摩擦起電的原理是什麼？

Some substances tend to give up electrons when they are brought in contact with other materials. On the other hand, some substances tend to attract electrons when they are brought in contact with other substances. The tendency for materials to give up or attract electrons can be arranged in a series called the triboelectric series, also called electrostatic series, with the materials that are most likely to become positively charged (i.e. the greatest tendency to lose electrons) be placed on top.

The triboelectric series can be found from the following web-page:

http://www.school-for-champions.com/science/static_materials.htm

Hence, by looking on the series, silk has a tendency to give up electrons, whereas plastic (polyethylene or PVC) has a tendency to attract electrons. By rubbing silk with plastic, then silk will become positively charged and plastic become negatively charged.

原理:
所有物體都是由原子組成。每一個原子都有相同數目的質子和電子。質子帶正電，電子帶負電。
正常狀況下，正負電荷保持平衡，而使物體保持電中性。 當我們將A.B兩個不同的絕緣體摩擦之後，如果A絕緣體上的電子跑到B絕緣體上，那麼A的正電荷會變得比較多而帶正電；另一方面，B因為從A那邊得到額外的電子，因此帶負電。