Build-up of static is caused by friction

• When certain insulating materials are rubbed together, negatively charged electrons will be scraped off one and dumped on the other

• This will leave the materials electrically charged, with a positive static charge on one and an equal negative static charge on the other

• Which way the electrons are transferred depends on the two materials involved

• The classic examples are polythene and acetate rods being rubbed with a cloth duster

Only electrons move- never positive charges

But +ve and -ve electrostatic charges are only ever produced by the movement of electrons. The positive charges definitely do not move.

A positive static charge is always caused by electrons moving away elsewhere. The material that loses the electrons loses some negative charge, and is left with an equal positive charge.

Too much static causes sparks

• As electric charge builds on an object, the potential difference between the object and the earth increases

• If the potential difference gets large enough, electrons can jump across the gap between the charged object and the earth-this is the spark

• They can also jump to any earthed conductor that is nearby-which is why you can get static shocks getting out of a car. A charge builds up on the car’s metal frame, and when you touch the car, the charge travels through you to earth

• This usually happens when the gap is fairly small

Like charges repel, opposite charges attract

• When two electrically charged objects are brought close together they exert a force on one another

• Two things with opposite electric charges are attracted to each other, while two things with the same electric charge will repel each other

• These forces get weaker the further apart the two things are

• These forces will cause the objects to move if they are able to do so. This is known as electrostatic attraction/repulsion and is a non-contact force

• One way to see this force is to suspend a rod with a known charge from a piece of string. Placing an object with the same charge nearby will repel with rod-the rod will move away from the object. An oppositely charged object will cause the rod to move towards the object