Eraser Shaving Magic!

A photo of my AP Economics text book with eraser shavings on its cover. Little did those eraser shavings know that they would soon be flying to my pencil!

In AP Economics last week, Justin Park and I were sitting next to each other working on a worksheet that Colonel had given us. After realizing that we had made a mistake, I used my eraser to correct the error and then brushed the eraser shavings onto the table. Having just learned about static electricity, I was curious to see whether I would be able to magically pick up the eraser shavings with my pencil by using statics. As I was rubbing my mechanical pencil through my hair, Justin looked at me as if I were crazy. Confused, he asked me, “What are you doing?” I explained to him that I was experimenting with static electricity and then asked him if he remembered anything about statics from AP Physics B. When he replied, “No,” I saw a perfect opportunity to re-educate him.

I began my explanation to Justin about static electricity by telling him that it is possible to charge two items by friction. What does this mean, you ask? It means that it is possible to rub two objects together to cause one to be charged positively and the other to be charged negatively. Charging by friction works because electrons have a tendency to prefer one type of object over another, a strange and amazingly useful phenomenon really. How did I know that rubbing my mechanical pencil in my hair would cause one object to become positive and the other to become

A sample Triboelectric Series. Items on top have a tendency to charge positive while items on the bottom have a tendency to charge negative.

negative? I know because of a handy list called the Triboelectric Series, a list that ranks the tendencies of objects to become negative or positive when charged by friction. The photo to the left is a Triboelectric Series and shows that, when two objects are rubbed together, the object on top will become positive (lose electrons) while the object on the bottom will become negative (gain electrons). This list also shows a pattern: objects on the top tend to be natural objects (air, human skin, hair) while objects on the bottom tend to be artificial or synthesized (PVC, polyester, teflon).

Now that we have a basic understanding of static electricity and the Triboelectric Series, we can explain why I was able to pick up the eraser shavings with my pencil. When I rubbed my hard-plastic mechanical pencil through my hair, my hair became positively charged and my pencil became negatively charged. After charging my pencil, I waved it over the eraser shavings and witnessed the shavings levitate off the table and stick on and bounce off my pencil. The fact that I was able to move the eraser shavings may seem strange at first because I only charged the pencil, not the shavings. Justin seemed confused, so I explained to him that the eraser shavings need not be charged because they are neutral. If a charged object comes in close contact with a neutral object, they will still attract because the neutral object has an abundance of both protons and electrons. In this case, the protons in the eraser shavings were attracted to the negatively charged mechanical pencil, causing the entire eraser shaving to fly up and stick to my pencil.

Justin confided to me that he does not remember much about electricity and magnetism because they were very difficult topics for him. I told him not to worry, I will always be here to re-educate him about electricity and magnetism whenever he wants as I find picking up eraser shavings with my negatively charged mechanical pencil extremely fascinating.