Do you know what an "atom" is? It is the smallest component of an element having the chemical properties of the element. Everything is made of atoms. Scientists so far have found only 115 different kinds of atoms. Everything you see around us is made of different combinations of these atoms. In the middle of each atom is a "nucleus." The nucleus contains two kinds of tiny particles, called protons and neutrons. These are very small partcles but there are particles even smaller than the protons and neutrons. These are called electrons, which revolve around the nucleus in orbits. The 115 kinds of atoms are different from each other because they have different numbers of protons, neutrons and electrons.
It will be easier for you to understand if we compare the model of the atom to the solar system. This is because both are similar in a way. As the sun is the center of the solar system, so also the nucleus is in the center of the atom. The electrons orbit around the nucleus just like the planets revolve around the sun. Just like the sun is the largest in the solar system, the nucleus is large compared to the electrons. And as the planets are so far away from the sun, the electrons are also very far away from the nucleus.
Protons, neutrons and electrons vary greatly different from each other. This is because they have their own properties, or characteristics. One of these properties is called an electrical charge. Electrical charge means the quantity of unbalanced electricity in a body. This depends on the number of electrons an atom has. The atom is mostly empty space. The nucleus is the positively charged dense center of an atom. The protons and neutrons in the nucleus are held together very tightly. Normally the nucleus does not change. But some of the outer electrons are held very loosely. They can move from one atom to another. An atom that looses electrons has more positive charges (protons) than negative charges (electrons). It is positively charged. An atom that gains electrons has more negative than positive particles. It has a negative charge.
This is similar to a boy who has some bad habits. The more he gives away those bad habits, the better he becomes. Similarly, the more an atom loses electrons, the more positive charge it has. Now if the boy gains more bad habits, the more bad he becomes. In a similar way, the more an atom gains electrons, the more negative charge it has.
A charged atom is called an "ion." Protons have a "positive" (+) charge and electrons have a "negative" (-) charge. Neutrons have no charge, they are neutral. The charge of one proton is equal in strength to the charge of one electron. When the number of protons in an atom becomes equal to the number of electrons, the atom becomes neutral. The atom itself has no overall charge
Some materials hold their electrons very tightly and so, electrons do not move through them very well. These things are called insulators. Plastic, cloth, glass and dry air are good insulators. Other materials have some hold their electrons loosely, and the electrons move through them very easily. These are called conductors. Most metals are good conductors.
How can we move electrons from one place to another? One very common way is to rub two objects together. If they are made of different materials, and are both insulators, electrons may be moved from one to the other. The more you rub the objects, the more electrons move, and more static charge is built up.
Static electricity is the imbalance of positive and negative charges. Two things with opposite charges (one positive and one negative) will attract, or pull each towards the other. Things with the same charge (two positives or two negatives) will repel, or push away from each other.
A charged object will also attract something that is neutral. If you charge a comb by rubbing it on your hair, it picks up extra electrons and has a negative charge. Holding it near a neutral object will make the charges in that object move.
1) A hard plastic comb, or a balloon,
2) A thread roll,
3) Pieces of dry cereal.
1) Tie a piece of cereal to one end of a piece of thread. Tape the other end of the thread to the edge of a desk.
2) Get a hard plastic comb. Make sure that it is really clean and free from any dirt and oil. Now just rub the comb through your hair(when it is dry) or a woolen blanket so that it gets charged with static electricity owing to the friction.
3) Now slowly bring the comb near the cereal. The cereal piece tied to the thread will swing to touch the comb. Hold it until the cereal moves away by itself. The cereal will tend to move away from the comb now.
Do you now understand why your comb was attracted the cereal piece? Simple. Combing the hair caused the electrons to be transferred from the hair to the comb. Since the comb was negatively charged with static electricity, the neutral cereal was attracted to it. When the cereal touched the comb, electrons were transferred to the cereal resulting in transfer of negative charge. But why did the cereal piece move away later? This is because both the comb and the cereal were negatively charged after a while. Hence, it led to repulsion.
Note: You should pass the comb through dry hair, and not after you have taken a bath.