4.2.1 Electric Charge: Charging by Friction

This section explains how solid materials become charged when rubbed together. The key concept is the transfer of electrons, which are negatively charged particles, between the materials.

The Nature of Electric Charge

All matter is made up of atoms, which contain protons, neutrons, and electrons. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. The fundamental unit of electric charge is the electron.

Charging by Friction

When two different solid materials are rubbed together, electrons are transferred from one material to the other. This process results in a net gain or loss of electrons by each material, leading to a net electric charge.

For example, if you rub a rubber balloon against your hair, electrons are transferred from your hair to the balloon. The balloon gains electrons and becomes negatively charged. Your hair loses electrons and becomes positively charged.

Why Only Negative Charge Transfer?

The transfer of charge during friction is primarily the movement of electrons. Protons within the atoms are not readily displaced. Therefore, the net charge gained or lost by each material is almost exclusively due to the transfer of electrons, which are negatively charged.

Table Summarizing Charge Transfer

Materials Rubbed Together	Material that Gains Electrons	Material that Loses Electrons	Net Charge of Gaining Material	Net Charge of Losing Material
Rubber and Hair	Rubber	Hair	Negative (-)	Positive (+)
Glass and Silk	Glass	Silk	Negative (-)	Positive (+)

Key Points

• Charging by friction involves the transfer of electrons.
• Electrons are negatively charged particles.
• One material gains electrons and becomes negatively charged.
• The other material loses electrons and becomes positively charged.
• The transfer is primarily of electrons, not protons.