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Name That Charge - help1

There are some fundamental principles that one will have to understand and use in order to successfully analyze all seven Name That Charge situations. Those fundamental principles are ...

  1. Electrons are negatively charged and protons are positively charged.
  2. Only electrons are able to move during electrostatic charging processes.
  3. Opposites attract and likes repel. Thus, electrons are attracted to positively-charged objects and repeled by negatively-charged objects and by each other.
  4. If a neutral object gains electrons, then it becomes negatively charged. If a neutral object loses electrons, then it becomes positively charged.

There are a few nearly-identical versions of this question. Two of the versions include:

Version 1:

A vinyl balloon is rubbed on a wool sweater. Vinyl has a greater affinity for electrons than wool. Once rubbed, what is the charge on the wool sweater?  What is the charge on the vinyl balloon? Once rubbed, what is the charge on the glass stirring rod? What is the charge on the cotton cloth?

Start with two neutral objects; then rub them together vigorously.

Version 2:

A glass plate is rubbed with a cotton cloth. Cotton has a greater affinity for electrons than glass. Once rubbed, what is the charge on the glass plate? What is the charge on the cotton cloth?


Start with two neutral objects; then rub them together vigorously.

This question is an example of charging by friction (or rubbing). Charging by friction involves bringing two neutral objects in close contact. Electrons are transferred from one object's atoms to the other object's atoms. The material that likes electrons the most (has the greater electron affinity) will be the object that acquires the electrons. Because there is an electron transfer between the two objects, one object becomes positively-charged and the other object becomes negatively-charged.

Charging by Friction