03x10 - Kayaks, Buildings and Handbrake Turns

[bunniefuu]

[Richard]
This is the Science of Stupid.

[electricity crackling]

[glass shatters]

Yes, this is the show that marries
complex science with simple stupidity.

[man screams]

We find backyard experimenters

who've set aside doubt,

second thoughts,

or anything resembling...

-[man] Oh. [bleep]
-[Richard] ...common sense.

Allowing us to examine the science

behind some key principles...

[man screams]

[Richard] ...such as angular momentum,

base of support,

and that most inescapable
of nature's forces,

gravity.

You can run,

but you cannot hide
from the Science of Stupid.

[glass shatters]

[electricity crackling]

In this show,
we'll explore sliding friction,

the all-important center of mass...

[man screams]

[Richard] ...and moments of inertia.

It's breathtaking stuff.

But first, this.

[glass shatters]

[electricity crackling]

[Richard] Now, Albert Einstein
probably didn't hang out

down his local pub with
a group of professional wrestlers.

But they would have had more
in common than you might think.

You see, for wrestlers
to entertain the crowds

without permanently maiming each other
is a real science.

[rock music playing]

This is a sport where
people with unique fashion sense

find imaginative ways
of throwing each other about.

[man screams]

But despite overwhelming medical evidence

as to why you should never
try this at home...

[audience gasps]

[Richard] ...some people still do.

Here's a guy attempting
the Harlem hangover.

I did say, "Attempting."

He's trying the senton splash.

Needs a bit of work.

And here's the rib cruncher.

That's not what it's called,
it's just what he did.

[man]
*** mate, that must have hurt!

[Richard] Do you think?

To understand why jumping on your mate
from the top of a wardrobe

doesn't make you a professional wrestler,

here are some key scientific principles

that they use to give us
the thrills and spills,

without giving themselves
the need to go to hospital.

Pushing off as hard as possible
maximizes his impulse

and take-off velocity.

As he falls, he builds momentum,

accelerating to a speed
of 23 feet per second.

But landing on a compliant surface

spreads the impact
over a longer period of time,

reducing the force
experienced by both wrestlers.

So, a successful jump

relies on momentum,
or indeed angular momentum,

if you fancy a flip,

not to mention spreading the impact

as much as possible
across a soft landing surface.

This guy is taking no chances.

[man, off-screen] Here he goes.

[Richard] Thick padding
and a thick mattress.

-[man, off-screen] My guy.
-[man 1] Whoa!

[Richard] But a thin grasp
of the rules of science.

Too little angular momentum on the jump

and an excessively angular back,

giving him the ability to kick himself
in the back of the head.

[man screams]

[Richard] Yeah, don't try this at home.

Now, what if you take the mat with you?

[screams]

Yeah, but you do still have to land on it.

[screams]

In wrestling, it's not just mats
and the bouncy floor of the ring

that spread the force of your impact.

It's also your opponent.

[inaudible chatter]

[Richard] Providing you can reach them.

To be honest, it would
have gone worse if he had.

This opponent seems willing to help
break the fall from--

Wait, is that a monkey?

[man screams]

[Richard] Oh, no, it's an ape.

If he'd landed on his friend,

he'd have had a shorter fall
and some extra cushioning.

[man screams]

But instead,
this cheeky chimp hit the ground

with momentum equivalent
to a 30-pound cinder block

traveling at 90 miles an hour.

[groaning]

[man] You all right, dude?

Yeah! We've got a star.

[Richard] Yeah, one star out of ten.

-Please...
-[man screams]

...don't ape this behavior.

[Richard chuckles]

[electricity crackling]

You know what?

For me, there's nothing quite so exciting

as when that first snow falls,

and I get to dust off my toboggan
and head out for some harmless fun.

Whee!

[man screams]

[Richard] Oh, never mind.

But if you enjoy hurtling down slopes

as much as he used to, why buy a toboggan?

There are plenty of
homemade options you can try.

These guys consider their air bed
to be suitable for snowy conditions.

Is that a fence?

-[loud crash]
-[Richard] Yeah, it is.

Whilst he thinks his oil drum
more suitable for grass.

[man screaming]

[Richard] Coming through.

[man] Take my glasses!

[woman] Do it. Do it.

[Richard] And some things
aren't suitable for anything.

-[man] Oh, my God.
-[woman screams]

-[man] Ow.
-[woman laughs]

[Richard] Except possibly
a world of pain and regret.

This is clearly a highly dangerous

and, therefore,
highly inadvisable activity.

But if you are intent
on fashioning your own homemade sled,

then you should know
that no downhill thrill

is complete without a large dose
of sliding friction.

The smoother the two surfaces in contact,

the lower the coefficient of friction.

So whatever your craft,

a smooth bottom on a smooth slope
is less likely to grip the surface,

helping you build momentum.

Less surface area in contact
doesn't necessarily mean less friction

because of the potential
for greater pressure

at the point of contact.

Got that? Okay.

By way of comparison, let's see how
that coefficient of friction works on ice.

[indistinct chatter]

[all scream]

[man screams]

[Richard] Yep, really well.

His minimal approach,
using his own back as a sled,

resulted in a very low
coefficient of friction.

So, a bit too slidey

unless you're keen to see
what's over the edge of that cliff.

These guys are off to a flying start.

Not much sliding friction there.

Bit more friction there.

-[loud thud]
-[Richard] Quite a lot there.

Sliding on steps means
less contact area with the tray,

but remember,
not necessarily less friction.

Still slid into a bin, though,

and a car.

He's experimenting with rolling friction

and gravelly friction.

The low amount of rolling friction

resulted in a high amount
of centrifugal force

and a high degree of pain.

Maybe try a less steep hill?

-[man] Are you all right?
-[groans]

[Richard] Well, that is a little less
steep but that is a roof.

So you do need to watch out for

the 6-foot drop at the end.

[man] That was so gnarly.

[Richard] Not so much gnarly,

more, I don't know, stupid?

Yep, never try this at home.

[electricity crackling]

[girl] I'm not prepared.

[Richard] Can you guess
which scientific principle

this girl is about to demonstrate?

[glass shatters]

[electricity crackling]

[girl] I'm not prepared.

[Richard] So, did you work out the science
she's about to show us?

[girl shrieks]

[all scream]

[Richard] Yes, it's centrifugal force
or lack thereof.

When the chain went slack at the top,

centrifugal force was diminished

and gravity took her
on the path of least resistance,

which was straight down.

[laughing]

[Richard] When I was a lad,

showing off meant leaning
nonchalantly against a wall

with one hand in your pocket,

or, if you really wanted to go next level,

both hands.

Cool.

These days,
people tend to take showing off

to a new level altogether.

Behold, the front flip.

Wait for it.

[screams]

[Richard] That was more like
a flip and a half.

But you get the idea.

Look, it can be impressive.

But, evidently, it's also extremely tricky

to pull off a forwards 360-degree flip

and land on your feet

without the accompaniment of acute pain.

But it can be done,
and here's the science to prove it.

Running and pushing off hard

gives him enough vertical velocity
to counter gravity.

For the flip, he needs angular velocity,

and the closer his mass is

to his center of rotation,
the faster he'll rotate.

He then untucks,
reducing his angular velocity,

slowing the rotation,

to land safely.

So it's partly about getting
enough air time to do your flip

before gravity
pulls you back down to earth.

And to give you that all-important height,

you need plenty of vertical velocity.

A bit like this.

But not exactly like this.

Nice flip but not enough height
for the second one.

Another method is to start from a height.

Although he might
have done better with less.

Yep, if it's two flips you want,

how about combining height and velocity?

[boy screams]

[Richard] Okay, you might need
a bit more of both.

Oh, that's it, mate. Rub it in.

If you can't manage the air time,

there is another way
to fit in that extra spin.

Remember angular velocity?

If not, here's a little rhyme
to jog your memory.

To take off and spin, tuck yourself in.

To slow down and land,
stretch out your hands and legs.

Catchy, I know, you can have that.

And here's what it looks like in practice.

Almost perfect. Have another go.

Not so perfect.

For landing, you need to untuck.

[boy screams]

[Richard] But a bit earlier than that.

He should have untucked here,

but he did it here.

[boy screams]

[Richard] Still, some people
don't untuck at all.

[man groaning]

[Richard] Like him.

And this is what happens
when you don't listen to my rhymes.

-[man groans in slo-mo]
-[Richard] Yeah.

Not making 'em up for fun, you know.

[bell rings]

And now for today's science lesson,

the part of the show where
I get to wear a groovy hat

and you get to learn about
a specific scientific principle.

The activities you are about to see
involve this principle,

but can you guess what it is?

A man enjoying a spot of sunbathing...

[laughter]

A girl who doesn't know her own strength,

and this guy.

[boy] Whoa!

[Richard] Ever heard the term,
"Skating on thin ice"?

Yes, the one thing
they all have in common

is that they're demonstrating
the principle of pressure.

If you're not sure what that is
or how it works, listen up.

A larger surface will distribute force

over a larger area,

resulting in lower pressure,

making it less likely
to penetrate the object.

Concentrating the force of the blow

into a small surface area

increases its pressure,

making it more likely to push through.

Now, as you've just seen,

if the applied force is large enough,

the pressure will be enough
to make the weaker object yield.

Mallet versus tomato,

you wouldn't put your money on the tomato.

I hope you've been paying attention,
because it's time for a little test.

Question one: If a force is applied
to a smaller surface area

is the pressure higher or lower?

♪ ♪

It's higher.

The force of the weight
of the bike and the rider

was focused into a small area
at the bottom of the wheel.

Yeah, you owe them a new ramp.

Question two:

What happens when the strengths

of two objects pressed together
are not equal?

Let's see.

[man] Yahoo-hoo!

[Richard] Yep, the weaker one
will yield first.

He's testing the strength
of that skylight.

-[man, off-screen] Careful.
-[glass shatters]

[Richard] Success!

By jumping up and down,
he increased the force

and, therefore, the pressure
and the skylight yielded.

[man screams]

And when he hit the concrete floor...

[man] My back!

-[man screams]
-[Richard] ...he yielded too.

Don't worry, he was okay, if a bit sore.

And finally, question three
of our science lesson.

Pressure is related
to surface area, but what else?

That's right, force.

These kids don't have quite enough.

But daddy does.

Force divided by surface area
equals pressure,

not to mention, happier kids.

[all cheering]

[Richard] This kid's got a nice thin stick

and a bit more force about him.

[indistinct chatter]

Okay, maybe a bit too much.

And here ends our lesson on pressure.

No, I don't think he
needs any more sweets.

[woman, off-screen]
You drop it with the stick.

[glass shatters]

[electricity crackling]

[Richard] Maybe it's because
I'm getting softer as I get older,

but there is something rather beautiful

about a father carrying his child aloft

upon his shoulders.

Look at them, father and child.

It's magical.

And look at him,

a grown man on top of another grown man.

[scattered screams]

It's less magical.

Yes, unfortunately,

carrying people around on shoulders

does not end with childhood,
but really it should.

And that's because of the precariousness
of a high combined center of gravity.

Allow me to explain.

Pop someone on your shoulders,

and you have two centers of gravity,

which makes for a higher

and more precarious
combined center of gravity.

The bigger the mass of
the person being carried

and the higher they are,
the less stable you will be.

If you move, the combined center
of gravity gains momentum,

meaning you're more likely to take
a tumble if you need to stop.

So, if you insist on carrying
another grown-up on your shoulders,

make sure they are as low as possible,

directly in line with your feet

and, ideally, not twice the size of you.

It is simple.

[laughter]

[Richard] But apparently,
not simple enough.

Oversized mass,

high combined center of gravity,

too far over base,

every box ticked.

[laughter]

He was okay, but please don't copy this.

Not sure what this game is,

but at least he's got some friends
to offer a larger base of support.

[man screams]

Just not a particularly competent one.

[woman] Mmm.

[Richard] Here's a method of lowering
that combined center of gravity

and raising it
and then lowering it again.

[women scream, crash]

That's a bit too low.

Bringing her legs together
narrowed the base of support,

and by rocking, she removed their
combined center of gravity beyond it.

[women scream, crash]

And added some unhelpful momentum.

But she's not the only one.

There's also these guys.

[men scream]

[Richard] Schoolboy error.

Running adds momentum

to an already precarious
combined center of gravity.

[men scream]

Oh, the shame of it.

[electricity crackling]

[Richard] Emergency stops,
by their very definition,

are generally reserved for emergencies,

the reason being that stopping suddenly

can have catastrophic results,
if done incorrectly.

But they are essential
for nearly all modes of transport.

There's the four-legged kind.

The four-wheeled kind.

Could be expensive.

And the two-wheeled kind.

[man screams]

Predominantly embarrassing.

If you do need to break hard and fast,

you're going to need
an understanding of

some of
Newton's fundamental laws of motion.

If an object is moving,
it's gonna want to keep moving.

And slowing it down only happens
when an opposing force is applied.

Here's how that works on two wheels.

When braking, inertia pulls the bike

and rider's combined center of mass

forwards onto the front wheel.

This gives the front wheel more traction.

But brake too hard with the front wheel,

and inertia combines
with the slowing force

to create an unpleasant
turning effect around the axle.

One method for countering
that nasty turning effect

when braking hard, is to lean back.

Another is to balance your braking
between the front and back brakes.

It's just something every biker knows.

Let's see if he knows.

-[man screams]
-[Richard] No.

No, he didn't know.

Lots of momentum plus excessive braking
on the front wheel,

led to a turning effect

and an upside-down
bike-on-top-of-man scenario.

Less momentum here...

[tires screech]

...but just enough for that to happen.

Classic inertia.

Bike stops, man keeps going,
nearly into car.

Oh, yeah, don't worry about the bike,
just check your phone's okay.

Phew!

Did you know that
your front brake provides

around 70% of your stopping power,

so the rear wheel has much less traction.

Maybe you did know that.

But does he?

[tires squeal]

Well, he does now.

He applied both, first his back brakes,

nice skid,

and then his front brakes.

Not so nice face-plant.

Okay, got the science,

it's time for a textbook emergency stop.

But watch out for the...

[man] Arghhhh! Ohh!

[Richard] Okay, he did apply his brakes
fairly early,

but the larger the mass...

[man screams, thuds]

[Richard] ...the more braking force
you need.

That's Newton for ya.

And if you thought his laws on motion
only affect you on two wheels...

[thuds]

[Richard] ...you'd be wrong.

[woman, off-screen]
She didn't press the brakes!

[Richard] She did.

She definitely did.

Please nobody tell mom!

[glass shatters]

[electricity crackling]

[Richard] That's all
the science-based idiocy we have time for

and more than enough evidence

to show why you should not attempt
any of the stunts you've just seen

because we'd love to
see you again in one piece,

for the next Science of Stupid.

[lively fiddle music]

[man screams]

[man screams]

[man screams]

[all scream]

[man screams]

[man screams]

[woman screams]

[man screams]

[man groans]

[indistinct chatter]