When certain different insulating materials are rubbed against each other they become electrically charged by friction. The charges stay still on the object.. therefore it is called static electricity.
This only happens with insulators, with conductors the charge moves through them and doesn't stay put!
This is an interactive program that allows you to see buildup and discharge of static charge.
Electrically charged objects attract small, light objects placed near to them. Heavier objects don't seem to be attracted!
Why is this?
If the electric force due to the attraction is bigger that the weight of the small object then it will jump up and stick to the charged object, because the static force of attraction pulling it up is greater than the force of gravity holding it down. This explains why statically charged objects get so dusty! The dust particles get pulled towards the statically charged object as their weight is smaller than the electric force from the charged object.
Attraction and Repulsion
When two electrically charged objects are brought close together, they exert a force on each other.
Two charged objects may either pull towards each other (attract) or push each other away (repel).
These observations can be explained in terms of two types of charge called:
positive (+) and negative (-)
Two objects which have the same type of charge repel.
Two objects which have opposite types of charge attract.
When two different materials are rubbed against each other, electrons, which have a negative charge, are rubbed off one material on to the other.
The material which gains electrons becomes negatively charged and the material which loses electrons is left with an equal positive charge.
When a charged object is brought near to a neutral one, the electric field produced by the charged object disturbs the electron clouds around the atoms in the neutral object, distorting them and causing a disturbance in the balance of charge in the neutral object.
The charged object 'induces' a charge disturbance in the object it approaches.
If a negatively charged rod is brought near to a neutral piece of paper the electrons on the surface of the paper retreat giving the surface a partial positive charge. This makes the paper attractive to the rod and it jumps up and sticks to it (providing it is not too heavy - because its weight will pull it down).
If a positively charged rod is brought near to a neutral piece of paper the electrons near the surface of the paper advance toward the rod giving the surface a partial negative charge. This makes the paper attractive to the rod and it jumps up and sticks to it (providing it is not too heavy - because its weight will pull it down).
Here is an experiment - you could try this at home with a polythene comb.
In an examonation you should be able,when provided with appropriate information about a situation in which static electricity is dangerous, to explain why it is dangerous and how precautions can be taken to ensure that the electrostatic charge is discharged safely.
Bending Water Jet - Do do this at Home!
Water molecules are 'polar'. That means they have an uneven charge distribution on them.
The oxygen atom has a little negative charge and the hydrogens have a little positive charge.
If a charged object (like a polythene comb rubbed with a cloth) is brought near to a stream of water the water molecules realign themselves within the stream so that the 'end of the molecule' that has an opposite charge to the object is facing the charged object. Opposite charges attract so the molecules pull towards the charged object and you see the stream bend as in the video - try it at home!
The Gold Leaf Electroscope - a detector for static charge
This instrument can be used to detect whether an object is charged.
A charged object induces a charge in two sheets of gold leaf - gold leaf is so light that the electrostatic force of repulsion is much stronger than the weight and the sheets move apart - the greater the charge, the stronger the force and the further apart they move!
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Why is this?
Click here to see an animation of lightning
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