Sucking Eggs

The old "egg in the bottle" trick.

 

 

 

Category - Heat & Temperature

Key Idea - Thermal Expansion

 

Purpose - A cool demonstration of air expanding on being heated and contracting when cooled.  It also shows the force of air pressure.
Nature -  Demonstration
Materials -  glass bottle with a mouth a bit smaller than the diameter of an egg, a hard boiled egg, some paper, matches
Method - 
  1. Peel the shell off the hard boiled egg.
  2. Light the paper with the matches and drop it into the bottle.
  3. When the paper is just about to burn out place the egg in the mouth of the bottle forming a light seal.
  4. As the the bottle cools the egg will be forced into the bottle.  The can be sped up by placing the bottle in cool water, but this isn't really necessary. 
Safety - Care with matches. 
Explanation - The hot air in the bottle expands upon heating, much of it leaving the bottle.  The egg then seals the bottle off the mouth of the bottle as the air inside cools.  The cooling air contracts taking up less space, creating a lower pressure inside than outside of the bottle.  The higher air pressure pushes the egg into bottle in it's effort to equalize the air pressures. 
Notes - The real trick is to get the egg out of the bottle!