06x14 - Demolitions, Dams and Ladders

[bunniefuu]

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

[Dallas off-screen] Engineering is the
ultimate testament to human ingenuity.

It has allowed us to slip the grip of
gravity and conquer the skies,

or pull minerals from deep within
the earth's crust.

Engineering is our
greatest achievement.

-[man off-screen] Watch out.
-[Dallas off-screen] Or at least

that's the theory.

This is the show where
we look what happens when

the engineeringly uneducated
make elementary errors.

Then we reveal
what went wrong.

And why with the help of such principles
of engineering as air foils.

Post and lintel.

And combustion engines.

So, strap yourself in.

[screams]

Because this is.

The Science of
Stupid Engineering.

In this show we'll be looking
at water jet propulsion.

Ladders.

And sails.

But first this.

Engineering is usually associated
with creating things

rather than destroying them.

But sometimes the old must give way to
the new and certainly the most

entertaining way to do
that is to blow things up.

To manage the
incredible forces involved

lots of planning is required to
ensure pinpoint perfect timing.

With the aim of a safe
and controlled result.

But don't forget
engineering lesson 101.

Always ensure the building
is empty prior to demolition.

When you need to remove a building one
of the safest ways to do it

is by using expl*sive
demolition.

expl*sives are placed strategically so
they take out supporting pillars

and walls.

Without proper support

gravity takes over pulling the rest of
the structure down

and the building collapses.

Explosions consist of rapidly
expanding gas

that helps by overcoming the material
strength of the structures nearby.

So care must be taken to use exactly the
right amount of expl*sives.

Too little won't fully break
the supporting pillars

and too much can cause fragments
to fly out of the structure.

Usually explosions are positioned and
timed so that the building collapses

inwards within its own footprint
to avoid damaging anything nearby.

They are spectacular and are
something of a crowd magnet.

You better pay attention,
blink and you'll miss it.

And stand back so the
expl*si*n misses you.

Here the detonations are correctly timed
so it collapses neatly in on itself.

But slightly too much expl*sive
has been used, which propels

debris outside the structure and right
into our camera man.

[man off-screen] Oh.

[Dallas off-screen] Still there aren't
many people who can claim to have been

hit by a collapsing building, so you
should really be pleased.

But what happens if you
use too little expl*sive?

[cheers]

[Dallas off-screen] Not a lot.

[man] OK, so now what?

[Dallas off-screen] So now someone has a
bit of explaining to do.

So what have we
learned so far?

Well, if you want something to fall down
you need to take out the supporting

pillars and the best way to do that,

is pretty much any
way other than that.

Take out the supporting pillar and
gravity will always take over,

leaving our construction worker to
beat a hasty retreat.

Alright, let's try a
different approach.

[man off-screen] Wow.

[Dallas off-screen]
Effective but painful.

There you go demolition,
smashing stuff.

Many of the quicker water craft use
water jet propulsion systems.

They make clever use of the fact that
water is denser than air,

so less acceleration of the
fluid is required

to create the same
thrust as a jet engine.

Apply this to a small boat

and that engineering
feels very exciting.

This jet sprint boat is like an aquatic
rally car, very fast,

extremely maneuverable
and powered by water jets.

Or you could use all that power to
boldly go where no boat has gone before,

up the rapids the wrong way.

The first patent for ships powered by
water jets was filed in 1892,

incredibly this is about a decade before
cars were mass produced and three years

before the first radio
signal was sent and received.

I'm sure things have moved on since then
so let's look at the science.

A rotating impeller draws water in and
accelerates it backwards,

the volumetric flow rate is always
constant so by channeling the water down

a narrower pipe it increases
the flow velocity.

As the rapidly moving water
leaves the back it imparts an equal and

opposite reaction force on the craft,
driving it forward.

This is Newton's third law.

You can precisely control the vector of
the resulting thrust to change direction

but you need to be careful or
things can quickly go wrong.

Newton's third law and the principle of
volumetric flow rate have been applied

to water jets for large vessels,
such as ferries and military craft

but the original use of water jet
propulsion systems

was in small leisure
craft, like speed boats and jet skis.

A holiday in paradise.

[woman screams]

[Dallas off-screen]
Sun, sea, sand.

And scary stupidity.

An inaccurate thrust
vector sends him off course

and the slope at the front
of the other jet ski

creates and impressive
parabolic trajectory.

[woman] Oh my God.

[Dallas off-screen] His partner doesn't
look very impressed though.

Luckily they were all fine.

You can use jet skis
to do amazing tricks.

But I think he's
in over his head.

To do a flip this guy needed to
lean back further on take-off

to create more angular momentum.

The water jet can only provide
thrust while it's in the water.

And with insufficient momentum,

he won't be
impressing his mates.

All the engineering principles
for powered jet boats

work in much the same way with hoses.

Admittedly they're
a bit less entertaining.

[man laughs]

[Dallas off-screen]
Most of the time.

The high pressure water coming out of
the hose

imparts an equal and opposite
force.

That's Newton's third law of motion and
a fun day on the building site.

[man off-screen] What
a bunch of idiots!

[Dallas off-screen] So,
that's water jet propulsion.

[man off-screen] Whoa.

[Dallas off-screen] Useful stuff as long
as you master the basics.

[Dallas off-screen] A pile of twisted
metal and a very excited crowd.

But can you guess what construction
calamity caused all this chaos?

[Dallas off-screen] We asked you what
engineering fail happened here.

The answer, of course, is
down to flexural strength.

The awning has sufficient flexural
strength to support its own weight

but not the weight of a group of
rowdy sports fans.

So, the structure collapses and gives
the crowd something else to cheer about.

[cheers]

[Dallas] Now it's time
for today's tool station

where we provide you with
an invaluable guide to

the efficient and safe use
of a wide array of tools.

Today's tool sounds a bit boring
when you look at the text spec

but ladders are
anything but dull.

Some ladders are wonders of engineering

that allow real life heroes to do their
thing.

Others can be turned to sporting
use if you can think of...

literally nothing
better to do.

But put even the smallest ladder in the
hands of a middle aged man with dirty

windows and it can be an
altogether different story.

[screams]

Between 1990 and 2005 more than 2.1
million people were treated in hospital

emergency departments for ladder related
injuries in the US alone.

So if you're keen to
avoid becoming a statistic

you better pay attention to
the engineering behind them.

The rungs of a ladder offer a very
narrow base of support,

meaning that our man will have to take
care to keep his center of mass above it

to avoid creating
a turning moment.

An unsecured ladder leaning against
something relies on friction

with the ground and object it's leaning
against to keep it in place.

The shallower the angle of the ladder
the more horizontal force on the

ground and vertical force on the wall,
increasing the risk of a slip.

[screams]

And lastly a ladder must have
sufficient flexural strength

to withstand the bending force
applied by the climber.

[man] Oh.

[Dallas] Right so that's basically
telling us to not lean too far away from

the ladder, make sure there's plenty of
friction with the ground,

ensure our ladders have
sufficient flexural strength

and keep the ladder angle steep.

Seems simple enough.

Remember the rungs of a ladder offer a
very narrow base of support,

which means you
don't want to be.

Yeah, doing that.

Our builder has chosen a
loose beam to hang on to

but when it gives way he leans
outside his base of support,

creates a turning affect
and justifies the presence of

health and safety experts
on building sites.

[man] Oh, oh.

[Dallas off-screen] Homemade is
an adjective you don't really

want to hear in front
of certain nouns.

Like flamethrower, grenade
and, of course, ladder.

[laughter]

Not only did our thrifty DIY
enthusiast fail to choose

materials with sufficient
flexural strength

but also place the ladder at
a relatively shallow angle,

ensuring his weight generated
plenty of bending force.

[laughter]

Now, what sort of surface reduces that
all important friction.

[woman] Ah.

[Dallas off-screen]
Oh yes, a smooth one.

Well, that's
ladders for you.

They're a bit up
and down really.

I don't think we've said enough
here at the Science of Stupid

but the humble sail
is an engineering marvel.

Until 1787 when John Fitch
pioneered the steamboat,

sails were the most effective way to
move people and goods around the globe.

These days sailing is used mostly for
leisure, so whether boating,

windsurfing or kiteboarding
are your idea of fun,

sails are your friend.

[screaming]

Well, usually.

We're all familiar with the
idea of a sail catching the

wind behind it to
push a boat forward

but thanks to some
clever engineering

you can also get your
boat to sail into the wind,

the techniques sailors
use is called tacking.

They zigzag across the wind and as the
air flow contacts the sail it changes

shape and becomes an air foil which
redirects the wind to the side.

This redirection will result
in drag in the direction

of the window and lift
perpendicular to it.

That sideways component is resisted by
hydrodynamic drag from the keel

producing a resultant
force that drives the boat

forward regardless of
wind direction.

But the force of wind on a
sail creates a turning affect

and sailors need to provide
an opposing turning affect

to resist the rotation or
the craft will capsize.

Someone who clearly understands air
foils and hydrodynamic drag

is Australian John Sanders.

He sailed staggering


without ever leaving the boat.

That took him
nearly two years.

Could this be a
future record breaker?

[laughter]

[screams]

Only if that record was
weirdest way to crash.

High wind speeds create a large drag
force on the sail, which imparts a

turning affect that rotates the boat

over the nose and results in a sink or
swim situation.

Yet, he seems to have
manage both at once.

[laughter]

Best leave this to
the professionals.

[screams]

[man off-screen] I've got
it, I've got it, I've got it.

[Dallas off-screen]
He clearly hasn't.

When out of the water the hulls can't
resist the sideways forces,

so slight changes in the angle of the
sail cause sharp turns and hard knocks.

I think they need
a change of tack.

When sailing's going well there's no
feeling like it, the wind in your hair.

[screams]

The boom in your face and of
course your butt in the sea.

And don't forget that
old sailor's motto,

when the boat turns downwind,
the boom will swing.

[screams]

Like that.

[Dallas] I was recently enjoying a fine
brunch with an engineer friend of mine.

And I explained that I was hoping to
modify a river in such a way that it

could become an attractive
habitat for beavers.

"Damn it," he shouted.

"There's no need for bad language," I
replied and I stormed out of the café.

It was only later that I realized he
was offering a solution

to my beaver-based conundrum.

Yes, dams count among the engineering
wonders of the world,

immense structures capable of holding
back vast bodies of water.

In the natural world beavers build dams
to create rustic wooden homes and deep

pools in which they can hide from
predators.

Which begs the question,

if our furry friends can build
a dam, how hard can it be?

[laughter]

Right, pretty hard it seems.

Okay, so this whole dam business seems a
bit trickier than it might appear.

So, before you head off to
stem the flow of a major river,

you might want to brush
up on the science.

To be effective a dam must be made of an
impermeable material with sufficient

strength to withstand not only its own
weight

but also the pressure of water
behind it.

Gravity dams are simply
huge mounds of material

that are held in place
by their own mass,

whereas arch dams bend into the body of
water they hold back,

their shape helps to
withstand hydrostatic pressure

by redirecting the
force downwards

and into the sides of the
river they are damming.

Okay, material choice
does seem key here.

I was planning to build a dam
to demonstrate the principles

but I was a few
billion dollars short.

Luckily our worldwide network of field
researchers

have been busy experimenting
with slightly cheaper materials.

One of our senior researchers came up
with a theory that ceiling plaster

might have a material strength similar
to that of concrete,

so he ran an experiment.

And he phoned
results straight in.

[man off-screen] The *******
ceiling has fallen down!

[Dallas off-screen] It turns out that
the strength of plaster

is well below
that of concrete.

Let's not forget that your
dam needs to be impermeable

to stop the water passing
straight through.

[man off-screen] Just relax.

[laughs]

[Dallas off-screen] Our young
researchers have conncluded that

trampoline fabric is not in fact
impermeable.

Yes, concrete is beginning to
look increasingly attractive.

Next our entire
Canadian research team

turned their attention
to material strength.

[cheers]

I think the result
is pretty clear,

plastic sheeting
isn't up to the job.

Well, that's dams for you, best left to
qualified engineers.

Sorry, and beavers.

So much engineering is huge
and impressive but let's not

overlook the importance
of the little things.

The humble bracket may not be especially
complicated but they are vital.

This arch is effectively two brackets
that join in the middle

and it can support not only its own
weight

but the weight of even the
largest of vehicles.

Whereas this shelf can't
support much at all.

One of the earliest examples of a
scrolled console bracket can be found in

the Temple Of Concord in Rome
and dates back to 7 BCE.

Let's see if things have
moved on since then.

An object with an attachment point at
one end is called a cantilever,

adding a weight means there
are two forces acting here.

Down from the load on the right and
upwards from the wall on the left.

These two forces separated by distance
create a turning moment.

[screams]

A bracket will resist the turning affect
by translating the downward force on the

cantilever into horizontal
force directed at the wall.

But this still applies
a stress to the fixings,

which can result in their tensile or
sheer strength being overcome.

[screams]

Cantilevered brackets
are intrinsically strong.

I mean, of course you need to
be careful not to overcome

their sheer strength but
that's not usually the issue.

Poor fixings are.

CCTV is a great idea to
secure your premises.

But it would have been a good idea to
secure the shelves first.

Removing the box from the back means
there's now more weight on the front

of the shelf, creating a turning moment,
and without a bracket,

the shelf collapses and gives his boss
something to whine about.

She's climbed the curtains
but how will she get down?

Yeah, that'll do.
Eight lives to go.

[man off-screen] Yep. Knew that was
going to happen.

[Dallas off-screen] As the
shelf is fixed in the middle

the cat creates a turning
effect by landing on one end

but the bracket's fixings have
insufficient sheer strength.

To avoid a kitty calamity.

Mum's always telling her not
to rollerblade in the house.

[woman] I'm going to hold
on to here for a sec.

[Dallas off-screen] But
she'll never find out.

Although that's gonna take
a little bit of explaining.

As she leans on the shelf she creates a
large and downward force

that overcomes the sheer strength of the
bracket's fixings.

So, there we go.

Brackets, a lot more
complicated than you'd think.

Apparently the American
physicist, Michio Kaku said,

"What we consider as impossible are
simply engineering problems.

There's no law of physics
preventing them."

He obviously hadn't
met any of this lot.

[man] Woah!

[music plays through credits]

[man] Relax.

[man] What a bunch of idiots.