I typically ask kids to read their definition of coriolis from the book.  Then I ask them to put it in their own words. <silence>   It is really hard to explain!  I usually show these videos as an almost complete explanation, then we discuss it in class and think of ways to demonstrate the effect on a small scale using a merry-go-round.

It is CRITICAL that you emphasise to students that coriolis effect has NOTHING to do with the way water spirals down a drain or a toilet.  Bust those misconceptions!

Here's a nice link to explain things a bit more:

http://www.ems.psu.edu/~fraser/Bad/BadCoriolis.html