Electric Force 7 2 OVERVIEW Force a push

Electric 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 �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 +ively and –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 amount of charge, increase amount of electric force Decrease amount of charge, decrease amount of electric force Increase distance between charged objects, decrease electric force Decrease distance between charged objects, increase electric force

Charging by Conduction: charging a neutral object by touching it to a charged object Transfer 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: rearranging of electrons of 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!