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E lectric Force! - 7.2. OVERVIEW. Force : a push or a pull Shooting a basketball pushing the ball Pulling a desk across a room Contact Forces : forces that have an effect ONLY on the objects that they touch See above examples . Electric Force : a push or pull between charged objects
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OVERVIEW • Force: a push or a pull • Shooting a basketball pushing the ball • Pulling a desk across a room • Contact Forces: forces that have an effect ONLY on the objects that they touch • See above examples
Electric Force: a push or pull between charged objects • Action-at-a-distance Forces: can apply force to an object without touching it • Ex. Electric Force
The Laws of Static Charge • In the past, action-at-a-distance charges were used to see how the 3 types of charges (+, -, neutral) interacted • DISCOVERY! • 2 +ively charged objects would repel each other • 2 –ively charged objects would repel each other • When +ivelyand –ively charged objects were attracted to each other • Charged objects (+/-) were attracted to neutral objects
Laws of Static Charge: • Like charges repel • Opposite charges attract • Neutral objects are attracted to charged objects • Charles Coulomb: electric force is proportional to charge • Increase the amount of charge, increase the amount of electric force • Decrease the amount of charge, decrease the amount of electric force • Increase the distance between charged objects, decrease the electric force • Decrease the distance between charged objects, increase the electric force
Charging by Conduction • The charging of a neutral object by touching it to a charged object • Transferring charge between objects through touching or rubbing • Example: Electroscope • When a negative object touches a neutral electroscope, electrons spread evenly over the metal leaves repel because of negative charge
Charging by Induction • The rearranging of electrons on a neutral object by bringing a charged object close to it • Example: • A negatively charged object will repel electrons in the knob • Because it’s a conductor, the electrons will move down to the leaves which will repel
The Attraction of Neutral Objects • Induction explains why neutral and charged objects attract each other • Balloon becomes negative after being rubbed in hair • Place balloon against the wall • the negative wall charges are repelled, leaving that part of the wall positive (attracting the balloon)
Putting Static Charge to Work • See Figure 7.14 (pg. 261) in Chapter 7 of textbook!