How do positive and negative charges affect each other

What makes plastic wrap cling? Static electricity. Not only are applications of static electricity common these days, its existence has been known since ancient times. The first record of its effects dates to ancient Greeks who noted more than years B. The very word electric derives from the Greek word for amber electron. Many of the characteristics of static electricity can be explored by rubbing things together.

Rubbing creates the spark you get from walking across a wool carpet, for example. Static cling generated in a clothes dryer and the attraction of straw to recently polished amber also result from rubbing.

Similarly, lightning results from air movements under certain weather conditions. You can also rub a balloon on your hair, and the static electricity created can then make the balloon cling to a wall. We also have to be cautious of static electricity, especially in dry climates. When we pump gasoline, we are warned to discharge ourselves after sliding across the seat on a metal surface before grabbing the gas nozzle. Attendants in hospital operating rooms must wear booties with aluminum foil on the bottoms to avoid creating sparks which may ignite the oxygen being used.

How do we know there are two types of electric charge? When various materials are rubbed together in controlled ways, certain combinations of materials always produce one type of charge on one material and the opposite type on the other. Since the glass and silk have opposite charges, they attract one another like clothes that have rubbed together in a dryer.

Two glass rods rubbed with silk in this manner will repel one another, since each rod has positive charge on it. Similarly, two silk cloths so rubbed will repel, since both cloths have negative charge.

Figure 2 shows how these simple materials can be used to explore the nature of the force between charges. Figure 2. A glass rod becomes positively charged when rubbed with silk, while the silk becomes negatively charged. More sophisticated questions arise.

Where do these charges come from? Can you create or destroy charge? Is there a smallest unit of charge? Exactly how does the force depend on the amount of charge and the distance between charges?

Such questions obviously occurred to Benjamin Franklin and other early researchers, and they interest us even today. Franklin wrote in his letters and books that he could see the effects of electric charge but did not understand what caused the phenomenon. Today we have the advantage of knowing that normal matter is made of atoms, and that atoms contain positive and negative charges, usually in equal amounts. Figure 3. This simplified and not to scale view of an atom is called the planetary model of the atom.

Negative electrons orbit a much heavier positive nucleus, as the planets orbit the much heavier sun. There the similarity ends, because forces in the atom are electromagnetic, whereas those in the planetary system are gravitational. Normal macroscopic amounts of matter contain immense numbers of atoms and molecules and, hence, even greater numbers of individual negative and positive charges. Figure 3 shows a simple model of an atom with negative electrons orbiting its positive nucleus.

The nucleus is positive due to the presence of positively charged protons. Nearly all charge in nature is due to electrons and protons, which are two of the three building blocks of most matter. The third is the neutron, which is neutral, carrying no charge.

Other charge-carrying particles are observed in cosmic rays and nuclear decay, and are created in particle accelerators. All but the electron and proton survive only a short time and are quite rare by comparison. The charges of electrons and protons are identical in magnitude but opposite in sign. Furthermore, all charged objects in nature are integral multiples of this basic quantity of charge, meaning that all charges are made of combinations of a basic unit of charge.

If the charge is negative, the field is directed toward the charge. All electric fields begin on a positive charge and end on a negative charge. If two positive charges interact, their forces are directed against each other. This creates a repellent force as shown in the illustration. The same occurs with two negative charges, because their respective forces also act in opposite directions. In contrast to the attractive force between two objects with opposite charges, two objects that are of like charge will repel each other.

That is, a positively charged object will exert a repulsive force upon a second positively charged object. This repulsive force will push the two objects apart. Similarly, a negatively charged object will exert a repulsive force upon a second negatively charged object. Objects with like charge repel each other. This electric force exerted between two oppositely charged objects or two like charged objects is a force in the same sense that friction, tension, gravity and air resistance are forces.

And being a force, the same laws and principles that describe any force describe the electrical force. According to Newton's third law, a force is simply a mutual interaction between two objects that results in an equal and opposite push or pull upon those objects.

Let's apply Newton's third law to describe the interaction between Object A and Object B, both having positive charge. Object A exerts a rightward push upon Object B.

Object B exerts a leftward push upon Object A. See diagram at right. These two pushing forces have equal magnitudes and are exerted in opposite directions of each other. Each object does its own pushing upon the other. Because of the away from nature of the mutual interaction, the force is said to be repulsive.

Now let's apply the same action-reaction principle to two oppositely charged objects - Object C positive and Object D negative. Object C exerts a leftward pull upon object D. Object D exerts a rightward pull upon Object C. Again, each object does its own pulling of the other.

Just as before, these two forces have equal magnitudes and are exerted in opposite directions of each other. However in this instance, the direction of the force on Object D is towards Object C and the direction of the force on Object C is towards object D. Because of the towards each other nature of the mutual interaction, the force is described as being attractive.

The interaction between two like-charged objects is repulsive. The interaction between two oppositely charged objects is attractive. What type of interaction is observed between a charged object and a neutral object?

The answer is quite surprising to many students of physics. Any charged object - whether positively charged or negatively charged - will have an attractive interaction with a neutral object. Positively charged objects and neutral objects attract each other; and negatively charged objects and neutral objects attract each other.

This third interaction between charged and neutral objects is often demonstrated by physics teachers or experienced by students in physics lab activities. For instance, if a charged balloon is held above neutral bits of paper, the force of attraction for the paper bits will be strong enough to overwhelm the downward force of gravity and raise the bits of paper off the table.

If a charged plastic tube is held above some bits of paper, the tube will exert an attractive influence upon the paper to raise it off the table. And to the bewilderment of many, a charged rubber balloon can be attracted to a wooden cabinet with enough force that it sticks to the cabinet.

Any charged object - plastic, rubber, or aluminum - will exert an attractive force upon a neutral object. And in accordance with Newton's law of action-reaction , the neutral object attracts the charged object. Because charged objects interact with their surroundings, an observed interaction provides possible evidence that an object is charged.

Suppose that you enter the physics classroom and observe two balloons suspended from the ceiling. Rather than hanging straight down vertically, the balloons are hanging at an angle, exhibiting a repulsive interaction as shown at the right.

The only way that two objects can repel each other is if they are both charged with the same type of charge. Thus, the repulsion of the balloons provides conclusive evidence that both balloons are charged and charged with the same type of charge.

One could not conclude that the balloons are both positively charged or both negatively charged. Additional information or further testing would be required to make a conclusion about the type of excess charge present upon the balloons.