizontal momentum

is transferred to the swing seat,

and his feet are pulled from under him.

This means his center of mass
is no longer above

his base of support...

[man] Ah!

[Dallas] And he literally hits the deck.

With hindsight, that wasn't a good idea.

Having seen the earlier results,

this researcher is taking a back seat
testing his swing seat

and he's getting his dog,
Daisy, to do the leg work.

[man, off-screen]
C'mon. up here Up here!

[dog whines]

[man] [laughing]

-[dog whines]
-[man laughing]

Poor Daisy...

she's not got this
swing thing figured out.

[Dallas]
Yeah, maybe stick to Frisbees.

She's better at that.

Having four legs means Daisy has

a more stable base of support
than a human,

but even this isn't enough
for her to overcome the transfer

of her horizontal momentum to the swing.

[man, off-screen] [laughing]

Finally! These researchers
are actually on the swing seat.

[man] Whoa!

[Dallas] Yup, when you get on,
you still have to stay on.

They push off with their feet,

which moves their combined center of mass

outside the base of support
of the swing seat,

causing it to pivot around its legs.

Thank you science.
You've made my decision.

I'm sticking to deck chairs.

[glass shatters]

[electricity crackling]

[glass shatters]

If you're still contemplating
messing about with buggies,

doing crazy stunts with trampolines,

testing tensile strength,

or pushing the limits of garden furniture,

then take a look at the following recap

and then have a quiet word with yourself.

[all scream]

[boy screams]

[woman yells]

[electricity crackling]

[man] Oh!

[men shout]

[people laugh]

[girl] Ah!

[man] Ah!

[man shouts]

[man laughing]

-[man, off-screen laughs]
-[dog whines]