Kind: captions
Language: en
what would happen if you dropped a penny
off the Empire State Building could it
kill someone walking on the sidewalk
below
what does it take to create a deadly
projectile
oh I'm gonna put this to the test with
original mythbuster Adam Savage he's
going up in a helicopter to throw
pennies at me no one hasn't heard that
story when you talk about it people like
oh yeah the penny from the Empire State
Building and when we went to the Empire
State Building every ledge below the
observation deck is filled with change
I just love the idea of all these people
they're not murderers but they're like
it's probably not true they're like
throwing pennies over the side think
it's probably not true
a penny weighs around two and a half
grams which is about half to a quarter
the weight of a bullet if you ignore air
resistance a penny dropped from the
Empire State Building which is 443
meters to the very top would accelerate
to over 300 kilometers per hour by the
time it hits the ground that's around
half as fast as a typical bullet
The MythBusters made Contraptions to
shoot pennies at each other Stephen
Colbert shot me in the ass with it a few
times how did it feel it's a baseball
pitcher throwing a penny hard at you
yeah it'll stay
but they never tried the ultimate test
dropping Pennies from the height of the
Empire State Building onto someone below
and that's what we're gonna do here with
Adam that'd be great watching it bounce
off your body yeah
yeah I say this thinking it's always
been my body up till now
first one I'll drop the pennies we'll
see if we're even gonna land you're
going to walk there and I'll throw a
second one that's good for you yeah and
then you're ready for the the full dump
yeah
I'm going underneath the helicopter
where Adam Savage is gonna drop a whole
bunch of pennies on me
I know I agreed to do this and I didn't
think I'd get hurt but as I'm walking
out onto the helicopter I started to
think no one has actually done this we
planned for pennies falling through
still air but the helicopter creates a
huge downdraft to support its weight
I hear them landing around
I start to imagine pennies gouging into
my shoulders you can see how tense my
body looks
ah one hit my helmet and three two one
that hit my shoulder ah
that's really good and three two one
they feel like tiny little bullets I
feel like I'm gonna be bruised after
this oh boy
okay
come on board
here we go doing the whole thing and
three two one
[Music]
[Applause]
[Music]
[Applause]
[Music]
unbelievable
there you have it a penny dropped from
the Empire State Building is not gonna
hurt
I mean it hurts a little but not a lot
you'll be all right
that was great I saw little dust clouds
all around you amazing tell me what it
was like down here I was terrified I got
out there and the rotor watch is so
heavy I'm like maybe we haven't we
haven't calculated for rotor wash
it stung to get hit by pennies falling
that far but it certainly wasn't fatal
so why aren't pennies more dangerous
well the reason is air resistance
the two up here and hopefully they'll
hit the ground at the same time take the
classic experiment of a hammer and
feather dropped simultaneously on the
moon in the near vacuum of the moon's
surface both objects speed up at the
same rate due to the moon's gravity and
they're both still accelerating when
they hit the ground at the same time
repeat the experiment on Earth
and of course the hammer lands way
before the feather if you watch the
feather closely you'll notice that it
doesn't speed up as it falls for most of
its Journey it's moving at a constant
speed known as its terminal velocity
terminal velocity is reached when the
force of gravity pulling an object down
is equal to the force of air resistance
pushing it up
in this case which object the hammer or
the feather experiences a greater force
of air resistance well I bet most people
would say the feather because its motion
is clearly affected by drag but the
answer is actually the hammer
air resistance is proportional to speed
squared and the hammer gets going much
faster than the feather so it
experiences the larger force of air
resistance but its weight is so much
greater that drag is negligible in
comparison and that's why the hammer
keeps speeding up while the feather
reaches terminal velocity early and just
stays at that speed it all comes down to
the ratio of weight to air resistance
every object has its own terminal
velocity the maximum speed it will reach
in free fall through still air and I
went indoor skydiving to experience this
firsthand
that was so amazing that was totally
wild objects that have the same size and
shape experience the same air resistance
but if one is heavier here I've got two
identical balls but this one has water
added to it so it's heavier then it has
a higher terminal velocity so it doesn't
float at the same wind speed as the
lighter object
conversely some objects are very
different in size and shape like a
person and a lacrosse ball and obviously
they have very different weights but
they also experience very different
forces of air resistance and the key
thing is that the ratio of their weight
to air resistance is the same for both
bodies so they have the same terminal
velocity which means they will both
float together in the tunnel if you
transported the skydiver and lacrosse
ball to the stratosphere they would
continue to fall together but their
joint terminal velocity would be much
faster
in 2012 Felix Baumgartner jumped from a
helium balloon 39 kilometers above sea
level after just 40 seconds of Free Fall
he reached a terminal velocity over 1300
kilometers per hour it was 25 percent
faster than the speed of sound making
him the first person to break the sound
barrier outside of a vehicle
what allowed him to do this was the lack
of air at that altitude air resistance
is directly proportional to the density
of air you're moving through and at that
altitude the air is 60 times less dense
than at sea level as he continued
falling into thicker atmosphere the
increasing air density reduced his
terminal velocity and by two and a half
kilometers above sea level he had slowed
to 200 kilometers per hour at which
point he opened his parachute
now rain also falls kilometers but
through the thicker air of the
troposphere
one of the coolest things in the Wind
Tunnel was to see water floating the
poured from a jug it quickly breaks up
into droplets the same size as raindrops
from around 0.5 to 4 millimeters in
diameter
and standing there you can experience
what it would be like to fall with
raindrops
[Music]
they have a low terminal velocity of
just 25 kilometers per hour and that's
what the wind speed was set to for this
demonstration and what you can see is
that raindrops aren't shaped like
cartoon raindrops they are closer to
spherical but a bit flatter on the
bottom where they encounter oncoming air
if a raindrop gets too big it flattens
out caves in in the middle and briefly
resembles a little parachute before
breaking up into smaller droplets so
raindrops aren't damaging but it's a
different story for hail
[Music]
every year in
Hale injures around 20 people and since
2000 it's caused four fatalities that's
because hail can reach terminal
velocities of over 200 kilometers per
hour that's around 10 times the terminal
velocity of rain
but why is its terminal velocity so much
higher even though ice itself is
slightly less dense than liquid water
the main thing is that hail can get much
bigger than a raindrop hailstones have
been measured up to 20 centimeters in
diameter now drag is proportional to
cross-sectional area so it scales with
radius squared whereas weight scales
with radius cubed so the bigger the
Hailstone the faster its terminal
velocity it also has more mass so it
carries even more kinetic energy and
packs a bigger punch when it hits
something
pennies reach terminal velocity after
falling only around 15 meters you can
see in this shot the average speed of
the penny is in the top of the frame is
the same as at the bottom of the frame
they aren't speeding up they've reached
terminal velocity so it wouldn't matter
if pennies were dropped on you from 15
meters or 300 meters or 3000 meters it
would feel the same because they would
be going the same speed
in fact we didn't take the helicopter
all the way up to Empire State Building
height because that wouldn't have
increased the speed of the pennies at
all and it would have just made aiming
much harder by the end I'm throwing to
account for this secondary air current
that's moving between you and the
helicopter and so the pennies are making
this like 12 foot Arc all the way over
and then coming back
one of the reasons pennies are so hard
to aim is because they flutter and
Tumble as they fall this tumbling
Behavior means pennies don't actually
have a single terminal velocity a penny
actually has two terminal velocities and
it oscillates between them so it's got
one on its face and one on its Edge I've
got a wind tunnel that can show you
exactly how that works it's really
beautiful well I gotta see that yeah
it's really neat throw to that
Adam built a custom wind tunnel to
witness this for himself so I went to
San Francisco to his cave to check it
out this is literally like my
MythBusters origin story this device I'm
so delighted to fire this up again it's
like looking at a piece of piece of
History how old is this 19 years old now
it's old enough to drive and vote but
not during there's people watching this
video you know yeah weren't alive when
we were making this
because of the holes which allow air to
escape this wind tunnel has a gradient
of wind speeds from around 100
kilometers per hour at the bottom up to
25 kilometers per hour at the top this
creates a little bit of back pressure
the pops the tongue depressors up here
and that back pressure is relieved by
these holes enough so that the penny
spins if a penny really has two
different terminal velocities it should
oscillate up and down in this wind
tunnel as a result
there you go
that's amazing to see it oscillate right
I know the fact that it goes up and down
and it comes back up again yeah oh wow
yeah it's just like honestly it was just
hanging out like that
when in 2003 I dropped the penny in the
top and it went up and down like I'm
still every single time I tell that
story I get goosebumps because I
remember that feeling of like oh wow we
made a separate video on Adam's channel
that discusses the wind tunnel in more
detail so check it out after this
so the reason pennies aren't dangerous
is because their terminal velocity is at
most about 80 kilometers per hour
yeah it's not going to hurt you that's
bust right
like old habit
but something more aerodynamic would
have a higher terminal velocity and this
has led some to suggest ballpoint pens
falling from a skyscraper like the
Empire State Building could be lethal
but supposedly yeah a pen a ballpoint
pen is as dangerous as a penny is
mythically dangerous yeah yeah like that
is meant to actually be lethal it's
worth really trying
these pens weigh about twice as much as
a penny and they have a smaller
cross-sectional area
so this will increase the ratio of
weight to drag but will it be enough
now because I'm not sure what will
happen I'm not putting my body on the
line for this one instead we'll use a
ballistics gel dummy here we go and
three
one
three two one
oh very close very close here we go
three two one
oh oh almost okay three two one
oh almost three two one okay last one
three two one
oh almost not getting it
the second to last drop we had almost no
Crosswinds at all so they dropped
perfectly down and kind of hit right
below where we were and they were all
cattywampus
if the myth was true I would expect to
see this everywhere right right that's
what I would expect to see and I don't
see a single one and I didn't after we
dropped them all
are you gonna call it I wow I will sure
I'll come back out of retirement to say
busted pens are not dangerous falling
from tall objects ballpoint pens with
their caps off yeah narrow metal pens
might still be dangerous but these
plastic ones still seem to have too much
drag relative to their weight for them
to achieve a high terminal velocity
one of the curious things about air
resistance is that it depends not only
on the cross-sectional area of the
object but also on its overall shape
this dependence is captured in a
dimensionalist number known as the drag
coefficient the drag coefficient is all
about how smoothly air can flow around
an object and without creating vortices
the word
from the French bull meaning ball so a
bullet is a small ball exactly what the
earliest bullets were but the drag
coefficient of a sphere is 0.5 so people
modified the shape to reduce drag and
eventually they settled on the modern
bullet shape which has a drag
coefficient between 0.1 and 0.3 so drag
coefficient is the reason a bullet is no
longer a bullet
so what would happen if you dropped a
bullet from a skyscraper not what you'd
expect instead of falling pointy side
down a bullet would tumble and likely
end up falling on its side
the thing is that cylinders tend to fall
on their sides if given enough chance
really but the object falls in relation
to the highest resistance it chooses it
ends up finding the highest resistance
that's the most stable why doesn't it
fall in lowest resistance nothing is
intuitive bullets if you let them
they'll fall and make bullet shaped
holes on their side
a bullet fired straight up slows down as
its kinetic energy is turned into
gravitational energy and at its highest
point which could be up to three
kilometers high it stops and then falls
back down at that moment it's just like
dropping a bullet from a really tall
building as it starts to fall it will
tumble and so it experiences far more
air resistance than on the way up and so
it's not going to get back a lot of that
energy that went into its height which
means that by the time it reaches the
ground it will be much slower than it
was shot now if the bullet isn't fired
completely vertical then it poses much
greater danger at the peak of its
trajectory only the vertical component
of velocity is zero it still maintains
its horizontal velocity and that
combined with the spin and parted to the
Bullet by the grooves inside the gun
barrel keep it moving pointy end
forwards
and so as the bullet comes back to the
ground it speeds up to a significant
fraction of its launch speed
there are hundreds of cases of people
being struck and killed by celebratory
gunfire from all over the world
now this is accidental but the concept
of dropping deadly projectiles on
enemies is almost as old as aircraft in
World War One these little pieces of
metal were dropped out of planes they
look like nails with little feathers on
the back to make sure they fall straight
they're called fleishettes which is
French for little arrow but somewhere up
to 15 centimeters long that is great
I totally want to make a thing that
shoots these
Dart a little heavier than a standard
Pub Dart and there were like endless
different shapes from a military
perspective the advantages were they
didn't require any explosives and they
were cheap to produce and deploy at
scale they could Pierce helmets leading
to enemy casualties and some nasty
injuries they found darts that had gone
through a rider and his horse
that's insane but I also just love the
idea of a guy in an open cockpit cloth
and wood plane just hurling handfuls of
dart's house that is like a 10 year
old's idea of warfare right then I'm
gonna hit him with darts later the U.S
created similar weapons called lazy dogs
which were a bit heftier used in the
Korean and Vietnam Wars the damage they
inflicted was indiscriminate and
unpredictable but at least they didn't
leave unexploded ordinances in the field
and militaries continue to use kinetic
projectiles to this day for example to
make Precision strikes on terrorist
leaders falling objects are also
dangerous in civilian life nearly 700
Americans die each year by being struck
by a falling object these range from
loose tiles and Bricks to Falling
construction tools Falling Rocks and
tree branches and even icicles death by
icicle is rare but they were a serious
enough concern that in the winter of
2014 streets around New York's One World
Trade Center were closed due to the
danger caused by icicles hanging on the
building
so which projectiles are lethal and
which aren't honestly a lot of them are
the lower limit of the energy required
to fracture a human skull is around 68
joules so anything that has kinetic
energy greater than that is very likely
to kill you a raindrop at terminal
velocity with its tiny mass will only
deliver two thousandths of a joule a
falling penny has about a fifth of a
joule but a baseball and the largest
Hailstone measure deliver more than 80
joules that is plenty to crack your
skull in 2014 a man was killed when he
was hit by a falling measuring tape that
had fallen 50 stories and this is just
calculating for blunt force trauma the
energy stored in a falling Flay chef is
not enough to crack your skull but it
can apply a large Force to a very small
area so yeah a penny falling from the
Empire State Building won't kill you a
pen likely won't either anything that
weighs a few grams and isn't aerodynamic
isn't going to be fatal but objects that
weigh more than a few hundred grams
traveling at terminal velocity are
likely to be deadly
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