I: d \"We\" 1: INTERACTIONS OF ELECTRIC CHARGES CHAPTER 1 THE INTERACTIONS OF ELECTRIC CHARGES In this chapter we will examine experimentally the basic aspects of electric interactions. Using three fundamental physical principles. conservation of charge. Coulomb's law, and the superposition principle. we will attempt to explain the results of our experiments. We will find that certain observations cannot easily be' explained. 1.1_ The basic properties of electric interactibns Whether or not you have previously Studied electricity. you have probably heard somewhere that electric interactions have the following basic properties: - There are two kinds of charge. called \"+\" and \"\".~ ' Like charges repel. unlike charges attract. The electric force: - is proportional to the amountsot' both charges. 0 acts along a line between the charges. and 0 decreases rapidly as the distance between the charges increases. Note that the description above is an informal one: later on we will make it more precise. We need a simple. inexpensive. reproducible method of producing electrically charged objects so that we can further explore the properties of electric interactions. A possible material is \"invisible tape" such as Scotch brand Magic\" Tape. (Note: cheaper generic brands of invisible tape often work better than Scotch Magic Tape for our peculiar purposesl You may have noticed that invisible tape frequently sticks to your hand when you pull a strip off the roll. it this behavior is due to electric interactions. then this tape may be a suitable experimental material. ' we will be using very simple apparatus. yet our experiments will raise fundamental questions about the nature of the electric interactions of atoms and molecules. 1.2 Is invisible tape electrically charged? tn the following sections we will see whether invisible tape exhibits all the properties of electric interactions in the list above. If it does. we can conclude that the tape becomes electrically charged when we strip it off or another piece of tape. and we can study the behavior of pieces or\" tapelas a concrete example of electric interactions. ' 1.2.1 Preparing a \"U" tape Use a strip of tape aboutzt) crn-or 8 inches long (about as long as this paper is widet. Shorter pieces are not exible enough. and longer pieces are difcult to handle. Fold over one end of the stnpto make a non-sticky handle