Static Electricity



The effects of static electricity were first discovered by the Greeks. In the sixth century BC the Greek philosopher Thales found that amber, when rubbed with fur, could attract little pieces of dry straw. The Greeks didn't understand what was happening, and thought of the experiments as tricks. However the peculiar effect did have its uses. In spinning silk using amber spindles, the attraction force would cause the threads to cling and that in turn made them easier to control. The Greek word for amber is in fact our word 'electron' and is the origin of the term electricity and all its derivatives.

It wasn't until almost 2000 years later, in the sixteenth century, that the physicist William Gilbert began to think about a model to describe what was happening in the materials responsible for the electrostatic effects. He proposed a fluid model for electricity, suggesting that objects that attracted other objects were becoming charged by being filled with a mysterious electrical fluid. Otto von Guericke in the seventeenth century noticed that it was also possible to cause repulsive electrical forces between objects. He also built friction machines to try and generate larger amounts of electricity. Many friction, or infulence machines followed, becoming powerful enough to generate small sparks.

In the eighteenth century, the Leyden jar was invented, and provided the first means of storing electricity. This century also saw Benjamin Franklin demonstrate that lightning was in fact electricity on a larger scale than the small infulence machines. By the nineteenth century the influence machine was a complex device, the most famous being the Wimshurst machine.

The effects of electrostatic repulsion can be demonstrated using simple to make apparatus. The dancing beads is a particularly simple but effective demonstration. It consists of a wooden frame and two perspex sides, with tiny polystyrene beads inside. When the top plate is rubbed, the beads jump towards the plate, and fall back down under gravity.





A simple acrylic rod and silk cloth can be used to generate a small charge, enough to be able to pick up small pieces of paper. Two acrylic rods and a polythene rod suspended at their midpoints should demonstrate the effects of electrostatic attraction and repulsion, since the two acrylic rods should both charge positively when rubbed, but the polythene will charge negatively.


The electroscope provides not only a good detector of static electricity, but again demonstrates the principle of electrostatic repulsion as the tiny gold leaf rises from the similarly charged rod.




Everyday examples include rubbing a balloon and getting it to stick to your hair, or the wall. Sitting on a plastic chair and rubbing your feet on a carpet should generate enough charge to cause a spark to pass to ground if the volunteer brings their knuckle near an earthed piece of metal.