Creating positive and negative charges

[DCypher]

Okay, last week in my in E & M physics class, we taped two pieces of tape together, then pulled them apart quickly. This caused one of them to have a positive charge and one to have a negative charge, what causes one to have negative and one too have positive from pulling them apart? Also which one is which, top positive, or bottom positive?

 

[DrPizza]

In order to determine which is positive, find a situation where it is more readily known which item is left with a positive charge and which is left with a negative charge. Then, use the item with a known charge to test your top and bottom tapes.

The exact mechanisms for this are unknown, but it has to do with one material "liking" to grab extra electrons more than another material likes to hang onto them.

For some research, I'd suggest doing a search for "triboelectric series"
Note: some materials may become positively charged in one scenario, and negatively charged in another scenario.

Here's a site with a list... but not much good information to help you further:
http://www.rfcafe.com/referenc...iboelectric_series.htm
it does explain that when you pick two items on that list, the one higher on the list will end up positively charged and the one lower on the list will become negatively charged when you rub them together. Be careful though, it's not the rubbing which causes the build up of static charge (which isn't so static sometimes), but rather the contact and separation of the surfaces. Rubbing them together just happens to increase the amount of contact and separation.

 

[DCypher]

could it be because the top tape is sticky, and the friction created by the stickiness pulls electrons off the other tape making it negative.

 

[DrPizza]

I'm not sure I would call adhesion or cohesion "friction"
Friction doesn't create static charge, rather it's the contact and separation between two materials. Rubbing two materials together, such as silk and a glass rod merely increases the amount of contact and separation that occurs.