have a positive charge, and any charged object repelled by a charged rubber rod (or attracted
to a charged glass rod) must have a negative charge.
Attractive electric forces are responsible for the behavior of a wide variety of commercial
products. For example, the plastic in many contact lenses, etafilcon, is made up
of molecules that electrically attract the protein molecules in human tears. These
protein molecules are absorbed and held by the plastic so that the lens ends up being
primarily composed of the wearer’s tears. Because of this, the lens does not behave as a
foreign object to the wearer’s eye, and it can be worn comfortably. Many cosmetics alsoare applied.
take advantage of electric forces by incorporating materials that are electrically
attracted to skin or hair, causing the pigments or other chemicals to stay put once they