Re: Why doesn't the milk overflow from the glass when you drop popcorn into it?

here's a web address for other information about popcorn: http://usgovinfo.about.com/library/weekly/aa011501b.htm

     I have not personally ever done this experiment, so I have to take
your word for it that it works this way. If you think about popcorn before
you pop it, you'll remember that each piece of popcorn comes from a very
small kernel. Once you add heat and pop it, it appears that you have more,
but what you really have is mostly air, and the moisture present in the
kernel before popping has dissipated (disappeared, really) into the air.
     So when you drop the piece into the milk, there should really be lots
of empty space inside the piece, where the milk can flow into many small
places.
  If you fill a glass with milk, and pour some dry cereal into it, much the
same sort of thing will happen. The milk looks solid, but the two
substances can share some of the same room.
   It might be interesting to try this with other liquids to see if you
have the same volume before and after you mix them. Just make sure you
don't use any liquids that might be flammable or could be damaging to your
skin.
Good Luck!