- a large jar (larger than a quart, like a pickle jar)
- popped popcorn, enough to fill half of the jar
- a ping pong ball
Fill up a large jar (larger than a quart, if possible) half way up with popcorn. Take a ping pong ball and push it to the bottom of the popcorn. Put the lid on and swirl the jar around. After a few seconds the ping pong ball will rise to the top of the popcorn.
Source: http://www.geocities.com/Heartland/Flats/4746/lessons.html, some changes by Jenny Smith