The Egg in the Bottle is just one of many phenomena that can be used to show that air exerts pressure.  This is important because many students do not think that air can exert pressure.  This demonstration allows students to witness with their own eyes that air goes exert pressure!!
 
 

How does the egg in the bottle demonstration work?  Well if you do not know what I am talking about, you can go to this page, THE EGG IN THE BOTTLE DEMONSTATION, and find out how to do the demonstration.  Please remember always to play it safe by having an adult help and supervise the demonstration.

If you know what I am talking about, you know that demonstration involves getting hard boiled egg without its shell into an empty bottle that cannot be pushed in very easily.  Yet, if you have ever seen this demo, you realize that the egg finally falls into the bottle.  But, what does the demonstrator do to get the egg into the bottle?
 
 

Observations:
 
 
 

The first thing that the demonstrator does is lights three matches and places them into the empty bottle.  Then, the demonstrator puts the egg on top of the bottle.  Soon after, the matches go out and the egg makes a slurping sound and is sucked into the bottle.
 
 
 
 

Now that we have taken a closer look to the steps of the demonstration, why does the egg fall in?

Explanation:

Heating the bottle causes the air, gas molecules to increase in temperature and begins to start bouncing and zipping around a lot faster.  As a result, the gas molecules begin to expand and force some of the gas molecules out of the bottle.  As long as the air is continuously being heated, the pressure of the fewer but hotter molecues inside is equal to that of the numerous molecules outside the bottle.  Yet, when the opening of the bottle is closed off by the egg, the fire eventually extinguishes itself.  In addition, the fewer air molecules (do to some escaping) inside the bottle being to cool and contract and reates a lower pressure inside the bottle than outside the bottle.  The greater pressure outside the bottle than inside the bottle is what utlimately forces the egg into the bottle!

Now, what if you want to get the egg out the bottle?

Well, if you turn the bottle upside down and blow into it, this will cause there to be an increase in the air pressure inside the bottle which will then cause the egg to pop back out!!