4C31.30 Drinking Bird


Heat engine, ideal gas law, evaporative cooling, relaxation oscillator


The drinking bird is a toy with a felt head on top of a glass tube containing methylene chloride. When the beak is wet, cooling by evaporation causes the vapour inside the tube to condense. Due to the pressure difference between the cold head and the warm bottom of the bird, the liquid in the body moves up the tube, changing the centre of gravity. After some time, the bird tips forward and dunk its head into the water. The pressure can then equilibrate between the bottom and top, and liquid pools at the bottom again, taking the bird out of the water. The cycle repeats until no more water is available.



  • [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.


  1. Fill up an empty cup with cold tap water.
  2. Wet the beak of the bird.
  3. Notice that the liquid slowly moves up the tube, during which the bird periodically swings back and forth and eventually dunk its head into the water.
  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


  • PIRA 4C31.30
  • Video Encyclopedia 15-12


  • Don't attempt this at home!

Last revised

  • 2018


Related AV

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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.