Surprising Science Demonstrations?

An anonymous reader writes: "I have been called upon to conduct some science workshops for children of various ages, and I'm looking for some good demos. In particular, I've found that demos are most effective at getting students to think when they give a surprising or unexpected result, such as the classic two-slit experiment (or, for the extreme crowd, demonstrating the Leidenfrost effect by sticking one's hand into a vat of molten lead [PDF]). I'd like the Slashdot crowd's suggestions." Please don't do the lead one.

Comments

well,

[kingofnopants]

well, you could always do the leidenfrost effect. Putting your hand in boiling lead is always a shocker!

here's a pdf explaing it:

http://www.wiley.com/legacy/college/phy/halliday 320005/pdf/leidenfrost_essay.pdf