What is a drinking bird toy?
A drinking bird toy, also known as a dippy bird, is a popular novelty item that seems to defy gravity as it perpetually tips forward to “drink” from a glass of water. The drinking bird toy consists of a glass tube body and head containing a fluid, usually methylene chloride, that has a low boiling point. The head is usually colored red or orange to resemble a bird.
When placed next to a glass of water, the drinking bird toy will tip forward until its beak touches the water. This causes the liquid in the head to evaporate and travel down to the bottom of the tube. As the head becomes lighter due to evaporation, the weight distribution shifts and causes the bird to tip back up. This motion causes the liquid to condense and flow back into the head, allowing the bird to tip forward and “drink” again, repeating the cycle perpetually.
Is it really perpetual motion?
At first glance, a drinking bird toy seems to represent a perpetual motion machine – a device that can operate indefinitely with no external power source or human intervention. However, perpetual motion in the literal sense is impossible according to the laws of thermodynamics. No machine can keep operating without an energy input.
The drinking bird toy is powered by the energy it absorbs from the surrounding air as the liquid inside evaporates and condenses. Therefore, it is not a true perpetual motion machine. Outside energy from the environment is required to keep the bird “drinking” continuously.
If the bird is placed in an environment where the liquid reaches an equilibrium and no longer evaporates and condenses, it will stop moving. For example, once the ambient temperature matches the evaporation temperature of the fluid inside, the bird will stop drinking until the environment changes again.
The thermodynamics behind how it works
The drinking bird toy acts as a heat engine, absorbing heat from its surroundings to do work. Here is a closer examination of the thermodynamics:
Evaporation
As the bird tips forward, the liquid in the head evaporates, absorbing heat from the air. This cools the head and makes it lighter. Evaporation of 1g of liquid takes about 580 calories of heat from the surroundings.
Condensation
When the bird tips back, the vapor condenses on the walls of the tube, releasing the absorbed heat. This returns the bird back to its original weight distribution. Condensation of 1g of liquid releases about 580 calories of heat back to the surroundings.
Gravity
The changing weight distribution of the fluid inside causes the bird to pivot up and down on its wooden base, powered by gravity.
Boiling point
The fluid used, usually methylene chloride, has a low boiling point of 104°F (40°C). This means ambient air temperature is enough to cause the liquid to evaporate and condense, unless the air temperature precisely matches the boiling point.
Vacuum
The long glass tube contains a partial vacuum above the liquid. This lowers the pressure and allows the liquid to evaporate and condense at room temperature. Without the vacuum, a much higher temperature would be required.
Uses as an educational toy
While the drinking bird toy is not a true perpetual motion machine, it remains a fascinating example of thermodynamics in action. It can teach important science concepts:
Phase changes
The evaporation and condensation of the enclosed liquid demonstrate liquid-gas phase changes in action. Students can observe how adding or removing heat causes the physical state to change.
Heat transfer
Heat from the surrounding air enables the phase changes. This demonstrates heat transfer concepts – how heat flows from warmer objects to cooler areas.
Equilibrium
The bird reaches a state of equilibrium with its environment when the evaporation and condensation rates balance out and the head weight stabilizes. This demonstrates how systems seek equilibrium even while absorbing and releasing heat.
Gravity
The weight shift from evaporation causes the bird to pivot, illustrating how gravity exerts a force on mass. Removing mass from the head causes the rest of the body to pivot downward.
Kinetic and potential energy
As the bird tips back and forth, it exchanges between kinetic energy (motion) and gravitational potential energy (height). This demonstrates the energy conversion in a swinging pendulum.
Using the drinking bird in the classroom
The drinking bird can be an engaging hands-on demonstration to accompany lessons in thermodynamics, physics, chemistry, and scientific inquiry. Here are some ways to incorporate it:
Challenge students to figure out how it works
Provide students with a drinking bird and have them hypothesize and test how it works. This teaches scientific inquiry methods. Does ambient temperature affect it? What if the air was humid? What liquid is inside?
Demo phase changes
Place the drinking bird next to a heat source like a lamp. Have students observe how the rate of “drinking” speeds up as the head gets warmer. Use this to demonstrate heating, evaporation, condensation, and cooling.
Compare bird designs
Obtain different drinking bird models and compare how structure relates to function. Compare amount of liquid, shape, center of gravity, beak length, etc. How do these design choices affect speed and duration of motion?
Study thermodynamics principles
Assign students a thermodynamics concept like heat transfer and have them explain how the drinking bird demonstrates it. This ties abstract concepts to a physical model.
Make predictions
Before adjusting variables like heat or humidity, have students predict how it will affect the speed of the bird. Test their predictions with experiments. Analyze results.
Build a homemade drinking bird
Provide materials for students to build their own drinking bird out of common items like plastic bottles. Compare designs and see if they operate on the same principle as a store-bought one.
Troubleshooting issues with drinking bird toys
While drinking bird toys usually work reliably with minimal intervention, sometimes issues arise. Here are some common problems and how to troubleshoot them:
| Issue | Possible Causes | Troubleshooting Tips |
|---|---|---|
| Bird tips over but does not swing back up | Insufficient evaporation and condensation | Check liquid level in head; refill with purified methylene chloride if too low. Ensure head is capped on tightly. Place bird in sunlight to warm head. |
| Bird does not tip over at all | Base is not balanced properly | Rest bird on very flat surface. Adjust base if needed so it can rock. Check that surface underneath is not sticky. |
| Bird rocks down but only partially up | Insufficient condensation to return to upright position | Make sure the head fully snaps back to empty interior liquid. If not, the interior vacuum may have leaked. Test by immersing bird head in hot water and watching for bubbles. |
| Bird rocks slowly | Insufficient heat or too viscous liquid | Move bird to a warmer spot. Consider replacing liquid with purified methylene chloride if too viscous. |
With proper care, a drinking bird toy can provide years of fascination and science education. Just be sure to provide ambient heat and proper balancing to keep the bird drinking perpetually.
Conclusion
While a drinking bird toy may seem to defy gravity and physics, it does require external energy input to operate. As such, it technically does not represent a true perpetual motion machine. However, it remains a captivating demonstration of thermodynamics and phase changes. When used creatively, it can engage students in the inquiry process while illustrating important science concepts like heat transfer, equilibrium, and kinetic/potential energy conversion. With some simple troubleshooting, drinking bird toys can continue functioning perpetually to spark curiosity and make physical science come alive.
