How does a Dippy Bird work?

A Dippy Bird is a strange-looking novelty toy, but how does it work? Marshall Brain breaks down the surprisingly sophisticated mechanics of the Dippy Bird in this episode.

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Episode Transcript

Speaker 1 (00:00):
Welcome to Brainstoff front House, stuff works dot Com where
smart happens. Hi. I'm Marshall Brain with today's question, how
does a dippy bird work? A dippy bird is a
toy that you'll frequently find it toy shops or novelty shops.

(00:23):
They cost about five dollars and they look a little bizarre.
A dippy bird has the following parts. First, two equal
size hollow glass bulbs, a long glass tube that connects
the bulbs, a fuzzy water absorbent material covering the head,
and often some kind of little top hat on the

(00:44):
head as well. Two plastic legs with a pivot connection,
and then some methylene chloride in the abdomen. This is
usually a reddish liquid In real life. Methylene chloride is
an industrial paint stripper and a solvent one thing that
dissolves easily. A methylene chloride is caffeine, so you'll often

(01:04):
see it used to decaffeinate things. Methylene Chloride helps make
a dippy bird work because it evaporates very easily. It
boils it just a hundred degrees fahrenheit or forty degrees celsius.
To operate a dippy bird, you get its head wet.
As the water evaporates off the head, fluid moves up

(01:24):
into the head, causing the bird to become top heavy
and dip forward. Once the bird dips forward, fluid moves
back into the abdomen, causing the bird to become bottom
heavy and tip back up. It'll tip up, and back
up and back essentially forever, as long as there's water
that can cool its head and the room is at
room temperature. Here's how a dippy bird works. When water

(01:48):
evaporates from the fuzz on the dippy bird's head, the
head is cooled. The temperature decrease in the head condenses
the methylene chloride vapor that's floating around in the tube anyway,
decreasing the vapor pressure in the head relative to the
vapor pressure in the abdomen. The greater vapor pressure in
the abdomen forces fluid up through the neck and into

(02:10):
the head. As the fluid enters the head, it makes
the dippy bird top heavy. The bird then tips, liquid
travels to the head and the bottom of the tube
is no longer submerged in the liquid. In the lower bulb.
Vapor bubbles travel through the tube and into the head.
Liquid drains from the head displaced by the bubbles, and

(02:32):
the fluid drains back into the abdomen, making the bird
bottom heavy. Then the bird tips back up and starts
the cycle over again. If the bird dips into a
cup of water so it's heads stays wet, the fuzzy
material absorbs water over and over again, and the cycle
just keeps repeating. Your warm hand can cause fluid in

(02:53):
the dippy bird to rise as well. If you hold
a dippy bird upright in your hand touching the abdomen,
the following happens. Your body heat warms the fluid in
the abdomen. The heat increases the vapor pressure in the
abdomen relative to the head, the reverse of what happens
when you get the head wet. The fluid rises into
the head in response to the pressure difference, moving from

(03:15):
high pressure to low pressure. The bird becomes top heavy
and it tips forward. Either way, you've created a little
heat engine when you look at a dippy bird that's
using the evaporation and condensation of a liquid to cause motion.
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(03:41):
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