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Rubbing a Glass Rod on Cloth

Static electricity is created when two materials are rubbed together. From the resulting friction, electrons from one material are transferred to the second material. The materials are left with a positive or negative electrical charge. In the 18th century, Benjamin Franklin discovered that glass rods generate static electricity when they are rubbed with a silk cloth. This glass rod experiment can be performed in the classroom to teach students about static electricity and electrical charges.

Things You'll Need

Two pith balls on string
Ring stand
10-inch glass rod
Silk cloth

Instructions

- 1
  Attach two pith balls on string onto a ring stand. Pith balls are small and light objects, such as Styrofoam balls covered in metallic paint, which easily take up an electrical charge from another object. They are used to demonstrate attraction and repulsion between electrical charges. Depending on the type of stand available, you will hang the string on a hook on the end of the stand, tie the string to the end of the ring stand or use another method. Consult your manufacturer̵7;s handbook for details regarding your ring stand specification.
- 2
  Place the back of your hand against the pith balls for at least 10 seconds to discharge the pith balls of any electrical charge. Hold the glass rod firmly in your left or right hand. Hold the silk cloth in your other hand, and rub the silk cloth along the length of the glass rod for at least 30 seconds. The glass rod is now positively charged and the silk cloth is negatively charged. Electrons from the glass rod have been transferred to the silk cloth.
- 3
  Touch the pith balls with the glass rod. The positive charge from the glass rod will transfer to the pith balls. Both the glass rod and the pith balls have a positive charge, and they will repel each other. The pith balls also have a positive charge and will repel each other.

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