Concepts

Heat engine, evaporative cooling, relaxation oscillator

Overview

The drinking bird is a heat engine driven by evaporating water absorbing heat from the surroundings. The bird bobs forward into the glass of water and recovers. It oscillates in the upright position for a few moments before bobbing into the water once more. It repeats this motion until no more water is available.

Details

Equipment

• [1] Drinking bird toy
• [1] Cup of water
• (Optional) [1] Plexiglass box
• (Optional) [1] Squeeze bottle containing alcohol.

Important Notes

• Methylene chloride is somewhat toxic. It can be inhaled and absorbed through the skin if the drinking bird breaks. Consult an MSDS for first aid and cleanup instructions.
• The drinking bird is fragile. Handle with care.

Script

1. Fill up an empty cup with cold tap water.
2. Wet the bird's head.
3. Notice that the liquid slowly moves up the tube, causing the bird to bob its head in the water.
4. Notice that the bobbing motion allows air pressure to equilibrate in the bird, allowing the liquid to pool on the bottom again and causing the bird to tilt its head up.

1. Place the plexiglass box over the bird. The evaporation will slow enough to stop the bobbing.
2. Squirt alcohol on the bird's head.
3. Replace the box. The bird will begin to bob again as the alcohol speeds up evaporation.

Additional Resources