2. Law of attractive forces Opposites attract Likes repel 7.1

3. Electrification by Contact Transfer of Electrons Contact –Friction –Separation of materials 7.1 When electrons transfer one material is left with a positive charge and the other with an equal amount of negative charge.

4. Compared to the electrons in carpet atoms, electrons are bound more tightly to the atoms in the soles of your shoes. When you walk on the carpet, electrons are transferred from the carpet to the soles of your shoes. Electrification by Contact 7.1 Electric Charge

5. The soles of your shoes have an excess of electrons and become negatively charged. The carpet has lost electrons and has an excess of positive charge. Electrification by Contact 7.1 Electric Charge http://www.youtube.com/watch?v =7KK48hQ78Kk = gas station

6. Induction No transfer of electrons Electrons move within an object because of another charged object May or may not have contact 7.1

7. The balloon on the left is neutral. The balloon on the right is negatively charged. It produces a positively charged area on the sleeve by repelling electrons. Induction 7.1 Electric Charge The rearrangement of electrons on a neutral object caused by a nearby charged object is called charging by induction.

8. If you reach for a metal doorknob after walking across a carpet, you might see a spark. Conductors and Insulators 7.1 Electric Charge The spark is caused by electrons moving from your hand to the doorknob.

9. A material in which electrons are able to move easily is a conductor. Conductors 7.1 Electric Charge The best electrical conductors are metals. The atoms in metals have electrons that are able to move easily through the material.

10. A material in which electrons are not able to move easily is an insulator. Insulators 7.1 Electric Charge Electrons are held tightly to atoms in insulators. Most plastics are insulators. The plastic coating around electric wires prevents a dangerous electric shock when you touch the wire.

11. Triboelectric Series Affinity for electrons varies based on material. triboelectric series puts them in order for us. Higher the material the greater the affinity for electrons When any two materials in the table are rubbed together, the one which is higher can be expected to pull electrons from the material which is. Higher materials gain electrons Lower Materials lose electrons 7.1

12. Grounding 7.1 Electric Charge A discharge can occur any time that charge builds up in one area. Providing a path for charge to reach Earth prevents any charge from building up. Earth is a large, neutral object that is also a conductor of charge.

13. Grounding 7.1 Electric Charge Any object connected to Earth by a good conductor will transfer any excess electric charge to Earth. Connecting an object to Earth with a conductor is called grounding.

14. Detecting Electric Charge 7.1 Electric Charge The presence of electric charges can be detected by an electroscope. One kind of electroscope is made of two thin, metal leaves attached to a metal rod with a knob at the top. The leaves are allowed to hang freely from the metal rod.

15. Detecting Electric Charge 7.1 Electric Charge When the device is not charged, the leaves hang straight down. Notice the position of the leaves on the electroscope when they are A uncharged, B negatively charged, and C positively charged.

16. 7.1 Section Check Question 1 A physics teacher rubs a glass object and a felt cloth together and the glass becomes positively charged. Which of the following statements are true? a.The glass gained protons during the rubbing process. b.The felt became charged negatively during this rubbing process. c. Charge is created during the rubbing process; it is grabbed by the more charge-hungry object. d. If the glass acquired a charge of +5 units, then the felt acquires a charge of -5 units. e. Electrons are transferred from glass to felt; protons are transferred from felt to glass. f. Once charged in this manner, the glass object and the felt cloth should attract each other. g. In general, glass materials must have a greater affinity for electrons than felt materials.

17. 7.1 Section Check Question 2 A. copper B. rubber C. wood D. water Which of the following is the best conductor of electricity?