Science Experiment: Bottled Tornado

I've seen this before, at the Thinktank and at a science day at the Erasmus Darwin house, but I never stopped to think about why it works until now.  What's supposed to happen, is that we make a tornado inside  a bottle.  We do this by getting two bottles, and making half centimeter holes in each of the bottlecaps.  We then glued the bottle caps together (we had to use really strong glue and let it dry for a long time).  Then we filled one bottle with water, and we put in some pink food colouring and glitter so we could see the currents in the water.  We screwed both bottles into the glued double bottlecap, to make this (except not sideways):

If you spin the top bottle carefully enough and hard enough, the water will start spinning around, and it will move along the sides of the bottle.  After we stop spinning, the water keeps moving -- this is called centripetal force.  I've heard of centrifugal force, which my dad says is the opposite of centripetal force, but I'm still confused.  He said centripetal force keeps "tripping" you in a circle, where centrifugal (with an "f" in it) force makes you "fly" off.  I don't think that helps.

Anyway, as the water goes along the side of the bottle, some of it slips through the outside of the hole in the bottlecap.  But this only happens if the water is spinning -- if it's not moving, the water doesn't go through the hole.  I learned that the empty bottle on the bottom is not actually empty, but full of air.  And if water is to go in to the bottom bottle, air must somehow escape from it, because the air is stopping the water from coming through.

When the water is spinning along the sides, air can come up through the middle -- and that's what a tornado does (except that's cold air failing with hot air).  So the tornado lets water go into the bottle bottle at the same time that air goes into the top!

Tornadoes are deadly.