When I rub two objects together, how would I know which becomes positive and which becomes negative? Is it some intensive property of the material?

Question

anonymous · Answer

Yes, it is. Some materials tend to lose electrons, while some tend to accept them. http://en.wikipedia.org/wiki/Triboelectric_effect

anonymous · Answer

It's not purely intensive but in general....

anonymous · Answer

Could you place something of known charge in the electrostatic field to see if there is attraction of it they repel?

anonymous · Answer

Different objects have a different "affinity" for electrons depending on what they consist of.  The object with a greater affinity will always become "-" whereas the lesser one will become "+".