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

Conservation of Energy with a Heavy Pendulum

[MichaelCrawford]

This is a very simple one that really impressed me when I saw it as a freshman at CalTech.

It helps to have a tall ceiling, or some high-up place you can tie a rope. At the other end of the rope you hang a heavy weight. At caltech they used a steel ball that must have weighed 100 pounds. Possibly you could use a bowling ball enclosed in a net bag.

What you do is pull the heavy weight some distance to one side. You will need to have the length of the rope and the distance of swing so that it just touches the tip of your nose when you pull it to the side.

Then let go, while facing the direction of swing. The heavy weight will swing across, then back and up - and come to a stop just as it touches the tip of your nose.

You have to stand there calmly and let it. Your amazed audience will think you're just about to get your face smashed in, but that doesn't happen. I think it was Prof. Ed Stone who did this.

As the weight swings, the potential energy from being raised in a gravitational potential will be converted into kinetic energy that reaches a maximum at the bottom of the swing. But when it comes back all that kinetic energy will get converted back to potential energy, and the kinetic energy will drop to zero just as it reaches the starting point.

If there is any friction from the air or flexing the rope it won't come all the way back to your nose.

You could also contact a local astronomy club and get them to show your kids a homemade telescope. I make them. Visit my page for some links, likely there is a club in your area.