07x19 - Gravity, G Force and Impact Events

[bunniefuu]

[Dallas]
This is the Science of Stupid in space.

[typewriter dings]

Space, the last unconquered frontier.

The question of what's out there

has intrigued mankind for millennia,

and the exploration of space
has come to represent

the very pinnacle
of man's technological achievements.

But if understanding
the emptiness of space

seems just too much
to get your head around,

don't worry.

Much of the science that helps explain
the wonders of the universe

can be demonstrated
right here on Earth,

so join us as amateur astronauts boldly go

where proper scientists
have gone more successfully before.

Marvel as they look to the heavens,

and unlock the mysteries of space

by studying cosmic scientific principles

like gravitational attraction,

functional fitness,
and autonomous robotics.

Prepare for launch.

It's the Science of Stupid in space.

[debris whizzing]

[crashing]

In this episode, we'll be looking at

how to experience high G force.

Not like that.

Impact experiments...

[boy groans]

...and gravity.

-[all exclaim]
-[woman, off-screen] Oh, my God.

[Dallas] But first...

this.

Humankind has long dreamed

of venturing into space

but it wasn't until 1961

when the first crude rocket

was finally able to throw off
the shackles of gravity

and cross the threshold.

It was a watershed moment,

the birth of a new epoch, the space age.

But all this wouldn't have been possible

without the rocket launch.

To achieve these staggering feats,

you need a staggering amount of power.

The good news is,
you don't need billions of dollars

and a team of scientists behind you
to have your own rocket launch.

In 2004, Civilian Space Exploration Team

became the first amateurs
to launch a rocket into space.

[man, off-screen] Whoa!

[laughter]

[Dallas] This isn't them.

[laughter]

Rockets are powered by combustion,

a process that requires oxygen,

and as there's no oxygen in space,

any rocket leaving the atmosphere

will need to take its own supply
as well as fuel,

but what other science
does lift-off rely on?

When the fuel burns,
it creates a large volume of hot gas

which needs to be released
at a controlled rate.

This hot gas is funneled out of a nozzle,

creating an equal and opposite reaction,

that's Newton's third law,
thrusting the rocket upwards.

And once that rocket takes off,

it's vital that it keeps
pointing straight,

being long and thin,
if it starts to rotate

it'll suddenly have
a lot more air resistance,

which could make it head
into unpredictable directions.

So, let the countdown begin

and let's see how
our amateur rocketeers are getting on.

Okay, these guys look like
they know what they're doing.

That is a serious bit of kit.

[man over PA] ...three, two, one.

[Dallas] Lovely launch, terrible
direction,

and I think you might have
just accidentally

declared w*r on Canada.

The launch starts well.

The fuel burns, creating a hot gas,
which is pushed out of the back,

but it starts to veer off course.

Something else goes wrong

and suddenly all that power

doesn't seem quite so much fun anymore.

Let's be more cautious
and have a look at a smaller rocket.

[boy] We're launching off
a rocket that, um...

Dad had when he was a kid.

[Dallas] Sounds like
an important heirloom.

You better be careful with it.

[Dad, off-screen] Oh, man!

[laughing]

What happened?

[boy] I don't know.

[Dallas] Perhaps I can help.

Your antique rocket looks like
it's mostly made of cardboard,

and as it ignited,

the housing couldn't contain
the rapidly expanding hot gases.

[Dad, off-screen] Holy smoke!

[Dallas] Well, that is another word for
it.

Yes, I suppose.

[electricity crackles]

[creaks]

[clatters]

Our atmosphere is the blanket of gases

that are held to the Earth
by its gravitational attraction,

and like a giant blanket,

our atmosphere maintains
the Earth's temperature,

but unlike a blanket,

it also provides the air we breathe.

That's really where the blanket metaphor
starts to break down.

Maybe the simplest way to look
at what our atmosphere does

is to do experiments somewhere

that doesn't technically have
an atmosphere,

like the moon.

[David Scott over radio]
In my left hand I have a feather.

In my right hand a hammer.

We're about to drop
the two of them here

and hopefully...

they’ll hit the ground at the same time.

How about that!

[Dallas] That proved Galileo was right
and that, due to gravity,

two objects will fall at the same rate,
regardless of weight,

but that doesn't work here on Earth.

The hammer falls faster

and that is because of air resistance.

The shape of the feather
means it suffers a lot more

from air resistance.

It may not seem like it,

but compared to the vacuum of space,

our atmosphere is very dense.

Think of this match as space debris

and the strike plate
as our atmosphere's air resistance.

The sudden increase in friction means

much of the falling object's
kinetic energy

is converted into heat.

Which is one of the reasons
why most things that enter our atmosphere

burn up before hitting the ground.

-[girl 1] Look at that sh**ting star!
-[girl 2, off screen] Yeah.

[Dallas] Our young friend isn't wrong,

but what is a sh**ting star?

[man, off-screen] It's huge.

[Dallas] It's any natural
or man-made object

burning up as it enters the atmosphere

as air resistance
causes frictional heating.

[man, off-screen] Look at it.
It's coming apart right now.

[woman, off-screen]
Yep, you can see the trail on it.

[Dallas] NASA estimates
that at least one piece

of man-made space junk
falls to Earth every day,

but most of them burn up

before they get through
the upper atmosphere.

This is an old rocket body,

but if you still want to wish on it,

be my guest.

We've a lot to thank our atmosphere for.

Parachuting, for example, is only possible

because of our planet's dense atmosphere.

[man, off-screen] Oh, look at that.

[Dallas] Which provides the air
resistance needed for a slow descent.

So, you couldn't do this in space,

and even here on Earth, it's quite tricky.

[man, off-screen] Heads up!

Oh!

[Dallas] Of course, parachutes also
need...

[man, off-screen] Heads up!

[Dallas] ...steering.

[woman, off-screen]
That's not supposed to happen.

[Dallas] Want another example?

[man, off-screen] Oh, my God!

[man]
What is he doing?

[Dallas] Well, I would have thought
that was obvious.

He's demonstrating
how friction causes heating.

[man, off-screen] Are you serious?

[Dallas] Okay, it's not a perfect
analogy,

but if you imagine the road
as our atmosphere,

and the remains of his wheel
are something plummeting to Earth,

then it sort of works.

[man, off-screen] Bro!

[debris whizzing]

[crashing]

Here's a quick question:

Why do you need to strap yourself down
to go for a job in orbit?

[creaks]

We asked you why you need to
tie yourself to a running machine

to jog in space.

Well, the International Space Station
is in orbit,

which means you and it

are constantly falling around the Earth

while never hitting the ground.

Not a problem here on Earth.

[both laughing and exclaiming]

[debris whizzing]

[crashing]

Americans have astronauts,

the Russians, cosmonauts,

but however you say it,

if you're heading to space,
you'll need prove

that you have the required
physical and mental attributes.

What author Tom Wolfe called
"the right stuff."

To find out who's got it,

candidates are run through
a barrage of tests.

Maybe the most famous of which

is the ability to withstand high G forces.

Looks fun, doesn't it?

[grunting, breathing heavily]

[grunting forcefully]

So if you want to find out
if you're made of the right stuff,

then how should you beat
the G force centrifuge?

G force results from
the acceleration of an object

relative to Earth's gravity.

Sitting still, we all experience 1G,

which our bodies are designed for,

but G force is increased
through acceleration.

By 2G, our bodies need to work
twice as hard

to pump sufficient blood
to keep our brains oxygenated.

By 4 or 5G, most people's hearts

can't summon the necessary blood pressure,

it starves their brains of oxygen,

and they pass out.

Well, it's been a long time
since the 1960s,

and now, at the dawn of a new space race,

we've decided to help out
by running our own tests,

and I know what you're thinking,

this all looks terribly costly.

Are you sure that you've got the budget
for such an undertaking?

Well, we may have had to economize a bit.

This guy's fashioned his own simulator

by using just an office chair
and a leaf blower.

You have to admire his ingenuity...

if not his balance.

-So, don't try this yourself.
-[screams]

It's a brave attempt,

but, sadly, he's not got
the physics quite right.

To experience significant G forces,

he needs to harness centrifugal force,

and for that,
he needs to be at a distance

from the axis of rotation.

By being in the middle,

mostly, all he's getting is dizzy.

A lot of the early astronauts
were military pilots,

so this kid is in
an ideal testing environment

to see if he's got the right stuff.

It looks like he's enjoying it so far.

[groans]

[exhales]

Maybe that wasn't a smile after all.

As the plane banks,
this kid is constantly accelerating,

this provides more than 6Gs

pulling the blood away from his brain
and causing him to do...

Well, that.

Our astronaut selection search continues.

[grunting]

But how is our trainee
remaining conscious at 6G?

Well, by using a special
breathing technique,

he's maintaining his blood's
oxygen content,

and by tensing his muscles,

he's forcing blood to continue
to travel to the brain.

No one said it was gonna be all glamour.

[electricity crackling]

[creaking]

[clatters]

Just 12 men have set foot
on the lunar surface.

You could fit them all into a mini bus.

Provided it's got
the right number of seats.

So you'd imagine that
if you were one of those dozen,

it would be the highlight of your life,

but Neil Armstrong said pilots
take no special joy in walking.

Pilots generally take pride
in a good landing,

not in getting out of the vehicle.

Which is weird because walking on the moon

looks like one of
the greatest things ever.

[Gene Cernan over radio]
Boy, is this a neat way to travel.

[Dallas] Partly, of course,
due to its low gravity.

Whereas back here on Earth, gravity...

[boy] Ahh!

[Dallas] ...can really get you down.

To understand gravity,
it helps to be clear

on the difference
between mass and weight.

No matter where I am in the universe,

my mass remains the same,

but my weight will change

depending on the gravitational attraction
I experience.

Thus, on the moon,

I'd have the same mass but I'd weigh less.

So there you go, a helpful dieting tip.

To successfully jump
on the surface of the Earth,

she must apply enough force

to overcome her own weight
due to gravity.

If she applies the same force
on the surface of the moon,

as simulated by this trampoline,

she will jump a lot higher

as the moon's lowered
gravitational attraction

means she will weigh less.

And she'll also take a lot longer

to hit the surface.

Every single object exerts
its own gravitational attraction.

It's just that the more massive it is

and the closer you are to it,

the greater that attraction will be.

Luckily, you don't need to travel
all the way into space

to conduct your own experiments
with gravity.

These young astrophysicists

have designed their own experiment

as to what it's like experiencing

the gravitational attraction of the moon.

[boy] Ah! Boom!

[screaming]

[Dallas] Makes you proud, doesn't it?

The Earth has a mass of


whereas the moon only has a mass
of 80 billion billion tons,



Because of this, the moon's gravity

is only 16% that of Earth's,

so you weigh less
and can jump much higher.

Conversely, Jupiter is much more
massive than Earth

and has 2.5 times the surface gravity.

Therefore, as these
researchers are simulating,

you would weigh
significantly more on Jupiter

due to its increased
gravitational attraction,

but life on Jupiter...

would be less forgiving.

[creaks]

Have you ever wondered

what a meteor entering
Earth's atmosphere looks like?

Well, wonder no more.

[whooshes]

But that was small
compared to the asteroid

that hit Earth 66 million years ago.

Believed to have led
to the extinction of the dinosaurs

along with three quarters
of all life on Earth.

It was what's known as an impact event

and our researchers
are running experiments

to understand what happened.

Calculating the velocity necessary
to wreak such havoc...

[people scream]

Investigating how solid rock
can be moved like a fluid.

[men, off-screen] Oh!

[Dallas] And creating a scale replica

of the crater left by the impact.

[boy groans]

But if you want to understand
impact events,

you'll need to get your head
around collisions,

momentum, and kinetic energy.

A moving object has momentum,

but what happens
to that momentum on impact

is largely dependent

on the composition of the surface it hits.

A solid surface can't dissipate
much of the kinetic energy,

so it's absorbed by the moving object.

A granular surface
can move on impact,

so some of the kinetic energy
can be absorbed

and dissipated.

The same applies

when the moving object
collides with a fluid.

So that's the rules as they apply
to regular objects on Earth,

but in space, things are a bit different.

Objects in the vacuum of space
experience no air resistance,

which means meteorites
can enter our atmosphere

at speeds of 44 miles per second,

and at that speed, when a large enough
meteorite hits a solid surface,

that surface will move

as though it was sand or even water.

So instead of acting like this...

it acts more like this.

It's a lot to take in, I know,

but, luckily, a number
of our researchers across the globe

have been working on some simple demos.

Did you know
that NASA uses squash courts

when studying impact events in space?

Okay, that's a-a lie,
but they should do.

Think about it. Watch.

[man grunts]

Our human meteorite builds up momentum,

which increases when he trips.

He's traveling a bit slower
than 40 miles per second,

so the wall doesn't dissipate
much kinetic energy,

but his face does.

[man grunts]

Okay, if we're gonna understand
the impact events featuring meteorites,

we're gonna have to use our imagination.

Imagine this boy is a giant meteorite

and the sand is
the solid surface of the Earth.

[boy screams]

[laughter]

Meteorite enters Earth's atmosphere
at great speed,

meteorite collides with Earth,

and solid surface acts like
a granular material,

absorbs kinetic energy,
and the crater is left.

[laughter]

I imagine the dinosaurs
had a slightly different reaction

to their impact event.

[man, off-screen] Loser.

[electricity crackling]

[creaking]

[Dallas] World-famous astrophysicist
Stephen Hawking once said,

"We have given our planet
the disastrous gift of climate change,"

and then reasoned,

"The only places to go are other worlds."

Easy enough for the professor to say,

not so easy to achieve,

but we don't shirk our responsibilities
here at the Science of Stupid,

so we're gonna try our best
to find somewhere suitable for human life.

Well, first, we humans require water.

The good news is,

water is abundant throughout the universe.

The bad news is
that almost all of it is frozen,

so we're gonna concentrate
our planetary search

on those zones around stars

which could contain liquid water.

These are known as
circumstellar habitable zones,

and as luck would have it,

there could be as many as


in them in our galaxy.

If a planet's too far from a star,
it will be too cold

and water on the surface
will remain frozen.

Too close to its parent star
and it'll be too hot

and all the water
on the surface will evaporate.

Scientists have nicknamed
circumstellar habitable zones

as Goldilocks zones

as they're not too hot
and not too cold.

The Earth, of course, lies well within
our solar system's habitable zone.

It's the only planet

known to have such stable bodies
of liquid water on its surface,

and this makes it the perfect spot
to generate and sustain life.

[kids] ♪ One, two, three, four, five ♪

♪ When's it going to be July? ♪

[Dallas] NASA's motto for the hunt
for extraterrestrial life is

"follow the water."

Of course, you can have
too much of a good thing.

[car horn honks]

[man laughs]

A planetary body outside
the Goldilocks zone,

like Jupiter's moon Europa,
is just too cold.

[man] It's moving. It went down.

[Dallas] The temperature never gets
above minus 225 degrees Fahrenheit,

so all the water on its surface
is permanently frozen.

[man laughs]

Ooh, looks like he's found
some that's still liquid.

[woman, off-screen]
[laughing] John's not gonna make it.

[record skipping]

[man] It's very cold!

-[Dallas] I bet.
-[woman snickers]

So what about Venus?

Well, if you love winter sports
with no snow or ice,

you might have to settle
for sandboarding on its dunes...

if you know how to.

[grunts]

[coughs]

It's thought that Venus might
once have been habitable.

but a runaway greenhouse effect

has led to an atmosphere 90 times
as thick as Earth's atmosphere

and a surface temperature of up to


[coughs]

So don't forget to pack your shorts.

[debris whizzing]

[crashing]

Well, that was all rather complicated,
but don't worry.

As astrophysicist
Neil deGrasse Tyson once said,

"The universe is under no obligation

-to make sense to you."
-[man] Five, four...

-[Dallas] Comforting stuff.
-[man] ...three, two...

-[Dallas] Oh, that's me.
-[man] ...one.

-[Dallas] Where's my helmet?
-[man] Ignition.

[indistinct chatter]

[grunts]

[boy] Boom! [screaming]

-[boy grunts]
-[man grunts]

[people scream]

[both laughing and exclaiming]

[men, off-screen] Oh!

[exhales]

[screams]

[man, off-screen] Oh! Heads up!

[grunting forcefully]