how to make a drinking bird toy

How Does It Work?

Only through this tiny glass tube can anything move between the two bulbs. The material that forms the beak is porous and resembles felt, covering the top bulb. There is a plastic top hat, purely decorative, atop the head. Tail feathers, which aid in balance, are attached to the bottom chamber. Everything is hanging from plastic legs, and it can bob up and down thanks to a horizontal metal piece that serves as a pivot. The drinking bird contains methylene chloride (CH2Cl2), a very flammable liquid.

Methylene chloride lacks color, so in order to improve the visual effect, coloring must be added. This liquid’s weak intermolecular bonds in the liquid state cause it to evaporate quickly, making it another highly volatile substance. Its boiling point is 39. 7 °C (103. 5 °F), and at room temperature, its vapor pressure is 46 kilopascals (while water’s vapor pressure is only 3 kPa). Because methylene chloride is somewhat toxic, cleaning up spills from drinking birds needs to be done carefully. Methylene chloride is frequently used as a paint remover, degreaser, and industrial cleaner. The majority of the residual air is then vacuumed out once the manufacturer adds the methylene chloride.

Now that the bird is almost completely empty, the extremely volatile liquid quickly evaporates, filling the area above the liquid with vapor. At this moment, the liquid and vapor above it reach a dynamic equilibrium inside the bird. As soon as equilibrium is reached, every time one molecule evaporates, another will condense, keeping the total amount of vapor inside the bird constant as long as the temperature doesn’t change. The drinking bird is activated by dipping its head into a glass of water and positioning it so that, when it tips its beak, it can reach into the glass of water. As soon as the head gets wet, an odd thing starts to happen. The liquid rises upward into his head like magic, filling it with liquid. The bird’s center of gravity then rises, making the head top heavy. The bird then topples over, takes another drink. The liquid returns to the bottom bulb as the bird topples over, reestablishing the low center of gravity. The bird returns to its upright posture and repeats the entire process.

Consider what happens to your own head when it gets wet to get an idea of what causes the fluid within the bird to rise. As long as the relative humidity remains below 10%, the water will start to evaporate right away. Furthermore, because evaporation is an endothermic process, it always results in cooling. This explains why you sweat when it’s hot; the sweat evaporates from your body to cool you instead of the sweat itself. Since breaking bonds requires energy, any phase change that necessitates this will be endothermic. As a result of this energy being extracted from the environment, the temperature there drops. As water evaporates from the bird’s head, the head starts to cool down right away. This is the most important thing to know about the functioning of the drinking bird.

The drinking bird would function the same if there was another way to cool the head. A portion of the vapor inside the head will condense into tiny liquid droplets when it starts to cool. A comparable process takes place at night when the air cools and water vapor condenses, resulting in the formation of dew on the ground. There is now less vapor pressure in the top bulb because some of the vapor condenses within the bird’s top chamber. Less vapor means less pressure. However, the bottom bulb’s vapor pressure has remained unchanged. The liquid is forced upward into the top chamber because the vapor pressure in the bottom bulb is now higher than the pressure in the top bulb. After the bird topples over, vapor rises to the top from the bottom until the pressure in both spheres equalizes, at which point the bird starts the process anew. Don’t say the liquid is sucked up into the top chamber—science never sucks!

Consider what happens when you use an ordinary drinking straw to get an idea of how a pressure differential causes the fluid within the bird to rise. There is a zone of lower pressure inside the straw when you suck liquid up into it. Due to the increased air pressure outside, the fluid’s surface is forced upward by downward pressure.

Here are some ideas for researching swinging bird behavior at different levels of complexity.

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Examine how the rate of evaporation and, consequently, the period of motion are altered by forced convection, such as that produced by a tiny fan pointed at the head.

There are many more topics that can be investigated. For instance, using tiny thermocouples to track the time dependence of the head and stem temperatures in each cycle and correlate them with the bird’s angular motion A steady state temperature differential between the two will result from heat entering the tube and traveling to the head. During a cycle, there may be variations in the temperatures of the head and the tube. These variations can be linked to heat transfer from the surrounding environment and enhanced evaporation because of convection created by the swinging motion. However, for this and other more difficult subjects, you would need to have access to a top-notch physics lab, seek advice from a physicist, and be prepared to devote more time to the project in addition to learning a little bit about heat and thermodynamics and the mechanics of rotational motion.

Calculate the bird’s motion period and the rate of evaporation, then connect the two. This can also be done when another liquid, like alcohol, is added to the beaker in place of the water. The bird can be put on a sensitive, accurate to zero electronic balance to determine the rate of evaporation. 001 g. Using a pipette, apply a few drops of the external liquid to the felt of the head. When the bird bends into its horizontal position, measure the change in mass of this liquid over time as well as the duration of motion without adding more liquid. Allow for the time spent in the horizontal position. Determine through experimentation the range of time over which the evaporation can be considered constant.

A student reading from ChemMatters magazine

This student reading is courtesy of ChemMatters, the ACS quarterly magazine division that explores chemistry behind everyday life. Learn more about ChemMatters, view free online content, or subscribe at acs.org/chemmatters.

For more than fifty years, both young and old have been enthralled with the captivating little science toy known as the drinking bird. The happy bird, the dippy bird, the happy dippy bird, and other variations on the same theme are some names for it. It resembles a bird and appears to be drinking from a glass of water as it bobs up and down. It will continue to bob up and down as long as it can get to the water. The drinking bird is made up of two long glass bulbs joined by a straight glass tube that extends deep into the bottom bulb.

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