_ THE _6 2006 V20 B

# _ THE _6 2006 V20 B - TAKE-HOME EXP. # 6 The Interaction of...

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TAKE-HOME EXP. # 6 The Interaction of Electric Charges * Please take the following assertions about electric interactions to be true. We'll refine the description a little later. There are two kinds of charges that can explain all electric phenomena. Let's call them "+" and "—", positive and negative. We'll use these "labels" for the charge to take advantage of their coincident use in arithmetic. This is at least one advantage over naming the two kinds of charge "Tom" and "Jerry" or "proton" and "electron". Notice also that the visual symbols are arbitrarily chosen; any two symbols can be used. "+" "—" "proton" "electron" Like charges ([+,+] or [—,—]) repel each other; unlike charges [+,—] attract each other. The electric force a) is proportional to the amounts of both interacting charges, b) acts along a straight line between the charges, and c) decreases rapidly as the distance between the charges increases. + + æ F æ F æ F æ F æ F æ F + We are all essentially blind to electric charge. You cannot see charges on objects; yet they cause the electric force which is the second strongest interaction in the universe. In the gravity interaction, the weakest in the universe, you can usually see the masses that act as the agents of 3rd-law pairs of gravity forces. For example, if you have ever walked near a cliff, you get clear sensory information that the edge is near. If you step over it, your body and the clearly visible Earth will interact freely. However, in reaching for a highly charged object, you don't get any sensory information that you are about to "step off" an electrical cliff. How can we humans get to see this invisible "charge" stuff more clearly in our imaginations? That's what we'll begin to do in this experiment. We will make electrically charged strips of cellophane tape, and examine how they interact with each other via the long-range electric force. * The design, approach, and excellence of this experiment is directly owed to Ruth Chabay and Bruce Sherwood, who use it in the first chapter of their truly innovative text Electric and Magnetic Interactions, John Wiley, 1995. I first heard of it elsewhere (Arnold Arons), but they carefully developed it into a workable prescription. Any mistakes are due to the present author.

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TAKE-HOME EXPERIMENT #6 THExp#6-2 ________________________________________________ Procedure For This Experiment The observations will require an inexpensive generic brand of "invisible tape", similar to Scotch ® brand Magic TM Tape. The latter doesn't work as well as the generic brands in the unusual property we need in this experiment, namely one in which we try to maximize the excess charge on the tape. ALERT! Everyone, including me, feels at first like a klutz when handling these tapes. Handling these tapes is easier than learning how to play a musical instrument, but it still takes practice. You cannot learn to play a piano by reading a book, and you cannot experience this without actually doing it. It might feel clumsy, but you'll soon get better at it.
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## _ THE _6 2006 V20 B - TAKE-HOME EXP. # 6 The Interaction of...

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