Introduction
The action of the “Drinking Bird” is stopped when it is covered with a large bell jar. It resumes its motion when the bell jar is removed.
The demonstration can be used to illustrate the expansion or contraction of gasses with changes in temperature as well as the energy change taking place during a liquid to gas phase change. The bird is a simple heat engine. The tail is at room temperature and is the heat source while the wel head is cooling due to evaporation on its surface and is the heat sink. As the gas in the tail expands with warming, the gas in the head contracts from cooling and the liquid rises up the neck tipping the bird over. Once tipped, the gases in the two ends mix, equilibrium is established, and the liquid returns to the tail. Placing the bell jar over the bird and beaker of water causes the humidity to approach 100% preventing evaporation and cooling of the head. Consequently, the bobbing stops until the bell jar is removed, the humidity surrounding the head decreases, and evaporation and cooling are resumed.
To Conduct Demonstration
- Ger the drinking bird to start bobbing by wetting its head and placing a 400mL beaker of water (spout toward the bird’s beak) adjacent to the bird to prevent it from turning upside down when it bobs
- Allow the bird to bob for awhile, and then cover the bird and beaker with the bell jar.
- After the bird stops bobbing, remove the bell jar, and the bird resumes its motion.
Reaction Time: 15 min
Safety
The bird contains Freon-11.