this toy has fascinated me since
childhood to me its motion is almost
hypnotic here's how it operates wet the
birds beak thoroughly with
room-temperature water the opaque
container makes him up chilled but it
isn't then stand it upright it'll take a
few seconds for it to start drinking
notice that all the action right now
takes place in the stem here as I speed
up the action you see liquid rising and
the bird rocking back and forth if I
return to normal speed you can see the
bird slowly very very slowly rock
forward until it takes a drink which you
will do again and again in this video
I'll detail the bridge clever
engineering design explain how it uses
thermodynamics and link its action to
some of the greatest and most impactful
devices created by engineers this toy
has a long history but its current
incarnation is due to Miles V Sullivan a
scientist at Bell Labs he specialized in
methods of manufacturing semiconductors
but as a sideline invented toys it's
reported that this bird delighted us
President Herbert Hoover an engineer who
failed to figure out how it worked and
it also defeated the great scientist
Albert Einstein who spent three and a
half months studying it it's reported
that he refused to take the bird apart
with the benefit of hindsight let's
start by exploring how it works and
examining the key engineering design
aspects first let's ask is the water
ornamental or essential at first the
bird acts just as if the water were
still there now let's speed up the
motion you see it 15 minutes it's still
drinking at 30 minutes of drinking 45
minutes still drinking 60 minutes still
drinking 75 minutes still drinking and 5
or 10 minutes later at 8 or 85 minutes
it takes its last drink the liquid still
rises a bit but it never rises enough to
make the bird tip over which shows that
the motion is not perpetual as long as
there's water the bird keeps drinking
let's look inside the bird to get an
idea of how it works underneath the
bird's hat
can fabric covering lies a glass bulb
smaller than the bulb at the base and
also rounder now watch as I put a few
drops of isopropyl alcohol on the top
bulb to cool it the liquid rapidly rises
to the head this changes the bird center
of gravity so that it will tilt forward
the head now fills with liquid and then
there it drinks it becomes upright and
the liquid drains from the head liquid
rises again to the head end the bird
drinks again this cycle repeats until
all of the isopropyl alcohol on the
bird's head evaporates why does the
liquid rise the place to begin is with
the birds manufacturer the bird is
filled through this tab a small pipe
built into the head with methylene
chloride dyed red which is then frozen a
vacuum applied to evacuate the air the
tap sealed and of course later hidden by
the birds hat and then the methylene
chloride melts it turns to liquid and
then some of the D vaporators turns into
vapor the key to the birds operation is
that the vapor in the head and in the
base are separated by the liquid in the
base it's hard to see but a tube extends
into the base nearly reaching the bottom
this separates the vapor in the base and
the vapor in the tube and of course the
head so it rests the pressure in these
two spaces are equal but when the birds
beak is wet the temperature falls and as
I'll explain in a moment the pressure in
the head drops below that in the base
and the liquid rises of course this
liquid in the head causes the bird to
tilt forward to drink and when it drinks
the vapor in the head and the base are
connected
the pressures nearly equalize the slug
of vapor rises to the top and some
liquid drains from the head and then the
cycle repeats to see that pressure
equalized they'll slow down the bird as
I tilted forward right now the head is
half full when I tilt it you see a slug
of vapor go from bottom to top
I've tilted it far enough forward that
the liquid in the head is below the top
of the tube and the liquid in the base
below the section of the tube that
almost reaches the bottom of the bird
this allows the pressure to equalize and
as the bird becomes upright the liquid
returns to the base before the cycle
starts again an operation it doesn't
tell quite this far forward and so the
pressures don't fully equalize why
though
does the pressure in the head drop as
the temperature falls you can see the
answer if I shoot cool compressed gas
across the bird's head as the cool gas
strikes you see liquid condensing inside
the head and as you see on the left this
causes the liquid in the base to rise
the cool gas withdraws energy is heat
from the head causing some of the
methylene chloride vapor inside to
condense to turn into a liquid this
decreases dramatically the amount of
vapor in the head liquid is a thousand
times more dense than vapor this in turn
lowers the pressure in the head and
causes the liquid to rise I used
compressed gas to cool the head because
I can control the amount of cooling the
bird though cools its head by drinking
the head is wrapped in fabric that
absorbs water as I put drops on its beak
you can see the water beads up at first
then saturates the fabric and spreads
rapidly across the bird's face on the
right side you can see it creeping to
the back of the head if I now turn the
bird around you can see that the water
has spread to the back as I continue
adding drops on the beak the saturated
area on the back increases when this
water evaporates into the air it removes
energy from the bulb as heat you feel
this effect every time you step out of
the shower the evaporating water
withdraws energy as heat and chills you
this evaporation this withdrawal of heat
lowers the temperature and begins the
condensation of the vapor which starts
the psycho as I showed you with a cool
compressed gas as long as the head is
wet and heat is withdrawn from it the
bird will always drink but if you were
to operate the bird in humid air it
would slow down because little water
would evaporate and if the air were at
100 percent humidity the bird would stop
because no water would evaporate at all
no to make this dramatic condensation
happen when the temperature is lowered
just slightly the evaporating water
lowers the temperature by about three
tenths of a degree the bird's designer
chose a highly volatile
liquid this means one who's blooding
point is near ambient temperature
because we're small changes in
temperature there's a large change from
the vapor to liquid into the variation
of pressure is large
watch what happens as I heat the base of
the bird with my hand you see that
liquid level in the base dropping that's
because energy from my hand is
converting some of the liquid into vapor
which increases the pressure in this
region and that causes the liquid to
rise to the head eventually I heat the
vapor so much that it shoots up the stem
now watch as I place my hand around the
head heat from my hand converts liquid
to vapor which increases the pressure
and forces the liquid back to the base
to test this explanation of the birds
operation let's activate the bird in
different ways as I noted it is the
temperature difference between its top
and bottom that drives liquid to rise to
the head so let's see what happens if I
point a light at the base of the bird
which I painted black so we'll absorb
the energy from the light better as I
heat the base of the bird the liquid
rises as before but the bird tips
backwards the wet-nosed tilted the
center of gravity and so I've added some
modeling clay to the nose to get the
bird to tilt forward and now when I turn
on the light the liquid rises the bird
drinks just as if there were liquid in
front of it until I turn the light off
and the bird drinks for a little bit
longer until eventually it comes to rest
next to let's see what happens if we use
this whiskey again thoroughly wet the
bird's beak with the liquid
and it upright and then we see again the
liquid rising in the bird and then it
drinks we can also now understand why
the birds rate of drinking differs among
the three methods I used to activate the
bird a heat lamp whiskey and water
roughly the heat bird takes three drinks
for every one of the water bird the
whisky bird takes two for every drink of
the water bird
the reason the bird drinks whisky faster
than water is because the rate of
evaporation of the alcohol is greater
than that of water
this means that heat is withdrawn faster
from the head and so more vapor
condenses in a shorter amount of time
which accelerates the pressure
difference the heat lamp causes the
greatest difference of all which
highlights how an engineer thinks about
this bird - an engineer this bird is a
heat engine the heat engine turns heat
differences into work mechanical motion
to see that recall that when the bird is
just about to drink that its head is at
a lower temperature than its base which
is at ambient temperature then when it
drinks the pressure in the head and base
start to equalized so the liquid returns
to the base but the overall temperature
of the bird is not just a little below
ambient temperature when it returns to
upright the base draws in energies heat
the head then rejects some energy as
heat and the bird drinks again these two
flows define a heat engine a device
operating in a cycle that absorbs heat
from a high temperature reservoir
converts part of it into work and
rejects the remainder into a low
temperature reservoir the fact that it's
a heat engine means it's related to the
great machines that make our globalized
world happen among those the mighty
steam turbine that generates electricity
the giant diesel engine that propels
container ships across the oceans
and the great gas turbine that flies us
around the globe I'm bill Hammack the
engineer guy