Ok, Mr. Know-It-All, here's the simple solution to your problem. Take a balloon and rub it on your head. When your hair frizzes up, that means that there is one kind of charge all built up on your hair. The other kind is built up on the balloon. Do this with another balloon on your friend's head and you'll have 2 balloons with the same kind of charge to use in your experiment.
You can accomplish the same thing by rubbing a piece of rubber with a piece of fur or a glass rod with silk. You might be interested in trying out an experiment like this one
Of course, these methods only produce two objects with more or less the same charge. If your experiment requires two objects with closely matched charges, you'll need to take other precautions. For example, you could take two very similar balls, hang them on strings in a room with dry air, then charge them from the SAME source. You might connect them with a thin wire, then touch the wire with something charged up by rubbing. That way, if one starts to charge up more, the cgharge will flow to the other until they're equal. Then you can carefully knock the wire away with an insulating stick.Perhaps most important, you can TEST if the two objects have the same charge by seeing if they're equally attracted to some other object of opposite charge held equally far from each of them. You can judge the attraction by the angle of the string from vertical.
Good luck with your project!
-Tamara (and mike)
(republished on 07/13/06)