You should understand Atomic Structure & Static Electricity before reading this article.
Before we learn the meaning of ‘triboelectric’ we will first learn a little about the discovery of ‘static electricity’.
The ancient Greek philosopher Thalus of Miletes was the first person to observe static electricity in action in 600 BC when he used amber in an ancient ‘experiment’.
Trees sometimes produce a poisonous sticky resin. The secreted resin acts like a sticking plaster and seals ‘wounds’ after a tree has been ‘injured’. These injuries occur following attacks by insects, lightning strikes, fires, and damage caused by high winds.
Resin is a form of natural ‘chemical warfare’. The chemicals inside tree resins can be harmful to poisonous fungi and often repel insects. The resins may even produce a smell that attracts insects that attack other insects that cause harm to trees.
Resins are mainly produced by ‘coniferous’ (cone bearing) trees. This forest contains coniferous trees that will all ‘secrete’ large amounts of resin when needed.
Over millions of years the resin can become fossilized producing ‘amber’. This photo shows different colors of amber.
Sometimes insects become trapped in the resin before the process of fossilisation begins. This gives ‘entomologists’* a valuable opportunity to study insects which died millions of years ago.
In 600BC Thales of Miletus was polishing a piece of amber with some fur when, to his surprise, he found that other objects such as hair and feathers temporarily stuck to the amber.
Thales of Miletus knew nothing about protons, neutrons and electrons. He explained the phenomenon of static electricity as amber being somehow ‘living’ and therefore able to attract other objects to it.
It is an interesting fact that the greek word for amber ήλεκτρον (ēlektron) was used in 1891 to name the first sub atomic particle discovered, the ‘electron’.
By rubbing amber with fur one of two things can happen:
1) either electrons from atoms in the fur migrate to atoms in the amber in which case the fur is positively charged and the amber is negatively charged or
2) electrons from atoms in the amber migrate to atoms in the fur in which case the amber is positively charged and the fur is negatively charged.
How do we know which of the two events is the correct one? The ‘triboelectric series’ tells us what we need to know!
Here is a simple ‘triboelectric’ list of different materials.The list shows which materials have a greater tendency to become positively charged (+) and which materials have a greater tendency to become negatively charged (−).
POSITIVE (ie ability to give up electrons) The more ‘positive’ the material, the greater the tendency for electrons to migrate from that material.
dry human skin (+++)
rabbit fur (+++)
human hair (++)
NEGATIVE (ie ability to gain electrons) The more ‘negative’ the material the greater the tendency for electrons to migrate to that material.
rubber balloon (-)
hard rubber (like a comb)(-)
silver and brass (- -)
polyester clothes (- -)
Styrofoam cups ( – – -)
Saran wrap (cling film)(- – -)
vinyl PVC (some shower curtains and wellington boots) (- – -)
A material towards the bottom of the series (- – -) when rubbed against a material towards the top of the series (+++) will become more negatively charged.
A material towards the top of the series, (+++)when rubbed against a material towards the bottom of the series(- – -) will become more positively charged.
The further away two materials are from each other in the series, the greater the electric charge transferred. (ie the greater the migration of electrons) Materials near to each other on the series may not exchange any charge.
Returning to the question above: What happens to the electric charge when you rub a piece of amber with fur?
As you can see from reading the list in the ‘triboelectric series’ the fur becomes positively charged and the amber negatively charged. The electrons in the fur atoms migrate to the atoms in the amber.
* an entomologist is someone who studies insects.