What is Static Electricity?

When work is done on an object, by moving a force through a distance, the object gains energy. As a result, the object might get hotter (gain thermal energy) or accelerate (gain kinetic energy) or be lifted upwards (gain gravitational energy). There is also another possibility; the object could gain electrical energy in the form of static electricity.

Conventional electricity is very hard to store. Electrical cells (and batteries) do not store electrical energy: instead, they store chemical energy that is transferred as electrical energy when a chemical reaction takes place inside the cell. When you recharge a cell (or battery) you are forcing the chemical reaction into reverse and therefore renewing the store of chemical energy so that more electrical energy can be transferred again later, when required.

Static electricity is a type of electrical energy that can be stored, although only for a limited amount of time.

Static electricity is electric change that is accumulated by moving electrons from one object to another when their two surfaces are rubbed together. The friction that exists between the two surfaces is a force and moving the two surfaces constitutes a distance, resulting in work being done and energy being transferred. As a result, both objects warm up but this energy transfer can also, when the right combination of materials is used, cause electrons to move from one object to the other.

Summary so far: To build up static electricity we must have two different materials that are moving with friction acting between their surfaces. It is also important that both objects are electrical insulators (or they are insulated from their surroundings).

When two suitable surfaces are rubbed together, the surface that loses electrons becomes positively charged and the surface that gains those same electrons becomes negatively charged. Given that this process simply involves moving electrons from one place to another, it should be obvious that the charges on the two surfaces must be equal in magnitude but opposite in polarity.

According to my copy of Nature’s Electricity, by Charles Adams, the most electropositive materials are; air, human hands, asbestos, rabbit fur and glass. The most electronegative materials are; Teflon®, silicon, vinyl (PVC) and polypropylene. Using this information, it would appear that one of the best ways to generate static electricity would be to rub an old vinyl record with a piece of rabbit’s fur.

More commonly, we can demonstrate this same effect using a rubber balloon and human hair. Rubbing these two materials together causes electrons to transfer from your hair to the balloon, leaving your hair positively charged and the balloon with an equal amount of negative charge.

Your hair, if it is fine and dry, may then “stand up” – but why does that happen?

The reason is that every individual hair has acquired some positive charge, and objects that have the same charges always repel each other. The most effective way for the loose strands of hair to move apart is by moving outwards, giving rise to the spikey-hair look that comic-book characters have when they get an electric shock.

Similarly, objects with opposite charges attract each other.

You might wonder why the balloon and hair don’t stick together since they have opposite charges. The answer is that they do, but the force we can apply to pull the balloon away is more than the force of attraction that exists between the balloon and the hair.

Finally, we need to think about how static electricity is discharged (removed). The easiest way is by giving the charge a route into the ground: this works because the Earth has an unlimited capacity to accept electrons from a negatively charged object – and to provide electrons if the object is positively charged. In both cases, the charged object becomes uncharged when a current flows between the ground and the charged object.

This is what happens when lightning (which is caused by a build-up of static electricity in clouds) strikes the ground. It is also what happens if you touch a metal object after building up your own static charge, perhaps by walking across a nylon carpet: the pain you would feel comes from a tiny spark that is caused by electrons moving from the negatively charged object to the positively charged object.

The spark is actually nothing other than the visible effect of an electric current moving through the air. In extreme cases, the spark that is caused by a static electricity discharge can start a fire or even cause an explosion. There is more about the dangers of static electricity here but if you would like to find out more on other websites then I strongly recommend the following;

• Static electricity and electrical charge — Science Learning Hub – great overall explanation with lots of information and some very clear diagrams.

• Stop Static Campaign | Petroleum Equipment Institute (pei.org) – video of a fire caused by static electricity when refuelling at a garage. Interestingly, the PEI has also tested the idea that cellphones can cause fires at petrol stations but it has been unable to find a single verifiable report of this actually happening.