What are some simple chemistry or physics "tricks" to use in a magic show for children?

levitation using a hidden supercooled magnet.

Homemade electromagnet
http://www.sciencebob.com/experiments/electromagnet.php

Suck a hard-boiled egg into a bottle with fire
http://www.doscience.com/act_archive/home_activities/egg_suck/egg.html

The magical moving pepper experiment.

I have always loved the one where you have a sodium silicate solution in a clear cup….looks like water. Call a kid up and have him mix in one spoonful of magic Wufool dust. (baking soda) Have them stir real good about ten times…start chanting abra-cadabra raise your magic wand and accidentally tip the cup towards your volunteer and they jump back in horror only to reveal the water is now a solid gel. <take a bow>

The mixture causes a chemical reaction between the silicate and the bicarbonate soda to form “water glass”.

@jaytkay Both good suggestions (for the electromagnet you can get the wire here). The whole point is to reinforce the underlying principle. In the case of electromagnets you show that steady electrical current creates a magnetic field, especially when wound many times around an iron core. In the case of the sucked egg, you show how strong air pressure really is.

@lonelydragon Another oldie but goodie, demonstrating the disruption of surface tension. Maybe precede that by first floating a steel needle, demonstrating the existence of surface tension “skin” by which many bugs walk on water, owing to mutual attraction of H2O molecules.

Don’t mixing of baking soda and vinegar. It’s a true chemical reaction, but because it generates CO2 gas it’s dramatic as well. Or get hold of a pH indicator dye like phenolphthalein that turns from clear to pink when exposed to acid.

And another oldie but goodie… we used to have fun with the cornstarch and water mixture thing when we were kids. Fun with viscosity! And setting magnesium on fire is always a good show but you have to be pretty careful and kind of know what you’re doing.

@lillycoyote Um, you can also blind people by burning magnesium. I would be hesitant there. Just because it’s hard to be “cool! metal on fire!” while not also harming people at the same time. Just my 2 cents.

Along those lines, however, you can burn lots of other things to make cool flames, like copper for a nice green flame, or potassium for purple. You can probably find metal salts without too much trouble. There’s a list of colors here.

@BhacSsylan I know. I said you have to be careful and know what you’re doing. My parents were both chemists so we did a lot of those little science trick things when I was growing up but they were professionals and knew what they were doing. I probably shouldn’t have mentioned it. It’s kind of from the don’t try this at home kids category.

I’ve found that simple chemical color changes get a lot of oohs and aahs. I can’t find the one that I used (which used some slightly rarer materials but could change between four colors), but here’s a link to a simple one. A simple Google search should yield dozens of slight variations on this.

The parabolic mirror 3d mirage illusion is really cool, safe and fun.