Everything we see around us — all ordinary matter — is made of atoms. Every atom consists of negatively-charged electrons and a positively-charged center called a nucleus. The nucleus is made of positively-charged protons and neutral-charged (neither positively- nor negatively-charged) neutrons. In a simple model of an atom, known as a Bohr model (see Figure 1), it is assumed that the electrons are spinning around the nucleus of the atom on paths called orbitals. One can visualize this by thinking of satellites orbiting the Earth, or the moon orbiting around the Earth. The positive charges of the protons in the nucleus attract the negative charges of the electrons orbiting around the nucleus (opposites attract), maintaining the electrons' orbit. Charge is a fundamental quantity in electricity. The smallest amount of charge that is known to exist is carried by an electron and has a charge of -1.602 x 10^-19 coulomb [C]. The other charge-carrying portion of the atom is the proton, which has a charge of +1.602 x 10^-19 coulomb [C]. The unit used to measure charge is known as the Coulomb, named after French engineer and physicist Charles Coulomb.

In an atom, the protons and neutrons that make up the nucleus are held together very tightly and rarely does the nucleus experience a change. However, some of the electrons that are associated with the atom are loosely held to their orbital. These electrons, which typically reside in the outer orbits, can move from one atom to another. When an atom loses electrons, it has more positive particles than negative particles, which results in a positive net charge for the atom. An atom that acquires electrons has more negative particles than positive particles and, thus, has a negative net charge.

If the atoms in a material hold the electrons in the outer orbits tightly, the electrons are less likely to move to another atom. Such materials are known as insulators. Alternatively, materials whose atoms willingly give up and accept electrons are known as conductors. Conductors allow electrons to move through the material easily.

It is possible to transfer (or move) electrons from one material to another. One way to do this is by rubbing two objects together. The longer that two objects are rubbed together, the larger the quantity of electron movement from one object to the other, which results in a charge build up on each object. Static electricity occurs when there is an imbalance of positive charges and negative charges.

Positive and negative charges behave similarly to the north and south poles of a magnet: Opposite poles attract and like poles repel. In the case of charges, a positive and negative charge pull towards each other. Positive charges repel other positive charges, and negative charges push away other negative charges. Therefore, an object that has a positive or negative charge build up (net charge) attracts an object that is neutral. For instance, when you rub a balloon on your hair or a piece of wool cloth, the balloon acquires additional electrons. If you hold the balloon against a wall, the balloon sticks. This is because the negatively-charged electrons on the balloon push away the negatively-charged electrons in the wall (like charges repel) and attract the positive charges in the wall (opposites attract), causing the balloon to stick to the wall. Additionally, when an object with charge build-up attracts a neutral object, the electrons tend to move to areas where the electrical charge is positive until the atoms in both objects are neutral or balanced. When a large number of electrons move in an effort to balance the atoms, there is a chance of seeing a spark. This spark is a result of static electricity.

Figure 2. The activity setup for using static electricity to attract an O-shaped cereal with a comb. copyright

Ask students why the cereal was attracted to the comb, but then moved away once the cereal touched the comb? (Answer: The rubber comb attracted the loosely-bound electrons that were on the student's hair or the piece of wool. Once the comb attracted the electrons, it gained a negative charge. The cereal initially has a neutral charge; therefore, it is attracted to the comb because of its different charge distribution. However, when the cereal touches the comb, it gains some of the comb's negative charge, and the cereal's charge distribution becomes the same as that of the comb. Next, the two objects repel each other since they are now "like objects," and as a result, the cereal moves away.)

Human Diagram: Ask for 12 volunteers. Have students create a human diagram of the Bohr model by setting up two chairs. Have two students walk in one direction around the first chair and two students around the second chair. This is the first shell of the atom. Next, have one student walk in the other direction around the first chair, and seven students walk around the second chair to represent the second shell of electrons. Explain to students that static electricity happens when the two atoms rub together and the single electron from the first atom is transferred to the seven-electron shell of the second atom.

Prediction: Have students predict the outcome of the activity before it is conducted. First, give an overview of the activity, then ask students the following question and have them write their answer on a piece of paper. Then, perform the activity.

Worksheet/Pairs Check: At the beginning of the activity, hand out the Fun Things to Do with a Rubber Comb Worksheet. Have students work individually or in pairs to complete the worksheet. Have students who work in pairs check each others' answers.

Student-Generated Questions: Have each student come up with one question of their own to ask the rest of the class. Be prepared to help some students form a question. Possible questions:

Question Races: Have each student group number off. Ask a question and call a number. The students with that number in the group run up to the board and write the answer for the question. The team who gets it right earns their team a point.