When insulating materials rub against each other, they may become electrically charged. Electrons, which are negatively charged, may be ‘rubbed off’ one material and on to the other. The material that gains electrons becomes negatively charged. The material that loses electrons is left with a positive charge.
When a polythene rod is rubbed with a duster, the friction causes electrons to gain energy. Electrons gain enough energy to leave the atom and ‘rub off’ onto the polythene rod.
If the rod is swapped for a different material such as acetate, electrons are rubbed off the acetate and onto the duster.
Both the rods and the duster are made of insulating materials. Insulators prevent the electrons from moving and the charge remains static. Conductors, on the other hand, cannot become charged, as the electrons can move through them.
Connecting a static charge to earth using a conductor (earthing) will remove the excess charge as electrons will move to cancel out the charge.
A charged object will experience non-contact force from another charged object. The type of force will depend on the type of charge (positive or negative) on the two objects.
If a negatively charged plastic rod is brought near to another negatively charged rod, the rods will move apart as they repel each other.
If a positively charged rod is brought close to a negatively charged rod, the rods will pull together as they attract each other.
The forces of attraction or repulsion are greater when the charged objects are closer.
If a cloth rubs a plastic rod and the cloth is pulled away from the rod slightly, will the rod and cloth attract, repel or experience no force at all?
The rod and cloth will attract. This is true as long as there is enough friction to transfer electrons.
In both cases, the opposite charges will attract.