Sometimes, when two different materials rubbed against each other, charges, (electrons,) are rubbed off of one material and on to the other. This process is called the triboelectric effect. The triboelectric scale, which if sometimes referred to as the electronegativity scale, helps to determine which materials attract electrons and which like to give away electrons.
In the winter, you may have rubbed a cat's fur only to shock the cat when you touched his ears. When you rubbed him charges were transferred. Either you rubber electron off the cat or the cat's fur rubbed electron's off of you. When touched the cat's ear, the excess charges were shared between the two of you and you got shocked.
Charge sharing
When two object touch each other or share a spark, charges are exchanged between the two objects. This is called "charge sharing." Charges are transferred between the two objects until a balance is reached.
For example:
If a metal ball had +6 units of charge and an identical metal ball had -4 units of charge, then when they touched, there would be a total of 2 units of charge, [6+(-4)]. Shared between the identical balls implies that each on would have 1 unit of positive charge.
Keep in mind this example uses metal balls. Metal balls will allow the charges to move. Plastic, insulating, balls would only allow the transfer of charge on the little spot where they touched -not from the whole sphere. Also in this example the balls are identical. Meaning they are the same size. If one ball was twice the size of the other, then the larger ball would get 2/3 the total charge and the smaller ball would get 1/3 the total charge.
Induction
Unlike the previous two methods, objects do not need to touch or share a spark. Induction is where a neutral body becomes polarized and acts like an charged body. When a body is polarized, the body behaves as if two sides of it have opposite charges -but the object has an net charge of zero. The can in the animation below becomes polarized. The charged balloon induces this polarization -without touching the can.
Try it.
You can try this on your own. Get an empty aluminum drink can and a balloon. Place the can on a level, flat table. Rub the balloon on your hair or clothing. Hold the balloon to the side of the can like the one in the animation. When the can begins to move towards the balloon, move the balloon so it does not touch the can. Have a race with a friend if you have two cans and two balloons.
by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)
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