# Plastic and Iron - static and magnetic

I'm wondering if when you have a ball that is made out of plastic but has an inner core of metal.

Would that ball if given friction produce static?

Or would the static from the outerside of the ball pass it to the inner iron ball and thus the static would disappear.

• What do you mean by static? Static electricity? – Surgical Commander Feb 18 '15 at 3:12

Consider a ball formed with a plastic outer surface surrounding a metal ball in its inner core. Will the plastic outer surface accumulate and retain a static electric charge (of electrons) when rubbed with fur/flannel/silk? Or, will the electrons flow from the surface of the ball and disappear into the inner iron ball?

Answer: Yes, the plastic outer surface will accumulate and retain a static electric charge because plastic is an insulator, and the electrons accumulated on the surface of the plastic sphere cannot flow through the insulator to the inner metallic core, nor can they flow on the surface of the insulator to distribute themselves to a lower energy configuration.

No, the negative charges will not disappear internally into the metallic ball in its center, again because the plastic is an insulator and will not allow flow below the breakdown voltage. There is an attraction between the surface electrons and the metallic center ball. The surface charges emit an $$E$$ field, which polarizes the metallic core. That is, the conduction electrons in the metal ball are repelled by the surface electrons, which causes the conduction electrons in the metal ball to move to the opposite side of the metal ball. This, in turn, leaves the near side of the metal ball with a positive charge. Thus, the electrons on the surface of the plastic are attracted to the positively charged region. But again, since the electron accumulation is on the surface of an insulator, those charges cannot flow through the bulk of the plastic insulator to neutralize that induced positively charged area on the metal ball.

Elaboration: When two insulators (with different electron affinities) are touched/rubbed (e.g., plastic and wool), electrons accumulate on the surface of the material with the greater electron affinity. A plastic ball has a greater affinity for electrons than fur.