What are some good science demonstrations that you have seen?

The best one I saw was the effect of liquid co2 on a raw egg. The egg was put in the CO2 and when it was taken out, the demonstrator took the shell off to prove it was frozen. It was rock solid. He handed it to someone in the front row to examine it, and said “pass it around so everyone can see.” It started to melt as it was passed from one warm pair of hands to another, and it didn’t make it past the third row. Yeuch.

One of my favorites is using red cabbage juice as a universal indicator.

Cutting a Mobius strip in half is another one!

Baking soda and vinegar in a film canister or other small container with a lid that can pop off.

Making slime.

Getting DNA from onions.

I could go on and on- can you tell I used to teach middle school science lab?

I was at the Exploratorium in San Francisco a few weeks ago. All of the science exhibits there are interactive (and way cool). One of my favorites was one that displayed how you could hear through your teeth, and just as well as you could through your ears.

There was a metal rod sticking out of a box that I presume was hooked up to some playing device. They asked you to put a straw over the metal rod (so as to not spread germs and such) and then bite down on the rod. When you bit down, you could instantly hear the music that was playing from the playing device. It was just like you had headphones on, but there were no headphones at all. More info.

That’s a great question, and a great example. But establishing a good vacuum in a transparent container and aranging the mechanism to drop both objects simultaneously would be a lot of work. The Belousov-Zhabotinsky reaction takes a few exotic chemicals but all are order-able online. It’sa pretty easy to set it up. And there are variations that can give interesting results.
The Belousov-Zhabotinsky reaction
Fast BZ Reaction
BZ reaction spiral

The Chemical Closk

You can google either reaction and find specifics as to how to create them.

In my high school chemistry class, our teacher made a point of demonstrating the spontaneous combustion of a small piece of white phosphorus. He put a piece of wet filter paper on top of a large graduated cylinder and the blob of P on top of that. As the phosphorus dried and subsequently burst into a very bright, white flame, it burned its way through the filter paper and filled the cylinder with thick white smoke.

This would have been impressive enough by itself, but he did all of this wordlessly while we were concentrating on a quiz he’d handed out. He didn’t grade the quiz; it was the setup for the prank. The man was positively diabolical in the gags he played on us throughout the year.

But I still remember the experiment.