Frictional Electricity

Static electrical charges can be easily obtained by rubbing a hard rubber rod or a glass rod. These rods are electrical non-conductors (insulators), from which the electrical charges can’t flow off. Thus, the electric charging remains for a longer period of time. Synthetic fabrics become electrically charged as well when they are rubbed, and a rustle and tiny sparks can be observed.

Which substances become negatively charged and which positively depends on their electron affinity. This term expresses how likely a substance is to draw up electrons. The substance with the higher electron affinity will always become negatively charged, the other one positively. Overall, no new charges are generated, though, but charges are only separated.

Rub a hard rubber rod with a woollen cloth and hang it in a way that it can rotate freely. Now rub a second hard rubber rod and move it close to the first one. What happens?

Repeat the experiment with two glass rods, and afterwards with one glass rod and one hard rubber rod. What can you observe now?

Both the two rubbed hard rubber rods and the two rubbed glass rods repel each other. In contrast, the glass rod and the hard rubber rod attract each other. The reason for this lies in the sign of the charges.

If you take a look at the table, you will notice that by rubbing a hard rubber rod with a woollen cloth, the rubber rod becomes negatively charged and the woollen cloth positively charged. After the rubbing, both hard rubber rods are negatively - so identically - charged. This is called like charges. If you rub glass with a woollen cloth, though, the woollen cloth becomes negatively charged and the glass rod becomes positively charged. Both glass rods are now positively - so again identically - charged. The glass rod and the rubber rod, on the other hand, are charged differently. This is also called opposite charges.

Now we come to an important law of physics:

William Gilbert (1540 - 1603) carried out the first scientific studies about these phenomena, which were already partially known to the Greek. The name electricity goes back to him. The Greek called the amber electron, which came to them as jewellery or as a commodity. As mentioned above, tiny sparks jump from Amber to a woollen cloth if the amber is rubbed with that cloth. Part of the historical amber road runs through Austria. The amber road was an important trade route from the Baltic Sea to southern and southeastern Europe, and had its crossing over the Danube near Hainburg (Carnuntum).